Effects of steroids on gonadotropic (GTH) cells in the pituitary of rainbow trout, Salmo gairdneri, shortly after hatching.

Immunocytochemical reactions with anti-h(uman) TSH beta and anti-c(arp) GTH beta indicate that in juvenile rainbow trout, the dorsal basophils of the proximal pars distalis (ppd) are TSH cells, and that the ventral ones are GTH cells. Small GTH cells first appear in some fish at D(ay) 50 following fertilization (= D17 from hatching), when gonads are still undifferentiated. GTH cells increase greatly in number and size after D100. Contrary to treatment with 11 beta (OH)androstenedione, addition of methyl testosterone, progesterone and 17 alpha (OH)progesterone stimulate the development of granular GTH cells in rainbow trout, shortly after hatching. It is suggested that steroid receptors in the brain or pituitary discriminate between 11-steroids and other steroids rather than between aromatizable androgens and other steroids.