The administration of 100 i.u. ovine prolactin to male crested newts has been shown to block spermatogenesis by producing a zone of degeneration in spermatogonia which are about to change into primary spermatocytes (Mazzi, Vellano & Toscano, 1967).
Since signs of inhibited function of adenohypophysial type II basophils, which may be regarded as producing follicle-stimulating hormone (FSH) (Mazzi, Peyrot, Anzalone & Toscano, 1966), had been observed in prolactin-treated animals, it was assumed that the antigonadal effect of prolactin was secondary to the inhibition of FSH-producing cells. To test this hypothesis, experiments involving the simultaneous injection of prolactin and FSH were carried out.
On 13 June 1967, 40 male newts in full spermatogenetic activity were divided into four groups of ten. The first group served as controls; the second group received 100–120 i.u. prolactin (ovine, NIH-P-S7) in 0·6% NaCl solution, divided into four injections of 0·1 ml. given every other day.