Solution of methodological problems in prorenin measurement and investigations of tissue renin-angiotensin systems in the female reproductive tract.

The literature has been provided with conflicting results concerning prorenin in rat plasma. The cause was investigated and we characterized severe methodological problems. Prorenin is in rats measured by its enzymatic property after trypsin activation. Besides activating prorenin, trypsin appeared to degrade renin substrate (angiotensinogen) and formed an unstable 'blank' which interfered in the prorenin measurement. An interfering sulphydryl enzyme was also found in plasma from nephrectomized rats. Identical 'blank' problems were also found in other animals such as pigs and cattle. These problems were solved and a new validated method was developed enabling the study of active renin and prorenin in species other than humans. Plasma prorenin was found primarily to originate from kidneys in rats as in other species although minor contribution of other tissues was likely. Evidence has accumulated during recent years supporting the existence of local tissue RAS's in ovary and uteroplacental unit. The presence of active renin and prorenin in female reproductive organs were verified in cattle and pigs. A marked species difference was found. Secretion of prorenin to plasma only seemed to take place in humans suggesting primarily a local function of reproductive RAS's. The concentration of prorenin varies during follicular maturation and pregnancy in reproductive tissues and fluids. A tissue incubation method was developed to study the bovine ovarian RAS in-vitro. The presence, formation, secretion and degradation of active renin in bovine ovarian follicles in-vitro indicate that active renin--and not prorenin as suggested earlier--is important in mediating effects of tissue RAS. Angiotensin II receptors are also present in high and varying densities in the ovary, uterus and placenta. Several potential effects, mediated through auto- or paracrine actions, are suggested. Ovarian RAS may affect oocyte maturation, ovulation, steroidogenesis and angiogenesis. The uteroplacental RAS may affect decidualization, angiogenesis, hormone synthesis, local blood flow and uterine contraction. Effects may, according to the marked species difference of RAS, vary between species. The understanding of tissue RAS's is in its infancy. The ovary seems to be a very good model in study of tissue RAS's and their possible relations to the bloodborne RAS. Further investigation may also benefit the reproductive endocrinology.