ENDOTHELIN IN THE OVINE UTERUS DURING THE ESTROUS-CYCLE AND EARLY-PREGNANCY

Endothelin, which has potent vasoconstrictor and mitogenic actions, wa s measured by radioimmunoassay in tissue extracts of sheep endometrium and myometrium and was found to be present in similar amounts in both tissues during the oestrous cycle and in increasing amounts during th e first 20 days of pregnancy (250-630 pg g(-1) wet weight). Immunoreac tive endothelin extracted from endometrium eluted at the same position as standard endothelin-1 on reverse-phase HPLC. Immunohistochemical t echniques demonstrated that during the oestrous cycle endothelin immun oreactivity was very low in caruncular and intercaruncular stroma, lum inal epithelium, outer and inner glandular epithelium, myometrium and blood vessels until after day 12 (oestrus: day 0). Staining increased in all but the inner glands to day 16 and the most intense staining wa s found in intercaruncular luminal epithelium and outer glands and in myometrium, although endothelin in tissue extracts did not change over this period. During early pregnancy (days 4-20), staining in intercar uncular areas and in myometrium increased slightly from day 4 to day 1 2 to a maximum which was maintained from day 15 to day 20. Intensity o f staining in caruncles increased only from day 15, particularly in th e epithelium. Immunoreactive endothelin was also present in the tropho blast cells of the embryo on day 20 of pregnancy. Strong endothelin im munostaining was observed in uteri from ovariectomized ewes, particula rly in epithelial cells and in blood vessels. The intensity of immunos taining in epithelium and stroma was increased slightly by oestradiol and decreased slightly by progesterone treatment, whereas treatment wi th oestradiol plus progesterone reduced staining intensity of endothel in in all types of tissue. Results of this study therefore demonstrate that immunoreactive endothelin-1 is present in the ovine uterus durin g the oestrous cycle and in increasing amounts during the first 20 day s of: pregnancy and is localized in most types of cell. Endothelin-1 i s regulated by ovarian steroids and pregnancy-related factors and may play an important role in the regulation of uterine blood flow, in ute rine development and the establishment of pregnancy.