Comparative reactivity of hamster cheek pouch microvessels to arginine vasopressin and angiotensin II.

Experiments were carried out to determine the relative sensitivity of hamster cheek pouch vessels to arginine vasopressin (AVP) and angiotensin II (AII). Hamsters were anesthetized with pentobarbital sodium (6 mg/100 g, ip), a plastic chamber inserted into the cheek pouch and the membrane exposed. The membrane was suffused continuously with bicarbonate-buffered Ringer's solution at 36 degrees C while constantly monitoring blood pressure. After stabilization (30 min) of the membrane, arterioles (30-80 microM diam) were selected for application of AVP or AII in a random fashion. The peptides were applied to the vessels through a micropipette (10-15 mM tip diam) over two minutes using a pump. Total volume delivered was always 20 microliters irrespective of the total amount of peptide (10(0)-10(-4) ng) applied. Vessel diameter was monitored continuously with a shearing device before, during and after the administration of the peptide. The following results were obtained tachyphylaxis was noted to AII but to AVP; the dose response curve for AVP was shifted to the left of that for AII with the threshold dose for AII one hundred times more than that of AVP and AVP had little effect on venules whereas AII produced venoconstriction. These results indicate that AVP is a more potent vasoconstrictor than AII, whereas AII is a more potent venoconstrictor.