As we have discussed in Hormonal Control of Spermatogenesis -
Spermatogenesis starts at the age of puberty due to a significant increase in the secretion of gonadotropin-releasing hormone (GnRH).
This is a hypothalamic hormone.
The increased levels of GnRH then act at the anterior pituitary gland and stimulate secretion of two gonadotropins – luteinising hormone (LH) and follicle-stimulating hormone (FSH).
LH acts at the Leydig cells and stimulates synthesis and secretion of androgens.
Androgens, in turn, stimulate the process of spermatogenesis.