Differences in cardiac but not in neuroendocrine responses in healthy volunteers after administration of two antimuscarinic agents, atropine and pirenzepine

Neuroendocrine and cardiac responses were studied in healthy volunteers with the classical muscarinic antagonist, atropine and the new antimuscarinic agent, pirenzepine. The secretion of prolactin (PRL) and growth hormone (GH) was increased after metoclopramide. Typically, an antidopaminergic drug such as metoclopramide decreases rather than increases GH concentrations in serum. Pretreatment with both atropine and pirenzepine abolished the increase of GH secretion, which suggests an important role of cholinergic mechanisms in the regulation of GH secretion. The increase of PRL secretion was not inhibited by the two muscarinic antagonists. With the doses used, antimuscarinic activities in serum were comparable after atropine and pirenzepine treatments for the most part of the study. Heart rate was, however, significantly increased during atropine and higher than during saline or pirenzepine treatments throughout the study period. When compared to placebo, pirenzepine lowered heart rate slightly but significantly. The exact mechanism of this effect is unclear. We conclude that in contrast to the identical neuroendocrine effects, the cardiac responses clearly differ during atropine and pirenzepine treatments which confirms the ability of pirenzepine to distinguish muscarinic receptor sites in the central nervous system from those of the heart.     

Difference in effects of pirenzepine and atropine on carbachol-induced pepsinogen secretion from isolated gastric glands

The effect of pirenzepine on carbamylcholine (carbachol)-stimulated pepsinogen secretion was compared with that of atropine in the isolated guinea pig gastric glands. Pirenzepine and atropine caused a dose dependent inhibition of carbachol-stimulated pepsinogen secretion. Moreover, pirenzepine as well as atropine produced a rightward shift in the dose response curve of carbachol-stimulated pepsinogen secretion but did not alter the maximum increase in pepsinogen secretion. Results therefore demonstrate that pirenzepine acts as a specific receptor antagonist in the interaction of carbachol with its receptor on gastric chief cells. However, pirenzepine was 50 times less potent than atropine in inhibiting pepsinogen secretion. Half maximal inhibitory concentration of pirenzepine was 2 X 10(-5) M when a maximally effective concentration of carbachol was used, while that of atropine was 4 X 10(-7) M. Results, therefore, suggest that muscarinic receptor on gastric chief cells to which pirenzepine binds may be an intermediate affinity type.     

A comparison of the antimuscarinic effects of pirenzepine and N-methylatropine on ganglionic and vascular muscarinic receptors in the rat

The antimuscarinic properties of pirenzepine and N-methylatropine were evaluated in two intact preparations by measuring A) the inhibition of increase in mean arterial pressure evoked by McN-A-343 in pithed rats through activation of ganglionic muscarinic receptors and B) the inhibition of fall in arterial pressure evoked by methacholine in anaesthetized rats through activation of vascular muscarinic receptors. To characterize the antimuscarinic potencies of pirenzepine and N-methylatropine, for both antagonists doses were calculated that produce a 10-fold shift to the right of the dose-response curves for A) the pressor response to McN-A-343 (i.v. administration) in pithed rats (D10-p.r.) and B) for the depressor effect to methacholine (i.v. administration) in anaesthetized rats (D10-an.r.), respectively. Whereas N-methylatropine was virtually equieffective in blocking both muscarinic responses (D10-an.r./D10-p.r. approximately equal to 1), pirenzepine, however, was considerably more potent at ganglionic than at vascular muscarinic receptors (D10-an.r./D10-p.r. approximately equal to 16). These data confirm the existence of excitatory ganglionic muscarinic receptors with high affinity for pirenzepine (M1) and provide evidence for the presence of M2 receptors - receptors which show a low sensitivity to pirenzepine - on vascular smooth muscle cells. To further characterize the anticholinergic properties of pirenzepine, its effect on the pressor response to DMPP, a nicotinic ganglionic stimulant, was investigated in pithed rats. A high dose of pirenzepine (1.13 mumol/kg), given i.v., did not affect nicotinic ganglionic transmission.     

