ONTOGENY OF GROWTH-HORMONE AND PROLACTIN SECRETION IN THE DOMESTIC-FOWL (GALLUS-DOMESTICUS)

Concentration of growth hormone (GH) and prolactin were measured in plasma from embryonic and neonatal chicks. GH was not detectable (<4 ng/ml) until after 17 days of incubation (6 ng/ml). The concentration increased progressively to 16 ng/ml on the day after hatching and then sharply to 50 ng/ml in 3-day-old chicks. Plasma concentrations of prolactin were low (<6 ng/ml) in 9-, 11-, and 13-day-old embryos, increased to 78 ng/ml after 17 days of incubation, then decreased to 37 ng/ml in 19-day-old embryos. On the day after hatching plasma prolactin concentration was 140 ng/ml but it fell progressively to 49 ng/ml in 5-day-old chicks. © 1979.