Brain Research, 105 (1976) 157-162
157
© Elsevier ScientificPublishing Company, Amsterdam - Printed in The Netherlands
Short Communications
A pressor response to intraventricular injections of carbachol
W. E. HOFFMAN AND M. IAN PHILLIPS Neurobehavior Laboratory, Department of Physiology and Biophysics, University of Iowa, Iowa City, Iowa 52242 (U.S.A.)
(Accepted December 10th, 1975)
Carbachol is a cholinergic agonist which is resistant to hydrolysis by acetylcholine esterase. It has mostly muscarinic, but some nicotonic activityL Angiotensin II is an octapeptide which is a physiologically active hormonal component of the renin-angiotensin system. Both carbachol and angiotensin II produce similar effects when injected into the brain. Carbachol produces drinking 2,a,5,9,1~,la, A D H release s,9 and natriuresisl, 9 when injected intracranially in the rat. Angiotensin II also yields drinking s,6,11,13, A D H release7,11 and natriuresis 1°. Swanson and Sharpe la have found that carbachol and angiotensin II induced drinking in the rat was obtained through mostly similar cannulae sites in the brain. In addition, intraventricular (i.v.t.) injections of angiotensin II produced a short latency pressor response 6,11. It has not been reported, however, whether carbachol produces a similar blood pressure effect. In an attempt to establish similarities and differences of the two dipsogenic agents we are carrying out a series of experiments. This paper focuses on the action of carbachol (i.v.t.) on rats in which drinking and blood pressure were recorded simultaneously. We find that carbachol produces a pressor response and this response appears to be mediated by central sympathetic stimulation and vasopressin release. The subjects were 22 male Sprague-Dawley rats (350-450 g), including 5 hypophysectomized male animals (Hormone Assay Co., Chicago). Three days before the start of the experiment each subject was implanted with a 14 mm, 22 g stainless steel cannula in the lateral ventricle. On the morning of the experiment each subject was anesthetized with ether and implanted with femoral artery and vein catheters. These catheters were led subcutaneously to the back and out through an incision where they were cemented to a wound clip. The animal was then returned to his home cage and allowed to recover from the anesthesia. Testing was begun 2 h later when the rat had fully recovered from anesthesia. A 30 g injector cannula, constructed so that the tip was flush with the implanted guide cannula, was used for i.v.t, injections. This injector cannula was connected via PE 10 tubing to a 25/A Hamilton syringe positioned close to the cage. For blood
158 pressure recording, the arterial c a t h e t e r t u b i n g was led outside the cage to a S t a t h a m P 2 3 G b b l o o d pressure transducer. H e a r t rate was m e a s u r e d with a B e c k m a n type 9857B c a r d i o t a c h o m e t e r t h a t was triggered by pressure pulses. M e a n b l o o d pressure, pulse pressure a n d h e a r t rate were all r e c o r d e d on a B e c k m a n R411 D y n o g r a p h recorder. D r i n k i n g was m e a s u r e d f r o m d r i n k i n g tubes, c a l i b r a t e d to 0.1 ml, a t t a c h e d to the h o m e cage. The chronic a n i m a l p r e p a r a t i o n a n d e x p e r i m e n t a l m e t h o d s allowed us to m a k e all the testing p r o c e d u r e s on unanesthetized, u n r e s t r a i n e d rats that were able to move freely a r o u n d their h o m e cage. N o r m a l , t h a t is n o n - h y p o p h y s e c t o m i z e d animals, were tested centrally with a dose range o f c a r b a c h o l ( c a r b a m y l c h o l i n e chloride, Sigma) from 0.025 ng to 250 ng, injected in a 5/zl artificial C S F vehicle (Elliott's B, T r a v e n o l L a b o r a t o r i e s ) . C o n t r o l 5 #1 C S F injections were also given to each animal. Blood pressure changes a n d d r i n k ing were r e c o r d e d for 30 min. A l l tests were s e p a r a t e d by 90 min. In an i n d e p e n d e n t experiment, 5 n o r m a l rats received 250 ng o f c a r b a c h o l infused intravenously to test for d r i n k i n g a n d pressor responses by this alternative route. H y p o p h y s e c t o m i z e d rats (n =: 5) were tested with a single i.v.t, dose o f 25 ng c a r b a c h o l . F o l l o w i n g c o m p l e t i o n o f the p r o t o c o l , rats were anesthetized with N e m b u t a l (0.2 ml/100 g) a n d 5/~1 methylene blue dye was injected t h r o u g h the ventricular cannulae. The chest cavity was then o p e n e d a n d the vascular system perfused with iso-
TABLE I EFFECTS OF CARBACHOL
Carbachol dose (ng)
i.v.t.
