Brain Research, 90 (1975) 115-132 ,~) Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
115
CHANGES IN REGIONAL BLOOD FLOW AND CARDIODYNAMICS ASSOCIATED WITH ELECTRICALLY AND CHEMICALLY INDUCED EPILEPSY IN CAT
NOBUTAKA DOBA, H. R I C H A R D BERESFORD AND DONALD J. REIS
Laboratory of"Neurobiology, Department of Neurology, Cornell University Medical College, New York, N. Y. 10021 (U.S.A.) (Accepted December 14th, 1974)
SUMMARY
Changes in cardiodynamics and regional blood flow were examined in chronically prepared paralyzed cats during seizures induced electrically by transcerebral or direct cortical stimulation or by administration of flurothyl ether (lndoklon) or pentylenetetrazol (Metrazol). Transcerebral and chemical stimuli produced the greatest vascular responses. During seizures there was an abrupt elevation of arterial pressure unassociated with consistent changes in heart rate. Vascular resistance was increased in femoral, renal and mesenteric arteries with variable reductions in blood flow. Resistance was decreased and flow passively increased in the c o m m o n carotid artery reflecting the loss of cerebral autoregulation. Cardiac output was unchanged. With seizures associated with large elevations of arterial pressure, the central venous and left ventricular end-diastolic pressures were markedly increased indicating incipient congestive failure. The pressor response was blocked by alpha-adrenergic blockade with phentolamine. Increased regional vascular resistance was abolished by regional sympathectomy. While either adrenalectomy or treatment with 6-hydroxydopamine alone failed to abolish the pressor response, combined, they did. Such treatment unmasked an atropine-sensitive bradycardia. The pressor response with seizures is a consequence of increased vascular resistance in viscera and muscles due to widespread activation of sympathetic neurons and release of adrenomedullary catecholamines. Co-activation of cardiovagal and cardiosympathetic neurons may underlie some associated arrhythmias. Cardiovascular events may serve, by redistribution of the cardiac output, to assure increased availability of oxygen and nutrients to brain to meet the metabolic demands of convulsions.
INTRODUCTION
Epileptic seizures in man or animals are associated with a marked elevation of
116 the systemic arterial pressure e 1.7, ls,eT,es,::m. While it is known that during convulsions there is a substantial increase in cerebral blood flow-',zv,zs,az, cerebral venous pressure z7 and an increase in resistance in the femoral arteries v, it has never been established if the elevation in arterial pressure is due to increased cardiac output or total peripheral resistance, and if'the latter if the vasoconstriction observed in femoral arteries v is widely distributed or only involves specific vascular beds. Such information is of interest for it raises the question as to whether the autonomic responses in epilepsy are generalized or involve selective and differentiated activation of the sympathetic nervous system l°.aa. in the present study we have therefore investigated in cat the changes in cardiodynamics and in the regional distribution of blood flow during convulsions produced electrically or by administration of convulsive agents. METHODS
General Twenty-five mongrel cats were anesthetized with ether. After insertion ofcannulae in the femoral artery, femoral vein and trachea, each animal was paralyzed with gallamine triethiodide (5 mg/kg, i.v.), and artificially ventilated with 2 ~ halothane in t00 ~ 02 delivered from a canister to a small animal respirator (Harvard Instrument Co.) via an anesthetic bag. The flow rate of halothane was adjusted so as to maintain adequate filling of the reservoir bag. End-tidal CO~ recorded by an infrared gas analyzer (Beckman LI) was maintained at 2-3 ~ throughout the experiment. The rectal temperature ranged from 36.5 to 38 °C, hypothermia being averted through use of a thermostatically regulated infrared lamp.
Recording of electroencephalogram ( EEG) The animal was placed in a stereotaxic frame and 3 small steel screws were placed in the skull. The first two screws were placed over the rostral portions of the parasagittal lobe on the surface of the dura mater and used as recording electrodes. The other screw was placed in the mid-portion of the occipital bone a n d served as an indifferent electrode. The E E G was recorded by an AC coupler (Beckman 9806A) with suitable amplification (100 #V/cm) and displayed on a polygraph (Beckman Dynograph Recorder, 504A).
Measurement of cardiovascularfunctions Systemic arterial pressure (BP) was recorded from a polyethylene catheter which was threaded up the femoral artery into the abdominal aorta and connected to a Statham P23Db transducer. The heart rate (HR) was computed from the blood pressure pulse by a cardiotachometer (Beckman 9857). End-tidal CO2 was sampled through a fine catheter placed in a tracheal cannula, and was recorded by an infrared gas analyzer (Beckman LB-1). All cardiovascular activity was displayed on a polygraph. Regional blood flow was recorded by a square-wave electromagnetic flowmeter
ll7 (Carolina Medical Electronics, types 322 and 332) 8. Flow probes (Carolina Medical Electronics, Ep 403R, 404R, and 420R) were applied to the femoral, renal, mesenteric and common carotid arteries and the ascending aorta. No more than two probes were inserted in an animal at any one time. However, in any one experiment flow changes in numerous beds might be sampled. Renal flow was never measured after a laparotomy since the operation may produce reflex effect on renal flow 16. After placement of the flow probe, the incision was closed and sutured areas were infiltrated with 2% procaine. Particular care was taken to assure mechanical stability of the arterial probe. The zero level of the flowmeter was established in situ before and after an experimental series by occluding the artery distally. At the termination of an experiment, the probes were calibrated by a standard method. In all instances mean blood flow was recorded through an integrated circuit built in the flowmeter. The mean arterial pressure (Pm) was derived from the formula (Ps + 2Pd)/3, where Ps was systolic pressure and Pd was diastolic pressure s. Regional vascular resistance (RVR) was conventionally obtained from the formula: RVR = Pro/Fro, where Fm was mean blood flow in a given vascular bed s. Cardiac output (CO) was estimated from the blood flow in the ascending aortaS, 2~. Total peripheral resistance (TPR) was calculated from the formula: TPR = (Pro - - CVP)/CO, where