Quantitative, histologische Untersuchungen des Hodenwachstums bei Bullen nach der Pubertät

Longitudinal growth of the seminiferous tubules in LH and FSH treated rats

New born Sprague Dawley rats were injected daily either with 50 (n=8), 100 (9) or 200 (10) mug FSH; with 50 (9), 100 (5), 200 (10) mug LH; with a combination of 50 mug FSH + 50 mug LH (10); or with the vehicle 0.9% saline (10). The animals were sacrificied at an age of 16 days. There was no influence of the hormones on the body weight. FSH caused a dose dependant stimulation of the testes growth (163, 186, 227 mg for the 50, 100 and 200 mug group; control 139 mg; diff. to control P less than or equal to 0.05, 0.01, and 0.01), whereas LH had no effect (123, 154 and 133 mg for the 50, 100 and 200 mug. LH group). The weight of the seminal vesicles was increased slightly by LH only (Diff. to control P less than 0l01). The serum androgen level was not changed by any of the treatments. The stage of the spermatogenesis was not altered by the hormones. There was no significant difference in the diameter of the seminiferous tubules. The higher testes weight after FSH administration was caused by an increase of length of the seminiferous tubules (25 m, 30 m and 35 m for 50 mug, 100 mug, and 200 mug FSH; control 23 m; diff.: P less than or equal to 0.05, less than or equal to 0.01, less than or equal to 0.01). The conclusion is that FSH has a specific effect on the longitudinal growth of the seminiferous tubules in prepubertal rats.

Dynamics of the follicle-stimulating hormone (FSH)-inhibin B feedback loop and its role in regulating spermatogenesis in the adult male rhesus monkey (Macaca mulatta) as revealed by unilateral orchidectomy

The purpose of this study was to document the morphological changes in the seminiferous epithelium that underlie the compensatory testicular hypertrophy observed in response to unilateral orchidectomy (UO) in the adult rhesus monkey and to describe the concomitant response in the endocrine feedback loops controlling testicular function in this species. Adult male monkeys were implanted with indwelling venous catheters; seven animals were then subjected to UO (data are presented from six) and three to sham UO. Profiles of circulating concentrations of FSH, LH, testosterone (T), inhibin B, and pro-alpha-C were monitored in 12-h series of sequential blood samples collected before, on the day of UO (day 0), and on days 1, 2, 4, 8, 16, 32, and 42 or 43 after UO. In the UO monkeys, the remaining testis was taken on day 44. Sertoli and germ cells in the removed and remaining testes were counted and expressed either as number per testis or, in the case of the differentiated spermatogonia (B1, B2, B3, and B4), as number per cross-section of the seminiferous tubule. UO was associated with a marked increase in the number of all germ cells more mature than undifferentiated spermatogonia (Ap) in the remaining testis. Sertoli cell number, on the other hand, did not change, and it is therefore reasonable to propose that the primary locus of the spermatogenic compensation was the differentiated spermatogonia. The additional finding that the relationship between the number of Sertoli cells and total germ cells in the remaining testis became robust (r = 0.92; P < 0.01 vs. r = 0.44; P > 0.05 for the removed testis) indicated that in the monkey, spermatogenesis does not normally operate at its ceiling. The increased drive to the seminiferous tubule of the remaining testis is hypothesized to be mediated by the sustained increase in FSH secretion that was observed after UO, although a role for increased testicular T production cannot be excluded. The stimulus for increased FSH secretion was presumably provided by the abrupt, 50% decline in circulating inhibin B levels. Interestingly, inhibin B secretion by the remaining testis was not dramatically affected by UO, and therefore, the deficit in circulating levels of this hormone and thus the error signal to FSH secretion were maintained for the duration of the experiment. In contrast, the changes in circulating LH and T concentrations were only transient, and within 48 h of UO, these hormonal parameters had returned to control values. The mechanisms by which the remaining testis rapidly acquires the capacity to double T production in the face of an unchanging LH drive remains to be determined. The foregoing body of evidence suggests that sperm output by the monkey testis is regulated by the circulating concentration of FSH and that in physiological situations, FSH secretion is insufficient to stimulate spermatogenesis to its ceiling. The results also indicate that FSH secretion is controlled by a feedback system in which the feedforward arm (FSH-inhibin B) is less robust than the feedback loop (inhibin B-FSH). Thus, a decrease in the inhibin B feedback signal results in a sustained increase in FSH secretion that drives the testes toward their spermatogenic ceiling, which is presumably set by Sertoli cell number.

Variation in hormonal feedback and reproductive performance in rams of different genotypes from birth through puberty

Comparative experiments were carried out for elucidate the mechanisms that establish and control sexual behaviour of rams. Fifty-four ram lambs 2 to 24 wk of age were used for each of two genotypes and their crosses. The genotypes examined were the highly fertile nonseasonal D'Man breed and the low fertile seasonal Timahdite breed as well as the crossbreed of these two genotypes. Morphological, spermatological, ethological and endocrine parameters were compared. There seems to be a breed-dependent difference in the luteinizing hormone (LH) releasing pattern after gonadotropin releasing hormone (GnRH) stimulation at a specific prepubertal time period. This in turn reflects a breed-dependent difference in behavioral response in similar stages of physical maturation. The difference in behaviour is much more marked than the difference in physical characteristics.