Actu Physiol Scand 1992, 146, 107-117
Adrenergic and non-adrenergic cardiovascular effects of thyrotropin-releasing hormone (TRH) in the anaesthetized rabbit E. E. S E L I G S O H N Department of Physiology and Medical Biophysics, Biomedical Centre, Uppsala University, Uppsala, Sweden
SELIGSOHN, E. E. 1992. Adrenergic and non-adrenergic cardiovascular effects of thyrotropin-releasing hormone (TRH) in the anaesthetized rabbit. Actu Physiol S c u d 146, 107-117. Received 19 August 1991, accepted 17 March 1992. ISSN 0001-6772. Department of Physiology and Medical Biophysics, Uppsala University, Sweden. The effects of thyrotropin-releasing hormone (TRH) on regional blood flows were studied in urethane-anaesthetized rabbits. Experiments were performed both with and without adrenergic antagonist pretreatment. The tracer microsphere method was used to measure blood flow. TRH (0.1 mg kg-l) caused an increase in mean arterial blood pressure (MAP) from 9.8f 1 to 11.8f0.8; a higher dose (1 mg kg-l) increased the blood pressure to 15.2f 1 kPa (P < 0.001). Total cerebral blood flow (CBF,,,) increased to 137f 10% ( P < 0.05) of control at the lower dose and to 214$16% ( P < 0.001), at the higher dose. A reduction in blood flow at both doses of TRH in several peripheral organs indicates that the pressor effect was mainly due to an effect on the peripheral vascular resistance. In prazosin-pretreated animals in which the MAP was normalized by ligation of the thoracic aorta, T R H elicited an increase in the CBF,,, to 131& 12”/6(P < 0.05) of control. In the iris, T R H caused vasodilation in prazosin-pretreated animals. In experiments with combined a- and b-adrenergic blockade, a non-adrenergic vasoconstricting effect of TRH was seen in some peripheral organs. The results indicate that T R H activates the sympathetic nervous system thus causing an increased vascular resistance and MAP; these effects are mediated mainly by an aladrenergic mechanism. In the spleen, the gastric mucosa and the adrenal glands, the vasoconstriction caused by T R H was partly non-adrenergic. The vasodilation seen in the small intestine and the anterior uvea after TRH treatment and adrenoceptor blockade may be explained by effects on the parasympathetic nervous system. The vasodilating effect of TRH in the brain does not seem to involve al- or j5’-adrenergic mechanisms. Key words : adrenergic antagonists, blood flow, blood pressure, brain, cardiovascular control, eye, peripheral resistance, rabbit, TRH, thyroliberin.
Thyrotropin-releasing hormone is a hypothalamic hormone which stimulates the release of thyrotropin and prolactin. Receptors for TRH have been identified and localized in the central nervous system (CNS) (Hokfelt et al. 1975, Ogawa et al. 1983) as well as in various peripheral tissues (Leppaluoto et al. 1978). I n addition to Correspondence : E. E. Seligsohn, Department of Physiology and Medical Biophysics, Box 572, S-75 1 23 Uppsala, Sweden.
