CORTICOSTERONE IN-VIVO INCREASES PITUITARY FOLLICLE-STIMULATING-HORMONE (FSH)-BETA MESSENGER-RIBONUCLEIC-ACID CONTENT AND SERUM FSH BIOACTIVITY SELECTIVELY IN FEMALE RATS

Experimental objectives were to determine: 1) if the native glucocorti coid, corticosterone (B), can selectively increase pituitary FSH and F SH beta messenger RNA (mRNA) in the presence or absence of a GnRH sign al; and 2) if B affects the biological activity of the gonadotropins. Metestrous female rats were implanted with cholesterol or B. Each impl ant group received 100 mu g GnRH antagonist or control injections ever y 48 h beginning at the time of implantation, and were killed 5 days l ater. B significantly increased bioactive serum FSH, with or without G nRH antagonist. GnRH antagonist decreased bioactive serum FSH. Immunor eactive serum FSH was not affected by any treatment. B did not affect bioactive serum LH, but GnRH antagonist significantly suppressed bioac tive serum LH. Immunoreactive serum LH was significantly lowered by ei ther B or GnRH antagonist. Neither bioactive nor immunoreactive pituit ary FSH or LH content were affected by B, GnRH antagonist, or combined treatments, and no treatment affected alpha or LH beta mRNA. B signif icantly increased FSH beta mRNA specifically, in the presence or absen ce of GnRH antagonist. These results demonstrate that corticosterone c an increase biological activity of secreted FSH and increase FSH beta mRNA in the absence of a GnRH signal, suggesting a direct effect on th e anterior pituitary gland.