THE IMMEDIATE RESPONSE OF THE PLASMA PROLACTIN LEVEL TO OESTROGEN INFUSIONS IN DAIRY COWS

Abstract

ABSTRACT Prolactin in blood plasma samples obtained from cows was determined by radioimmunoassay. During infusion of 2 mg or 4 mg 17β-oestradiol/hour there was a depression of the prolactin level, which seemed to be pronounced during infusions of 6 or 12 mg 17β-oestradiol/3 hours. In the experiments in which 2-6 mg 17β-oestradiol were administered a 2-5 fold increase in the plasma prolactin concentrations occurred after the infusions were completed. In the experiment with 12 mg 17β-oestradiol the depression was sustained for 3 hours after infusion; the subsequent increase the next few hours was comparatively small.