Inactivation of arginine vasopressin by rat-kidney slices

Abstract

Highly purified arginine vasporessin, in the presence of rat-kidney slices, was shown to disappear at a rapid rate from the incubation medium. The disappearance of vasopressin from the incubation medium was not due to the presence of degradative enzymes in the medium which were liberated from either broken or intact cells. The apparent first-order rate constant was consistently reproducible with slices taken from different animals on successive days and was shown to be proportional to the weight of kidney tissue. Above 3 IU of vasopressin/ml., the apparent k75 fell progressively as the concentration of hormone was increased; half-maximal velocity was achieved at a concentration of 55 [mu]M. Below pH 6.0, little or no loss of vasopressin occurred, whereas the optimum rate of disappearance of hormone was observed over the pH range 7-10. The mean k75 values were found to be 0.0109 + 0.0005 min.-l at 25[degree] and 0.0026 + 0.004 min.-l at 7[degree]. Dinitrophenol (0.1 or 1 m[image]), diisopropyl phosphorofluoridate (1 m[image]), trypsin inhibitor (1 mg/ml), ethylenediaminetetra-acetate (0-04 [image]), and phosphate (0.2 [image]) did not affect the rate of loss of vasopressin from the incubation medium; p-chloromercuribenzoate (1 m[image]) and oxytocin (15 IU/ml) induced 30 and 50% inhibition respectively. The vasopressin which disappeared from the incubation medium could not be recovered from the kidney slice and had apparently undergone inactivation. This was confirmed by the use of [S35]vasopressin prepared biosynthetically.