In vitro degradation of some arginine-vasopressin analogs by homogenates of rat kidney, liver and serum.

Enzymatic degradations of arginine-vasopressin (AVP) and its [7-sarcosine]-substituted analogs were performed using homogenates of rat kidney, liver and serum. Under the experimental conditions used in this work, [Sar7]AVP and the parent hormone were inactivated much faster by the kidney cortex and liver homogenates than the remaining analogs, which were additionally modified at position 1 and did not contain the N-terminal amino group. Analytical data of the degradation products showed that, in the case of AVP and [Sar7]AVP, there were two major sites of cleavage: Tyr-Phe and Arg-Gly. The analogs which lack free N-terminal amino groups were deactivated very slowly. In these cases the main degradation product resulted from the cleavage of the Arg-Gly bond. The most surprising result observed during the incubation of AVP and its analogs with rat serum was the relatively high enzymatic stability of the parent hormone compared with the modified analogs. In contrast, the fastest degradation rate was found for [Cpp1,Sar7]AVP, which contains the bulky cyclopentamethylene moiety in position 1. The cleavage of the Arg-Gly peptide bond was exclusively responsible for the inactivation of all peptides with rat serum. The results showed that the degradation of vasopressin analogs in various blood and tissue samples differed both in speed and pattern of inactivation.