Alterations in Serum FSH/LH Ratios in Relation to the Estrous Cycle, Pseudopregnancy, and Gonadectomy in the Mouse

Abstract

Changes in mouse serum FSH and LH during the estrous cycle and pseudopregnancy were determined by the NIAMD Rat FSH and LH radioimmunoassay systems. The principal characteristics of these changes; namely, a surge of serum LH on the late afternoon and early evening of proestrus; significant elevation of serum FSH on the late afternoon of proestrus; and maximal elevation of serum FSH at the time of ovulation, are very similar to those previously observed in the rat estrous cycle (4). A 10-fold decrease in the ratio of concentrations of serum FSH and LH occurred during a period of IS hr between late afternoon of proestrus, when both LH and FSH were elevated, and early morning of estrus, when only FSH was elevated. Serum FSH and LH levels were low throughout pseudopregnancy, until the onset of the proestrus and estrus which terminated the pseudopregnant period. At that time the characteristic periovulatory increments in both serum FSH and LH concentration occurred. SO days after gonadectomy, male mouse serum FSH and LH concentration had only doubled; 50 days after gonadectomy, female mouse serum FSH had increased substantially, but to a level only half that of the male, while female mouse serum LH had increased to a level equal to that of the gonadectomized male. (Endocrinology91: 910, 1972)