Effects of luteolysis during late pregnancy on pituitary responsiveness to gonadotrophin-releasing hormone in the rat.

We investigated whether the increase in the gonadotrophin response to gonadotrophin-releasing hormone (GnRH) during the last days of pregnancy and the occurrence of parturition on day 22 of pregnancy in rats are due to the increase in the plasma concentrations of oestradiol-17 beta after luteolysis, which occurs around day 20. In a first series of experiments we studied the effects of s.c.

Glucose and insulin responses during mixed meals or infusion of glucose in pregnant and lactating rats.

We studied the glucose tolerance in freely moving rats throughout pregnancy and lactation and during the first week after weaning. Dioestrous virgin rats served as controls. Basal glucose and insulin levels were determined after a 2-hr fasting period.

Pituitary responsiveness to LHRH during pregnancy in the rat: effect of progesterone.

The LH and FSH responses to a standard infusion of LHRH were studied on days 8, 12, 15, 17, 19, 21 and 22 after conception as well as on day 23, i.e. after parturition.

Minor interference of low-dose pulses of GnRH with the positive effect of oestradiol on the pituitary gland.

In the ovariectomized rat we investigated the effects of prolonged treatment with oestradiol and 'physiological' pulses of exogenous GnRH on the GnRH-responsiveness of the pituitary gland. Rats were for 20 h pre-treated with either GnRH (3-ng pulses of 3 min duration every 20 min) or saline and for 19 h with either oestradiolbenzoate (OB; 3 micrograms/sc injection) or oil. Then LH and FSH responses were evoked by continuous test infusions of GnRH at the rates of either 60, 100, 150 or 1000 ng/h, lasting 10 h.