Form Of Renin Research Articles

Biochemical characteristics of human renin expressed in transgenic mice.

1. Biochemical properties of human renin expressed in transgenic mice (hRN8-12 mice) carrying the human renin gene (Fukamizu et al. Biochem Biophys Res Commun 1989; 165: 826-32) were examined. The optimum pH of the enzymic activity against human angiotensinogen was 5.5 for both plasma and renal human renin in the hRN8-12 mice. Plasma concentrations of human active and inactive renin in the plasma of hRN8-12 mice were 16.7 +/- 2.8 and 79.9 +/- 14.0 pmol of angiotensin Ih-1 ml-1, respectively, thereby indicating that the predominant form of plasma human renin is the inactive form, as is the case in humans. 2. The molecular masses of plasma human active and inactive renin and renal human active renin in the hRN8-12 mice were estimated to be 46 kDa, 48 kDa and 44 kDa, respectively, as determined by h.p.l.c. on G3,000SW. 3. Human renin in the hRN8-12 mouse kidney was bound to a concanavalin A-Sepharose column, and was eluted with alpha-methyl-D-mannoside, showing that this renin is glycosylated, as is native human renin. 4. Low sodium treatment of the hRN8-12 mice for 2 weeks increased plasma human active renin, renal human renin and renal human renin mRNA levels by 2.6-, 3.8- and 2.8-fold, respectively. Thus, the biosynthesis and secretion of renal human renin in these transgenic mice are obviously stimulated by sodium depletion.

Analysis of latent forms of renin using antibodies raised against the propart segment of human prorenin: validation with representative samples of ovarian cyst and follicular fluids.

Antisera were raised against synthetic peptides from the prosegment of human prorenin. The use of each of these for detection of the appropriate prosegment region of prorenin was validated by development of an ELISA protocol standardised with recombinant prorenin present in culture medium conditioned by myeloma cells transfected with a prorenin expression plasmid. Detection of the respective epitopes in the prosegment required prior exposure of the prorenin in the medium to acid pH in order to partially unfold the prorenin molecule by dislodging the prosegment from the main body of the protein. By these ELISA protocols, the form of latent renin present in representative samples from ovarian cyst and follicular fluids was analysed; one follicular cyst fluid was found to contain full-length prorenin whereas the fluid from a benign cyst and ovarian follicular fluid samples contained the precursor in truncated form.

Highest concentrations of prorenin and human chorionic gonadotropin in gestational sacs during early human pregnancy.

Prorenin is not only the biosynthetic precursor of renin; under certain circumstances in vitro prorenin exhibits reversible intrinsic renin activity and can form angiotensin from renin substrate with or without cleavage of the prosequence. Prorenin is the predominant form of renin synthesized by reproductive organs (ovary, chorion laeve of the placenta, uterine decidua). Its plasma concentrations increases 10-fold throughout pregnancy to 10-100 times that of renin; amniotic fluid prorenin concentration is even higher. No data are available of gestational fluid prorenin concentrations during early pregnancy. For the first 10 weeks there are two gestational cavities; the chorionic cavity then disappears and the smaller amniotic cavity becomes predominant. In this study we measured prorenin, renin, renin substrate and hCG in fluid aspirated from gestational sacs during the first trimester of gestation (predominantly chorionic) and during the second and third trimesters (amniotic). Seventeen patients had amniocentesis during the second or third trimester. Nine patients underwent selective abortion of multiple pregnancy at 7-12 weeks gestation. One patient underwent surgery at 5 5/7 weeks (26 days after conception) for a tubal pregnancy. Second and third trimester amniotic fluid prorenin maximum velocity (Vmax) (16 and 3 sacs, respectively) averaged 6,100 +/- 1,700 (SD) and 1,930 +/- 760 ng/mL.h, respectively (i.e. 1,700 and 540 ng/L.s). In gestational fluid collected before 8 weeks, prorenin Vmax was 10-fold higher, averaging 62,500 +/- 40,000 ng/mL.h (17,000 ng/L.s). The concentration was 140,000 ng/mL.h (39,000 ng/L.s) in the 5 5/7 week tubal pregnancy. In sharp contrast, at 10-12 weeks gestation (n = 3) prorenin Vmax was only 260 +/- 114 ng/mL.h (72 ng/L.s); human CG was also highest before 8 weeks (276,500 +/- 110,900 IU/L) and lowest at 10-12 weeks (1210 +/- 540 IU/L) with intermediate levels occurring later in pregnancy. This study shows that the highest biological levels of prorenin yet detected (close to 1 micrograms protein/mL) occur in gestational sacs in early pregnancy, consistent with a role for the renin-angiotensin system in embryonic development or placentation.

