Regulation of alpha subunit synthesis by gonadal steroid feedback in the sheep anterior pituitary.

Cell-free translations of ovine pituitary RNA were used to examine the amount of alpha subunit synthesized in the presence and absence of physiological levels of gonadal steroids. Two animal groups were used: 1) no feedback-castrate ewes exhibiting high serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) and 2) negative feedback-castrate ewes treated with estradiol and progesterone which suppressed LH and FSH secretion. Cytoplasmic RNA was extracted from the pituitaries, translated in a wheat germ cell-free system, and alpha subunit identified by specific immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gels. Low amounts of alpha subunit (0.06% of total incorporated trichloroacetic acid-insoluble cpm) were seen in steroid-treated castrate ewes which also exhibited low serum LH and FSH concentrations. The amount of alpha translated by pituitary RNA from untreated castrates was significantly higher than those amounts from the steroid-treated castrates (p less than 0.02). The decreased amount of translated alpha subunit in steroid-treated castrates was probably not due to unique in vitro translation properties since the isotope incorporated/microgram of RNA and the amount of translated growth hormone and prolactin were similar for all RNAs. The results obtained from this animal model system suggest that the chronic negative feedback action of gonadal steroids on the gonadotropic hormones is effected, in part, via inhibition of synthesis of the alpha subunit of LH and FSH.