its endocrine effects, TRH elicits behavioural changes, tremor, analepsis, and stimulation of respiration, visceral movements and gastric acid secretion (Horita et al. 1986). Today TRH is recognized as a neurotransmitter. I t has been proposed that TRH is involved in the control of the autonomic nervous system and cerebral blood flow (CBF) in the rabbit (Koskinen 1986a, Seligsohn & Koskinen 1991). In these animals TRH was found to cause peripheral vasoconstriction, cerebral vasodilation and increased blood
107
108
E . E . Seligsohn
pressure (Koskinen & Bill 1984, HugosonSeligsohn & Koskinen 1989). T h e effects of TRI-I on regional blood flows in other species such as cats (Mirzoyan et a / . 1985) and rats (Koskinen 1989a) have also been reported. Various effects of TRH on several neurotransmitter systems have been proposed and effects on neuronal actkit>- have been described (Yarbrough 1979). However, the peripheral vasoconstrictor and cerebral vasodilating mechanisms o f T R H are not fully understood. T h e peripheral vasoconstriction is, to a large extent, due to an actil-ation of the sympathetic nervous system (Koskinen 1986a). I n rats, there is evidence that stimulation of both sympathetic and parasympathetic actkit!- occurs (Koskinen 1989a). T h e cerebral vasodilation elicited by TRH seems to be due to activation of an intrinsic cerebral vasodilator pathway (Koskinen 1986a) and this pathwav seems to include an yohimbinesensitive r,-adrenergic component (Seligsohn & Koskinen 1991). I n this study the involvement of' an 2,-adrenergic component in the cardiovascular effects of TRH was investigated. I t was found that a major part of the peripheral vasoconstrictor effects were mediated by J adrenoceptors but not all of the effects were abolished after z,-adrenoceptor blockade with prazosin. I t seemed possible that such vasoconstrictor effects might be caused b!- NPY or ATP co-released with noradrenaline. Therefore, the effects of TRH were investigated also after blockade with phenoxybenzamine and propranolo1 at doses that should block adrenergic as well as histamine, serotonin and acetylcholine receptors. TRI-I has been shown to increase CBF at doses of 0.025, 0.050 and 2 mg kg,' in the anaesthetized rabbit (Koskinen & Bill 1984, Koskinen 1986 b). Recentll-, Faden (1989) reported that in rats, the administration of TRH analogue, Yhl 14673, improves the neurological outcome following traumatic brain and spinal cord injury. Faden's results indicate a doseresponse relationship with maximal response at moderate doses and diminishing effect at higher doses. Therefore in the present study different doses of TRIi (0.1 and 1.0 mg kg-') were used in the experiments with the adrenergic blocking agent. T h e results have been reported in part at the Scandinavian Physiological Society meeting, Uppsala, Sweden, May 1991.
,-
MATERIALS AND METHODS New Zealand white rabbits of either sex weighing between 1.5-3.3 kg were used. The animals were anaesthetized with a 2506 solution of urethane in a dose of 7 ml kg-' infused into a marginal ear vein. The animals were tracheotomized and artificially ventilated with a Palmer pump. Both femoral arteries were cannulated with polyethylene catheters. One was used for measurements of mean arterial blood pressure (AIAP) and heart rate (HR), the other for blood sampling. X vein was cannulated and used for drug delivery. The free flow method with tracer microspheres was used to determine the regional blood flows (,Urn & Bill 1972). The microspheres were injected directly through a polyethylene catheter into the left ventricle entered via a brachial artery. Fifteen pm spheres labelled with 141Ce, "'Sn or '"'Ru were used (KEN Chemicals, Boston, MA, USA). Arterial blood gases (Po2, Pco,) and pH were determined at intervals with an ABL 300 acid-base analyzer (Radiometer, Copenhagen, Denmark). Any deviations in the acid-base balance were corrected by administering sodium bicarbonate and/or changing the ventilation rate. Heparin" (Kabi Vitrum, Stockholm, Sweden), 500 IU kg-' was given intravenously (i.v.) to prevent clotting. Tubocurarine (Tubocuran", Nordisli Droge, Copenhagen, Denmark or tubocurarine-chloride, Sigma Chemical Company, St Louis, 3110, US.4) 0.5-1 mg kg-' was administered i.v. to induce skeletal muscle relaxation. Body temperature was recorded by a rectal thermistor and maintained at about 38 "C with a heating pad. In order to elucidate the effects of T R H on the s!