Endogenous regulation of the pineal melatonin secretion inGallus domesticus

Abstract

The serum melatonin (MT) levels in laying hens (Gallus domesticus) subjected to different light/dark (L/D) cycles have been measured. In order to study the levels of circulating MT in blood it was necessary to establish a specific and very sensitive radioimmunoassay (RIA). Our MT-RIA was developed after raising anti-MT antibodies in Rabbits. The RIA was performed by using3H-MT as tracer. The standard curve covered the range of 0.022–0.345 pmol/vial and theK D value for MT was estimated at 1.37×1010 l/mol. The antiserum specificity has been analysed; none of the common MT analogues showed cross-reactivity strong enough to interfere with MT measurement. The intra- and inter-assay variability for serum samples were 7.2 and 15.3%, respectively. The L/D experiment for 12L/12D, 16L/8D and 8L/16D cycles showed a typical nighttime rise in serum MT; the duration of that rise was directly proportional to the hours of darkness. Continuous light eliminated the serum MT rhythmicity. However, a rhythmical secretion of serum MT was present under continuous darkness for almost two weeks. Our results support the hypothesis of the presence of an endogenous regulation of the pineal MT secretion in laying hens.