CVP was central venous pressure measured through a polyethylene catheter inserted into the right atrium through the femoral vein. Stroke volume (SV) was calculated from the formula: SV = CO/HR. Left ventricular enddiastolic pressure (LVEDP) was measured through a catheter threaded down the left common carotid artery and positioned in the left ventricle. Induction of seizures After catheters and flow probes were in place, the animal was taken from the stereotaxic frame and placed in a supine or recumbent position without restraint. The wound edges were infiltrated with procaine (2 ~ ) and lidocaine ointment (2 ~o) was applied to the corneas. Halothane in 100 ~ 02 was then replaced by room air. During the remainder of the experiment paralysis was maintained by periodically administrating gallamine, the trachea cleared and wounds reinjected with procaine. Any additional surgical procedures were performed after the animal was anesthetized with 2 halothane. With such care arterial pressure and heart rate remained at control levels during the duration of the experiment. One hour after stopping halothane, seizures were induced by one of 4 different procedures. (1) Flurothyl ether (Indoklon) (0.05-0.075 hal) was injected by a small syringe through a hole in a tracheal cannula during the inspiratory phase of artificial ventilation. (2) Pentylenetetrazol (PTZ) (Metrazol) (10 mg/kg, i.v.) was injected into the femoral vein. (3) Transcerebral stimulation was performed by passing DC current (170 V, 100 mA, 1-sec pulse) from a device used for electroconvulsive therapy (Model B24, Medcraft Electronic Co.) through saline-soaked gauzes attached with a clip to the ears. (4) Direct cortical stimulation was performed through two thin monopolar electrodes consisting of a stainless steel wire (diameter 0.006 in.) coated with Teflon and bared at the tip for 1 mm and carried in a No. 28 stainless steel hypodermic needle.
118 The electrodes were placed bilaterally in the rostral portion of the marginal gyrus via small holes that were drilled through the parietal bone with a dental drill. These electrodes were fixed to the skull with dental acrylic cement. Seizures were induced by stimulation through both electrodes (cathodes) with a 10-sec train of square wave pulses of 0.5 msec duration at a stimulus frequency of 50 Hz, delivered t'rom a pulse generator (Devices, Digitimer) through a constant current stimulus isolation unit (Devices MK IV). The stimulus current was 2-5 mA. The anode was a skin clip. In any one animal seizures could be produced repeatedly by the various methods described above following stimulus-free intervals of 10-15 min. The stimulus parameters used for electrical stimulation and the dose of convulsive agents were established in preliminary studies to predictably initiate a single seizure sustained for at least 20 sec (see Table !).
Experimental maneuvers (1) Autonomic blockade. Alpha-adrenergic blockade was achieved by administration of phentolamine (1 mg/kg, i.v. CIBA), beta-adrenergic blockade by propranolol (1 mg/kg, i.v. Sigma Chemical Co.) and cholinergic blockade by atropine sulfate (0.2 mg/kg, i.v. Elkins,Sinn, Inc.). (2) Regional sympathetic denervation. Denervation of the renal artery was accomplished by transection of the renal nerves via a retroperitoneal approach. The femoral artery was denervated by transection of both the sciatic and femoral nervesS,40. (3) Bilateral adrenalectomy. Both adrenals were removed through a laparotomy. Careful efforts were made to maintain homeostasis. (4) Chemical sympathectomy. Acute chemical sympathectomy was performed by adaptation of the method of others 9,a3 by systemic administration of 6-hydroxydopamine (6-OHDA) hydrobromide (Regis Chemical Co.). In brief, each animal received 100 mg/i.v, divided into 3 equal doses of 33 rag. After each injection, heart rate and blood pressure were permitted to return to control levels before another injection was made, and at least 30 rain was allowed to elapse between any two successive injections. After the first dose of 6-OHDA, l0 ml of 5 ~ dextran was administered intravenously to present hemoconcentration 13. The solution of 6-OHDA was prepared before injection by dissolving the drug in physiologic saline containing ascorbic acid (1 mg/ml) to block auto-oxidation. Seizures were not induced until at least 2 h after the first injection of 6-OHDA. Tyramine hydrochloride (Sigma Chemical Co.) was used to assess the efficiency of chemical sympathectomyg, tz. The dose-response relationship was examined prior to and after administration of 6-OHDA with the graded injection of tyramine hydrochloride (20-200 #g/kg, i.v.). After 2 h from the completion of the full dose of 6O H D A (100 rag/animal, i.v.), the dose-response curve was shifted to the right with marked reduction both in amplitude (P < 0.01) and duration at all dosages.
Evaluation of data For quantitative assessment of the changes in any cardiovascular parameter, the
119 20 CVP (cm H20)
10 0
Femoral arterial 20 flow (ml / min) 0~Renal arterial flow (ml / min)
Heart rate (bpm)
20 0 260 F 180 L 3OO
~
Blood pressure (mm Hg) 200
loo
EEG
100pV
I t FLUROTHYL ~"1~~ ~~'
lmin
I
Fig. l. Changes in arterial pressure, heart rate (in beats/min, bpm), blood flow in the renal and femoral arteries, and central venous pressure (CVP), during a convulsion produced by flurothyl ether in paralyzed artificially ventilated cat. See text for details.
responses during at least 3 representative seizures and preseizure control values were averaged for each animal. The means (control and seizure) were then used as a single value for that animal. Statistical evaluation was prefaced by comparing poststimulus to prestimulus value for the group, the n representing the number of animals, by use of a paired t-test 3s. P < 0.05 were considered significant. RESULTS
(I) Character of seizures Seizures produced electrically by direct cortical or transcerebral stimulation or by the administration of the epileptogenic agents, flurothyl ether (Indoklon) or pentylenetetrazol (PTZ; Metrazol) were characterized by widespread spike and wave activity recorded over the cerebral cortex. The duration of the seizures evoked by the various methods in part differed. Seizures (as defined by the presence of spike and wave activity on the cortex) induced by direct cortical stimulation persisted the longest (59.5 ~ 2.5 sec; n = ! 8); those initiated by transcerebral stimulation were the briefest
120
CVP (cm H20) Femoral arterial flow (ml I mint
31t
Renal arterial flow (mll min) Heart rate (bpm)
260 [-- . . . . .
