Japan. J. Pharmacol. 26, 339-346 (1976)
CENTRALLY OF
339
MEDIATED
INTRACISTERNAL IN Hikaru
CARDIOVASCULAR APPLICATION
ANESTHETIZED OZAWA
OF
EFFECTS CARBACHOL
RATS
and Toshio UEMATSU
Department of Pharmacology, Pharmaceutical Institute, Tohoku University, Aobayama, Sendai 980, Japan Accepted February 9, 1976
Abstract-The pressor response to the intracisternal (i.e.) injection of carbachol (1 µg) in anesthetized rats was analyzed. This response was significantly reduced by the intravenous (i.v.) injection of guanethidine (5 mg), hexamethonium (10 mg) or phen tolamine (5 mg), and conversely, potentiated by i.v. desmethylimipramine (0.3 mg), while propranolol (0.5 mg) i.v. selectively inhibited the enlargement of pulse pressure and the tachycardia following i.e. carbachol (I ug). On the other hand, the pressor response to i.e. carbachol (1 ,g) was almost completely blocked by i.e. atropine (3 µg) or hexamethonium (500 µg), and significantly reduced by i.e. chlorpromazine (50 lag) but significantly potentiated by i.e. desmethylimipramine (30 µg). The pressor response to i.e. carbachol (I yg) remained unchanged after sectioning of the bilateral cervical vagal nerves but disappeared after sectioning of the spinal cord (C7-C8). From the above result it is suggested that the pressor response to i.e. carbachol originates in the central muscarinic mechanism, is exerted through the central and peripheral adren ergic mechanisms, and that the sympathetic trunk is the main pathway.
It has been already reported that i.v. physostigmine or the central application of choli nomimetic agent causes a pressor response in conscious or anesthetized dogs, cats and rats (1-10). Although it has so far been accepted that the pressor response to i.v. physostigmine is a consequence of the increased sympathetic activity resulting from an action of the drug on the central nervous system (11-14), there is still little evidence that the pressor response to the central application of other cholinomimetic agents is also a consequence of the in creased sympathetic activity due to the central action of the drug. The present study was undertaken to analyze the characteristics of the pressor response following i.c. carbachol in anesthetized rats. MATERIALS AND METHODS Male Wistar rats weighing 300-350 g were anesthetized with a-chloralose (80 mg/kg i.v.)-urethane (500 mg/kg i.v.) and in order to repeatedly inject the drugs intracisternally, a fine polyethylene cannula was inserted into the cisterna magna through the punctured core of the dura at the spinal C1-C2 level. The tip of the inserted cannula was placed on a point 10 mm from the core of the dura toward the pons and medulla so that the drugs would act on the limited area. The outside cannula was then fixed to the surrounding tissues using a-cyanoacrylate. Systemic blood pressure was recorded from the right common carotid artery via a
340
H. OZA WA & T. UEMATSU
pressure transducer (Nihon Kohden, MPU-0.5) on a polygraph (Nihon Kohden, RM-180 or San-ei Instrument, 8S). Heart rate was recorded by using a pulse rate tachometer (Nihon Kohden, RT-5 or San-ei Instrument, 2130) triggered by the pulse of the blood pressure. Drugs used were acetylcholine chloride (Daiichi), bethanechol chloride (Eisai) , oxo tremorine (Nakarai Chemicals), carbachol chloride (Nakarai Chemicals), 1,1-dimethyl-4 phenylpiperazium iodide (DMPP, Nakarai Chemicals), atropine sulfate (Wako Chemicals), hexamethonium bromide (Yamanouchi), guanethidine sulfate (Takeda), phentolamine mesylate (Takeda), propranolol hydrochloride
hydrochloride
(Sumitomo
(Shionogi) and desmethylimipramine
Chemicals) , chlorpromazine hydrochloride (Geigy-Fujisawa).
Drugs were dissolved in physiological saline , and the solutions (10-20 "I/rat) were injected intracisternally through the inserted cannula , and flushed immediately with saline (10 pl). 0.5 ml/kg of the solutions was injected intravenously from the inserted cannula into the jugular vein. All doses are expressed as pg/kg or mg/kg of salts .
RESULTS Effects of intravenous (i.v.) injections of some sympatholytic agents and desmethylimipramine on the pressor response to intracisternal (i.c.) carbachol The mean of the maximum rises in blood pressure following i.e. carbachol (1 pg) in 30 rats was 44±4.4/254-3.3 (systolic/diastolic, standard error) mm Hg . Although a rise in blood pressure was usually observed following i.e. carbachol (1 ,ug), the changes in heart rate to i.e. carbachol (1 fig) were not always consistent. A bradycardia in one case and in another case a tachycardia was predominantly observed, respectively.
