Relationship of in vitro gonadotropin binding to bovine testes and the onset of spermatogenesis.

SUMMARY Concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were determined in serum of crossbred beef bulls during pubertal development. Serum LH ranged between .5 and 2.0 ng/ml with highest concentrations observed as 12 months of age. Serum FSH varied considerably among individuals but mean concentrations were within the normal range (50 to 100 ng/ml). Neither LH nor FSH increased at the time when testosterone increased or spermatogenesis entered meiosis. Specific binding of 12 SI.labeled human chorionic gonadotropin (hCG) and 12 s I-labeled FSH to the bovine testis was demonstrated by autoradiographic localization techniques. Binding of 12 s I-hCG and 12 s I-FSH was preferentially located over interstitial tissue and semi-niferous epithelial cells, respectively. An abundance of binding sites in newborn and 4-month-old calf testes shows that receptors for LH and FSH are present in the immature bovine testis. Initiation of spermatogenesis was assessed by estimating the number of testicular sperm by histological and cytometric techniques follow-for purified FSH and FSH antisera used in this study. The technical assistance of Ms. Becky Chmelka and cooperation of the Nebraska Agricultural Experiment Station, University of Nebraska, Lincoln, are acknowledged. SMention of a trade name, proprietary product or specific equipment does not constitute a guarantee or warranty by the U. S. Department of Agriculture and does not imply its approval to the exclusion of ing castration of bull calves at monthly intervals from birth to 12 months. Although sperma-togenesis was qualitatively complete at 7 months, spermatogenesis and total daily sperm production were highest in 12-month-old animals. A high correlation (r = .98, P<.O1) was found between sperm per gram testis and total daily sperm production. A parallel increase in serum testosterone of young bulls and testes weight (r = .95, P<.01) and total daily sperm production (r = .87, P<.05) suggest that initiation of spermatogenesis could be dependent on increased testosterone.