Effects of IGF1 and GnRH on gonadotropin subunits in the pituitary cells of the Indian freshwater catfish, Heteropneustes fossilis (Bloch).

Insulin-like growth factor 1 (IGF1) is a key somatotropic hormone that controls growth and metabolism, thereby conveying growth status to the reproductive endocrine system. The regulation of gonadotropin-releasing hormone (GnRH) to synthesize and release both the gonadotropin hormones (FSH and LH) is well documented. Numerous attempts have been made to understand the interaction of gonadotropic (reproductive) and somatotropic (growth) axis, but the dynamics of their interaction are still not clear at the pituitary level among teleost. The present study bioinformatically demonstrated protein-protein interaction of IGF1 with the proteins of both somatotropic and gonadotropic axes suggesting a cross-talk between them. In vitro, the effects of IGF1 alone or in combination with GnRH on pituitary transcripts for follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were examined. Experiments were conducted with dispersed pituitary cells of the catfish, Heteropneustes fossilis, to determine the time- and dose-dependent response of IGF1 and GnRH alone or in combination to assess fshβ and lhβ. The results showed a time-dependent effect with maximum transcripts level at 1 h of exposure. IGF1 and GnRH showed dose-dependent effects on differential expression of both transcripts when administered alone, with maximum fshβ and minimal lhβ levels at the higher dose. A synergistic impact on both the transcripts was observed in the presence of IGF1 and GnRH. Collectively, the study suggests that IGF1 plays a crucial role in regulating the synthesis of hormones in the catfish by interacting between the gonadotrophs and somatotrophs at the pituitary level.