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At least 109 records · Page 6Linked to original sources
PubMed1999

Isolation of a muscarinic alkaloid with ocular hypotensive action from Trophis racemosa.

A muscarinic alkaloid with a quaternary nitrogen was isolated from Trophis racemosa. Aqueous solutions (0.5%-2%) of the chloride salt of the alkaloid produced dose-dependent reductions of intra-ocular pressure ranging from 6.6 +/- 0.7 mmHg to 15.7 +/- 0.3 mmHg, (p < 0. 001, n = 5) in dogs. Atropine (0.1 mL of a 1% solution) and pirenzepine at a non selective antagonist dose (0.1 mL of 0.5% solution) for M(1) and M(3) receptors blocked the reduction of intra-ocular pressure, but alpha-adrenoceptor blockade with phenoxybenzamine (0.1 mL of a 1% solution) did not block the reduction of intra-ocular pressure. On the isolated guinea-pig ileum and trachea, the alkaloid produced contractions which were inhibited by atropine (6 x 10(-7) M or 0.4 microg/mL) and by pirenzepine at a non-selective antagonist dose (3.1 x 10(-6) M or 1.3 microg/mL) for M(1) and M(3) receptors. But neither selective blockade of M(2) receptors with gallamine (1.7 x 10(-6) M or 1.5 microg/mL) nor selective blockade of M(1) receptors with pirenzepine (7 x 10(-9) M or 3 ng/mL) inhibited the alkaloid-induced contractions. There was also no inhibition of the alkaloid-induced contractions in the presence of ganglionic nicotinic receptor blockade with pentolinium (5.6 x 10(-7) M or 0.3 microg/mL) and hexamethonium (1.7 x 10(-6) M or 0.6 microg/mL), but nicotine-induced contractions were inhibited by these ganglionic blockers. These results suggest that a muscarinic alkaloid from Trophis racemosa produced ocular hypotension via M(3) receptor stimulation in dogs.

Acetylcholine↗
PubMed1975

Effects of phentolamine, dihydroergocristine and isoxsuprine on the blood pressure and heart rate in normotensive, hypotensive and hypertensive rats.

Phentolamine, dihydroergocristine and isoxsuprine were compared for their effects on the blood pressure in anaesthetized normotensive rats, in rats made hypotensive by ganglionic blockade or by pithing and in rats with noradrenaline-induced hypertension. Their ability to inhibit pressor responses elicited by electrical stimulation of the posterior hypothalamus and of the sympathetic outflow from the spinal cord was also investigated. All three drugs appeared very potent in inhibiting noradrenaline-induced hypertension and caused a dose-dependent fall in blood pressure in normotensive rats, which however was less pronounced with dihydroergocristine than with phentolamine and isoxsuprine. In hypotensive rats, dihydroergocristine caused a rise in blood pressure. At higher doses than those required to block noradrenaline-induced hypertension, the three drugs inhibited pressor responses elicited by electrical stimulation and were equally active on peripherally- and centrally-evoked responses. Simultaneous recording of heart rate and blood pressure, both in anaesthetized and in pithed rats, indicated a reflex origin for phentolamine-induced tachycardia and a direct cardiac stimulation for isoxsuprine. Reflex changes of heart rate were not observed with dihydroergocristine.

Animals↗
PubMed1979

Unimportance of perivascular H+ AND K+ activities for the adjustment of pial arterial diameter during changes of arterial blood pressure in cats.

The role of perivascular H+ and K+ in the adjustment of pial arterial diameter during changes in arterial blood pressure was investigated in chloralose anesthetized cats. Blood pressure was reduced by i.v. mecamylamine or pentolinium and was increased by i.v. hypertensin. Pial arterioles and arteries with a control diameter ranging from 37--218 microns at a spontaneous mean arterial blood pressure of 128 +/- 16 (SD) mm Hg were studied. Vascular diameter as measured by TV image splitting showed the typical reactions, i.e. constriction during increase (up to 200 mm Hg) and dilation during decrease in blood pressure (down to 60 mm Hg). Perivascular H+ and K+ activities were measured using pH microelectrodes (Hinke type) and K+ ion exchanger microelectrodes, respectively. Under control conditions perivascular pH was 7.25 +/- 0.11 (SD) and K+ activity was 2.46 +/- 0.65 (SD) mM, respectively. During changes in blood pressure the vascular reactions of pial arteries were not accompanied by significant alterations in perivascular H+ or K+ activity. From these data it can be concluded that mechanisms other than those which are mediated by H+ or K+ are involved in the adjustment of pial arterial diameter during changes in arterial blood pressure.

Angiotensin II↗
PubMed1983

Simultaneous mechanisms on exocrine pancreatic secretion initiated by alcohol in the conscious dog.

Modifications of pancreatic secretion induced by the infusion of alcohol were investigated in seven Thomas fistula dogs. Acute intravenous injections of low doses of alcohol induced a significant increase of all parameters of pancreatic secretion. On the contrary the acute intravenous injection of high doses of alcohol induced a significant decrease of pancreatic secretion. A prolonged-alcohol intravenous infusion producing a stable blood alcohol level provoked at first a decrease of pancreatic secretion, significant only for protein output, followed by a significant increase of all parameters of pancreatic secretion. A spontaneous return to prealcohol values of pancreatic secretion was observed in all cases even if the blood alcohol level remained high and stable and despite four hours of experimentation. Upon the background of a stable blood alcohol level, pentolinium did not suppress alcohol-induced stimulation of water and bicarbonate outputs but did abolish the postalcohol changes in protein secretion. Furthermore, atropine abolished all postalcohol changes in pancreatic secretion. Consequently, there are two responses (inhibition and stimulation) to alcohol which coexist in normal dogs. They are related to the blood alcohol levels and are transitory. These responses involve the vagus nerves. Alcohol appears to stimulate the exocrine pancreas through receptors at different levels of the nervous system.

Animals↗