Characterization of the central muscarinic cholinoceptors involved in the cholinergic pressor response in anesthetized dogs.

Previous reports have shown that an intracisternal (i.c.) injection of acetylcholine in the dog increases both arterial blood pressure and plasma levels of noradrenaline and vasopressin via central muscarinic receptors. The aim of the present study was to characterize the central muscarinic cholinoceptor subtypes involved in such central cholinergic responses in anesthetized male Beagle-Harrier dogs (n = 12). For this purpose, we studied the relative potency of various muscarinic receptor antagonists to block the acetylcholine-induced pressor responses (30 microg kg(-1) i.c.). The acetylcholine-induced pressor response was inhibited in a dose-dependent manner by the i.c. administration of the non-selective muscarinic receptor antagonist atropine (ID50 = 0.5 microg kg(-1)), the muscarinic M receptor antagonist pirenzepine (ID50 = 0.45 microg kg(-1)), the muscarinic M2 receptor antagonist methoctramine (ID50 = 8.5 microg kg(-1)) and the muscarinic M3 receptor antagonist para-fluoro-hexahydro-sila-difenidol (ID50) = 43.7 microg kg(-1)). The order of potency of these four muscarinic receptor antagonists was: atropine = pirenzepine > methoctramine >> para-fluoro-hexahydro-sila-difenidol. In order to confirm the selectivity for muscarinic M1 receptors of this dose of pirenzepine, we checked that 40- to 50-fold higher concentrations were necessary to block a typical muscarinic M2 receptor response (bradycardia) and a typical muscarinic M3 receptor response (endothelial vasodilation) compared with methoctramine and para-fluoro-hexahydro-sila-difenidol, respectively. These results suggest that the pressor response elicited by intracisternal injection of acetylcholine in anesthetized Beagle-Harrier dogs is mediated through the activation of the muscarinic M1 cholinoceptor subtype.

Effect of losartan on afferent nerve stimulation.

The present study was undertaken to investigate the effects of losartan, a non-peptide angiotensin II subtype 1 (AT1) receptor antagonist, on both the pressor responses elicited by stimulation of afferent vagal nociceptive fibres and the involvement of the sympathetic nervous system (evaluated by plasma levels of noradrenaline and its co-neurotransmitter neuropeptide Y) in dogs. Electrical stimulation of the afferent fibres of the vagus (1, 5, 10 and 20 Hz) elicited a frequency-dependent increase in blood pressure and heart rate. Plasma noradrenaline levels only increased after stimulation at frequencies of 10 and 20 Hz. Plasma neuropeptide Y levels did not change. Losartan (10 mg/kg i.v.) induced both a decrease in resting blood pressure and an increase in basal plasma levels of noradrenaline and neuropeptide Y. Losartan failed to modify the magnitude of the electrically-evoked pressor and positive chronotropic responses. The angiotensin AT1 receptor antagonist elicited a fall in plasma noradrenaline values after a 1 Hz stimulation and abolished the increase in plasma noradrenaline levels induced by the 10 (but not 20) Hz stimulation. The data suggest that angiotensin AT1 receptors are not directly involved in acute pressor responses induced by stimulation of afferent vagal fibres. Moreover, the results show that, besides its sympatho-inhibitory effect, losartan can exert a sympatho-excitatory action as shown by the increase in the plasma levels of both noradrenaline and its coneurotransmitter, neuropeptide Y.

Lack of haemodynamic effects of nitric oxide on post-capillary pulmonary hypertension induced by acute sino-aortic denervation.

