DAILY CONCENTRATIONS OF GONADOTROPHINS AND PROLACTIN IN THE SERUM OF PREGNANT OR LACTATING HAMSTERS

Abstract

SUMMARY The concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH) and prolactin in serum at 09.00 h on each day of pregnancy and 9 selected days of lactation in the hamster were determined by radioimmunoassays. The concentration of FSH on day 1 of the 16-day pregnancy was approximately fivefold greater than the levels on subsequent days. Concentrations of LH decreased on each of the first 3 days of gestation, rose slightly during mid-pregnancy, and then tended to decline during the last trimester. The concentration of prolactin increased approximately twofold from day 1 to day 3, remained elevated until day 8, and then gradually returned during the last half of gestation to the level on day 1. The concentrations of the three hormones on the first 4 days of pregnancy differed markedly from the concentrations during the oestrous cycle. Parturition had occurred and lactation begun by 09.00 h on day 16 of pregnancy (day 1 of lactation) and the levels of hormone on this day were unchanged from the levels on day 15 of pregnancy. Thereafter, the concentration of FSH increased two- to fourfold while the levels of LH increased until day 3 but then returned to the levels found at day 1. Concentrations of prolactin remained unchanged after day 1 of lactation, except for a decrease on day 2.