Abstract

The present study addresses the role of prolactin as a regulator of migratory fattening in European quail (Coturnix coturnix). Plasma prolactin levels in captive birds undergoing migratory fattening in an outdoor aviary and in the laboratory were measured by radioimmunoassay with an antibody raised against recombinant-derived chicken prolactin. No strong association between prolactin and migratory fattening was apparent, and prolactin levels were more closely related to daylength, with the highest concentrations being reached on long days. Plasma prolactin profiles were similar in intact and castrated male quail. Prolactin was secreted in a daily rhythm, with the highest concentrations occurring early in the photophase. However, when birds were food-restricted for 50 days during a migratory phase, there was no difference in fat deposition between birds food-deprived for the first half of the daily photophase compared with those deprived for the second half. Fattening was reduced in the food-restricted birds relative to ad libitum-fed controls, but there was no difference in plasma prolactin levels between the groups. Injections of ovine prolactin (4 mg/kg) significantly increased food intake and body mass of birds maintained on long days, but there were no differences in fattening between birds injected in the morning compared with those injected in the afternoon. Collectively, these results do not support a major role for prolactin in the regulation of migratory fat deposition in European quail.

Journal of Endocrinology (1995) 146, 71–79

The presence and possible physiological roles of alpha-melanocyte-stimulating hormone (alpha-MSH) in the peripheral tissues of birds have not been established. By a combination of RT-PCR, immunocytochemistry and in situ hybridization, we have examined alpha-MSH expression in the eye of the chicken during development. In the 1-day-old chick, alpha-MSH was expressed in the retinal pigment epithelial (RPE) cells, and also at a lower level in the cone cells. The melanocortin receptor subtypes, CMC1, CMC4 and CMC5, were expressed in the layers of the choroid and the neural retina, but not in the RPE cells. It is probable that the RPE cells secrete alpha-MSH to exert paracrine effects on the choroid and neural retina. During embryonic development, alpha-MSH immunoreactivity in the RPE cells was initially detected at embryonic day 10, and increased in intensity as development proceeded. No cone cells were stained with anti-alpha-MSH antiserum in any of the embryonic stages tested. The immunoreactivities for two prohormone convertases, PC1 and PC2, were co-localized to the RPE cells with a pattern of staining similar to that of alpha-MSH. Despite containing alpha-MSH immunoreactivity, the RPE cells in 1-day-old chicks expressed no immunoreactivity for the endoproteases. Furthermore, in a 3-day-old chick, pro-opiomelanocortin mRNA was detectable by in situ hybridization only in the photoreceptor layer and not in the RPE cells. These results suggest that the RPE cells and the cone cells are intraocular sources of alpha-MSH in the embryonic and postnatal life of the chicken respectively. Embryonic expression of alpha-MSH in the RPE cells implies a possible role for the peptide in ocular development.