1. The aims of the present experiments were to define a new experimental model of pulmonary hypertension induced by a post-capillary mechanism and to assess the haemodynamic effects of nitric oxide on post-capillary pulmonary hypertension. 2. Cardiopulmonary variables of 28 male beagle dogs, anaesthetized with chloralose, 16 spontaneous breathing and 12 with assisted ventilation, were studied before and after sino-aortic denervation (SAD). The haemodynamic effects of inhaled nitric oxide (25 p.p.m., 10 min). N(omega)-nitro-L-arginine methyl ester (20 mg kg-1, i.v.), urapidil (0.5 mg kg-1-, i.v.) and propranolol (300 micrograms kg-1, i.v.) were studied after SAD. 3. SAD induced an acute and transient pulmonary hypertension, more marked in spontaneous breathing dogs. This pulmonary hypertension involved a post-capillary mechanism, secondary to the left ventricular haemodynamic effects of the acute increase of left ventricular after-load induced by systemic hypertension. In fact, the increase of mean pulmonary arterial pressure after SAD and the decrease of this parameter after urapidil or propranolol were strongly correlated with the variations of pulmonary capillary wedge pressure. Furthermore, no significant change in pulmonary vascular resistance was found after SAD or administration of alpha or beta-adrenoceptor antagonists. 4. Inhaled nitric oxide did not reverse pulmonary hypertension induced by SAD. N(omega)-nitro-L-arginine methyl ester had no significant haemodynamic effect of pulmonary circulation. 5. In conclusion, the lack of effect of inhaled nitric oxide and nitric synthase inhibitor on pulmonary circulation parameters SAD suggest that endothelium-derived oxide is not involved in the mechanisms leading to post-capillary pulmonary hypertension.

Spectral analysis of blood pressure and heart rate, catecholamine and neuropeptide Y plasma levels in a new model of neurogenic orthostatic hypotension in dog.

The aim of the study was to compare changes in blood pressure (BP) and heart rate (HR) variability, catecholamine and neuropeptide Y (NPY) plasma levels induced by passive head-up tilt in normal and sino-aortic denervated (SAD) chloralose-anaesthetized dogs. In controls, 80 degrees head-up tilt test failed to change BP and increased HR. Plasma noradrenaline and NPY levels (but not adrenaline) significantly rose. In SAD dogs, head-up tilt test induced a marked and reproducible decrease in BP without any change in HR or noradrenaline and NPY plasma levels. In SAD dogs, spectral analysis in supine position was characterized by reduced variability in the high frequency (HF) band of the HR spectrum without changes in low frequency (LF) bands of both HR and systolic blood pressure (SBP). Head-up tilt test increased the LF component of SBP variability and decreased the HF component of HR variability in controls but failed to modify HR and BP variabilities in SAD dogs. In conclusion, sino-aortic denervation in dogs elicits a reproducible postural fall in BP with impaired adaptation of sympathetic nervous system activity. This model may be of value in evaluating the pharmacological effects of drugs for the management of orthostatic hypotension.

A study of tolerance to apomorphine.

1. The present study was designed to investigate tolerance to several pharmacological effects of apomorphine. 2. Changes in blood pressure, heart rate, plasma noradrenaline levels, rectal temperature, respiratory rate and retching plus vomiting were compared after administration of apomorphine (200 micrograms kg-1, i.v. as a bolus) or saline at different time intervals (30, 120 and 720 min) in four groups of chloralose-anaesthetized dogs. 3. The first administration of apomorphine induced a significant decrease in blood pressure and rectal temperature, a marked rise in heart rate with no change in noradrenaline plasma levels or respiratory rate. Emesis occurred in 71% of the animals. 4. A second administration of apomorphine 30 min later failed to modify blood pressure or heart rate. In contrast, the magnitude of apomorphine-induced changes in blood pressure and heart rate was similar to that observed after the first administration when apomorphine was given 120 or 720 min later. 5. The apomorphine-induced decrease in rectal temperature evoked by a second dose of apomorphine was less marked when given 30 and 120 min after the first dose and unchanged when given 720 min later. 6. The number of animals exhibiting retching and vomiting was lower when apomorphine was reinjected after 30 min than when the time between two successive injections of apomorphine was 120 or 720 min. 7. These results show that tolerance to apomorphine involves its cardiovascular, hypothermic and emetic effects. The time course of tolerance to repeated injections of apomorphine is longer for its hypothermic than for its hypotensive or emetic effects. This suggests a tissue-specific regulation of D2 dopamine receptors to repeated injections of apomorphine.

Effects of pentobarbital and etomidate on plasma catecholamine levels and spectral analysis of blood pressure and heart rate in dogs.

