Skin graft survival in the uterine lumen of ewes treated with progesterone.

An experiment was conducted to determine the effect of progesterone on survival of skin transplants placed in the uterine lumen of ovariectomized ewes. Animals were treated for 30 days with either a corn oil vehicle (n = 4) or progesterone at 50 (n = 3) or 200 mg/day (n = 3). An autograft and allograft were then placed in each uterus, and treatments were continued for an additional 30 days before grafts were examined for survival. All autografts were present 30 days after grafting and most appeared healthy upon histological examination. Allografts placed into the uterine lumen of progesterone-treated ewes were present 30 days after grafting but were necrotic in histological appearance. Allografts placed within the uterus of corn oil-treated ewes were completely resorbed. Uterine secretions that accumulated in the uterine lumen were examined for inhibitory effects on [3H-methyl]thymidine incorporation by lymphocytes stimulated with phytohemagglutinin (PHA). The total amount of immunosuppressive activity in the uterine lumen was greater (P less than 0.05) for progesterone-treated ewes than for corn oil-treated ewes. Concentrations of progesterone in uterine secretions of progesterone-treated ewes ranged from 0.3 to 3.4 ng/ml. Thymidine incorporation into PHA-stimulated lymphocytes was not affected by in vitro treatment with up to 500 ng/ml of progesterone. In conclusion, progesterone delayed resorption of skin allografts placed in the uterine lumen. Results are consistent with the hypothesis that progesterone mediated this effect by stimulating the secretion of immunosuppressive substances into the uterine lumen.