Plasma Half-Lives of Vasopressin and Oxytocin Analogs After iv Injection in Rats

SummaryThe curve-fit method for estimating plasma half-lives from vasopressor responses in rats (2) was used to estimate the plasma half-lives of vasopressin and oxytocin analogs substituted in the 1, 1 and 6, and 8 positions. Deamino-vasopressin and 1-hydroxy-oxytocin did not seem to be long-acting. Deamino-dicarba analogs of arginine-vasopressin and arginine-vasotocin were long-acting to the same degree, respectively, as deamino-vasopressin and deamino-vasotocin. Three 8-substituted analogs of oxytocin, [8-ornithine]-oxytocin, [8-glutamine]-oxytocin, and [8-proline]-oxytocin, were also long-acting.