If hypothalamic hormones will decrease then it will affect spermatogenesis and spermiation in him. Hypothalamus releases GnRH ( Gonadotrophin releasing Hormones ) which stimulate the pituitary to secrete gonadotropins – LH ( Luteinising Hormone) & FSH ( follicle stimulating Hormone) .
LH acts on Leydig Cells ( in Testis) and stimulates secretion of androgens which stimulate spermatogenesis.( formation of sperm from spermatogonia)
FSH acts on Sertoli cells (in testis) and stimulates secretions of some factors which help in spermiogenesis.( transformation of spermatids to sperms).