Comparison of the results of the treatment with pirenzepine combined with cimetidine and sucralfate of stomach ulcer resistant to cimetidine

Increased inhibition of gastric acid release through simultaneous blockade of H2-receptors and muscarine-receptors or administration of gastroprotective agent is theoretically justified in patients with peptic ulcer unresponsive to cimetidine. The study involved 70 patients with peptic ulcer previously treated with cimetidine in daily dose 1000 mg for 6 weeks without an effect. Patients were divided into two groups: group 1 treated with cimetidine plus pirenzepine, and group 2 given sucralfate in daily dose 4.0 g. Pirenzepine to patients of group 1 was given in a single dose of 50 mg before bedtime. Both groups were comparable in age, sex, disease onset, smoking, gastric acid secretion, and ulcer size. Healing was evaluated with endoscopic technique following 2 and weeks of therapy. Ulceration healed up within 2 weeks in 40% of patients treated with cimetidine combined with pirenzepine and in 31.4% patients treated with sucralfate. After 4 weeks, healing of ulceration was 71.4% and 68.6%, respectively. Large ulcers (over 1 cm in diameter) and previous partial gastrectomy did not affect healing rate. The obtained results suggest that administered therapies enable recovery in over 2/3 of patients with peptic ulcer unresponsive to a 6-week therapy with cimetidine alone.     

Biliary lipid secretion in hypercholesterolemia.

A report on the effects of primary bile acid ingestion alone or in combination with plant sterols on serum cholesterol levels, biliary lipid secretion, and bile acid metabolism. Biliary bile acid and cholesterol secretion were measured in four patients with type IIa hypercholesterolemia before and after randomized treatment periods. During these periods either a bile acid mixture (cholic-chenodeoxycholic 2:1, a proportion similar to that endogenously synthesized in health), at a level of 20 mg/kg, or the same mixture plus sitosterols, 200 mg/kg, was fed. Serum cholesterol and the cholesterol saturation of fasting-state bile was also measured. Pretreatment biliary lipid secretion was within normal limits. Bile acid kinetic measurements were also recorded before treatment and showed that cholic acid synthesis was disproportionately decreased relative to that of chenodeoxycholic acid, a finding previously reported by others. Administration of the bile acid mixture increased biliary bile acid secretion in 3 of 4 patients, but did not influence biliary cholesterol secretion. The combination of sitosterol-bile acid, however, caused a relative decrease in cholesterol secretion in bile, and fasting-state bile became unsaturated in all patients. No change in fecal neutral sterol excretion occurred during the beta-sitosterol-bile acid regimen, suggesting that simultaneous bile acid feeding blocks the compensatory increase in cholesterol synthesis known to be induced by beta-sitosterol feeding in hypercholesterolemic patients. Serum cholesterol levels also fell modestly during the sitosterol-bile acid regimen, the decrease averaging 15%. We conclude that the abnormally low rate of bile acid synthesis in patients with type IIa hyperlipoproteinemia does not influence biliary lipid secretion; that increasing the input of the two primary bile acids into the enterohepatic circulation does not increase biliary cholesterol secretion or lower serum cholesterol levels in such patients; and that the usual increase in cholesterol synthesis induced by beta-sitosterol feeding does not occur if bile acids are administered simultaneously.     

