REGULATION OF PITUITARY OVULATING HORMONE CONCENTRATION IN THE IMMATURE RAT TREATED WITH PREGNANT MARE SERUM

Abstract

SUMMARY The concentration of luteinizing hormone (LH) in the pituitary gland of the 28-day-old female rat increased from a value of 8·0 μequiv./mg fresh anterior pituitary at zero time to 20·1 μg at 51 h after treatment with 30 i.u. pregnant mare serum (PMS). The level then fell to 8·1 μg at 56 h. PMS had no effect on pituitary LH levels in the ovariectomized rat. Three daily injections of 5·0 μg of oestradiol benzoate caused an increase in pituitary LH levels to 16·1 μg at 51 h after the onset of the oestrogen treatment. This value is not significantly different from the level (20·1 μg/mg fresh weight) found in the intact, PMS-treated, immature rat. Uterine weights were also comparable for the two groups. Treatment with lower doses of oestradiol benzoate had no effect on pituitary LH levels and also failed to increase the uterine weight to values comparable with those obtained after PMS treatment. Treatment of 28-day-old, intact, female rats with 2 mg of progesterone at 24 h after the PMS injection resulted in a significant drop in pituitary LH levels.