Physiology Control of Spermatogenesis

Control of Spermatogenesis

* The testes are controlled by two gonadotropic hormones secreted by the anterior pituitary, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Both of these hormones are produced by the same cell type, the gonadotrope.

* Both hormones in both sexes act on the gonads by activating cAMP.

Feedback Control of Testicular Function

* LH and FSH act on separate components of the testes.

* LH acts on the Leydig cells to regulate testosterone secretion.

* FSH acts on the Sertoli cells to enhance spermatogenesis.

* Secretion of both LH and FSH from the anterior pituitary is stimulated by a single hypothalamic hormone, gonadotropin-releasing hormone (GnRH).

* GnRH is released in bursts once every two to three hours, with no secretion occurring in between.

* The blood concentration of GnRH depends on the frequency of these bursts in secretion.

* This pulsatile secretion of GnRH stimulates ongoing LH and FSH secretion.

* However, LH and FSH are segregated to a large extent into separate secretory vesicles in the gonadotrope and are not secreted in equal amounts because other regulatory factors influence how much of each gonadotropin is secreted.

* Testosterone influences the secretory rate of LH and FSH.

* Testosterone, the product of LH stimulation in the Leydig cells, acts in negative feedback fashion to inhibit LH secretion in 2 ways:

1. The predominant negative-feedback effect of testosterone is to decrease the GnRH release by acting on the hypothalamus, thus indirectly decreasing both LH and FSH release by the anterior pituitary.

2. Testosterone acts directly on the anterior pituitary to selectively reduce LH secretion.

* The latter action explains why testosterone exerts a greater inhibitory effect on LH secretion than on FSH secretion.

* FSH and testosterone play critical roles in controlling spermatogenesis, each exerting its affect by acting on Sertoli...