INHIBIN-ALPHA, BETA(A) AND BETA(B) SUBUNIT MESSENGER-RIBONUCLEIC-ACIDLEVELS IN CULTURED RAT PITUITARY - STUDIES BY A QUANTITATIVE RT-PCR

Recent studies have demonstrated that inhibins and activins both play not only endocrine roles but also local regulatory roles in gonadotoro pin secretion. There has been controversy as to the subtype of rat pit uitary inhibin/activin. We studied the levels of inhibin alpha, beta(A ) and beta(B) subunit mRNAs by a quantitative reverse transcription-po lymerase chain reaction (RT-PCR) and the changes in their levels by ad ding inhibin alpha, beta(A) and beta(B) mRNA antisense oligonucleotide s and inhibin A, activin A or GnRH to cultured rat anterior pituitary cells. This study demonstrated the level of 3 mRNAs to be 1.6 x 10(-2) , 0.75 and 3.4 x 10(-2) molecules/cell with a molar ratio of 1:50:2. A stimulatory role for activin B in FSH secretion was suggested as beta (B) mRNA antisense oligonucleotide decreased FSH secretion. The beta(B ) mRNA level tended to be decreased by the addition of activin A, but the decrease was not statistically significant. GnRH did not affect al pha and beta(B) mRNA levels when administered singly. The level of bet a(B) mRNA was not changed by any of the above treatments. In conclusio n, the presence of inhibin alpha, beta(A) and beta(B) subunit mRNAs in the rat anterior pituitary with the greatest abundance of beta(A) was demonstrated by using RT-PCR. Activin B or activin AB may play import ant roles in FSH secretion in an autocrine or a paracrine fashion, and activin A may play an indirect role in FSH secretion.