Evidence that human chorionic gonadotropin/luteinizing hormone receptor down-regulation involves decreased levels of receptor messenger ribonucleic acid.
 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.