Enhancement of colonic motor response to feeding by central endogenous opiates in the dog

The role of endogenous opiates in the colonic motor response to feeding has been investigated in four dogs chronically fitted with two strain gages on the proximal and distal colon and a cannula in cerebral lateral ventricle. A daily meal stimulated the colonic motility during 8-10 hrs. The colonic motility index was significantly higher during this period when an enkephalinase inhibitor, tiorphan, was intracerebroventricularly (i.c.v.) administered at a dose of 0.1 mg/kg before the meal. This effect was blocked by a previous i.c.v. administration of naltrexone (0.1 mg/kg) and reproduced by (D-Ala2, Met5) enkephalinamide (DALAMIDE) at a dose of 50 mg/kg. I.c.v. administration of tiorphan or DALAMIDE did not modify the colonic motility in dogs fasted for 48 hrs. The postprandial motility index remained unchanged after intravenous administration of tiorphan or DALAMIDE at the same dosages. These results provide evidence for a central control of the colonic motor response to feeding by endogenous enkephalins in dogs.     

A comparison of the effects of pirenzepine and atropine on gastric acid secretion,salivary secretion and pupil diameter in the rat

The ability of pirenzepine and atropine, given i.v., to inhibit gastric acid and salivary secretion and increase pupil diameter has been assessed in the rat. Pirenzepine had a similar potency against acid secretion, ED50 0.71 (0.41 to 1.1) mg.kg^?1, and salivary secretion, ED50 0.50 (0.43 to 0.59) mg.kg^?1, whilst its potency was less in the eye, ED50 1.8 (1.6 to 2.1) mg.kg^?1. Astropine however, was more potent in reducing salivary secretion, ED50 0.012 (0.010 to 0.016) mg.kg^?1, and increasing pupil diameter, ED50 0.028 (0.025 to 0.031) mg.kg^?1 than in inhibiting gastric acid secretion, ED50 0.056 (0.037 to 0.083) mg.kg^?1. Therefore, that quantity of pirenzepine which inhibits gastric acid secretion by 50% will have only a slight effect on the eye and will inhibit salivary secretion by a similar magnitude. In contrast, the amount of atropine required to inhibit acid secretion by 50% will significantly increase pupil diameter and abolish salivary secretion.     

Differential stimulation of S-adenosylmethionine decarboxylase by difluoromethylornithine in the rat colon and small intestine.

The effects of sodium cyclobutyrate, a synthetic hydrocholeretic drug, on biliary lipid secretion and on the biliary outputs of several plasma-membrane enzymes were investigated in anaesthetized rats. Administration of a single oral dose of cyclobutyrol (0.72 mmol/kg body wt.) reduced biliary concentration and output of cholesterol and phospholipid. However, bile acid secretion was not significantly modified. This uncoupling effect of lipid secretion remained even when the choleretic response to the drug had ceased. It additionally led to a statistically significant decrease in the cholesterol/bile acid and phospholipid/bile acid molar ratios and in the lithogenic index of the bile. The biliary outputs of the plasma-membrane enzymes alkaline phosphatase and gamma-glutamyltransferase were markedly reduced by the drug. When cyclobutyrol was administered to rats which had been previously fed with a high-cholesterol diet, the effects of cyclobutyrol persisted, but were less marked. Our results demonstrate that the bile acid-independent choleresis induced by cyclobutyrol (related to its pharmacokinetic effect) is accompanied by a pharmacodynamic action that selectively reduces the secretion of biliary lipids. This is due to an uncoupling of the secretion of cholesterol and phospholipids from that of bile acids. Possible explanations for the biliary response to cyclobutyrol are discussed.     

Results of an experimental study of the pharmacokinetics of polymyxin B sulfate]

Pharmacokinetics of polymyxin B sulfate of Soviet production was studied in various species of animals with the use of different administration routes and dosage. After a single intramuscular administration of the drug to dogs in doses of 1.1 and 2.2 mg/kg the antibiotic was detected within 5 hours at the maximum level during the 1st hour. A two-fold increase of the dose was accompanied by 1.5 times increase in the antibiotic level. Repeated administrations of polymyxin B sulfate in a dose of 4.5 mg/kg did not result in an increase in the blood level as compared to a single use of the drug. When polymyxin B sulfate was administered intravenously, the concentration peak was observed in 15 minutes independent of the dosage. Later the antibiotic level decreased. The maximum level of the drug in the mice was observed 1 hour after its intramuscular administration in a dose of 8 mg/kg, the highest levels being registered in the kidney tissues and urine.     

