Time course and role of luteinizing hormone and follicle‐stimulating hormone in the expansion of the Leydig cell population at the time of puberty in the rhesus monkey ( Macaca mulatta )

Summary In higher primates, development of the adult population of Leydig cells has received little attention. Here, the emergence of 3β‐hydroxysteroid dehydrogenase (HSD3B) positive cells in the testis of the rhesus monkey was examined during spontaneous puberty, and correlated with S‐phase labeling in the interstitium at this critical stage of development. In addition, the relative role of luteinizing hormone ( LH ) and follicle‐stimulating hormone ( FSH ) in initiating the pubertal expansion of Leydig cells was studied by precociously stimulating the juvenile testis in vivo with pulsatile 11‐day infusions of recombinant LH and FSH , either alone or in combination. At the time of castration, testes were immersion fixed in Bouin's, embedded in paraffin, and sectioned at 5 μm. Leydig cells/testis were enumerated using HSD3B as a Leydig cell marker. Leydig cell number per testis increased progressively during puberty to reach values in the adult approximately 10 fold greater than in early‐pubertal animals. The rise in cell number was associated with an increase in nuclear diameter. That the pubertal expansion of Leydig cell number was driven primarily by the increase in LH secretion at this stage of development was suggested by the finding that precocious stimulation of mid‐juvenile monkeys with LH , either alone or in combination with that of FSH , resulted in a 20–30 fold increase in the number of HSD3B‐positive cells. Interestingly, precocious FSH stimulation, alone, also resulted in appearance of Leydig cells as indicated by the occasional HSD3B‐positive cell in the interstitium. The nuclear diameter of these Leydig cells, however, was less than that of those generated in response to LH .