-mpathetic nerves to the head region, the cervical sympathetic chain was unilaterally identified and sectioned about 1 cm below the upper cervical ganglion. Blood flow data for the sectioned side were then compared with the data for the intact side. Dose-response relationship of TRH. In the first series of experiments (n = 6), control blood flows were first measured and then 0.1 mg kg-' T R H was given i.v. Five min after the injection of TRH, the second blood flow determination was made. After another 15 min an injection of 1 mg kg-' TRH was given i.v. and blood flows measured 5 min later. Eflects of TRH after a,-adrenergic blockade. In the second group of animals (n = 7). 0.5 mg kg-l of prazosin, an a,-adrenergic blocking agent, was given i.v., followed 15 min later by 0.1 mg kg-' of TRH. In this group, the blood pressure was very low and the CBF,", response to T R H might be reduced due to near maximal vasodilation caused by autoregulatory mechanisms. Therefore, in the third group of experiments (prazosin-plus-ligation) (n = 6), prazosin was again used, however the blood pressure was normalized in the cranial part of the body by ligating the thoracic part of the aorta; onlj- cerebral blood flow was
TRH, adrenergic blockade and bloodjow evaluated. In these experiments, the procedure differed in some respects from that described above. Blood pressure recording was performed through an ear artery and a brachial artery was cannulated in order to collect blood samples. A brachial vein was cannulated for drug injections. Thoracotomy was performed and a loose ligature was placed around the descending aorta near the aortic arc. After the i.v. administration of 0.5 mg kg-' prazosin, the blood pressure was elevated to approximately control level by ligation of the descending aorta. A control blood flow measurement was performed followed by the i.v. administration of 0.1 mg kg-' of T R H and after another 5 min the second blood flow measurement was made. Effects of TRH a f e r a- and ,/-adrenergic blockade. In the fourth and fifth groups of animals, 50 mg kg-' of phenoxybenzamine was given slowly i.v. followed by 2 mg kg-' of the ,/-adrenoceptor blocking agent propranolol. Phenoxybenzamine is a non-specific blocking agent at the dose used, blocking not only al- and uzadrenoceptors but also the effects of histamine, serotonin and acetylcholine (Furchgott 1972). The blood pressure fell during the infusion but was partly restored by the i.v. infusion of 30-40 ml of a mixture (1 : 1) of Macrodex (Pharmacia, Uppsala, Sweden) and Rehydrex (Pharmacia, Uppsala, Sweden). At least 15 min after the Macrodex/Rehydrex infusion, the blood flow was determined. Then 0.1 mg kg-' ( n = 7) or 1 mg kg-' ( n = 7) of T R H was given i.v. and 5 min later the last blood flow measurement was made. In all experiments the animals were killed by intracardial administration of saturated KCI after the last microsphere injection. Organs and tissue samples were autopsied and placed in preweighed plastic tubes. The radioactivity of the samples was analyzed by gamma spectrometry. The brain was removed and samples were collected including : grey matter, white matter, hippocampal region, caudate nucleus, thalamic region, hypothalamic region, collicles, pons-mesencephalon, medulla oblongata, cerebellum and spinal cord (Cl-C3). Remaining parts of the brain were placed in separate pre-weighed plastic tubes and were also analysed. Total cerebral blood flow (CBF,,,) was calculated to include all parts of the brain, except medulla oblongata and cerebellum. Cardiac output (CO) was calculated as CO = Q x CPMi x CPM;', where Q = reference blood flow, CPMi = reference radioactivity and CPM, = injected radioactivity. The regional peripheral vascular resistance (VR) was calculated as VR = MAP x Q;' where MAP is given in kPa and P,= tissue blood flow in g min-l g tissue-' and the VR values are expressed as vascular resistance unit (VRU). The following drugs were used: TRH, lot no. 125F-59201 (Sigma), prazosin HCI, lot no. 73604201 (Pfizer Inc., New York, USA) phenoxybenzamine
109
(DibenylineB, SK & F, Welwyn, Garden City, England), propranolol (InderaP, ICI-Pharma, Macclesfield, England). All drugs were dissolved in saline except prazosin which was dissolved in distilled water. Statistical evaluation of the results within treatments was made by analysis of variance (ANOVA) with repeated measurements. The two-tailed Student's ttest for paired observations was used as a postANOVA test. The level of significance was adjusted with Bonferroni's correction. Values given in of control have been analysed with the two-tailed Student's t-test for paired observations. The level of significance was set at P < 0.05. All results are given as means SE.
