Endocrine control of mammalian testicular ontogenesis

The endocrine control of ontogenesis of the male gonad involves the development of the gonad itself and, at the same time, the development of the endocrine system. During the impubertal phase, the seminiferous tubules contain supporting cell and gonocytes, both of which increase in number by mitotic divisions. Over this period, the pituitary secretion of both FSH and LH increases, FSH progressively and LH in pulsatile fashion. In the interstitial tissue, the numbers of Leydig cells also increase. The increase in LH secretion and in leydig cell numbers leads to an increase in testosterone secretion, so that a little before puberty the system of LH-testosterone feedback is fully operational. The testicle then reaches the prepubertal phase, where the supporting cells stop dividing and differentiate to become the highly specialised Sertoli cells. Thereafter, their numbers remain almost constant. the gonocytes now begin rapidly dividing and differentiating, their rate of division resulting in a drastic increase in testicular size. The end result of their division and differentiation is that the testicle begins to produce spermatozoa. Very few are produced at first, but eventually production reaches adult levels and the testis begins to show normal spermatogenic cycle. Also during this phase, the pulsatile secretion of LH and testosterone continue and the secretion of FSH increases. The developments of these two systems are not unrelated. The division of the supporting cells and their maturation into Sertoli cells are under the control of LH in synergy with FSH, while the differentiation of primordial cells into spermatogonia and the subsequent production of spermatozoa are under the control of FSH, LH and testosterone.