Secretion of which hormone first increases significantly at puberty in human males?

Spermatogenesis starts at the age of puberty due to significant increase in the secretion of gonadotropin releasing hormone (GnRH). GnRH then stimulates the secretion of gonadotropins (FSH and LH) by the anterior pituitary gland. LH acts at the Leydig cells and stimulates synthesis and secretion of androgens. Testosterone is the principal androgen.