The Secretion of a Uterine Specific, Purple Phosphatase by Cultured Explants of Porcine Endometrium Dependency upon the State of Pregnancy of the Donor Animal1

Abstract

Explants of endometrium from the porcine uterus secrete labeled proteins into the growth medium when incubated in vitro in modified Eagle’s MEM⁴ containing radioactive L-leucine. Tissue from 60 day pregnant animals secrete about 30 times as much radioactive material into the medium in 24 h as explants taken from nonpregnant animals on Day 3 of the estrous cycle. The secretions by tissue from pregnant animals were also qualitatively distinct and contained appreciable quantities of 2 basic proteins, lysozyme and a uterine-specific phosphatase. The latter was identical to an iron-containing purple protein previously purified either from uterine secretions of progesterone treated, nonpregnant animals or from allantoic fluid. This protein is believed to be involved in iron transport from mother to fetus. Explants from the endometrium of animals on Days 30, 45, 60, 75, 90 and 105 of pregnancy showed considerable differences in their capacities to produce the purple protein. Production was maximal by Day 60 tissue (2 mg/g tissue/24 h), but very low in tissue from late pregnancy (Day 105), an observation which may have considerable implication with regard to dietary iron supplementation of the pregnant sow. Neither the presence of progesterone nor estradiol-17β in the incubation medium altered the quantity or quality of the proteins produced by the explants during the 24 h incubation. We conclude that it is the hormonal environment of the endometrium at the time of surgery which primarily governs the quantity and quality of the proteins by short term cultured explants.