Cytological Factors that Support Nonparallel Secretion of Luteinizing Hormone and Follicle-Stimulating Hormone during the Estrous Cycle*

Gonadotropes from cycling female rats were studied to investigate possible mechanisms for the nonparallel release of LH and FSH. The percentages of total gonadotropes increased from 14% during estrus (E) to 18% by diestrous day 2. More of these cells became multihormonal on the morning of proestrus (P; from 46% during diestrus to 69%). Since LHcontaining cells increased from 7% at E to 13.3% during early proestrus, this suggests that monohormonal FSH cells may have contributed by synthesizing LH. Gonadotrope cell areas were greatest just before the LH surge (P 1600 h). Microdensitometric measurements demonstrated that the amount and density of immunoperoxidase stain for either gonadotropin subunit were highest during the midafternoon of P. Interestingly, the amount of stain for LH continued to increase during the LH surge, suggesting that the stain had detected newly synthesized LHβ (13). At the same time, the average density of the LHβ stain decreased. In contrast, the amount, concentration, and density ...