Caffeine potentiates the enhancement by choline of striatal acetylcholine release.

We investigated the effect of peripherally administered caffeine (50 mg/kg), choline (30, 60, or 120 mg/kg) or combinations of both drugs on the spontaneous release of acetylcholine (ACh) from the corpus striatum of anesthetized rats using in vivo microdialysis. Caffeine alone or choline in the 30 or 60 mg/kg dose failed to increase ACh in microdialysis samples; the 120 mg/kg choline dose significantly enhanced ACh during the 80 min following drug administration. Coadministration of caffeine with choline significantly increased ACh release after each of the choline doses tested. Peak microdialysate levels with the 120 mg/kg dose were increased 112% when caffeine was additionally administered, as compared with 54% without caffeine. These results indicate that choline administration can enhance spontaneous ACh release from neurons, and that caffeine, a drug known to block adenosine receptors on these neurons, can amplify the choline effect.     

Stimulation of brain mast cells by compound 48/80, a histamine liberator, evokes renin and vasopressin release in dogs

Because degranulation of brain mast cells activates adrenocortical secretion (41, 42), we examined whether activation of such cells increases renin and vasopressin (antidiuretic hormone: ADH) secretion. For this, we administered compound 48/80 (C48/80), which liberates histamine from mast cells, to pentobarbital-anesthetized dogs. An infusion of 37.5 microg/kg C48/80 into the cerebral third ventricle evoked increases in plasma renin activity (PRA), and in plasma epinephrine (Epi) and ADH concentrations. Ketotifen (mast cell-stabilizing drug; given orally for 1 wk before the experiment) significantly reduced the C48/80-induced increases in PRA, Epi, and ADH. Resection of the bilateral splanchnic nerves (SPX) below the diaphragm completely prevented the C48/80-induced increases in PRA and Epi, but potentiated the C48/80-induced increase in ADH and elevated the plasma Epi level before and after C48/80 challenge. No significant changes in mean arterial blood pressure, heart rate, concentrations of plasma electrolytes (Na+, K+, and Cl-), or plasma osmolality were observed after C48/80 challenge in dogs with or without SPX. Pyrilamine maleate (H1 histaminergic-receptor antagonist) significantly reduced the C48/80-induced increase in PRA when given intracerebroventricularly, but not when given intravenously. In contrast, metiamide (H2 histaminergic-receptor antagonist) given intracerebroventricularly significantly potentiated the C48/80-induced PRA increase. A small dose of histamine (5 microg/kg) administered intracerebroventricularly increased PRA twofold and ADH fourfold (vs. their basal level). These results suggest that in dogs, endogenous histamine liberated from brain mast cells may increase renin and Epi secretion (via the sympathetic outflow) and ADH secretion (via the central nervous system).     

Evidence for Multiple Muscarinic Receptor Subtypes in Human Brain

Pirenzepine, a compound with selective antimuscarinic activity, was used to distinguish muscarinic acetylcholine receptor subtypes in normal human brain. Hill coefficients and IC50 values derived from the inhibition of specific [3H]L-quinuclidinyl benzilate receptor binding suggest the presence of two muscarinic binding sites, differing both in affinity for pirenzepine and in tissue distribution.     

A new prostaglandin E1 analogue (CL-115,574) II. Effects on gastric acid secretion in the dog

The efficacy of CL-115,574, a prostaglandin E₁ analogue, as an acid antisecretory agent was evaluated in dogs. CL-115,574 inhibited acid secretion maximally at an oral dose of 20 μg/kg causing 100% inhibition of acid secretion up to one hour after administration, with significant inhibition of secretion (30%) still present nearly four hours after drug administration. The wide disparity between the maximally effective antisecretory dose 20 μg/kg and the dose at which reproducible side effects occurred (1 mg/kg) suggests that this compound may be developed as an antisecretory compound for use in man.     

