Pulsatile plasma LH rhythms in normal and androgen sterilized ovariectomized rats: effects of estrogen treatment

Plasma luteinizing hormone (LH) was determined in sequential venous samples obtained at 10 min intervals from rats which had been ovariectomized 20 days earlier. Normal (nonandrogenized) castrates exhibited pulsatile rhythms in plasma LH with a peak to peak time of approximately 30 min. Castrated androgen sterilized rats (ASR) also exhibited pulsatile plasma LH rhythms, but most were of the 40 to 60 min peak to peak type. In normal rats, when either 0.1 or 0.1 μg estradiol benzoate (EB) was administered on Day 17 and sequential blood collections were obtained on Day 20 after ovariectomy, the pulsatile rhythm was still present; however, pulse amplitudes were reduced and the average plasma LH concentration for individual animals over a 2 hr collection period was progressively lowered as the EB dosage was increased. Pituitary LH concentration increased in these EB treated normal castrates. Administration of either 0.1 or 1.0 μg EB to castrated ASR markedly decreased average plasma LH concentrations and, in the 1.0 μg EB group, completely abolished the pulsatile LH discharges. In contrast to normal castrates, pituitary LH concentration failed to increase following EB treatment and, in fact, decreased after 1.0 μg EB administration. These studies suggest that early androgen sterilization not only impairs the cyclic, but also the tonic LH release mechanism.