SMOOTH-MUSCLE MYOSIN-II AND ALPHA-SMOOTH MUSCLE ACTIN EXPRESSION IN THE BABOON (PAPIO-ANUBIS) UTERUS IS ASSOCIATED WITH GLANDULAR SECRETORYACTIVITY AND STROMAL CELL-TRANSFORMATION

The objective of this study was to investigate the localization and ho rmonal regulation of smooth muscle myosin II (SMM II) and ct smooth mu scle actin (alpha SMA) in the baboon uterus, since cytoskeletal protei ns are involved in secretory function and morphological transformation . Uterine tissue was obtained from baboons 1) during the menstrual cyc le, 2) following steroid treatment of ovariectomized baboons, 3) durin g pregnancy (Days 14-60 postovulation [PO]), and 4) during simulated p regnancy (Days 18-32 PO). Tissues were processed for immunocytochemica l localization of SMM II or alpha SMA with specific polyclonal or mono clonal antibodies, respectively, SMM II stained all smooth muscle cell s of blood vessels and myometrium regardless of treatment. Glandular e pithelial staining was present only in endometrium obtained during the luteal phase or following estrogen and progesterone treatment. Staini ng intensity was greater in the basalis than in the functionalis. The number of glands staining positive for SMM II on Days 18-32 of pregnan cy and simulated pregnancy was variable, Glandular stain was absent af ter Day 32 PO. These immunocytochemical data were confirmed by immunob lot analysis of glandular cytosolic extracts. Stromal staining for SMM II II was present under the luminal epithelium during simulated pregn ancy (Days 18-32), on Day 25 of steroid treatment in the simulated-pre gnant controls, and in nonimplantation sites during pregnancy. In cont rast, alpha SMA staining was low or absent in all uterine cell types i n ovariectomized baboons. Under estrogen-dominated conditions (follicu lar phase and estrogen treatment), alpha SMA staining was present in s mooth muscle cells, and this staining persisted throughout the remaini ng treatment periods. Glandular epithelial staining for alpha SMA was absent in all treatment groups. However, aSMA staining in stromal fibr oblasts underneath the luminal epithelium was evident as early as Day 14 of pregnancy and Day 18 of simulated pregnancy. The number of strom al fibroblasts that stained positive increased in the surface region o f the functionalis between Days 18 and 32 PO, and the staining extende d throughout the upper functionalis region. There was a decrease in th e number of positively stained stromal fibroblasts, particularly at th e implantation site, between Days 32 and 40 of pregnancy. By Days 50-6 0 of pregnancy, this staining was almost absent. The induction of aSMA in stromal fibroblasts in the functionalis region in pregnant baboons was confirmed by immunoblot analysis of stromal cell cytosol extracts . We conclude that the progesterone-induced glandular expression of SM M II may be involved in uterine secretory function and that aSMA expre ssion in stromal fibroblasts during pregnancy and after long-term ster oid treatment is associated with the decidualization process.