~
...~.-~---..~-~_~-_
l
220 L
200 Blood pressure 150 Imm Hg) IO0 EEG
lOOpV
I
I
tPTZ (20mg, iv) I min Fig. 2. Changes in arterial pressure, heart rate, blood flow in renal and femoral arteries, and central venous pressure (CVP) during a burst of repetitive seizures produced by pentylenetetrazol (PTZ) (20 rag, i.v.) in paralyzed artificially ventilated cat. (22.0 ± 1.0; n .... 14) while the duration of seizures induced chemically by either flurothyl ether or P T Z lasted approximately 45 sec. In most instances the seizures occurred as a continuous uninterrupted burst of cortical high voltage activity (e.g. Fig. 1). In some instances, however, the seizures appeared in repetitive bursts lasting up to 1 min (Fig. 2). Since the animals in this study were paralyzed, no motor manifestations of the seizure discharge were observed. However, all animals exhibited pupillary dilatation, retraction of the nictitating membrane, and profuse salivation in association with activation of the EEG.
(I1) Cardiovascular changes with seizures As previously noted~-5,7,1s,ev,zs, 32 seizures initiated by any means were associated with elevations in systolic, diastolic and mean arterial pressures (Figs. 1-7, Tables I and II). Sometimes, but not invariably, the rise of arterial pressure was preceded by a slight fall (Figs. 1 and 5). The onset of the alteration of arterial pressure began within the first 3 sec of the appearance of cortical electrical activity, peaked from 50 to 30 sec and remained elevated, sometimes for minutes, after the cortical E E G returned to normal. The magnitude of the elevation of arterial pressure varied with the mode of evoking the seizures, Under the conditions of this study transcerebral stimulation produced the largest elevation of mean arterial pressure (Table i) with peak elevations averaging 212 m m Hg: Chemical stimulation (Table 1) increased
TABLE I
CHANGES IN CARDIOVASCULAR DYNAMICS D U R I N G SEIZURES PRODUCED ELECTRICALLY (TRANSCEREBRAL) OR CHEMICALLY (ELUROTHYL ETHER) IN PARALYZED CAT
Electrieal stimulation (transcerebral)
Control
(n)
Seizure
Chemical stimulation (flurothyl ether) °o o[" control
Seizure
198 7 454 0.440 241 2.0 11
(n)
Control
(24) (19) (5) (5) (24) (5) (10)
% of control
(24) (15) (13) (8)
15.6 37.8 16.2 2.8
-4,
2.2 9.3 2.0 0.2
± 2.7 ±2.2 ± 1.7 ± 2.8
173"* 727** 279*** 72**
119 ns 41"** 59** 203***
155'** 350*** 100ns 152" 107" 95 ns 275***
0.7 0.3 0.5 0.1
± ± ± ± ~ ± 3
128 2 453 0.289 226 2.1 4
± -: ± :L
" 2 L0 ± 48 ± 0.054 :t- 4 ± 0.5 ± 1
155"** 800*** 107 ns 160"** 93* 105 ns 633**
212 8 491 0.479 219 2.1 19
=- 5 ± 2 -- 36 ± 0.094 :~ 5 ± 0.5 _-+-4
(14) (13) (5) (5) (14) (5) (5)
~ 4 ± 0 ± 13 ± 0.031 ± 3 4_. 0.1 ± l
19.3 11.1 14.8 66.0
137 1 459 0.298 235 2.0 3
(24) (15) (13) (8) 9.0 5.2 5.8 3.9
16.2 ± 1.3 26,8:1_2.0 25.3 :! 2.8 32.5 ± 1.5
2.9 -11.9+_: 10.7 = 79.4 =:
1161"** 419' 587* 81 *
20*** 52*** 47*** 203***
(13) (11) (8) (10)
22.0 5.0 16.6 0.1
0.4 1.9 2.3 5.5
14.6 ~ 1.3 2 2 . 5 4 - 1.8 22.8 ~_ 3.1 39.0 ± 2.0 0.6 0.3 0.8 0.1
3 1 45 0.054 4 0.3 2
Values were m e a s u r e d at the time o f m a x i m u m elevation of arterial pressure, n ~ n u m b e r of animals. All values expressed as m e a n L S.E. of mean. A b b r e v i a t i o n s : BPm, m e a n arterial pressure; CVP, central v e n o u s pressure; C O , cardiac o u t p u t ; H R, heart rate; L V E D P , left ventricular end-diastolic p r e s s u r e ; SV, stroke volume. Significance (P < 0.05): * P < 0.05; ** P .< 0.01 ; *** P < 0.001. ns - n o t significant. See M e t h o d s for m e t h o d of statistical analysis.
BPm ( m m Hg) CVP (cm H20) CO (ml/min) T P R (ram H g • m i n / m l ) H R (beats/rain) SV (ml/beat) L V E D P (ram Hg)
Regional blood flow (ml/min) F e m o r a l artery R e n a l artery M e s e n t e r i c artery C o m m o n carotid artery
116.1 24.7 44.0 2.9
~ ~ -~
: ± -~ ±
(13) (1 l) (8) (10)
10.0 5.9 7.5 3.6
Regional vascular resistance (ram Hg • min/ml) F e m o r a l artery R e n a l artery Mesenteric artery C o m m o n carotid artery
122 TABLE I1 C H A N G E S IN ( A R D I O V A S C U L A R D Y N A M I C S D U R I N G S E I Z U R E S P R O D U C E D BY D I R E C T C O R ' r I ( ? A L S I I M U I a, TION IN C A ' r
Values were measured at the time of peak elevation of arterial pressure. All values, abbreviations and symbols are expressed as in Table I.