Occasionally there
was not any significant change in heart rate. This pressor response to i .e. carbachol (1 ,ug) was significantly reduced after treatment with i.v. guanethidine (5 mg), phentolamine (5 mg) or hexamethonium (10 mg), and on the other hand, significantly potentiated after treatment with i.v. desmethylimipramine (0.3 mg). Propranolol (0.5 mg) i.v. did not show any signi
Fin. 1. Effect of the intravenous (i.v.) injection of guanethidine (Gua .), phentolamine (Phent.) or propranolol (Prop.) on the pressor response to the intracisternal (i.c.) injection of carbachol in anesthetized rats. Data in upper and lower charts were obtained from two different rats (Chart speed: 5 mm/min). BP: blood pressure (mm Hg), HR: heart rate (beats/min)
CENTRAL
EFFECTS
OF
INTRACISTERNAL
FIG. 2. Effect of the intravenous (i.v.) injec tion of hexamethonium (C6) or desme thylimipramine (DMI) on the pressor response to the intracisternal (i.c.) injec tion of carbachol in anesthetized rats. Data in upper and lower charts were obtained from two different rats (Chart speed: 5 mm/min). BP: blood pressure (mm Hg), HR: heart rate (beats/min)
to i.e. carbachol
the enlargement tachycardia
duced.
(I lug), although
of pulse pressure and the
observed
carbachol
occasionally
(1 tag) were
by i.e.
significantly
These typical responses
re
are illus
trated in Figs. 1, 2 and total responses summed
341
FIG. 3. Effects of intravenous (i.v.) injection of some sympatholytic agents and des methylimipramine (DMI) on the pressor response (systolic blood pressure) to the intracisternal (i.c.) injection of carbachol (1 µg) in anesthetized rats. Ordinate: change in blood pressure (BP, delta mm Hg). Abscissa: drugs treated 10-30 min before the second carbachol injection. Gua.: guanethidine (5 mg), C6: hexame thonium (10 mg), Phent.: phentolamine (5 mg), Prop.: propranolol (0.5 mg) White and black columns show the mean of the responses to i.e. carbachol before and after treatment with some sympatholytics and DMI, respectively. The values in parentheses and vertical bars indicate number of animals and standard errors, respectively. *: p
CENTRALLY OF
339
MEDIATED
INTRACISTERNAL IN Hikaru
CARDIOVASCULAR APPLICATION
ANESTHETIZED OZAWA
OF
EFFECTS CARBACHOL
RATS
and Toshio UEMATSU
Department of Pharmacology, Pharmaceutical Institute, Tohoku University, Aobayama, Sendai 980, Japan Accepted February 9, 1976
Abstract-The pressor response to the intracisternal (i.e.) injection of carbachol (1 µg) in anesthetized rats was analyzed. This response was significantly reduced by the intravenous (i.v.) injection of guanethidine (5 mg), hexamethonium (10 mg) or phen tolamine (5 mg), and conversely, potentiated by i.v. desmethylimipramine (0.3 mg), while propranolol (0.5 mg) i.v. selectively inhibited the enlargement of pulse pressure and the tachycardia following i.e. carbachol (I ug). On the other hand, the pressor response to i.e. carbachol (1 ,g) was almost completely blocked by i.e. atropine (3 µg) or hexamethonium (500 µg), and significantly reduced by i.e. chlorpromazine (50 lag) but significantly potentiated by i.e. desmethylimipramine (30 µg). The pressor response to i.e. carbachol (I yg) remained unchanged after sectioning of the bilateral cervical vagal nerves but disappeared after sectioning of the spinal cord (C7-C8). From the above result it is suggested that the pressor response to i.e. carbachol originates in the central muscarinic mechanism, is exerted through the central and peripheral adren ergic mechanisms, and that the sympathetic trunk is the main pathway.
