Biology of Reproduction, Vol 23, 948-954, Copyright © 1980 by Society for the Study of Reproduction

Developmental Changes in the Ability of Follicle Stimulating Hormone to Stimulate Estrogen Synthesis in vivo by the Testis of the Rat

¹ Medical Research Council Group in Reproductive Biology, University of Western Ontario, London, Ontario, Canada N6A 5C1

Injection of FSH into immature rats is known to stimulate the synthesis of estradiol by the testis. Experiments were designed to determine whether age influenced the response of the gonads to such gonadotropin stimulation. At 2, 6, 12, 18, or 24 days of age Sprague-Dawley-derived rats were injected i.p. with 200 ng NIH-FSH-S13/g BW or an equivalent volume of vehicle. Six hours later the animals were killed, and the concentration of testosterone and estradiol was determined in methanolic extracts purified by Sephadex LH-20 column chromatography prior to RIA. In control animals the concentration of testosterone in the testes decreased steadily from 611 ± 90 ng/g at 2 days of age to 9 ± 4 ng/g at 24 days of age. The concentration of estradiol showed a parallel decline from 298 ± 28 pg/g to 24 ± 5 pg/g. FSH injection had no effect on the concentration of testosterone in the gonads; however, the concentration of estradiol was increased by FSH injection at all ages tested except 24 days. The largest incremental response was noted at 12 days when the FSH treatment increased the concentration of estradiol to 580 ± 64 pg/g. The possibility that the estrogen response was due to the LH which contaminated the FSH preparation was tested. LH alone or combined with FSH was injected i.p. at 5 to 50 ng NIH-LH-S21/g BW. At all doses tested LH had no measurable effect on the concentration of estradiol in the testes. When combined with 200 ng/g of FSH the same doses of LH had no more stimulatory effect on estrogen synthesis than injection of FSH alone. These data show that in vivo treatment of infant rats with FSH increases the amount of estradiol in the testes. The effect is not due to LH contamination of the FSH preparation. The responsiveness of the rat testes to FSH changes with age. While the 12-day-old rat seemed most responsive, significant stimulation of estrogen concentration was also noted at 2, 6, and 18 days of age. The smallest increase of concentration occurred at 18 days, and by 24 days of age FSH was unable to alter measurably the concentration of estradiol in the testes.

Note:
ACKNOWLEDGMENTS I wish to thank Dr. B. V. Caldwell for the antitestosterone serum and Dr. G. D. Niswender for the antiestradiol serum used in the RIAs. The gift of oFSH and oLH from the NIH Pituitary Hormone Distribution Program made these studies possible. Special thanks are due to Mr. Vaclav Pitelka, who did the bulk of the technical work, and Mr. John Bologna, who tended the forest of chromatographic columns which these studies required.

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