Transcortical stimulation
BPm (mm Hg O) CVP (cm H20) CO (ml/min) TPR (mm Hg - min/ml) HR (beats/min) SV (ml/beat) LVEDP (mm Hg)
Control
(n)
Seizure
% of "o/ttrol
121 i 2 3 .k 0 452 5:14 0.293 -- 0.014 229 ::!: 5 2.1 5 0.1 5 I
(24) (19) (5) (5) (24) (5) (10)
161 ± 4 4 5_ I 512 ± 20 0.349 ~g 0.018 247 5 5 2.3 .L 0.1 3 2
133 133 113 119 108 110 60
*** ns * * * ns ns
16.0 -L 1.2 26.6 1.6 19.7 ~ 0.5 37.2 ~ 1.4
(18) (9) (9) (5)
15.7 =: 1.4 28.7 ± 2.0 12.4 ~ 1.1 65.2 L 4.6
98 108 63 175
ns ns *** ***
(18) (9) (9) (5)
11.8 ~ 5.5 ± 14.3 k 2.7 ~
144 122 223 75
* * *** ***
Regional bloodflow (ml/min) Femoral artery Renal artery Mesenteric artery Common carotid artery
Regional vascular resistance (ram Hg • miu/ml) Femoral artery Renal artery Mesenteric artery Common carotid artery
8.2 :!: 0.5 4.5 _: 0.1 6.4 i 0.1 3.6 1.4
1.3 0.3 1.2 0.1
Differs from control: * P < 0.05, ** P < 0.01, *** P < 0.001; ns == not significant. arterial pressure a b o u t as much. O n the other hand, direct cortical stimulation (Table lI) elicited p e a k elevations o f m e a n arterial pressure which were substantially smaller than those initiated by other means. Since direct cortical stimulation p r o d u c e d the m o s t p r o l o n g e d seizures, it is evident that the d u r a t i o n o f the seizure and the magnitude o f the rise o f arterial pressure do not correlate. In general, the responses e v o k e d by transcerebral s t i m u l a t i o n or by the chemical agents were qualitatively similar and exhibited stereotyped and patterned circulatory responses, differing only in the m a g n i t u d e o f the c o m p o n e n t parts, and can be discussed as a group. In Table I the c a r d i o v a s c u l a r responses to transcerebral stimulation or, for brevity in response to one o f the agents, flurothyl ether, are tabulated. On the other hand, the c a r d i o v a s c u l a r changes associated with direct cortical stimulation (Table II) were substantially different and will be discussed separately, below.
(III) Cardiovascular changes with seizures evoked eleetrically by transcerebral stimulation or chemically by convulsants ( A ) Changes in cardiodynamics, total peripheral resistance, and central venous pres.sure Seizures p r o d u c e d electrically by transcerebral shock, or chemically, were
123 associated with substantial elevations in the total peripheral resistance (Table 1). Despite small individual and group variations in heart rate, never greater than 10 ~ of control, the cardiac output was unchanged and stroke volume remained constant indicating that the increase in arterial pressure is entirely due to an increased peripheral resistance. During the peak elevation of arterial pressure, left ventricular end-diastolic pressure was usually increased (Table I). Since cardiac output is maintained in the face of an elevation of total peripheral resistance during seizures it is probable that the force of myocardial contraction is also increased. The central venous pressure was also substantially elevated during seizures (Figs. 1 and 2, Table I) rising 8-fold during seizures produced by transcerebral stimulation and 3-4-fold in chemically induced seizures (Table I). In addition, frequent bouts of ventricular arrhythmias were observed during the peak rise of arterial pressure in association with seizures produced by any means.
( B) Changes in regional blood flow and resistance Rapid and marked changes in regional blood flow and resistances in the femoral, renal, mesenteric, and carotid arteries occurred during convulsions (Figs. 1 and 2; Table I). During seizures renal (Figs. 1 and 2) and mesenteric arterial blood flows were reduced by nearly 50 ~,, and regional resistances were substantially elevated. The changes in flow occurred within the first 5 sec of the onset of the seizure and persisted for many seconds following its cessation (Figs. 1 and 2). When seizures were repetitive (Fig. 2), reduction in regional flow might be relatively sustained throughout the ictal state. Often, at the onset of seizures, there was a small and transient increase in femoral arterial flow (Figs. 1 and 2). Femoral blood flow then returned to control or even reduced levels in association with an increase in femoral arterial resistance, paralleling the elevation of systemic pressure. With electrically induced seizures, femoral arterial resistance increased 10-fold (Table I). With chemically induced seizures, changes of femoral resistance were less pronounced (Table I). In contrast to the response in other vascular beds, blood flow increased and resistance decreased in the common carotid artery during seizures. These changes probably reflect the well established associated increase in cerebral blood flow z,zT,'-'8,3".
(C) Peripheral rnechan&ms of cardiovascular changes with seizures We next sought to establish the nature of the peripheral mechanisms mediating the elevation of arterial blood pressure and changes in regional blood flow and resistances associated with seizures. (1) Adrenergic blockade. The systemic administration of the a-adrenergic antagonist phentolamine (1 mg/kg, i.v.) entirely blocked the elevation of arterial pressure and alterations in regional vascular resistances associated with seizures (Fig. 3). The/3-adrenergic antagonist, propranolol (1 mg/kg, i.v.), had no such effect. (2) Cholinergic blockade. Atropine sulfate administered systemically (0.2 mg/kg, i.v.) blocked the initial bradycardia which accompanied seizures induced by trans-
