Endocrine control of testicular somatic and premeiotic germ cell development in the immature testis of the primate Macaca mulatta
Authors: Schlatt Stefan , Arslan Muhammad , Weinbauer Gerhard F , Behre Hermann M , Nieschlag Eberhard 
Published: December 2008

Schlatt S, Arslan M, Weinbauer GF, Behre HM, Nieschlag E. Endocrine control of testicular somatic and premeiotic germ cell development in the immature testis of the primate Macaca mulatta. Eur J Endocrinol 1995:133:235–47. ISSN 0804–4643
Four groups (N = 3 per group) of juvenile rhesus monkeys (Macaca mulatta, 14–20 months old) received either vehicle or highly purified human follicle-stimulating hormone (FSH; 10 IU kg−1 day−1), human chorionic gonadotropin (hCG; 250 IU every alternate day) or both hormones for a period of 4 weeks. Testicular volume and weight increased more than twofold after single and more than sixfold after combined hormone treatment. Serum and intratesticular testosterone were at supraphysiological levels in hCG-treated animals and rose even more after combined treatment; a minor elevation of intratesticular testosterone was also observed after FSH treatment. Serum inhibin was elevated after hCG or FSH treatment and increased more than twofold during the first 3 weeks of combined treatment. Semiquantitative analysis of cell numbers showed a statistically non-significant increase in Sertoli cells and Ad- and Ap-spermatogonia after single hormone treatment. Combined treatment induced a further increase in the number of spermatogonia. Leydig cells were only encountered after hCG treatment; their number was more than threefold higher after combined treatment compared with hCG alone. Follicle-stimulating hormone stimulated Sertoli cell and Ap spermatogonia proliferation but did not induce morphological differentiation of Sertoli cells, peritubular cells or Leydig cells. Human CG treatment, however, induced Sertoli cell proliferation and morphological differentiation. It had effects on spermatogonial proliferation but induced differentiation of peritubular cells. Combined treatment initiated the greatest morphological and functional differentiation of Sertoli cells, peritubular cells, Leydig cells and spermatogonia. Flow cytometric analysis confirms an increase of mitotically active cells. The observations show that FSH and testosterone can induce Sertoli cell proliferation. Morphological differentiation of Sertoli cells may be mediated indirectly by environmental and paracrine stimuli released from peritubular cells, whose differentiation is androgen dependent. Leydig cells are stimulated mainly by hCG. Our present and previous data lead us to propose that FSH contributes to the final number and activity of Leydig cells, which secrete immunoreactive inhibin in response to hCG. Spermatogonial proliferation is under the control of FSH, whereas the survival of germ cells is dependent on Sertoli cell function. The observed rise in the number of mitotically inactive Ad-spermatogonia can be explained by a transformation of Apspermatogonia into resting Ad-spermatogonia.
E Nieschlag. Institute of Reproductive Medicine of the University, Steinfurter Str. 107, D-48149 Münster, Germany