The present paper investigates the effects of two anaesthetic drugs (pentobarbital and etomidate) on both short-term variabilities of systolic blood pressure (SBP) and heart rate (HR) using fast Fourier transformation and catecholamine plasma levels. HR and BP were continuously recorded through an arterial catheter and blood samples were taken from the jugular vein. Spectral analysis was performed first in the conscious state and six minutes after induction of anaesthesia on a series of 256 consecutive BP and HR values (delta t: 2 Hz). The area under the curve (AUC) was determined in the low-frequency component of the SBP (LF: 40-150 mHz), in the high-frequency band of HR (HF: respiratory frequency +/- 50 mHz) and in the total frequency spectra. Results were normalized by calculation of the ratio between AUC of LF and HF and the total AUC of the corresponding spectrum (TS). Etomidate (2 mg/kg i.v.) induced a significant increase in TS and LF without changing the LF/TS ratio or the HR variability when compared with the awake period. Catecholamine plasma levels did not change. In contrast, pentobarbital (30 mg/kg i.v.) decreased the values of LF, HF, LF/TS and HF/TS and catecholamine plasma levels. These results suggest that pentobarbital decreases the activity of the two components of the autonomic nervous system whereas etomidate induces only minimal changes.

Central cardiovascular effects of acetylcholine in the conscious dog.

1. The effects of central cholinomimetic drugs on cardiovascular and vasoactive hormonal responses (blood pressure, heart rate, catecholamines, vasopressin, atrial natriuretic factor, neuropeptide Y plasma levels and plasma renin activity) were investigated in conscious Beagle dogs. For this purpose a catheter was chronically implanted into each dog's cisterna magna to allow repeated central injections in the awake animals. 2. Intracisternal acetylcholine (20 micrograms kg-1) significantly increased systolic and diastolic blood pressure. These changes were accompanied by an initial short term tachycardia followed by a long lasting bradycardia. Intracisternal acetylcholine also increased noradrenaline, adrenaline and vasopressin plasma levels, decreased plasma renin activity but did not modify plasma levels of neuropeptide Y and atrial natriuretic factor. 3. The effects of acetylcholine were completely abolished by pretreatment with intracisternal injection of the muscarinic antagonist, atropine (5 micrograms kg-1) but not by the intracisternal injection of the nicotinic antagonist, mecamylamine (25 micrograms kg-1). 4. The present results demonstrate that there are qualitative and quantitative differences between the central cardiovascular effects of acetylcholine in conscious dogs compared to what we previously reported, using a comparable protocol, in anaesthetized dogs. Under both conditions, we observed a central cholinergically mediated increase in blood pressure secondary to an increase in sympathetic tone and vasopressin release but these responses were shorter (less than 10 min) in the conscious dogs than in anaesthetized dogs (more than 10 min). Moreover, we detected in the response to the central cholinergic stimulation in the conscious dogs a significant increase in plasma adrenaline levels and biphasic changes in heart rate which were not described previously in the anaesthetized dog.

[Adverse drug effect notifications by nurses and comparison with cases reported by physicians]. / Notifications d'effets indésirables par le personnel infirmier et comparaison avec celles des médecins.

The aim of the present study was to investigate the characteristics of adverse drug reactions reported by hospital doctors and nurses from Toulouse University Hospital between 1992 and 1993. During these two years, doctors and nurses reported 1498 and 164 adverse drug reactions respectively. Nurses reported significantly more cutaneous side effects than doctors (50 vs 24 per cent). Doctors reported significantly more neuropsychiatric, haematologic, hepatic or renal side effects than nurses. Imputability (causal relation) score of adverse drug reactions given by nurses was higher than that of doctors: nurses reported more observations with imputability equal to I3 (likely: 55 vs 46 per cent) and less with imputability equal to I1 (doubtful: 3 vs 23 per cent). Serious side effects (as defined by WHO) were more often seen by doctors (19 per cent) than by nurses (10 per cent). The more frequently suspected drugs were antiinfectious agents (35 per cent) and analgesics (7 per cent) for nurses, and neurotropic drugs (23 per cent) for doctors. Side effects reported by nurses were mainly observed after parenteral administration (48 per cent) whereas doctors reported mostly side effects seen after oral route (66 per cent). This study underlines the characteristics of adverse drug reactions which can be reported by nurses.

