HORMONAL AND PHOTOPERIODIC MODULATION OF TESTICULAR MESSENGER-RNAS CODING FOR INHIBIN ACTIVIN SUBUNITS AND FOLLISTATIN IN CLETHRIONOMYS-GLAREOLUS, SCHREBER/

Photoperiodic and hormonal modulation of mRNAs for testicular inhibin/ activin subunits and follistatin were studied in a seasonally breeding rodent, the bank vole (Clethrionomys glareolus). Photoperiod-induced testicular regression had no effect on the relatively low steady-state levels of follistatin mRNA. Inhibin alpha (I alpha) and beta B (I bet a B) mRNA levels were significantly higher in regressed than in active gonads, but inhibin beta A was undetectable. The effect of gonadotrop in administration on testicular weight and mRNA concentrations differe d between the sexually active and quiescent voles. Neither FSH (1.2 U/ kg; s.c. for 5 days) nor hCG (600 IU/kg; s.c. for 5 days) affected tes ticular weight in sexually active voles, whereas both gonadotropins si gnificantly increased testicular weight in photo-regressed individuals . FSH had no effect on I alpha or I beta B mRNA concentrations in the active testes, whereas excessive hCG challenge induced a decrease in t he steady-state levels of these mRNAs. FSH induced an increase in Ia m RNA concentrations in the regressed gonad, whereas both gonadotropins concomitantly down-regulated I beta B mRNA levels. In conclusion, the high expression of I alpha and I beta B mRNA in the regressed testis i mply autocrine and paracrine roles for inhibin/activin in the quiescen t; gonad of seasonal breeders. Inhibin alpha-subunit expression is at least partly under the control of FSH in the bank vole testis. J. Exp. Zool. 281:336-345, 1998. (C) 1998 Wiley-Liss, Inc.