Purification and characterization of human truncated prorenin.

Posttranslational processing of enzymatically inactive prorenin to an active form participates in the control of the activity of a key system involved in blood pressure regulation, growth, and other important functions. The issue is complicated because renin can be produced by a number of tissues throughout the body, in addition to the kidney, but the mechanism by which they process prorenin to renin is unknown and difficult to determine because of the small amounts of renin present. In the juxtaglomerular cell of the kidney, a 43 amino acid prosegment is cleaved from the amino terminus of prorenin to generate renin of molecular weight 44,000 [Do, Y. S., Shinagawa, T., Tam, H., Inagami, T., & Hsueh, W. A. (1987) J. Biol. Chem. 262, 1037-1043]. Using human uterine lining or a recombinant human prorenin system, we employed the same approach as that used in kidney, ammonium sulfate precipitation at pH 3.1 followed by pepstatin and H-77 affinity chromatography or gel filtration, to purify to homogeneity a 45,500-MW totally active renin. The specific activity of the active truncated prorenin was 850 Goldblatt units (GU)/mg of protein for chorion-decidua renin and 946 GU/mg of protein for recombinant renin, both similar to that reported for pure human renal renin. Both forms of renin cross-reacted with an antibody generated against 44,00-MW pure human renal renin and with an antibody generated against a peptide identical to the carboxy-terminal one-third of the prosegment.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of human active renin heterogeneity.

A method for the separation and quantitation of multiple forms of active renin in human plasma is described. Shallow gradient isoelectric focusing of plasma resolved active renin into seven distinct components in each of 10 healthy normal individuals. Plasma renin activity focused at isoelectric points of 5.71, 5.57, 5.47, 5.22, 5.08, 4.93, and 4.82 with corresponding proportions of 16.3, 15.4, 21.1, 20.3, 14.0, 10.0, and 2.5%. Silicon dioxide treatment of plasma significantly increased the yield of renin in the focusing gels. Although each individual plasma sample contained the same seven renin forms, there was variability in the relative proportions of the multiple renin forms between individuals. This variance was significantly greater than the variance introduced by the determination itself. The same seven active renin forms were also present in human renal cortical tissue. In conclusion, a method for the determination of multiple renin forms in plasma and renal cortical tissue is presented. At least seven active multiple renin forms were resolved in human plasma and renal cortex.

Acute Stimulation of Renin Secretion Changes the Multiple Form Profile of Active Plasma Renin

Active renin is composed of multiple forms with variable isoelectric points. In this study, the relative proportions of five major active renin forms in human peripheral venous plasma were compared before and 2 h after stimulation of renin secretion with both converting enzyme inhibition (quinapril) and upright posture in five patients with essential hypertension. The five major active renin forms were separated by shallow gradient isoelectric focusing and quantitated by radioimmunoassay of generated angiotensin I. Plasma renin activity increased from 1.2 to 5.1 ng AI/mL/h (P less than .05). This was accompanied by a significant increase in the proportions of the two most basic renin forms and a significant decrease in the proportion of the most acidic form in venous plasma. Although the mechanism cannot be determined from this study, the altered renin form profile observed could have resulted from preferential renal secretion and/or altered hepatic extraction of the more basic forms. An altered renin form profile in response to acute stimulation has important physiologic implications. Since the relatively basic renin forms are preferentially degraded they possess shorter half-lives. Additionally, the multiple forms of active renin may be functionally heterogenous. Thus, acute stimulation of renin secretion may result in circulating renin with a shorter duration of action and different functional effects than renin released under steady state conditions.

