PLASMA PROLACTIN IN UNDISTURBED CANNULATED MALE RATS; EFFECTS OF PERPHENAZINE, FREQUENT SAMPLING, STRESS AND CASTRATION PLUS OESTRONE TREATMENT

Abstract

Blood was collected from undisturbed male rats by means of chronically indwelling intrajugular cannulae and the plasma prolactin (PRL) concentration was determined by a radioimmunoassay. The effect of perphenazine, frequent bleeding, handling and brief ether stress in normal males and of stress in castrated estrone treated males was determined. The plasma PRL concentration in undisturbed intact males was low. Castration plus estrone treatment for 3 or 7 wk had little or no effect on the PRL concentration. Neither frequent blood sampling nor removal of 3 ml blood over a period of 5 h affected plasma PRL concentration. I.v. administration of perphenazine caused a striking and prolonged increase in plasma PRL in intact males. Brief handling or mild ether stress caused a significant rise in PRL within 2 min in intact males; 15-20 min later PRL had returned to the undisturbed level. Brief ether stress in estrone treated castrates induced a comparable pattern of PRL release, although of greater magnitude. In these animals, a 2nd stress 1 h later induced a similar response. Chronic cannulation neither affects the unstressed PRL level nor interferes with the ability of the adenohypophysis to release PRL. When rats are handled a truly stress free sample can only be obtained when the blood is drawn within 1 min after the initial disturbance of the animal. Estrone treatment increases the responsiveness of male rats to stress-induced PRL release.