ABSTRACT
Two alternative variants of 5'-untranslated sequence of the rat growth hormone receptor (GHR) mRNA were previously described. These variants of mRNA appear to be produced by the splicing of primary transcripts initiated from alternative promoters. We employed the ribonuclease protection assay to reveal these two variants of the GHR mRNA in RNA preparations from the liver of male, normal female, and pregnant female rats. All tissues examined contain approximately the same amount of the GHR mRNA with type II 5'-untranslated sequence. To the contrary, the content of type I variant shows very pronounced sexual differences; its level is very low in the male liver, approximately equal to that of the type II variant in the female liver, and further increases in the pregnant female liver. These data suggest that the higher content of the GHR observed in the female liver and its elevation during gestation result from the accumulation of "female specific" type I variants of the GHR mRNA.