Relationships between kallikrein secretion, kallikrein excretion and beta-adrenoceptors in kidney cortical slices from neurogenic hypertensive dogs.

1. Sinoaortic denervation (SAD) in dogs is characterized by an increase in blood pressure and heart rate as well as the development of renal morphological lesions similar to those observed in essential hypertension in human subjects. To assess the effect of SAD on the secretion of kallikrein kinin systems (KKS), we studied the in vitro secretion of kallikrein by renal cortical slices of normal and neurogenic hypertensive dogs (1 and 18 months after SAD). The method using renal cortical slices allowed the study of secretion of kallikrein independently of renal perfusion pressure. The number of renal beta-adrenoceptors was measured by [125I]-cyanopindolol binding. 2. SAD was associated with a marked increase in urinary kallikrein excretion at one month and a significant decrease at 18 months when compared with controls. Both changes were statistically significant (P < 0.05). Concurrently, a progressive increase in in vitro kallikrein secretion was observed (+80 +/- 10% and +179 +/- 48%, 1 and 18 months after SAD, respectively). Moreover, the cortical slices obtained from sinoaortic denervated dogs contained more kallikrein than the control cortical slices (+32 +/- 16% and +55 +/- 7%, 1 and 18 months after SAD, respectively). 3. Renal beta-adrenoceptor number significantly (P < 0.05) decreased 18 months after SAD from 18 +/- 2 to 8 +/- 3 fmol mg-1 protein without any change in affinity constant. 4. Although there was no test of association, because the number of renal beta-adrenoceptors decreased whereas kallikrein secretion increased, the present data could suggest a beta-adrenoceptor-mediated inhibition of kallikrein secretion. These results show that although the urinary kallikrein is decreased, the tissue secretory capacities are enhanced. This could suggest a renal compensatory mechanism possibly involved in tissue protection in dogs after SAD, although such a mechanism is not sufficient to reverse hypertension.

[Absence of the effect of nitric oxide on pulmonary and systemic hypertension induced by sino-aortic denervation]. / Absence d'effet du monoxyde d'azote sur l'hypertension artérielle pulmonaire et systémique induite par la défrénation sino-aortique.

Inhaled nitric oxide, a selective pulmonary vasodilator, reverses hypoxic pulmonary vasoconstriction and is an effective treatment in some cases of human pulmonary hypertension. Localization of nitric oxide synthase had indicated a neural role for nitric oxide. Thus, we studied the interactions between inhaled nitric oxide and systemic and pulmonary vascular reactivity in acute neurogenic hypertension. In 6 male beagle dogs (mean weight: 15 +/- 1 kg), anesthetized by chloralose (8 cg/kg) and in spontaneous ventilation, the hemodynamic effects on systemic and pulmonary circulation of inhaled nitric oxide (12 ppm) were studied before and after acute sino-aortic denervation. The hemodynamic effects of intravenous propranolol (300 micrograms/kg) were studied after denervation. Mean arterial pressure (MAP), pulmonary capillary pressure (PCP), mean arterial pulmonary pressure (MAPP), cardiac input (CI) and oxygen venous saturation (SvO2) were measured. [table: see text] Sino-aortic denervation causes an acute and transitory pulmonary hypertension due to a double mechanism: a post-capillary hypertension (increase PCP) secondary to an increase left ventricular post-charge by systemic hypertension and a precapillary hypertension. In fact, vascular pulmonary resistances increase from 1.8 +/- 0.1 to 3.4 +/- 0.8 uW after denervation (p < 0.05). Change in pulmonary vascular reactivity induced by catecholamines is probably involved. Propranolol but not inhaled nitric oxide reverse pulmonary hypertension due to sino-aortic denervation.

Naloxone does not prevent apomorphine-induced emesis or hypotension in dogs.

