A detailed in vitro characterization of the basal follicle-stimulating hormone and luteinizing hormone secretion rates during the rat four-day estrous cycle.

Abstract

Studies were undertaken to determine the relative basal anterior pituitary gland FSH and LH release rates in vitro for rats killed by decapitation at 1 of 15 times during the 4- day estrous cycle and to ascertain if these basal release rates correlated with changes in serum gonadotropin concentrations. Trunk blood was collected, and serum was assayed for FSH and LH. Half of the anterior pituitary gland was homogenized and assayed for FSH and LH. The other half was placed in culture medium for a 30-min preincubation and then placed in fresh media for a 2-h incubation (basal FSH and LH release). Serum FSH concentration rose in association with a rise in serum LH levels during the afternoon of proestrus (first phase of FSH release). Whereas serum LH levels fell during the evening of proestrus, the serum FSH concentration remained elevated through 2400 h on estrus (second phase of FSH release). The basal FSH release into medium increased markedly during late proestrus and showed a highly significant positive ...