Regional and systemic haemodynamic effects of some vasopressins: structural features of the hormone which prolong activity.
Cardiac output and regional blood flows to myocardium, gut, uterus and kidney were determined in anaesthetised female rats by a single injection of 86RbCl. The haemodynamic responses were measured at various time intervals up to 2 h after single I.V. injections of lysine-vasopressin and the following of its analogues: a) with extended peptide chains at the N-terminal (including "hormonogens") Nalpha-glycyl-glycyl-lysine-vasopressin, Nalpha-glycyl-glycyl-glycyl-arginine-vasopressin and Nalpha-D-valyl-lysine-vasopressin, b) "carba" modifications desamino-carba6-arginine-vasopressin, desamino-carba6-D-arginine8-vasopressin, desamino-carba6-ornithine8-vasopressin, desamino-dicarba-arginine-vasopressin and c) other steric alterations - desamino-D-arginine8-vasopressin and desamino-N-methylarginine8-vasopressin. Sub-pressor doses of lysine-vasopressin were followed by marked reductions in gut and uterus blood flows which reached a peak at 10 min. and had completely receded by 60 min. The presence of steric alterations in the C-terminal tripeptide of the molecule- D-arginine or N-methylarginine in sequence position 8 - practically completely eliminated vascular activity. The same was true for Nalpha-D-valyl-lysine-vasopressin. None of the latter three analogues showed any inhibitor properties to the action of lysine-vasopressin. The two hormonogens (triglycyl N-terminal extensions) had to be given in doses 10 times greater to obtain a vasoconstrictor effect in gut and uterus equivalent in amplitude to that of a lysine-vasopressin, but this effect was still present to the same degree 2 h later with the hormonogen of lysine-vasopressin, and was only starting to return to baseline values at the same time with the arginine-vasopressin hormonogen. The vascular potency of both mono-carba L-analogues was higher than that of lysine-vasopressin, and the effect was as prolonged as with the hormonogens. The dicarba analogue also showed a prolonged action, but with much reduced potency. No significant changes in renal or myocardial blood flows were observed at all. Molecular features of vasopressin smooth muscle activity were discussed, and a receptor model was proposed. It was suggested that the -S-S-, -CH2CH2-bridges in the above analogues are not directly bound in the peptide-receptor complex and constitute the limiting factor determining complex duration, or persistence of the active peptide in the "receptor compartment". These results provide an experimental basis for possible clinical application of triglycyl-vasopressin and carba-vasopressin in bleeding from both gut and uterus and for induction of menstruation.