124 EFFECTOF PHENTOLAMINE ON PRESSORRESPONSES TO SEIZURES 200 ....
----] Restingstate ~ eizure
~
no]8 150 o~
100--
Control Phentolamine *Differs from restingpressure(p
115
CHANGES IN REGIONAL BLOOD FLOW AND CARDIODYNAMICS ASSOCIATED WITH ELECTRICALLY AND CHEMICALLY INDUCED EPILEPSY IN CAT
NOBUTAKA DOBA, H. R I C H A R D BERESFORD AND DONALD J. REIS
Laboratory of"Neurobiology, Department of Neurology, Cornell University Medical College, New York, N. Y. 10021 (U.S.A.) (Accepted December 14th, 1974)
SUMMARY
Changes in cardiodynamics and regional blood flow were examined in chronically prepared paralyzed cats during seizures induced electrically by transcerebral or direct cortical stimulation or by administration of flurothyl ether (lndoklon) or pentylenetetrazol (Metrazol). Transcerebral and chemical stimuli produced the greatest vascular responses. During seizures there was an abrupt elevation of arterial pressure unassociated with consistent changes in heart rate. Vascular resistance was increased in femoral, renal and mesenteric arteries with variable reductions in blood flow. Resistance was decreased and flow passively increased in the c o m m o n carotid artery reflecting the loss of cerebral autoregulation. Cardiac output was unchanged. With seizures associated with large elevations of arterial pressure, the central venous and left ventricular end-diastolic pressures were markedly increased indicating incipient congestive failure. The pressor response was blocked by alpha-adrenergic blockade with phentolamine. Increased regional vascular resistance was abolished by regional sympathectomy. While either adrenalectomy or treatment with 6-hydroxydopamine alone failed to abolish the pressor response, combined, they did. Such treatment unmasked an atropine-sensitive bradycardia. The pressor response with seizures is a consequence of increased vascular resistance in viscera and muscles due to widespread activation of sympathetic neurons and release of adrenomedullary catecholamines. Co-activation of cardiovagal and cardiosympathetic neurons may underlie some associated arrhythmias. Cardiovascular events may serve, by redistribution of the cardiac output, to assure increased availability of oxygen and nutrients to brain to meet the metabolic demands of convulsions.
INTRODUCTION
Epileptic seizures in man or animals are associated with a marked elevation of
116 the systemic arterial pressure e 1.7, ls,eT,es,::m. While it is known that during convulsions there is a substantial increase in cerebral blood flow-',zv,zs,az, cerebral venous pressure z7 and an increase in resistance in the femoral arteries v, it has never been established if the elevation in arterial pressure is due to increased cardiac output or total peripheral resistance, and if'the latter if the vasoconstriction observed in femoral arteries v is widely distributed or only involves specific vascular beds. Such information is of interest for it raises the question as to whether the autonomic responses in epilepsy are generalized or involve selective and differentiated activation of the sympathetic nervous system l°.aa. in the present study we have therefore investigated in cat the changes in cardiodynamics and in the regional distribution of blood flow during convulsions produced electrically or by administration of convulsive agents. METHODS
General Twenty-five mongrel cats were anesthetized with ether. After insertion ofcannulae in the femoral artery, femoral vein and trachea, each animal was paralyzed with gallamine triethiodide (5 mg/kg, i.v.), and artificially ventilated with 2 ~ halothane in t00 ~ 02 delivered from a canister to a small animal respirator (Harvard Instrument Co.) via an anesthetic bag. The flow rate of halothane was adjusted so as to maintain adequate filling of the reservoir bag. End-tidal CO~ recorded by an infrared gas analyzer (Beckman LI) was maintained at 2-3 ~ throughout the experiment. The rectal temperature ranged from 36.5 to 38 °C, hypothermia being averted through use of a thermostatically regulated infrared lamp.
Recording of electroencephalogram ( EEG) The animal was placed in a stereotaxic frame and 3 small steel screws were placed in the skull. The first two screws were placed over the rostral portions of the parasagittal lobe on the surface of the dura mater and used as recording electrodes. The other screw was placed in the mid-portion of the occipital bone a n d served as an indifferent electrode. The E E G was recorded by an AC coupler (Beckman 9806A) with suitable amplification (100 #V/cm) and displayed on a polygraph (Beckman Dynograph Recorder, 504A).
Measurement of cardiovascularfunctions Systemic arterial pressure (BP) was recorded from a polyethylene catheter which was threaded up the femoral artery into the abdominal aorta and connected to a Statham P23Db transducer. The heart rate (HR) was computed from the blood pressure pulse by a cardiotachometer (Beckman 9857). End-tidal CO2 was sampled through a fine catheter placed in a tracheal cannula, and was recorded by an infrared gas analyzer (Beckman LB-1). All cardiovascular activity was displayed on a polygraph. Regional blood flow was recorded by a square-wave electromagnetic flowmeter
ll7 (Carolina Medical Electronics, types 322 and 332) 8. Flow probes (Carolina Medical Electronics, Ep 403R, 404R, and 420R) were applied to the femoral, renal, mesenteric and common carotid arteries and the ascending aorta. No more than two probes were inserted in an animal at any one time. However, in any one experiment flow changes in numerous beds might be sampled. Renal flow was never measured after a laparotomy since the operation may produce reflex effect on renal flow 16. After placement of the flow probe, the incision was closed and sutured areas were infiltrated with 2% procaine. Particular care was taken to assure mechanical stability of the arterial probe. The zero level of the flowmeter was established in situ before and after an experimental series by occluding the artery distally. At the termination of an experiment, the probes were calibrated by a standard method. In all instances mean blood flow was recorded through an integrated circuit built in the flowmeter. The mean arterial pressure (Pm) was derived from the formula (Ps + 2Pd)/3, where Ps was systolic pressure and Pd was diastolic pressure s. Regional vascular resistance (RVR) was conventionally obtained from the formula: RVR = Pro/Fro, where Fm was mean blood flow in a given vascular bed s. Cardiac output (CO) was estimated from the blood flow in the ascending aortaS, 2~. Total peripheral resistance (TPR) was calculated from