Abstract
1. The blood pressure response to ranatensin, an undecapeptide from the skin of the frog, Rana pipiens, has been studied in various experimental animals.2. Ranatensin raised blood pressure in the dog and rabbit. The response was not altered by atropine, phentolamine, propranolol or hexamethonium, suggesting a direct peripheral vasoconstrictor action. In both animals ranatensin was about one-tenth as potent as angiotensin. Tachyphylaxis to ranatensin did occur, but there was no cross-tachyphylaxis with angiotensin, bradykinin, or noradrenaline.3. The peptide lowered blood pressure in the monkey, being as potent as eledoisin. The response was not altered by atropine, phentolamine, propranolol, tripelennamine, tetraethylammonium, bretylium, or methysergide. This again suggests a direct peripheral action on vascular smooth muscle. There was no tachyphylaxis to the depressor action, nor was there cross-tachyphylaxis with angiotensin, eledoisin, bradykinin, or noradrenaline.4. Ranatensin did not alter the blood pressure in cats and had a variable action in the guinea-pig with a rapid onset of tachyphylaxis.5. Ranatensin has a variable effect on the blood pressure in the rat that is related to the basal level of blood pressure. When the blood pressure is high, the response to the peptide is hypotension. Ranatensin raises blood pressure in the rat when the basal blood pressure is low. The pressor response to ranatensin appears to be due, in part, to the release of noradrenaline from peripheral sympathetic nerve endings.6. The composite action of ranatensin on blood pressure of various experimental animals is unlike that of any other peptide. Its hypertensive action in the dog or rabbit, together with a potent hypotensive action in the monkey, readily distinguishes it from all other vasoactive peptides.