It has been already reported that i.v. physostigmine or the central application of choli nomimetic agent causes a pressor response in conscious or anesthetized dogs, cats and rats (1-10). Although it has so far been accepted that the pressor response to i.v. physostigmine is a consequence of the increased sympathetic activity resulting from an action of the drug on the central nervous system (11-14), there is still little evidence that the pressor response to the central application of other cholinomimetic agents is also a consequence of the in creased sympathetic activity due to the central action of the drug. The present study was undertaken to analyze the characteristics of the pressor response following i.c. carbachol in anesthetized rats. MATERIALS AND METHODS Male Wistar rats weighing 300-350 g were anesthetized with a-chloralose (80 mg/kg i.v.)-urethane (500 mg/kg i.v.) and in order to repeatedly inject the drugs intracisternally, a fine polyethylene cannula was inserted into the cisterna magna through the punctured core of the dura at the spinal C1-C2 level. The tip of the inserted cannula was placed on a point 10 mm from the core of the dura toward the pons and medulla so that the drugs would act on the limited area. The outside cannula was then fixed to the surrounding tissues using a-cyanoacrylate. Systemic blood pressure was recorded from the right common carotid artery via a
340
H. OZA WA & T. UEMATSU
pressure transducer (Nihon Kohden, MPU-0.5) on a polygraph (Nihon Kohden, RM-180 or San-ei Instrument, 8S). Heart rate was recorded by using a pulse rate tachometer (Nihon Kohden, RT-5 or San-ei Instrument, 2130) triggered by the pulse of the blood pressure. Drugs used were acetylcholine chloride (Daiichi), bethanechol chloride (Eisai) , oxo tremorine (Nakarai Chemicals), carbachol chloride (Nakarai Chemicals), 1,1-dimethyl-4 phenylpiperazium iodide (DMPP, Nakarai Chemicals), atropine sulfate (Wako Chemicals), hexamethonium bromide (Yamanouchi), guanethidine sulfate (Takeda), phentolamine mesylate (Takeda), propranolol hydrochloride
hydrochloride
(Sumitomo
(Shionogi) and desmethylimipramine
Chemicals) , chlorpromazine hydrochloride (Geigy-Fujisawa).
Drugs were dissolved in physiological saline , and the solutions (10-20 "I/rat) were injected intracisternally through the inserted cannula , and flushed immediately with saline (10 pl). 0.5 ml/kg of the solutions was injected intravenously from the inserted cannula into the jugular vein. All doses are expressed as pg/kg or mg/kg of salts .
RESULTS Effects of intravenous (i.v.) injections of some sympatholytic agents and desmethylimipramine on the pressor response to intracisternal (i.c.) carbachol The mean of the maximum rises in blood pressure following i.e. carbachol (1 pg) in 30 rats was 44±4.4/254-3.3 (systolic/diastolic, standard error) mm Hg . Although a rise in blood pressure was usually observed following i.e. carbachol (1 ,ug), the changes in heart rate to i.e. carbachol (1 fig) were not always consistent. A bradycardia in one case and in another case a tachycardia was predominantly observed, respectively.
Occasionally there
was not any significant change in heart rate. This pressor response to i .e. carbachol (1 ,ug) was significantly reduced after treatment with i.v. guanethidine (5 mg), phentolamine (5 mg) or hexamethonium (10 mg), and on the other hand, significantly potentiated after treatment with i.v. desmethylimipramine (0.3 mg). Propranolol (0.5 mg) i.v. did not show any signi
Fin. 1. Effect of the intravenous (i.v.) injection of guanethidine (Gua .), phentolamine (Phent.) or propranolol (Prop.) on the pressor response to the intracisternal (i.c.) injection of carbachol in anesthetized rats. Data in upper and lower charts were obtained from two different rats (Chart speed: 5 mm/min). BP: blood pressure (mm Hg), HR: heart rate (beats/min)
CENTRAL
EFFECTS
OF
INTRACISTERNAL
FIG. 2. Effect of the intravenous (i.v.) injec tion of hexamethonium (C6) or desme thylimipramine (DMI) on the pressor response to the intracisternal (i.c.) injec tion of carbachol in anesthetized rats. Data in upper and lower charts were obtained from two different rats (Chart speed: 5 mm/min). BP: blood pressure (mm Hg), HR: heart rate (beats/min)
to i.e. carbachol
the enlargement tachycardia
duced.
(I lug), although
of pulse pressure and the
observed
carbachol
occasionally
(1 tag) were
by i.e.
significantly
These typical responses
re
are illus
trated in Figs. 1, 2 and total responses summed
341
FIG. 3. Effects of intravenous (i.v.) injection of some sympatholytic agents and des methylimipramine (DMI) on the pressor response (systolic blood pressure) to the intracisternal (i.c.) injection of carbachol (1 µg) in anesthetized rats. Ordinate: change in blood pressure (BP, delta mm Hg). Abscissa: drugs treated 10-30 min before the second carbachol injection. Gua.: guanethidine (5 mg), C6: hexame thonium (10 mg), Phent.: phentolamine (5 mg), Prop.: propranolol (0.5 mg) White and black columns show the mean of the responses to i.e. carbachol before and after treatment with some sympatholytics and DMI, respectively. The values in parentheses and vertical bars indicate number of animals and standard errors, respectively. *: p
