Interactions of Follicle-Stimulating Hormone and Luteinizing Hormone in Controlling Estradiol Synthesis by the Testis of the Infant Rat

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Abstract
Experiments were conducted to assess the relative contribution of FSH and luteinizing hormone (LH) to the regulation of estradiol secretion by the testis of the 12 day old rat. In an in vivo model system, stimulation of the whole testis with NIH[National Institutes of Health]-FSH-S13 (5% LH activity) caused an 8-fold increase in testosterone secretion within 1 h followed by a 5-fold increase in estradiol secretion. Qualitatively, simiilar findings were obtained from whole testes incubated in tissue culture medium 199. The in vitro system was used to further examine the response of the testes to LH and FSH. Testes exposed to a variety of doses of LH or 10 ng/ml of highly purified FSH (3 .times. 13, 1% LH activity) showed no change in estradiol secretion. A synergistic effect was observed when purified FSH and LH were combined, provided the LH concentration exceeded 25 pg/ml. FSH secretion in infant rats apparently maintains the aromatizing capacity of the seminiferous tubule at a level such that availability of aromatizable substrate becomes a major factor in the rate of tubular estrogen formation.