Effect of Neuromedin S (NMS) on ghrelin suppressed testosterone secretion in adult male rhesus monkey

Abstract

Neuromedin S (NMS), a 36 amino ac id peptide, identified in rat brain as li gand for the G protein-coupled receptor FM4/TGR-l , also termed neuromedin U receptor type-2 (NMU2R). Its central expression is restri cted to the suprachi asmatic nucleus and involved in the regul ation of dark li ght rhythms and suppression of fo od intake. Ghrelin on the other hand is a 28 amino acid peptide produced in the stomach and has a stimulatory role in food intake and energy homeostasis. Stimulatory role of NMS and inhibitory ro le of ghrelin on hypothalami c pituitary gonadal axis (HPG) is reported in rodents. The potenti al contribution of these two peptides in the control of reproductive ax is in hi gher primates remains unex plored. [n the present stud y the stimul atory rol e of N MS was investi gated on ghrelin suppressed testosterone secretion in adult male rhesus monkeys. Four adult mal e rhes us monkeys were used in this stud y. Fifty nmol ofNMS and g ghrelin were inj ected through a teflon cannul a impl anted in saphenous vein . Blood samples were collected indiv iduall y fo r NMS and ghrelin 60 min befo re and 120 min afterNMS and ghrelin administration at 15 min intervals. To study the effect o f NMS on ghrelin suppressed plasma testosterone secretion sampl es were coll ected 45 min before the administration of ghrelin, then NMS was administered after 60 min of ghrelin inj ection and sampl es were coll ected for 120 min after NMS inj ection. The plasma testosterone concentrati ons were determined by using specific Enzyme Immunoassay (E[A). Ghrelin significantl y (P<0.05) decreased plasma testosterone secretion af1er 45 min and levels remained low till 60 min. NMS blocked this decline caused by ghrelin and fU11her stimulated (P<O.OO 1) plasma testosterone secretion from 30 to 60 min after its administration. In conclusion the present study s uggests that NMS has an ability to restore the inhibitory effect of ghrelin on testosterone secretion and further stimulated testosterone secretion in adult male rhesus monkey . This response might he regulated through HPG axis however fLll1her study is recommended to understand the exact mechanism of acti on of these two peptides in regul ation of reproducti ve behav iour in primates.