Cultured pituitary cell GtH response to GnRH at different stages of rainbow trout spermatogenesis and influence of steroid hormones

Using primary cultures of whole dispersed pituitary cells collected from rainbow trout at different stages of spermatogenesis, basal and GnRH-induced GtH release and cell GtH content were studied in control and steroid-pretreated cultures. Steroid pretreatments were performed for 3 days with 11-ketotestosterone (11KT) and 17α-hydroxy,20β-dihydroprogesterone (17α20βP) at levels corresponding to those circulating at the time of spermiation (50 and 20 ng/ml, respectively). In control cultures, basal GtH release and cell GtH content increased with the stage of spermatogenesis in a characteristic pattern as predicted from in vivo results concerning plasma and pituitary GtH contents. The pituitary response to salmon GnRH (sGnRH) also varied as indicated by the decrease in the minimal effective dose of GnRH able to induce a significant GtH release with the advancement of spermatogenesis: 10−7 M at the spermatocyte stage, 10−9 M at prespermiation and spermiation. Steroid pretreatments were shown to have a direct effect on pituitary gonadotrophs and particularly on pituitary response to sGnRH, depending on the stage at which they are applied. At the beginning of spermatogenesis both of them induced an increase in GtH release and at prespermiation they have a slight negative effect, significant only with 17α20βP. At spermiation they have no effect except for 17α20βP which increased the response to 10−8 M of sGnRH. Results are discussed in relation to hormonel changes (gonadotropin and steroid) observed by different authors during the sexual cycle