The actions of angiotensin II on the isolated portal vein of the rat

Isolated rat portal vein suspended in Krebs bicarbonate medium showed regular rhythmic activity and contracted in response to angiotensin II, noradrenaline, adrenaline, tyramine, acetylcholine, serotonin and histamine. Angiotensin II was 3–10 times as potent as noradrenaline on a weight basis. Responses to angiotensin II were unchanged in the presence of antagonists to these drugs, excepting high concentrations of phentolamine. Electrical stimulation or noradrenaline did not potentiate responses to angiotensin II; angiotensin II did not potentiate responses to noradrenaline. Angiotensin II acts directly on the smooth muscle of rat portal vein; its action is independent of noradrenaline. Spontaneous contractions and responses to angiotensin II and noradrenaline were transiently depressed and then potentiated in media made hyperosmolar by addition of NaCl, sucrose or urea. Responses were depressed in hypo-osmolar low NaCl solution but unaffected by isosmolar low NaCl. An increase of intracellular potassium concentration would not alone account for the entire effect of increased osmolarity.