Evidence for heterogeneity of glycosylation of human renin obtained by using lectins.

1. In this study, the carbohydrate structure of pure human renin was examined by using various lectins. 2. Pure renin could be separated into three forms by concanavalin A chromatography, a concanavalin A-unbound form, a loosely bound form and a tightly bound form, termed renins A, B and C, respectively. Renins A, B and C accounted for 3, 13 and 84%, respectively, of the purified renin. These forms were all present in individual human plasma and the relative proportions in plasma were 27 +/- 3, 33 +/- 4 and 39 +/- 5% (means +/- SEM) for renins A, B and C, respectively (n = 5). 3. Each form, electroblotted on to the nitrocellulose sheet after gel electrophoresis, was incubated with five peroxidase-labelled lectins, lentil lectin, erythroagglutinating phytohaemagglutinin, wheat-germ agglutinin, Ricinus communis agglutinin and peanut agglutinin. The protein was stained with 4-chloro-1-naphthol. 4. The staining pattern obtained with these lectins was significantly different among the three forms of human renin, confirming that they have different carbohydrate structures. Furthermore, the positive staining of human renin with erythroagglutinating phytohaemagglutinin, wheat-germ agglutinin and Ricinus communis agglutinin was in contrast with the lack of binding of rat renin to these lectins. 5. These results indicate the renal secretion of differently glycosylated multiple forms of human renin. The carbohydrate structure of human renin appears to differ from that of rat renin.

Analysis of Active Renin Heterogeneity

Active renin is a heterogeneous enzyme that can be separated into multiple forms with high-resolution isoelectric focusing. The isoelectric heterogeneity may result from differences in glycosylation between the different forms. In order to determine the relationship between active renin heterogeneity and differences in composition or attachment of oligosaccharides, two separate experiments were performed: (i) Tunicamycin, which interferes with normal glycosylation processing, increased the proportion of relatively basic renin forms secreted into the incubation media by rat renal cortical slices. (ii) Endoglycosidase F, which enzymatically removes carbohydrate from some classes of glycoprotein, similarly increased the proportion of relatively basic forms when incubated with active human recombinant renin. In addition, further studies with inhibitors of human renin activity revealed that the heterogeneous renin forms were similarly inhibited by two separate renin inhibitors. These results are consistent with the hypothesis that renin isoelectric heterogeneity is due in part to differences in carbohydrate moiety attachment and that the heterogeneity of renin does not influence access of direct renin inhibitors to the active site of renin.

Isoelectric Heterogeneity of Human Prorenin (Inactive Renin) in Body Fluids

Using flat bed isoelectric focusing, inactive renins from various body fluids were compared. Normal plasma inactive renin demonstrated six consistent peaks at pH 4.98, 5.14, 5.29, 5.47, 5.63 and 5.91, the largest being 5.29, 5.47 and 5.63. The isoelectric pattern of ovarian follicular fluid inactive renin was similar, with slight shifts at major peaks to a higher pH. Pregnancy plasma had inactive renin patterns like normal human plasma as did pleural fluid, lymphocoele fluid and plasma from anephric humans. Amniotic fluid inactive renin showed a markedly different pattern with major peaks at pH 5.00, 5.16 and 5.30. Fetal plasma (cord blood) also showed differences with only four peaks at 5.24, 5.40, 5.58 and 5.83. We conclude that human prorenin isoelectric patterns are similar for plasma, ovarian and most tissue fluid prorenins, but different for fetal plasma and amniotic fluid suggesting that these forms of renin do not cross the placental barrier.

