DAILY VARIATIONS IN 2-[I-125]MELATONIN SPECIFIC BINDING IN THE GOLDEN-HAMSTER RETINA

DAILY variations in melatonin content and 2-[I-125]melatonin specific binding in retinas of golden hamsters were studied. Both parameters sh owed significant variations throughout the 24 h period. Maximal specif ic binding was observed at 24.00 h, while melatonin content peaked at 04.00h. Saturation studies performed at 12.00 and 24.00 h indicated th at the maximal concentration of 2-[I-125]melatonin binding sites (B-ma x) was significantly higher at 24.00 h than at 12.00 h, whereas the di ssociation constant (K-d) remained unchanged. As 2-[I-125]melatonin sp ecific binding decreased at times when retinal melatonin content was h igh, these findings suggest that daily variations in retinal melatonin levels may be implicated in the regulation of the density of melatoni n binding sites, probably through mechanisms of up- and down-regulatio n induced by melatonin on its own binding sites.