The Binding Property and Function of Melatonin Receptor in Peripheral Tissues-Chick Embryonic Vessels and Young Rat Leydig Cells

This dissertation, "The Binding Property and Function of Melatonin Receptor in Peripheral Tissues-chick Embryonic Vessels and Young Rat Leydig Cells" by Xiaofei, Wang, 汪嘵飛, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled 'The Binding Property and Function of Melatonin Receptor in Peripheral Tissues- Chick Embryonic Vessels and Young Rat Leydig Cells' submitted by Wang Xiao-Fei for the Degree of Doctor of Philosophy at the University of Hong Kong in May, 2001 Melatonin receptors were identified and characterized in the chick embryonic aorta and pulmonary artery. 2-[125I]iodomelatonin binding sites in the chick embryonic aorta and pulmonary artery were stable, reversible, saturable, specific and of high affinity. Autoradiographic studies on the blood vessel and radioreceptor binding assay on the cultured vascular smooth muscle cells showed that 2- [125I]iodomelatonin binding sites was located in the smooth muscle layer in the aorta and pulmonary artery. Guanosine 5'-O-3-thiotriphosphate (GTPyS) reduced the Bmax and increased the Kd of 2-[125I]iodomelatonin binding sites in the chick embryonic aorta and pulmonary artery. The effect of GTPyS on 2-[125I]iodomelatonin binding sites showed that these binding sites may be coupled to a melatonin receptor-guanine nucleotide binding protein effector system, thus suggesting that the arterial 2- [125I]iodomelatonin binding site may mediate a cascade of intracellular events via a G- protein. The 2-[125I]Iodomelatonin binding capapcity was higher in the embryo than that in post-hatched chicks. The 2-[125I] iodomelatonin binding sites were down- regulated by melatonin itself and up-regulated by phenylephrine, a selective agonist of cti-adrenergic receptor, the predominant receptor to the sympathetic nervous system, which is the most important extrinsic control of the vascular system. We also demonstrated that melatonin potentiated the phenylephrine-induced contraction of aortic rings and intracellular calcium transient in culture vascular smooth muscle cells from the chick embryonic aorta and pulmonary artery, but melatonin itself had no effects on either the contraction and basal [Ca2]]j. This strongly supported that melatonin binding sites in the chick embryonic aorta and pulmonary artery were physiological functional receptors. The melatonin receptor in embryonic aorta and pulmonary artery may regulate the embryonic vascular smooth muscle cell activity by modulation of the cci-adrenergic receptor. In mammalian gonads, functional studies indicated that it is one of sites of action of melatonin. However, previous binding studies have yielded inconsistent results. In present study, using RT-PCR and in situ hybridization, we firstdemonstrated that both of two subtypes of melatonin receptors, Meli and Melib, were expressed in rat Leydig cells. Our data have provided evidence that melatonin directly acts on two systems-vascular and reproductive systems via melatonin receptors, which forms the basis for the future research endeavors. DOI: 10.5353/th_b3040907 Subjects: Melatonin - Receptors Pulmonary artery Leydig cells Chicks - Physiology Rats - Physiology