RESULTS There were no differences in resting CBFs between the side with an intact sympathetic supply and the sectioned side. No differences in CBFs were found between the two sides during the experiments, therefore only the CBF values for the side with an intact sympathetic supply are given. Dose-response relationship of TRH Arterial blood gases were within normal range and not affected by the administration of T R H . Basal values for H R and CO were 3 18 f 17 min-' and 499 f 141 g min-', respectively. No significant changes were observed in H R or C O during the experiments. The injection of 0.1 mg kg-' T R H caused an increase in MAP from 9.8 _+ 1 to 11.8f0.8 kPa and 1 mg kg-I of T R H further increased the MAP to 15.2f 1 kPa ( P < 0.001). In spite of the increase in blood pressure, both doses of T R H caused a decrease in blood flow in several organs investigated (Fig. 1). No significant effects were seen in the small intestine. The lower dose of T R H failed to reduce the blood flow in the spleen and triceps muscle, however it caused a statistically significant increase in VR in both tissues. After the higher dose of TRH, there was a statistically significant increase in VR in all investigated peripheral organs except the jejunum (data not shown). Total peripheral vascular resistance (TPR) was not affected by the lower dose of T R H (116 9 yo of control value) but the higher dose caused an increase in T P R to 176+9y0 ( P < 0.001) of control. T h e effects of unilateral sympathotomy were seen in some extracranial tissues for example the submandibular gland: the VR was lower on the sectioned side as compared with the intact side
110
E. E. Seligsohn ,Jejunum
Gastric mucosa Pancreas Spleen
Shn Tnreps muscle 0
25
50
75
125
150
5%
Fig. 1. Peripheral blood floiis in *(, of control after the administration of 0.1 mg kg-I ( 1.0 nig kgg' of 1 R H 01= 6 ) . * P < 0.05 ** P < 0.01 ; *** P < 0.001 as compared with control (Student's r-test).
(a)
LT
Adrenergic and non-adrenergic cardiovascular effects of thyrotropin-releasing hormone (TRH) in the anaesthetized rabbit E. E. S E L I G S O H N Department of Physiology and Medical Biophysics, Biomedical Centre, Uppsala University, Uppsala, Sweden
SELIGSOHN, E. E. 1992. Adrenergic and non-adrenergic cardiovascular effects of thyrotropin-releasing hormone (TRH) in the anaesthetized rabbit. Actu Physiol S c u d 146, 107-117. Received 19 August 1991, accepted 17 March 1992. ISSN 0001-6772. Department of Physiology and Medical Biophysics, Uppsala University, Sweden. The effects of thyrotropin-releasing hormone (TRH) on regional blood flows were studied in urethane-anaesthetized rabbits. Experiments were performed both with and without adrenergic antagonist pretreatment. The tracer microsphere method was used to measure blood flow. TRH (0.1 mg kg-l) caused an increase in mean arterial blood pressure (MAP) from 9.8f 1 to 11.8f0.8; a higher dose (1 mg kg-l) increased the blood pressure to 15.2f 1 kPa (P < 0.001). Total cerebral blood flow (CBF,,,) increased to 137f 10% ( P < 0.05) of control at the lower dose and to 214$16% ( P < 0.001), at the higher dose. A reduction in blood flow at both doses of TRH in several peripheral organs indicates that the pressor effect was mainly due to an effect on the peripheral vascular resistance. In prazosin-pretreated animals in which the MAP was normalized by ligation of the thoracic aorta, T R H elicited an increase in the CBF,,, to 131& 12”/6(P < 0.05) of control. In the iris, T R H caused vasodilation in prazosin-pretreated animals. In experiments with combined a- and b-adrenergic blockade, a non-adrenergic vasoconstricting effect of TRH was seen in some peripheral organs. The results indicate that T R H activates the sympathetic nervous system thus causing an increased vascular resistance and MAP; these effects are mediated mainly by an aladrenergic mechanism. In the spleen, the gastric mucosa and the adrenal glands, the vasoconstriction caused by T R H was partly non-adrenergic. The vasodilation seen in the small intestine and the anterior uvea after TRH treatment and adrenoceptor blockade may be explained by effects on the parasympathetic nervous system. The vasodilating effect of TRH in the brain does not seem to involve al- or j5’-adrenergic mechanisms. Key words : adrenergic antagonists, blood flow, blood pressure, brain, cardiovascular control, eye, peripheral resistance, rabbit, TRH, thyroliberin.