the formula: TPR = (Pro - - CVP)/CO, where CVP was central venous pressure measured through a polyethylene catheter inserted into the right atrium through the femoral vein. Stroke volume (SV) was calculated from the formula: SV = CO/HR. Left ventricular enddiastolic pressure (LVEDP) was measured through a catheter threaded down the left common carotid artery and positioned in the left ventricle. Induction of seizures After catheters and flow probes were in place, the animal was taken from the stereotaxic frame and placed in a supine or recumbent position without restraint. The wound edges were infiltrated with procaine (2 ~ ) and lidocaine ointment (2 ~o) was applied to the corneas. Halothane in 100 ~ 02 was then replaced by room air. During the remainder of the experiment paralysis was maintained by periodically administrating gallamine, the trachea cleared and wounds reinjected with procaine. Any additional surgical procedures were performed after the animal was anesthetized with 2 halothane. With such care arterial pressure and heart rate remained at control levels during the duration of the experiment. One hour after stopping halothane, seizures were induced by one of 4 different procedures. (1) Flurothyl ether (Indoklon) (0.05-0.075 hal) was injected by a small syringe through a hole in a tracheal cannula during the inspiratory phase of artificial ventilation. (2) Pentylenetetrazol (PTZ) (Metrazol) (10 mg/kg, i.v.) was injected into the femoral vein. (3) Transcerebral stimulation was performed by passing DC current (170 V, 100 mA, 1-sec pulse) from a device used for electroconvulsive therapy (Model B24, Medcraft Electronic Co.) through saline-soaked gauzes attached with a clip to the ears. (4) Direct cortical stimulation was performed through two thin monopolar electrodes consisting of a stainless steel wire (diameter 0.006 in.) coated with Teflon and bared at the tip for 1 mm and carried in a No. 28 stainless steel hypodermic needle.
118 The electrodes were placed bilaterally in the rostral portion of the marginal gyrus via small holes that were drilled through the parietal bone with a dental drill. These electrodes were fixed to the skull with dental acrylic cement. Seizures were induced by stimulation through both electrodes (cathodes) with a 10-sec train of square wave pulses of 0.5 msec duration at a stimulus frequency of 50 Hz, delivered t'rom a pulse generator (Devices, Digitimer) through a constant current stimulus isolation unit (Devices MK IV). The stimulus current was 2-5 mA. The anode was a skin clip. In any one animal seizures could be produced repeatedly by the various methods described above following stimulus-free intervals of 10-15 min. The stimulus parameters used for electrical stimulation and the dose of convulsive agents were established in preliminary studies to predictably initiate a single seizure sustained for at least 20 sec (see Table !).
Experimental maneuvers (1) Autonomic blockade. Alpha-adrenergic blockade was achieved by administration of phentolamine (1 mg/kg, i.v. CIBA), beta-adrenergic blockade by propranolol (1 mg/kg, i.v. Sigma Chemical Co.) and cholinergic blockade by atropine sulfate (0.2 mg/kg, i.v. Elkins,Sinn, Inc.). (2) Regional sympathetic denervation. Denervation of the renal artery was accomplished by transection of the renal nerves via a retroperitoneal approach. The femoral artery was denervated by transection of both the sciatic and femoral nervesS,40. (3) Bilateral adrenalectomy. Both adrenals were removed through a laparotomy. Careful efforts were made to maintain homeostasis. (4) Chemical sympathectomy. Acute chemical sympathectomy was performed by adaptation of the method of others 9,a3 by systemic administration of 6-hydroxydopamine (6-OHDA) hydrobromide (Regis Chemical Co.). In brief, each animal received 100 mg/i.v, divided into 3 equal doses of 33 rag. After each injection, heart rate and blood pressure were permitted to return to control levels before another injection was made, and at least 30 rain was allowed to elapse between any two successive injections. After the first dose of 6-OHDA, l0 ml of 5 ~ dextran was administered intravenously to present hemoconcentration 13. The solution of 6-OHDA was prepared before injection by dissolving the drug in physiologic saline containing ascorbic acid (1 mg/ml) to block auto-oxidation. Seizures were not induced until at least 2 h after the first injection of 6-OHDA. Tyramine hydrochloride (Sigma Chemical Co.) was used to assess the efficiency of chemical sympathectomyg, tz. The dose-response relationship was examined prior to and after administration of 6-OHDA with the graded injection of tyramine hydrochloride (20-200 #g/kg, i.v.). After 2 h from the completion of the full dose of 6O H D A (100 rag/animal, i.v.), the dose-response curve was shifted to the right with marked reduction both in amplitude (P < 0.01) and duration at all dosages.
Evaluation of data For quantitative assessment of the changes in any cardiovascular parameter, the
119 20 CVP (cm H20)
10 0
Femoral arterial 20 flow (ml / min) 0~Renal arterial flow (ml / min)
Heart rate (bpm)
20 0 260 F 180 L 3OO
~
Blood pressure (mm Hg) 200
loo
EEG
100pV
I t FLUROTHYL ~"1~~ ~~'
lmin
I
Fig. l. Changes in arterial pressure, heart rate (in beats/min, bpm), blood flow in the renal and femoral arteries, and central venous pressure (CVP), during a convulsion produced by flurothyl ether in paralyzed artificially ventilated cat. See text for details.
responses during at least 3 representative seizures and preseizure control values were averaged for each animal. The means (control and seizure) were then used as a single value for that animal. Statistical evaluation was prefaced by comparing poststimulus to prestimulus value for the group, the n representing the number of animals, by use of a paired t-test 3s. P < 0.05 were considered significant. RESULTS
(I) Character of seizures Seizures produced electrically by direct cortical or transcerebral stimulation or by the administration of the epileptogenic agents, flurothyl ether (Indoklon) or pentylenetetrazol (PTZ; Metrazol) were characterized by widespread spike and wave activity recorded over the cerebral cortex. The duration of the seizures evoked by the various methods in part differed. Seizures (as defined by the presence of spike and wave activity on the cortex) induced by direct cortical stimulation persisted the longest (59.5 ~ 2.5 sec; n = ! 8); those initiated by transcerebral stimulation were the briefest
120
CVP (cm H20) Femoral arterial flow (ml I mint
31t
Renal arterial flow (mll min) Heart rate (bpm)
260 [-- . . . . .