INJECTIONS
Blood pressure increase (ram Hg ) *
5 #1 CSF control 1~ 0 0,025 4 :{: 1 0.25 15 ± 3 2.5 18 ± 4 25 34±3 250 33 ± 4
P
< < < <
157
© Elsevier ScientificPublishing Company, Amsterdam - Printed in The Netherlands
Short Communications
A pressor response to intraventricular injections of carbachol
W. E. HOFFMAN AND M. IAN PHILLIPS Neurobehavior Laboratory, Department of Physiology and Biophysics, University of Iowa, Iowa City, Iowa 52242 (U.S.A.)
(Accepted December 10th, 1975)
Carbachol is a cholinergic agonist which is resistant to hydrolysis by acetylcholine esterase. It has mostly muscarinic, but some nicotonic activityL Angiotensin II is an octapeptide which is a physiologically active hormonal component of the renin-angiotensin system. Both carbachol and angiotensin II produce similar effects when injected into the brain. Carbachol produces drinking 2,a,5,9,1~,la, A D H release s,9 and natriuresisl, 9 when injected intracranially in the rat. Angiotensin II also yields drinking s,6,11,13, A D H release7,11 and natriuresis 1°. Swanson and Sharpe la have found that carbachol and angiotensin II induced drinking in the rat was obtained through mostly similar cannulae sites in the brain. In addition, intraventricular (i.v.t.) injections of angiotensin II produced a short latency pressor response 6,11. It has not been reported, however, whether carbachol produces a similar blood pressure effect. In an attempt to establish similarities and differences of the two dipsogenic agents we are carrying out a series of experiments. This paper focuses on the action of carbachol (i.v.t.) on rats in which drinking and blood pressure were recorded simultaneously. We find that carbachol produces a pressor response and this response appears to be mediated by central sympathetic stimulation and vasopressin release. The subjects were 22 male Sprague-Dawley rats (350-450 g), including 5 hypophysectomized male animals (Hormone Assay Co., Chicago). Three days before the start of the experiment each subject was implanted with a 14 mm, 22 g stainless steel cannula in the lateral ventricle. On the morning of the experiment each subject was anesthetized with ether and implanted with femoral artery and vein catheters. These catheters were led subcutaneously to the back and out through an incision where they were cemented to a wound clip. The animal was then returned to his home cage and allowed to recover from the anesthesia. Testing was begun 2 h later when the rat had fully recovered from anesthesia. A 30 g injector cannula, constructed so that the tip was flush with the implanted guide cannula, was used for i.v.t, injections. This injector cannula was connected via PE 10 tubing to a 25/A Hamilton syringe positioned close to the cage. For blood
158 pressure recording, the arterial c a t h e t e r t u b i n g was led outside the cage to a S t a t h a m P 2 3 G b b l o o d pressure transducer. H e a r t rate was m e a s u r e d with a B e c k m a n type 9857B c a r d i o t a c h o m e t e r t h a t was triggered by pressure pulses. M e a n b l o o d pressure, pulse pressure a n d h e a r t rate were all r e c o r d e d on a B e c k m a n R411 D y n o g r a p h recorder. D r i n k i n g was m e a s u r e d f r o m d r i n k i n g tubes, c a l i b r a t e d to 0.1 ml, a t t a c h e d to the h o m e cage. The chronic a n i m a l p r e p a r a t i o n a n d e x p e r i m e n t a l m e t h o d s allowed us to m a k e all the testing p r o c e d u r e s on unanesthetized, u n r e s t r a i n e d rats that were able to move freely a r o u n d their h o m e cage. N o r m a l , t h a t is n o n - h y p o p h y s e c t o m i z e d animals, were tested centrally with a dose range o f c a r b a c h o l ( c a r b a m y l c h o l i n e chloride, Sigma) from 0.025 ng to 250 ng, injected in a 5/zl artificial C S F vehicle (Elliott's B, T r a v e n o l L a b o r a t o r i e s ) . C o n t r o l 5 #1 C S F injections were also given to each animal. Blood pressure changes a n d d r i n k ing were r e c o r d e d for 30 min. A l l tests were s e p a r a t e d by 90 min. In an i n d e p e n d e n t experiment, 5 n o r m a l rats received 250 ng o f c a r b a c h o l infused intravenously to test for d r i n k i n g a n d pressor responses by this alternative route. H y p o p h y s e c t o m i z e d rats (n =: 5) were tested with a single i.v.t, dose o f 25 ng c a r b a c h o l . F o l l o w i n g c o m p l e t i o n o f the p r o t o c o l , rats were anesthetized with N e m b u t a l (0.2 ml/100 g) a n d 5/~1 methylene blue dye was injected t h r o u g h the ventricular cannulae. The chest cavity was then o p e n e d a n d the vascular system perfused with iso-
TABLE I EFFECTS OF CARBACHOL
Carbachol dose (ng)
i.v.t.
INJECTIONS
Blood pressure increase (ram Hg ) *
5 #1 CSF control 1~ 0 0,025 4 :{: 1 0.25 15 ± 3 2.5 18 ± 4 25 34±3 250 33 ± 4
P
< < < <
