DIFFERENTIAL EXPRESSION OF PROGESTIN RECEPTOR ISOFORMS IN THE HYPOTHALAMUS, PITUITARY, AND ENDOMETRIUM OF RHESUS MACAQUES

The progestin receptor exists in at least two isoforms: a long form (P R-B) and a short form (PR-A), which can be separated and detected with Western blot analysis. It has been suggested from in vitro transfecti on experiments that differential expression of the two isoforms may pr ovide one mechanism for tissue specific actions of progesterone (P). H owever, more information from in vivo experimentation is needed. It ha s been reported that P down-regulates the expression of PR in the endo metrium and pituitary of E primed macaques. However, PR protein and PR messenger RNA expression in the hypothalamus is maintained with P tre atment of E-primed macaques. Thus, there is tissue-specific regulation of PR by its cognate ligand in the nonhuman primate. To gain insight into the tissue-specific regulation of PR by P, we questioned whether differential expression of the isoforms of PR exists in the endometriu m, pituitary, and hypothalamus of rhesus monkeys. The expression of PR -A and PR-B was examined after E (28-30 days) and E + P (14 days E + 1 4 days E + P) treatment in the primate endometrium, pituitary, and hyp othalamus. After E or E + P treatment, the levels of PR-A were 5 times higher than PR-B in the endometrium. PR-A was 1.6-fold higher than PR -B in the pituitary. In the hypothalamus, the ratio of A to B ranged f rom less than 1 (B exceeds A) to unity (A and B equimolar). There was no difference in the ratio of A to B between E-treated and E + P-treat ed groups in any tissue examined. These observations (a) provide furth er support of the hypothesis that differential expression of the isofo rms of PR may subserve the tissue specific actions of P and (b) also s uggest that P does not differentially affect the expression of the iso forms of its cognate receptor in the endometrium, pituitary, or hypoth alamus.