~
...~.-~---..~-~_~-_
l
220 L
200 Blood pressure 150 Imm Hg) IO0 EEG
lOOpV
I
I
tPTZ (20mg, iv) I min Fig. 2. Changes in arterial pressure, heart rate, blood flow in renal and femoral arteries, and central venous pressure (CVP) during a burst of repetitive seizures produced by pentylenetetrazol (PTZ) (20 rag, i.v.) in paralyzed artificially ventilated cat. (22.0 ± 1.0; n .... 14) while the duration of seizures induced chemically by either flurothyl ether or P T Z lasted approximately 45 sec. In most instances the seizures occurred as a continuous uninterrupted burst of cortical high voltage activity (e.g. Fig. 1). In some instances, however, the seizures appeared in repetitive bursts lasting up to 1 min (Fig. 2). Since the animals in this study were paralyzed, no motor manifestations of the seizure discharge were observed. However, all animals exhibited pupillary dilatation, retraction of the nictitating membrane, and profuse salivation in association with activation of the EEG.
(I1) Cardiovascular changes with seizures As previously noted~-5,7,1s,ev,zs, 32 seizures initiated by any means were associated with elevations in systolic, diastolic and mean arterial pressures (Figs. 1-7, Tables I and II). Sometimes, but not invariably, the rise of arterial pressure was preceded by a slight fall (Figs. 1 and 5). The onset of the alteration of arterial pressure began within the first 3 sec of the appearance of cortical electrical activity, peaked from 50 to 30 sec and remained elevated, sometimes for minutes, after the cortical E E G returned to normal. The magnitude of the elevation of arterial pressure varied with the mode of evoking the seizures, Under the conditions of this study transcerebral stimulation produced the largest elevation of mean arterial pressure (Table i) with peak elevations averaging 212 m m Hg: Chemical stimulation (Table 1) increased
TABLE I
CHANGES IN CARDIOVASCULAR DYNAMICS D U R I N G SEIZURES PRODUCED ELECTRICALLY (TRANSCEREBRAL) OR CHEMICALLY (ELUROTHYL ETHER) IN PARALYZED CAT
Electrieal stimulation (transcerebral)
Control
(n)
Seizure
Chemical stimulation (flurothyl ether) °o o[" control
Seizure
198 7 454 0.440 241 2.0 11
(n)
Control
(24) (19) (5) (5) (24) (5) (10)
% of control
(24) (15) (13) (8)
15.6 37.8 16.2 2.8
-4,
2.2 9.3 2.0 0.2
± 2.7 ±2.2 ± 1.7 ± 2.8
173"* 727** 279*** 72**
119 ns 41"** 59** 203***
155'** 350*** 100ns 152" 107" 95 ns 275***
0.7 0.3 0.5 0.1
± ± ± ± ~ ± 3
128 2 453 0.289 226 2.1 4
± -: ± :L
" 2 L0 ± 48 ± 0.054 :t- 4 ± 0.5 ± 1
155"** 800*** 107 ns 160"** 93* 105 ns 633**
212 8 491 0.479 219 2.1 19
=- 5 ± 2 -- 36 ± 0.094 :~ 5 ± 0.5 _-+-4
(14) (13) (5) (5) (14) (5) (5)
~ 4 ± 0 ± 13 ± 0.031 ± 3 4_. 0.1 ± l
19.3 11.1 14.8 66.0
137 1 459 0.298 235 2.0 3
(24) (15) (13) (8) 9.0 5.2 5.8 3.9
16.2 ± 1.3 26,8:1_2.0 25.3 :! 2.8 32.5 ± 1.5
2.9 -11.9+_: 10.7 = 79.4 =:
1161"** 419' 587* 81 *
20*** 52*** 47*** 203***
(13) (11) (8) (10)
22.0 5.0 16.6 0.1
0.4 1.9 2.3 5.5
14.6 ~ 1.3 2 2 . 5 4 - 1.8 22.8 ~_ 3.1 39.0 ± 2.0 0.6 0.3 0.8 0.1
3 1 45 0.054 4 0.3 2
Values were m e a s u r e d at the time o f m a x i m u m elevation of arterial pressure, n ~ n u m b e r of animals. All values expressed as m e a n L S.E. of mean. A b b r e v i a t i o n s : BPm, m e a n arterial pressure; CVP, central v e n o u s pressure; C O , cardiac o u t p u t ; H R, heart rate; L V E D P , left ventricular end-diastolic p r e s s u r e ; SV, stroke volume. Significance (P < 0.05): * P < 0.05; ** P .< 0.01 ; *** P < 0.001. ns - n o t significant. See M e t h o d s for m e t h o d of statistical analysis.
BPm ( m m Hg) CVP (cm H20) CO (ml/min) T P R (ram H g • m i n / m l ) H R (beats/rain) SV (ml/beat) L V E D P (ram Hg)
Regional blood flow (ml/min) F e m o r a l artery R e n a l artery M e s e n t e r i c artery C o m m o n carotid artery
116.1 24.7 44.0 2.9
~ ~ -~
: ± -~ ±
(13) (1 l) (8) (10)
10.0 5.9 7.5 3.6
Regional vascular resistance (ram Hg • min/ml) F e m o r a l artery R e n a l artery Mesenteric artery C o m m o n carotid artery
122 TABLE I1 C H A N G E S IN ( A R D I O V A S C U L A R D Y N A M I C S D U R I N G S E I Z U R E S P R O D U C E D BY D I R E C T C O R ' r I ( ? A L S I I M U I a, TION IN C A ' r
Values were measured at the time of peak elevation of arterial pressure. All values, abbreviations and symbols are expressed as in Table I.
