Tissue renin and prorenin increase in female cats during the reproductive cycle without commensurate changes in plasma, amniotic or ovarian follicular fluid.

The renin gene is expressed, primarily as prorenin, in the ovary, uterus and placenta. High concentrations of prorenin are present in human ovarian follicular and amniotic fluids and ovarian secretion causes increases in plasma prorenin at mid-menstrual cycle and during pregnancy. Plasma prorenin is low but detectable in nephrectomized human subjects. Comparative studies in female cats revealed several differences. Cat plasma prorenin became undetectable after bilateral nephrectomy. Neither plasma prorenin nor renin increased during pregnancy. Renin and prorenin were undetectable in ovarian follicular, amniotic and allantoic fluids. Human chorionic gonadotropin-induced ovulation caused only small increases in plasma prorenin. In contrast, renin and prorenin were clearly present in extracts of reproductive tissues. Ovarian total renin was lowest during anestrus (169 +/- 27 ng/g per h) and estrus (258 +/- 58 ng/g per h) and increased with ovulation (385 +/- 31 ng/g per h). Higher ovarian levels were found during pseudopregnancy (1370-2030 ng/g per h) and early pregnancy (1312-2700 ng/g per h) and in the placental chorion disc of early pregnancy (1755-1184 ng/g per h). In the uterus, the level was 98-183 ng/g per h during gestation. These results demonstrate that, in marked contrast to humans, only the cat kidney secretes prorenin into body fluids. Nonetheless, total renin increases in cat ovaries during follicle maturation, ovulation, pregnancy and pseudopregnancy, in the uterus during gestation and in the placental chorion disc. These results are consistent with an autocrine or paracrine role for the tissue renin system in cat reproductive tissues.