Previous data have shown that apomorphine-induced respiratory depression can be reversed by the opiate antagonist, naloxone. The present study investigates the influence of naloxone on cardiovascular changes and vomiting elicited by apomorphine in dogs. In chloralose-anaesthetized animals, naloxone (0.02 mg/kg i.v.) failed to modify either the decrease in blood pressure and the biphasic changes (bradycardia followed by a long-lasting tachycardia in heart rate or the characteristics (occurrence, latency, duration) of the emesis elicited by apomorphine (200 micrograms/kg i.v.). In contrast, in conscious animals, naloxone (0.02 mg/kg i.v.) increased both the number and the duration (but not latency) of vomiting induced by a lower dose of apomorphine (30 micrograms/kg i.v.). These data show that apomorphine-induced vomiting and arterial hypotension do not involve opiate receptors.

Effects of insulin on the release of neuropeptide Y, [Met5]enkephalin and catecholamines from dog adrenal medulla.

Insulin-induced hypoglycaemia is a well-known stimulating factor for the release of adrenaline from adrenal medulla. The present experiment investigates the co-release of catecholamines and neuropeptides (neuropeptide Y and [Met5]enkephalin) from the adrenal medulla in chloralose-anaesthetized dogs after intravenous administration of insulin (0.3 U/kg). The increases in noradrenaline, adrenaline and [Met5]enkephalin were 29.6-, 23.8-, and 27.9-fold basal values, respectively whereas the neuropeptide Y increase was only 1.6 times the baseline. These results show that adrenal [Met5]enkephalin and catecholamines exhibit the same pattern of co-release which is not the case for adrenal neuropeptide Y.

[Physiological mechanisms of cardiovascular adaptation to orthostatism. Role of the sympathetic nervous system and pharmacological implications]. / Mécanismes physiologiques de l'adaptation cardiovasculaire à l'orthostatisme. Rôle du système nerveux végétatif et implications pharmacologiques.

The main physiological adaptative systems occurring during orthostatism are discussed. The nervous mechanisms and especially baroreceptor pathways allow a rapid adaptation to the new hemodynamic conditions whereas hormones (mainly vasopressin) are involved later. The role of baroreflex and cardiocirculatory mechanisms is explained by the description of adaptative mechanisms in giraffe, an animal with its brain so far above the ground. The changes in adrenoceptor receptivity and the adaptative homeostatic mechanisms of the autonomic nervous system during orthostatism in human are discussed. Their characterization might allow to propose new pharmacological approaches for the treatment of orthostatic hypotension.

Effects of clonidine, dihydralazine and splanchnic nerve stimulation on the release of neuropeptide Y, MET-enkephalin and catecholamines from dog adrenal medulla.

Various neuropeptides are costored together with catecholamines in the adrenal medulla. The concurrent release (evaluated by adrenal vein plasma levels) of these neuropeptides [neuropeptide Y (NPY), met-enkephaline (ME)] and catecholamines [adrenaline (A) and noradrenaline (NA)] from the adrenal gland was examined in chloralose-anesthetized dogs after intravenous administration of clonidine (10 micrograms/kg) and dihydralazine (1 mg/kg). These results were compared to those obtained after the stimulation of the right splanchnic nerve at 1, 5 and 10 Hz frequencies. The increment in the release of catecholamines and neuropeptides was evaluated for dihydralazine and splanchnic nerve stimulation. Dihydralazine (at its maximal effect) induced a significant preferential increase in catecholamines (expressed as mean (SEM): NA: 17.3 (5.4) fold, A: 13.1 (2.6) fold) and ME (16.0 (7.1) fold) versus basal values. However, the significant increase in NPY-LI was only 2.0 (0.4) times the baseline. Splanchnic nerve stimulation induced a frequency-dependent increase in catecholamines and neuropeptides. When the stimulation frequency was increased from 1 Hz to 5 Hz, NA and A levels increased 17.9 (4.3) and 14.0 (2.2) fold, respectively and ME levels 14.1 (3.0) fold. By contrast, NPY-LI was increased only 2.3 (0.3) fold under the same conditions. Increasing the stimulation frequency from 5 Hz to 10 Hz resulted in similar elevations of NA, ME, and NPY-LI adrenal plasma levels (about 4 times) whereas A only increased twice. Clonidine decreased catecholamine and ME adrenal plasma levels (the maximal percent decrease when compared with control values was about 75%) whereas NPY adrenal plasma levels remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

[Mechanism of receptor regulation during repeated administration of drugs]. / Mécanismes de régulation des récepteurs lors d'administration répétée de médicaments.