Thyrotropin-releasing hormone is a hypothalamic hormone which stimulates the release of thyrotropin and prolactin. Receptors for TRH have been identified and localized in the central nervous system (CNS) (Hokfelt et al. 1975, Ogawa et al. 1983) as well as in various peripheral tissues (Leppaluoto et al. 1978). I n addition to Correspondence : E. E. Seligsohn, Department of Physiology and Medical Biophysics, Box 572, S-75 1 23 Uppsala, Sweden.
its endocrine effects, TRH elicits behavioural changes, tremor, analepsis, and stimulation of respiration, visceral movements and gastric acid secretion (Horita et al. 1986). Today TRH is recognized as a neurotransmitter. I t has been proposed that TRH is involved in the control of the autonomic nervous system and cerebral blood flow (CBF) in the rabbit (Koskinen 1986a, Seligsohn & Koskinen 1991). In these animals TRH was found to cause peripheral vasoconstriction, cerebral vasodilation and increased blood
107
108
E . E . Seligsohn
pressure (Koskinen & Bill 1984, HugosonSeligsohn & Koskinen 1989). T h e effects of TRI-I on regional blood flows in other species such as cats (Mirzoyan et a / . 1985) and rats (Koskinen 1989a) have also been reported. Various effects of TRH on several neurotransmitter systems have been proposed and effects on neuronal actkit>- have been described (Yarbrough 1979). However, the peripheral vasoconstrictor and cerebral vasodilating mechanisms o f T R H are not fully understood. T h e peripheral vasoconstriction is, to a large extent, due to an actil-ation of the sympathetic nervous system (Koskinen 1986a). I n rats, there is evidence that stimulation of both sympathetic and parasympathetic actkit!- occurs (Koskinen 1989a). T h e cerebral vasodilation elicited by TRH seems to be due to activation of an intrinsic cerebral vasodilator pathway (Koskinen 1986a) and this pathwav seems to include an yohimbinesensitive r,-adrenergic component (Seligsohn & Koskinen 1991). I n this study the involvement of' an 2,-adrenergic component in the cardiovascular effects of TRH was investigated. I t was found that a major part of the peripheral vasoconstrictor effects were mediated by J adrenoceptors but not all of the effects were abolished after z,-adrenoceptor blockade with prazosin. I t seemed possible that such vasoconstrictor effects might be caused b!- NPY or ATP co-released with noradrenaline. Therefore, the effects of TRH were investigated also after blockade with phenoxybenzamine and propranolo1 at doses that should block adrenergic as well as histamine, serotonin and acetylcholine receptors. TRI-I has been shown to increase CBF at doses of 0.025, 0.050 and 2 mg kg,' in the anaesthetized rabbit (Koskinen & Bill 1984, Koskinen 1986 b). Recentll-, Faden (1989) reported that in rats, the administration of TRH analogue, Yhl 14673, improves the neurological outcome following traumatic brain and spinal cord injury. Faden's results indicate a doseresponse relationship with maximal response at moderate doses and diminishing effect at higher doses. Therefore in the present study different doses of TRIi (0.1 and 1.0 mg kg-') were used in the experiments with the adrenergic blocking agent. T h e results have been reported in part at the Scandinavian Physiological Society meeting, Uppsala, Sweden, May 1991.