Comparative physiological characteristics of the action of pentagastrin on gastric secretion in fish, frogs, turtles and chickens]

The same preparation of pentagastrin, which is highly effective in dogs (threshold dose 0.3 mug/kg), has been tested on fishes, frogs, tortoises and hens. In fishes (rays), the threshold dose was equal to 50 mug/kg; the drug only increased juice secretion, but did not decrease pH of the juice. In frogs, the effective dose was equal to 25, in tortoises -- to 50 mug/kg, the drug increasing the secretion of both the juice and HCl. The effect of the drug exhibits seasonal variations, being absent in winter period. In hens, the threshold dose is equal to 5 mug/kg; the drug increases both the volume of the juice and HCl production. In frogs and hens, similar to that in dogs (tortoises were not studied in this respect), pentagastrin also increases the production of proteases of gastric juice. It is suggested that in the animals studied pentagastrin is a specific stimulator of gastric secretion.     

Effect of prostaglandin F2 alpha on biliary secretion in the rat

The effects of PGF2 alpha on biliary secretion of rats have been investigated. PGF2 alpha' at the dose of 100 micrograms/kg, produces a choleretic activity during the first 20 min after the injection. The effects are discussed by comparison to those observed in dogs, where a mechanism involving the canicolar level has been hypothesized.     

Central oxotremorine antagonist properties of pirenzepine

Pirenzepine, the prototype M1 muscarinic receptor antagonist, is an important compound for investigating the functional significance of M1 receptors at the integrated level of behavior but may have limitations imposed by its physical chemistry. Like the nonselective antagonist methylatropine, pirenzepine is highly hydrophilic and crosses the blood-brain-barrier with difficulty. We compared methylatropine with pirenzepine, given intraperitonealy, as antagonists of the behavioral effects of peripheral or central muscarinic activation. Lever-press responses of male Sprague-Dawley rats were maintained under a schedule requiring 10 responses for each food delivery. Administration of oxotremorine or the quaternary analog oxotremorine-M decreased rates of responding by at least 90%. Both methylatropine and pirenzepine antagonized the behavioral effects of oxotremorine-M; maximum reversal was 70%. Although methylatropine was about 30 times more potent than pirenzepine as an antagonist of the peripheral muscarinic activity of oxotremorine-M, it was inactive as an antagonist of oxotremorine when given in doses up to 153 mumol/kg. Pirenzepine, however, reversed oxotremorine-induced behavioral effects, with a maximum antagonism of 50%. These results suggest that pirenzepine interacts with central muscarinic receptors when administered systemically without producing marked behavioral effects of its own. Systemically administered pirenzepine may thus be a useful tool in further investigations of the relevance of M1 receptors to behavioral function.     

Naloxone antagonism of diazepam-induced feeding in the Syrian hamster

Three experiments investigated the effects of the intragastric administration of the benzodiazepine diazepam on feeding in non-deprived Syrian hamsters ($\text{mesocricetus auratus}$). In the first experiment diazepam (0, 0.5, 1.0, 2.0, and 4.0 mg/kg) produced dose dependant increases in feeding. 4.0 mg/kg of diazepam produced significantly more feeding than the other doses tested and the lowest dose tested (0.5 mg/kg) produced a significant increase in feeding. In the second experiment naloxone (10 mg/kg) partially antagonized the effect of 4 mg/kg of diazepam on feeding. In the third experiment the ability of naloxone (0.1, 1.0, 5.0, 10.0 or 20 mg/kg) to reduce feeding produced by either 4 mg/kg or 2 mg/kg of diazepam was tested. Naloxone partially antagonized the effects of 4 mg/kg of diazepam on feeding in a dose dependant manner. While 2 mg/kg of diazepam produced significantly less feeding than 4 mg/kg, naloxone did not antagonize the effect of 2 mg/kg on feeding. The results suggest that two mechanisms are involved in diazepam-induced feeding in hamsters. The high dose of diazepam may produce increased feeding by activating the endorphin system while the low dose of diazepam produces increased feeding via a naloxone insensitive mechanism.     

