DEVELOPMENTAL-CHANGES OF TESTICULAR ACTIVIN AND FSH RECEPTOR MESSENGER-RNA AND PLASMA FSH AND INHIBIN LEVELS IN THE RAT

To investigate the changes in the FSH receptor and the activin recepto r during sexual maturation in rat testes, we examined the mRNA levels of the receptors by Northern blot analysis. With a full length rat act ivin receptor cRNA probe in this study, Northern blot analysis reveale d two activin receptor mRNAs(6Kb and 3Kb) in testes. The large messeng er (6Kb) was low on day 7, and gradually increased by day 35. On the o ther hand, the small messenger(3Kb) was low on day 7, began to increas e on day 21, and had increased dramatically by day 35. Therefore, comp ared with our previous data, developmental changes in the mRNA of the activin receptor of male and female gonads showed certain differences. The expression of 3Kb activin receptor mRNA in rat testis may be rele vant to the stimulated spermatogenesis in this period. 2.4Kb and 5.5Kb FSH receptor mRNA were revealed on day 7 and decreased to 80% on day 14 and remained at the same level. The Scatchard plots of FSH binding data showed that the binding affinities of testicular FSH were constan t at each stage of development. Changes in the mRNA level in FSH recep tor were followed by changes in the concentration of FSH receptor in t estis. The rise in the plasma FSH level was concomitant with the decre ase in the plasma inhibin level by day 14.