,-
MATERIALS AND METHODS New Zealand white rabbits of either sex weighing between 1.5-3.3 kg were used. The animals were anaesthetized with a 2506 solution of urethane in a dose of 7 ml kg-' infused into a marginal ear vein. The animals were tracheotomized and artificially ventilated with a Palmer pump. Both femoral arteries were cannulated with polyethylene catheters. One was used for measurements of mean arterial blood pressure (AIAP) and heart rate (HR), the other for blood sampling. X vein was cannulated and used for drug delivery. The free flow method with tracer microspheres was used to determine the regional blood flows (,Urn & Bill 1972). The microspheres were injected directly through a polyethylene catheter into the left ventricle entered via a brachial artery. Fifteen pm spheres labelled with 141Ce, "'Sn or '"'Ru were used (KEN Chemicals, Boston, MA, USA). Arterial blood gases (Po2, Pco,) and pH were determined at intervals with an ABL 300 acid-base analyzer (Radiometer, Copenhagen, Denmark). Any deviations in the acid-base balance were corrected by administering sodium bicarbonate and/or changing the ventilation rate. Heparin" (Kabi Vitrum, Stockholm, Sweden), 500 IU kg-' was given intravenously (i.v.) to prevent clotting. Tubocurarine (Tubocuran", Nordisli Droge, Copenhagen, Denmark or tubocurarine-chloride, Sigma Chemical Company, St Louis, 3110, US.4) 0.5-1 mg kg-' was administered i.v. to induce skeletal muscle relaxation. Body temperature was recorded by a rectal thermistor and maintained at about 38 "C with a heating pad. In order to elucidate the effects of T R H on the s!-mpathetic nerves to the head region, the cervical sympathetic chain was unilaterally identified and sectioned about 1 cm below the upper cervical ganglion. Blood flow data for the sectioned side were then compared with the data for the intact side. Dose-response relationship of TRH. In the first series of experiments (n = 6), control blood flows were first measured and then 0.1 mg kg-' T R H was given i.v. Five min after the injection of TRH, the second blood flow determination was made. After another 15 min an injection of 1 mg kg-' TRH was given i.v. and blood flows measured 5 min later. Eflects of TRH after a,-adrenergic blockade. In the second group of animals (n = 7). 0.5 mg kg-l of prazosin, an a,-adrenergic blocking agent, was given i.v., followed 15 min later by 0.1 mg kg-' of TRH. In this group, the blood pressure was very low and the CBF,", response to T R H might be reduced due to near maximal vasodilation caused by autoregulatory mechanisms. Therefore, in the third group of experiments (prazosin-plus-ligation) (n = 6), prazosin was again used, however the blood pressure was normalized in the cranial part of the body by ligating the thoracic part of the aorta; onlj- cerebral blood flow was
TRH, adrenergic blockade and bloodjow evaluated. In these experiments, the procedure differed in some respects from that described above. Blood pressure recording was performed through an ear artery and a brachial artery was cannulated in order to collect blood samples. A brachial vein was cannulated for drug injections. Thoracotomy was performed and a loose ligature was placed around the descending aorta near the aortic arc. After the i.v. administration of 0.5 mg kg-' prazosin, the blood pressure was elevated to approximately control level by ligation of the descending aorta. A control blood flow measurement was performed followed by the i.v. administration of 0.1 mg kg-' of T R H and after another 5 min the second blood flow measurement was made. Effects of TRH a f e r a- and ,/-adrenergic blockade. In the fourth and fifth groups of animals, 50 mg kg-' of phenoxybenzamine was given slowly i.v. followed by 2 mg kg-' of the ,/-adrenoceptor blocking agent propranolol. Phenoxybenzamine is a non-specific blocking agent at the dose used, blocking not only al- and uzadrenoceptors but also the effects of histamine, serotonin and acetylcholine (Furchgott 1972). The blood pressure fell during the infusion but was partly restored by the i.v. infusion of 30-40 ml of a mixture (1 : 1) of Macrodex (Pharmacia, Uppsala, Sweden) and