BIOACTIVE FORMS OF GONADOTROPIN-RELEASING-HORMONE IN THE BRAIN OF AN INDIAN MAJOR CARP, CATLA-CATLA (HAM)

Two forms of biologically active gonadotropin releasing hormones were isolated from the hypothalami of Catla catla. Gonadotropin releasing h ormone activity was studied in vitro using enzymatically dispersed car p pituitary cell incubation system. Gonadotropin released into the med ium was measured by carp gonadotropin-radio immune assay. Acetic acid extracted hypothalamic material was subjected to acetone fractionation . Among the three protein pellets obtained at different time periods ( AC I, AC II and AC III), AC II exhibited the gonadotropin releasing ho rmone activity. Gel filtration of AC II through Sephadex G-25 column s howed three protein peaks (SG I, SG II and SG III) and only SG II demo nstrated strong gonadotropin releasing hormone activity. Elution of SG II through FPLC Mono Q column (an anion exchanger) in NaCl gradient p rogramme showed one unadsorbed (MQ I) and three adsorbed (MQ II, MQ II I and MQ IV) protein peaks. MQ III, which was eluted with 51% NaCl, ex hibited gonadotropin releasing hormone activity. Surprisingly, unadsor bed fractions, MQ I, also showed gonadotropin releasing hormone activi ty. MQ I was therefore subjected to FPLC Mono S (a cation exchanger) c olumn chromatography where a highly active gonadotropin releasing horm one enriched peak, i.e., MS III, could be eluted with 45% NaCl. These findings show that Catla catla hypothalamus has two forms of gonadotro pin releasing hormones one anionic (carp gonadotropin releasing hormon e I) and another cationic (carp gonadotropin releasing hormone II). Th ese two forms of gonadotropin releasing hormones were,also active in h eterologous carp species, rohu (Labeo rohita), mrigal (Cirrhinus mriga la) and an exotic common carp (Cyprinus carpio). Combined activity of two forms of gonadotropin releasing hormones was significantly greater as compared to any of the single form.