Integumentary Effects of Prolactin in the Lower Vertebrates

Prolactin was first known as a stimulator of mammary secretion.It has since been found to induce secretion in the sebaceousglands of the mammal as well. It likewise stimulates secretoryactivity in the avian cropsac and in the mucous glands of fishesand of amphibians when thyroid hormone is also present. Prolactinhas mitogenetic effects on a variety of structures includingthe amphibian stratum corneum and induces growth of the tailfin in larval anurans and in both larval and adult newts. Prolactincauses the regression of cornified tubercles in the skin ofthe newt yetsynergizes with androgen in the presence of thethyroid hormone to induce the formation of keratinized nuptialpads. A similar synergism between prolactin and steroidal hormonesproduces avian incubation patches. There is indication thatprolactin may facilitate the growth of hair in mammals but detailedinformation is lacking. Effects on pigmentation are attributedto prolactin in two fishes.