PUTATIVE MELATONIN RECEPTORS IN THE BLIND MOLE-RAT HARDERIAN-GLAND

The blind mole rat (Spalax ehrenbergi) displays daily and seasonal rhy thms. Melatonin, secreted nocturnally by the pineal gland, is also pro duced in the harderian gland and affects its morphology in rodents. We report here on the presence of putative melatonin receptors in the bl ind mole rat harderian gland, located in the microsome-enriched fracti on of the cells. Equilibrium I-125-melatonin binding studies indicated high- and low-affinity melatonin binding sites in the female (apparen t Kd 10 pM and 2.4 nM, respectively) and low-affinity sites in the mal e (apparent Kd 2.6 nM) mole rat. The binding sites were not significan tly affected by season. Castration increased the density of high-affin ity binding sites in males and low-affinity binding in females. I-125- melatonin binding to the gonadectomized mole rat preparation was inhib ited by serotonin>2-iodomelatonin greater than or equal to memelatonin >5-methoxytryptamine. The guanine nucleotide analogs, guanosine 5'O-[3 -thio-triphosphate] and guanosine 5'-O-[2-thio-diphosphate], inhibited specific I-125-melatonin binding, whereas 5'-guanylyl imido-diphospha te was less potent. These results indicate for the first time the pres ence of GTP-sensitive melatonin binding sites in the blind mole rat ha rderian gland, and suggest that their expression is under control of s ex steroids. (C) 1997 Wiley-Liss, Inc.