pituitrin and oxypressin

Apparent pressor receptor dissociation rate constants for arginine vasopressin, arginine vasotocin, oxytocin, oxypressin, and [1-deamino, 9-D-alanineamide]arginine vasopressin were estimated by the following method. Two minutes after injection of a moderate dose of agonist into urethane-anesthetized rats prepared for recording mean blood pressure, a large dose of inhibitor was injected. Under these conditions, in the first few moments after inhibitor injection, there should be no rebinding of the agonist after it dissociates, because vacant receptors should be immediately occupied by inhibitor. The rate of the blood pressure drop at the initiation of inhibition was calculated and used as an estimate of the dissociation rate of the agonist. Apparent dissociation rate constants thus estimated were 1.1, 1.1, 6.9, 5.8, and 13.9 min-1 for arginine vasopressin, arginine vasotocin, oxytocin, oxypressin, and [1-deamino, 9-D-alanineamide]arginine vasopressin, respectively. These rate constants were inversely related to the pressor potencies (435, 250, 5, 3, and 0.7 U/mg, respectively) of these five compounds. Such a relationship is to be expected if decreased potency is in part due to a faster "off" rate from pressor receptors.

Topics: Animals; Arginine Vasopressin; Blood Pressure; Computer Simulation; Female; Half-Life; Kinetics; Oxytocin; Rats; Receptors, Cell Surface; Vasopressins; Vasotocin

To try to compare receptor compartment kinetics, receptor binding, and binding-response coupling for two smooth muscle types in vivo, pressor and uterine responses to oxypressin, an equipotent analog of oxytocin and vasopressin, were studied simultaneously in urethane-anesthetized, pentolinium-indomethacin treated rats. Access of peptide to the pressor and uterine receptor compartments and peptide-receptor dissociation rate had a negligible effect on the two responses. During both injections and infusions, the blood pressure response seemed to be determined largely by plasma levels of oxypressin. The uterine response to oxypressin, however, was paradoxical. The heights of individual uterine contractions seemed to be determined throughout by plasma oxypressin concentrations. The interval between contractions also seemed to be determined by plasma peptide concentrations during injections. However, as plasma peptide increased and reached steady state during infusion, contraction interval behaved as if plasma peptide concentrations were decreasing. This effect was more marked at the beginning of infusion. The implication of these results is that binding determines the pressor response to oxypressin and binding-response coupling does not change. In contrast, although binding determines the uterine response to oxypressin during injection and binding-response coupling appears constant, some factor in addition to binding affects the contraction interval portion of the uterine response and modifies the apparent binding-response coupling of this parameter during infusion.

Topics: Animals; Blood Pressure; Estrus; Female; Oxytocin; Rats; Rats, Inbred Strains; Receptors, Angiotensin; Receptors, Vasopressin; Uterine Contraction; Vasopressins