Suppression of renin secretion by propranolol in salt-depleted dogs

d, 1-propranolol was infused into salt-depleted, conscious dogs at two dosages: 1 mg/kg followed by 0.60 ? 0.67 mg/kg/hr, and 5 mg/kg followed by 1.57 ? 1.76 mg/kg/hr. At both dosages, propranolol decreased plasma renin activity (PRA), plasma aldosterone concentration, and heart rate significantly. Renin substrate concentration remained unchanged. PRA was suppressed with the higher dosage but not with the lower dosage, to values found with dietary salt loading. Mean arterial blood pressure (MABP) remained unchanged with the low-dose infusions, but decreased significantly with the high-dose infusions. The data suggest that the mechanism(s) for the increase in PRA with low-salt diets is sensitive to propranolol and that the effect of propranolol on MABP is dependent on the salt intake and on the dose administered.     

Relationship between the antitussic and analgesic activity of substances

The authors studied relationship between the antitussic and analgesic activity of substances. The antitussic effect of codeine, tilidine, tramadol and pentazocine has been studied in nonanesthetized healthy cats. The drugs except tilidine, were administered intraperitoneally in a dose of 10 mg/kg body weight. Tilidine was administered intramuscularly in the same dose. Cough induced in nonanesthetized cats by mechanical irritation of laryngopharyngeal and tracheobronchial areas was evaluated by changes of the lateral tracheal pressure. A significant decrease of the subsequent cough parameters was observed after the application of codeine, tilidine, tramadol and pentazocine. Naloxone given 5 min before the application of the drug has not prevented the cough-suppressing effect due to codeine. Naloxone alone administered in a dose of 1 mg/kg body weight has not significantly influenced the experimentally-induced cough reflex in nonanesthetized cats.     

The hyperglycemic effect of S-nitrosoglutathione in the dog.

The present study investigates the pharmacological activity of the nitric oxide (NO) donor S-nitrosoglutathione (GSNO) on the plasma glucose and insulin levels in healthy normoglycemic dogs. The plasma nitrate and nitrite concentrations were measured by a commercial autoanalyzer and taken as the biochemical markers of in vivo nitric oxide formation. Plasma glucose levels were measured by the glucose oxidase method, while the insulin levels were determined by radioimmunoassay. The possible effect of the coadministration of ascorbic acid (vitamin C) and GSNO on plasma glucose levels was also examined. In healthy normoglycemic dogs, administration of 35 and 50 mg/kg of GSNO caused a dose-dependent increase in postprandial plasma glucose levels. The plasma glucose levels were significantly elevated at the 1.5-, 2.0-, and 2.5-h time intervals of the oral glucose tolerance test at both concentrations of GSNO (P < 0.05). These values were significantly higher than those obtained using captopril (control). Furthermore, coadministration of 35 mg/kg of GSNO and 50 mg/kg ascorbic acid enhanced the postprandial hyperglycaemic effect observed for the administration of only 35 mg/kg of GSNO. There was a 35-100% increase in plasma nitrate concentration on administration of both doses of GSNO. Intravenous administration of GSNO (35 mg/kg) and captopril (20 mg/kg) significantly decreased the mean arterial blood pressure and increased the heart rate. The blood pressure-lowering effect of these drugs was more pronounced on systolic than on diastolic blood pressure (P < 0.05). These results suggests that in healthy normoglycaemic dogs: (a) nitric oxide released from GSNO increases postprandial plasma glucose levels and inhibits glucose-stimulated insulin secretion, (b) ascorbic acid enhances the postprandial hyperglycaemic effect of GSNO, probably by increasing the release of NO, and (c) GSNO decreases mean arterial blood pressure and increase heart rate in normotensive dogs.