Rehydrex (Pharmacia, Uppsala, Sweden). At least 15 min after the Macrodex/Rehydrex infusion, the blood flow was determined. Then 0.1 mg kg-' ( n = 7) or 1 mg kg-' ( n = 7) of T R H was given i.v. and 5 min later the last blood flow measurement was made. In all experiments the animals were killed by intracardial administration of saturated KCI after the last microsphere injection. Organs and tissue samples were autopsied and placed in preweighed plastic tubes. The radioactivity of the samples was analyzed by gamma spectrometry. The brain was removed and samples were collected including : grey matter, white matter, hippocampal region, caudate nucleus, thalamic region, hypothalamic region, collicles, pons-mesencephalon, medulla oblongata, cerebellum and spinal cord (Cl-C3). Remaining parts of the brain were placed in separate pre-weighed plastic tubes and were also analysed. Total cerebral blood flow (CBF,,,) was calculated to include all parts of the brain, except medulla oblongata and cerebellum. Cardiac output (CO) was calculated as CO = Q x CPMi x CPM;', where Q = reference blood flow, CPMi = reference radioactivity and CPM, = injected radioactivity. The regional peripheral vascular resistance (VR) was calculated as VR = MAP x Q;' where MAP is given in kPa and P,= tissue blood flow in g min-l g tissue-' and the VR values are expressed as vascular resistance unit (VRU). The following drugs were used: TRH, lot no. 125F-59201 (Sigma), prazosin HCI, lot no. 73604201 (Pfizer Inc., New York, USA) phenoxybenzamine
109
(DibenylineB, SK & F, Welwyn, Garden City, England), propranolol (InderaP, ICI-Pharma, Macclesfield, England). All drugs were dissolved in saline except prazosin which was dissolved in distilled water. Statistical evaluation of the results within treatments was made by analysis of variance (ANOVA) with repeated measurements. The two-tailed Student's ttest for paired observations was used as a postANOVA test. The level of significance was adjusted with Bonferroni's correction. Values given in of control have been analysed with the two-tailed Student's t-test for paired observations. The level of significance was set at P < 0.05. All results are given as means SE.
RESULTS There were no differences in resting CBFs between the side with an intact sympathetic supply and the sectioned side. No differences in CBFs were found between the two sides during the experiments, therefore only the CBF values for the side with an intact sympathetic supply are given. Dose-response relationship of TRH Arterial blood gases were within normal range and not affected by the administration of T R H . Basal values for H R and CO were 3 18 f 17 min-' and 499 f 141 g min-', respectively. No significant changes were observed in H R or C O during the experiments. The injection of 0.1 mg kg-' T R H caused an increase in MAP from 9.8 _+ 1 to 11.8f0.8 kPa and 1 mg kg-I of T R H further increased the MAP to 15.2f 1 kPa ( P < 0.001). In spite of the increase in blood pressure, both doses of T R H caused a decrease in blood flow in several organs investigated (Fig. 1). No significant effects were seen in the small intestine. The lower dose of T R H failed to reduce the blood flow in the spleen and triceps muscle, however it caused a statistically significant increase in VR in both tissues. After the higher dose of TRH, there was a statistically significant increase in VR in all investigated peripheral organs except the jejunum (data not shown). Total peripheral vascular resistance (TPR) was not affected by the lower dose of T R H (116 9 yo of control value) but the higher dose caused an increase in T P R to 176+9y0 ( P < 0.001) of control. T h e effects of unilateral sympathotomy were seen in some extracranial tissues for example the submandibular gland: the VR was lower on the sectioned side as compared with the intact side
110
E. E. Seligsohn ,Jejunum
Gastric mucosa Pancreas Spleen
Shn Tnreps muscle 0
25
50
75
125
150
5%
Fig. 1. Peripheral blood floiis in *(, of control after the administration of 0.1 mg kg-I ( 1.0 nig kgg' of 1 R H 01= 6 ) . * P < 0.05 ** P < 0.01 ; *** P < 0.001 as compared with control (Student's r-test).
(a)
LT
