Injection of pseudopregnant rats with pharmacological doses of hCG leads to a characteristic decrease in LH/hCG binding by the isolated luteal cells. The steady state levels of LH/hCG receptor mRNA were determined in rat ovaries during hCG-induced down-regulation of the receptor. Northern blots were performed using a 20-mer probe corresponding to a guanine cytosine-rich carboxyl-terminal untranslated region of the LH/hCG receptor cDNA. The hybridization of the probe to LH/hCG receptor mRNA was highly specific, since the probe hybridized only to rat luteal cell RNA fraction, with no signal detected in nontarget tissues. The LH/hCG receptor level was quantitated by [125I]hCG binding to the isolated membrane fractions from the corresponding treatment and control groups. Examination of mRNA levels of the receptor during hCG-induced down-regulation showed a steady decrease from 0-24 h, followed by a gradual increase to control levels from 24-72 h corresponding to days 8-9 of pseudopregnancy. The [125I]hCG-binding activity during down-regulation paralleled the mRNA profile in both the experimental and control groups. Examination of the levels of mRNA for alpha-actin showed no change during this period, suggesting that the loss of LH/hCG receptor mRNA at 24 h was not due to a general loss of mRNA in luteal cells. These results suggest that hCG-induced down-regulation of the LH/hCG receptor in luteal cells involves regulation of the receptors at the message level.

Sex-limited protein (Slp) is expressed in adult male mice. A 160-basepair fragment 2 kilobases upstream of the gene serves as an androgen-dependent enhancer of chloramphenicol acetyltransferase expression in transient transfection assays in cells with endogenous or cotransfected androgen receptor. One element that is necessary, but not sufficient, for induction is a consensus glucocorticoid (or hormone) response element (HRE). This element binds to the mouse androgen receptor in vitro, but with apparent weak affinity. Induction by the HRE is greatly augmented by an accessory sequence within the 160 basepairs, suggesting that cooperative interactions confer strong response to androgen. Additional elements within the enhancer modulate induction, positively or negatively, and exhibit cell-specific behavior. Of particular interest are two degenerate HREs that are adjacent to the consensus sequence; they show no independent activity, but are functionally significant in conjunction with other elements. The complexity of this enhancer may reflect biological mechanisms that ensure specificity of hormonal response and allow gene expression to respond to changes in hormone concentration.