Bioactive forms of gonadotropin releasing hormone in the brain of an Indian major carp, Catla catla (Ham.).

ABSTRACT

Two forms of biologically active gonadotropin releasing hormones were isolated from the hypothalami of Catla catla. Gonadotropin releasing hormone activity was studied in vitro using enzymatically dispersed carp pituitary cell incubation system. Gonadotropin released into the medium was measured by carp gonadotropin-radio immuno 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 hormone activity. Gel filtration of AC II through Sephadex G-25 column showed three protein peaks (SG I, SG II SG III) and only SG II demonstrated strong gonadotropin releasing hormone activity. Elution of SG II through FPLC Mono Q column (an anion exchanger) in NaCl gradient programme showed one unadsorbed (MQ I) and three adsorbed (MQ II, MQ III and MQ IV) protein peaks. MQ III, which was eluted with 51% NaCl, exhibited gonadotropin releasing hormone activity. Surprisingly, unadsorbed fractions, MQ I, also showed gonadotropin releasing hormone activity. MQ 1 was therefore subjected to FPLC Mono S (a cation exchanger) column chromatography where a highly active gonadotropin releasing hormone enriched peak, i.e., MS III, could be eluted with 45% NaCl. These findings show that Catla catla hypothalamus has two forms of gonadotropin releasing hormones one anionic (carp gonadotropin releasing hormone I) and another cationic (carp gonadotropin releasing hormone II). These two forms of gonadotropin releasing hormones were also active in heterologous carp species, rohu (Labeo rohita), mrigal (Cirrhinus mrigala) 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.