Reproductive stage- and sex-dependant effects of neurohypophyseal nonapeptides on gonadotropin subunit mRNA expression in the catfish Heteropneustes fossilis: An in vitro study

In the present study, in vitro effects of synthetic vasotocin (VT), isotocin (4Ser, 8Ile- oxytocin; ITb) and the recently cloned IT gene paralog product (8Val-lsotocin, ITa) were studied on the expression of pituitary gonadotropin (GtH) subunit mRNA levels. In male pituitaries of early (preparatory phase) and late (pres-pawning phase) recrudescing catfish, Heteropneustes fossilis, VT (10 nM, 100 nM and 1000 nM) stimulated fsh beta expression dose-dependently. But in females, the dose-dependent effect was found only in the preparatory phase. In males, VT stimulated lh beta expression only at higher doses. In females, VT produced a significant dose-dependent increase of the lh beta expression only in the prespawning phase. VT stimulated the expression of gp alpha, dose-dependently in the preparatory phase in males and in the prespawning phase in females. The incubation of the pituitaries with ITb did not alter the fsh beta expression in either sex in both preparatory and prespawning phases. In males, ITb stimulated the expression of lh beta and gp alpha only at the highest concentration (1000 nM) in both phases. In females, ITb stimulated both lh beta and gp alpha expression only at 1000 nM in the preparatory phase and dose-dependently in the prespawning phase. The incubation of the pituitaries with ITa produced effects similar to ITb on the expression of fsh beta, lh beta, and gp alpha. The results show that the basic peptide VT modulates both fsh beta and lh beta expressions, which are influenced by the sex and reproductive stage. The neutral peptide ITA/ITb exerts an insignificant effect on the fsh beta expression regardless of sex or season. Both VT and ITa/ITb elicit a significant effect on the lh beta expression in late recrudescent phase especially in females. (C) 2018 Elsevier Inc. All rights reserved.