The effects of drugs is mainly explained by their action on specific receptors located on target cells. However, the receptors are can be regulated by changes into the levels of the physiological neurotransmitter and/or by drugs. A chronic treatment by an agonist induces a desensitization leading to a decrease in cellular response. The desensitization is "homologous" when it only involves the activated pathway and "heterologous" when a decrease in the response to other factors (transmitters, drugs) appears. At the molecular level, desensitization is explained by covalent modification of the receptors by phosphorylation catalyzed by a variety of protein kinases. A long term stimulation elicits an internalization of the receptor followed by degradation: this mechanism is called "down regulation". In contrast, treatment with antagonists can induce hypersensitization (i.e. increase in the cellular response) with up regulation. The consequences of these notions are discussed in term of both clinical pharmacology and pharmacovigilance.

[Co-release of neuropeptides and catecholamines by adrenal medulla]. / Colibération des neuropeptides et des catécholamines par la médullosurrénale.

Different neuropeptides are costored together with catecholamines in the adrenal medulla. The concurrent release of these neuropeptides [neuropeptide Y (NPY), met-enkephalin (ME)] and catecholamines (adrenaline and noradrenaline) from the adrenal gland was examined in chloralose-anesthetized dogs after intravenous administration of dihydralazine (1 mg/kg) and insulin (0.3 U/kg). These results were compared to those obtained after the stimulation of the right splanchnic nerve at 1, 5 and 10 Hz frequencies. Baroreflex involvement or hypoglycemia induced a significant preferential increase in CA and ME versus basal values: around 16 fold for dihydralazine and 28 fold after insulin administration. In opposite, increase in NPY was only two times baseline. Splanchnic nerve stimulation induced a frequency-dependent increase in catecholamines and neuropeptides. At the lower frequencies (1 to 5 Hz), splanchnic nerve stimulation elicited a parallel increase in catecholamines and ME (13 to 17 fold basal values). By contrast, NPY increases 2 fold in the same conditions. At the higher frequencies (5 to 10 Hz), we observed a parallel (4 fold) increase in NA, ME and NPY adrenal plasma levels. In conclusion, the present data indicate that both adrenal ME and catecholamines (mainly NA) always exhibit a parallel fashion of corelease which is not the case for NPY and that different populations of chromaffin vesicles could be preferentially mobilized according to different physiological and pharmacological patterns.

Renal morphological changes after sinoaortic denervation in dogs.

The present study investigates morphological renal lesions in sinoaortic-denervated dogs 1 (n = 6) and 18 (n = 5) months after sinoaortic denervation compared with sham-operated controls (n = 8). After 1 month, a marked hyalinization and moderate thickening of the media of arterioles and small interlobular arteries were observed. These changes associated with edema and intimal thickening led to a narrowing of the lumen. In glomeruli, increase of mesangial matrix was focally present in all cases and associated with mesangial proliferation. In four of six cases, some glomeruli appeared retracted, with a large urinary space. A focal area of interstitial fibrosis occurred in just one case. After 18 months, similar but more pronounced vascular lesions were present, with marked hyperplasia of the media. Glomerular changes were characterized by mesangial lesions associated with focal glomerular sclerosis and thickening of Bowman's capsule. Tubulointerstitial lesions were more prominent in this group, with the presence of tubular epithelial changes and casts. Focal interstitial fibrosis, infiltrates, or both were demonstrated in all cases. These morphological lesions were associated with an increase in arterial blood pressure, proteinuria, and natriuresis and a decrease in urinary kallikrein. These results show that chronic sinoaortic denervation in dogs is associated with renal lesions similar to those observed in other well-established experimental and clinical hypertensive states.