ABSTRACT
The mechanism by which 5-HT produces relaxations of the rat caecum has been examined. Propranolol and cocaine markedly attenuated the relaxations whereas tetrodotoxin had no effect. Higher doses of propranolol and cocaine (greater than 10(-6) M), as well as reserpinization, converted the relaxations into contractions. There was a residual relaxation resistant to propranolol, cocaine and reserpine treatment. High doses of 5-HT (greater than 10(-5) M) were thus thought to relax the rat caecum indirectly, through the release of noradrenaline from the tissue by a tyramine-like action. The relaxations do not seem to be due only to the release of noradrenaline.
Subject(s)
Cecum/physiology , Muscle Contraction , Muscle Relaxation , Serotonin/physiology , Animals , Cecum/drug effects , Cocaine/pharmacology , In Vitro Techniques , Muscle Contraction/drug effects , Muscle Relaxation/drug effects , Propranolol/pharmacology , Rats , Reserpine/pharmacology , Serotonin Antagonists , Tachyphylaxis , Tetrodotoxin/pharmacologySubject(s)
Muscle Relaxants, Central , Plant Extracts/pharmacology , Africa, Western , Animals , Female , In Vitro Techniques , Male , Mice , Motor Activity/drug effects , Plants, Medicinal/analysis , RatsABSTRACT
The inhibitory effects of cryptolepine and its interaction with prostaglandin E (2), indomethacin, adrenaline and acetylcholine have been investigated on the isolated rabbit duodenum. Cryptolepine (10-20 microg ml (-1)) or adrenaline (0.5-1 microg ml (-1)) or indomethacin (10-20 microg ml (-1)) abolished or reduced pendular contractions and relaxed the tissue. Cryptolepine (20 microg ml (-1)) produced an initial contraction before relaxation of the tissue. Cryptolepine (10-20 microg ml (-1)) abolished responses of the duodenum to added prostaglandin E (2) and acetylcholine, but failed to reduce prostaglandin production. The results suggested that cryptolepine antagonises prostaglandin, but has no inhibitory effect on its synthesis or release.
Subject(s)
Alkaloids/pharmacology , Indoles , Muscle Contraction/drug effects , Muscle, Smooth/drug effects , Parasympathetic Nervous System/drug effects , Quinolines , Synaptic Transmission/drug effects , Animals , Female , Guinea Pigs , Ileum/drug effects , In Vitro Techniques , Indole Alkaloids , MaleSubject(s)
Alkaloids/pharmacology , Calcium/pharmacology , Indoles , Muscle, Smooth, Vascular/drug effects , Norepinephrine/antagonists & inhibitors , Prostaglandins E/pharmacology , Quinolines , Animals , Dinoprostone , Female , In Vitro Techniques , Indole Alkaloids , Male , Mesenteric Arteries/drug effects , RatsABSTRACT
Decreasing the concentration of sodium in Meng's solution produced a non-parallel shift of the dose-response of acetylcholine on the intestine of the Giant African Snail Achatina fulica. This decrease in sodium decreases the sensitivity of the tissue to acetylcholine and sensitivity was not restored with several washings. The response to decrease calcium is very similar to that of sodium. In the case of potassium however 10% K+ produced less depression in sensitivity than 25% which even caused less depression of sensitivity compared with 50% potassium. The results show an abundance of spare receptors.