Transcortical stimulation
BPm (mm Hg O) CVP (cm H20) CO (ml/min) TPR (mm Hg - min/ml) HR (beats/min) SV (ml/beat) LVEDP (mm Hg)
Control
(n)
Seizure
% of "o/ttrol
121 i 2 3 .k 0 452 5:14 0.293 -- 0.014 229 ::!: 5 2.1 5 0.1 5 I
(24) (19) (5) (5) (24) (5) (10)
161 ± 4 4 5_ I 512 ± 20 0.349 ~g 0.018 247 5 5 2.3 .L 0.1 3 2
133 133 113 119 108 110 60
*** ns * * * ns ns
16.0 -L 1.2 26.6 1.6 19.7 ~ 0.5 37.2 ~ 1.4
(18) (9) (9) (5)
15.7 =: 1.4 28.7 ± 2.0 12.4 ~ 1.1 65.2 L 4.6
98 108 63 175
ns ns *** ***
(18) (9) (9) (5)
11.8 ~ 5.5 ± 14.3 k 2.7 ~
144 122 223 75
* * *** ***
Regional bloodflow (ml/min) Femoral artery Renal artery Mesenteric artery Common carotid artery
Regional vascular resistance (ram Hg • miu/ml) Femoral artery Renal artery Mesenteric artery Common carotid artery
8.2 :!: 0.5 4.5 _: 0.1 6.4 i 0.1 3.6 1.4
1.3 0.3 1.2 0.1
Differs from control: * P < 0.05, ** P < 0.01, *** P < 0.001; ns == not significant. arterial pressure a b o u t as much. O n the other hand, direct cortical stimulation (Table lI) elicited p e a k elevations o f m e a n arterial pressure which were substantially smaller than those initiated by other means. Since direct cortical stimulation p r o d u c e d the m o s t p r o l o n g e d seizures, it is evident that the d u r a t i o n o f the seizure and the magnitude o f the rise o f arterial pressure do not correlate. In general, the responses e v o k e d by transcerebral s t i m u l a t i o n or by the chemical agents were qualitatively similar and exhibited stereotyped and patterned circulatory responses, differing only in the m a g n i t u d e o f the c o m p o n e n t parts, and can be discussed as a group. In Table I the c a r d i o v a s c u l a r responses to transcerebral stimulation or, for brevity in response to one o f the agents, flurothyl ether, are tabulated. On the other hand, the c a r d i o v a s c u l a r changes associated with direct cortical stimulation (Table II) were substantially different and will be discussed separately, below.
(III) Cardiovascular changes with seizures evoked eleetrically by transcerebral stimulation or chemically by convulsants ( A ) Changes in cardiodynamics, total peripheral resistance, and central venous pres.sure Seizures p r o d u c e d electrically by transcerebral shock, or chemically, were
123 associated with substantial elevations in the total peripheral resistance (Table 1). Despite small individual and group variations in heart rate, never greater than 10 ~ of control, the cardiac output was unchanged and stroke volume remained constant indicating that the increase in arterial pressure is entirely due to an increased peripheral resistance. During the peak elevation of arterial pressure, left ventricular end-diastolic pressure was usually increased (Table I). Since cardiac output is maintained in the face of an elevation of total peripheral resistance during seizures it is probable that the force of myocardial contraction is also increased. The central venous pressure was also substantially elevated during seizures (Figs. 1 and 2, Table I) rising 8-fold during seizures produced by transcerebral stimulation and 3-4-fold in chemically induced seizures (Table I). In addition, frequent bouts of ventricular arrhythmias were observed during the peak rise of arterial pressure in association with seizures produced by any means.
( B) Changes in regional blood flow and resistance Rapid and marked changes in regional blood flow and resistances in the femoral, renal, mesenteric, and carotid arteries occurred during convulsions (Figs. 1 and 2; Table I). During seizures renal (Figs. 1 and 2) and mesenteric arterial blood flows were reduced by nearly 50 ~,, and regional resistances were substantially elevated. The changes in flow occurred within the first 5 sec of the onset of the seizure and persisted for many seconds following its cessation (Figs. 1 and 2). When seizures were repetitive (Fig. 2), reduction in regional flow might be relatively sustained throughout the ictal state. Often, at the onset of seizures, there was a small and transient increase in femoral arterial flow (Figs. 1 and 2). Femoral blood flow then returned to control or even reduced levels in association with an increase in femoral arterial resistance, paralleling the elevation of systemic pressure. With electrically induced seizures, femoral arterial resistance increased 10-fold (Table I). With chemically induced seizures, changes of femoral resistance were less pronounced (Table I). In contrast to the response in other vascular beds, blood flow increased and resistance decreased in the common carotid artery during seizures. These changes probably reflect the well established associated increase in cerebral blood flow z,zT,'-'8,3".
(C) Peripheral rnechan&ms of cardiovascular changes with seizures We next sought to establish the nature of the peripheral mechanisms mediating the elevation of arterial blood pressure and changes in regional blood flow and resistances associated with seizures. (1) Adrenergic blockade. The systemic administration of the a-adrenergic antagonist phentolamine (1 mg/kg, i.v.) entirely blocked the elevation of arterial pressure and alterations in regional vascular resistances associated with seizures (Fig. 3). The/3-adrenergic antagonist, propranolol (1 mg/kg, i.v.), had no such effect. (2) Cholinergic blockade. Atropine sulfate administered systemically (0.2 mg/kg, i.v.) blocked the initial bradycardia which accompanied seizures induced by trans-
124 EFFECTOF PHENTOLAMINE ON PRESSORRESPONSES TO SEIZURES 200 ....
----] Restingstate ~ eizure
~
no]8 150 o~
100--
Control Phentolamine *Differs from restingpressure(p