Relationship of Follicular Fluid Prorenin to Oocyte Maturation, Steroid Levels, and Outcome ofin VitroFertilization*

Prorenin (PR) is present in high concentrations in the follicular fluid (FF) of the preovulatory follicle. It is the predominant form of renin detected in FF. Its biosynthesis and secretion from the ovary are regulated by gonadotropins. In the present study we measured PR and steroid levels in FF from 136 follicles. Follicular fluids were obtained, 36 h after hCG injection, from 41 ovarian-stimulated patients who underwent follicle puncture and oocyte retrieval for in vitro fertilization. We related FF PR to steroid levels and to the stage of oocyte-cumulus complex maturation. PR levels in 62 FF containing mature healthy fertilized oocytes averaged 2620 +/- 157 (+/- SE) ng/mL.h (728 +/- 44 ng/L.s; range, 1020-6880 ng/mL.h, 283-1911 ng/L.s). A subgroup of 16 of these follicles containing mature oocytes were from 7 women who conceived, in which PR levels spanned only the lower range from 1030-2720 ng/mL.h (286-756 ng/L.s). No patient conceived with FF PR above 2800 ng/mL.h (778 ng/L.s), yet one third of all mature follicles were above this range. Lower levels of PR were detected in FF containing immature oocytes (germinal vesicle stage) associated with either compact (1665 +/- 480 ng/mL.h; 463 +/- 133 ng/L.s; n = 22; P less than 0.02) or expanded (1785 +/- 193 ng/mL.h; 496 +/- 54 ng/L.s; n = 24; P less than 0.005) cumulus mass; a subgroup (n = 5) of follicles with immature oocytes and compact cumulus had very high levels of FF PR, ranging from 3830-7520 ng/mL.h (1064-2089 ng/L.s), while the remainder had levels less than 1300 ng/mL.h (361 ng/L.s). Progesterone and estradiol (E2) were lower in FF surrounding immature oocytes associated with compact (P less than 0.005) or expanded (P less than 0.02) cumulus, than in those containing mature oocytes. Testosterone (T) and androstenedione were measured in only a fraction of the samples; there were no apparent differences between follicles containing mature and immature oocytes. However, T and androstenedione levels were high in the subgroup of follicles containing immature oocytes and very high levels of PR. Of the hormones measured, T revealed the most striking relationship with PR (r = 0.62; n = 49; P less than 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

Renal secretion and hepatic clearance of human multiple renin forms.

Human active renin can be separated into at least five forms by isoelectric focusing. The present study assessed the preferential renal secretion and hepatic degradation of renin forms in humans. The renin form profile of secreted renal renin was determined before transplant in an ex vivo kidney donor perfusion system and compared with the peripheral plasma multiple renin form profile of normal subjects. The effect of hepatic degradation on renin forms was assessed in hepatic vein plasma in comparison with infrarenal vena cava plasma in hypertensive patients during renal vein renin studies. The results revealed a significantly greater proportion of the more basic forms in the perfusate of donor kidneys compared with normal plasma. In hypertensive patients the proportion of the more basic renin forms in the hepatic vein was significantly decreased in comparison with the infrarenal vena cava. Thus, the human kidney may preferentially secrete the more basic renin forms. In contrast, the liver preferentially degrades the more basic forms, giving these forms a shorter plasma half-life. The preferential secretion and clearance of the more basic forms of renin may contribute to short-term control of human renin-angiotensin system activity.

Isolation and characterization of renin-expressing cell lines from transgenic mice containing a renin-promoter viral oncogene fusion construct.

We constructed transgenic mice containing a renin-promoter SV40 T antigen fusion transgene with the intention of inducing neoplasia in renin-expressing cells and isolating renin-expressing cell lines in vitro. We examined six kidney tumors from mice representing three different transgenic lines and found they expressed their endogenous renin gene. Initially, five nonclonal kidney tumor-derived cell lines were established which expressed their endogenous renin gene in addition to the transgene. They retained active renin intracellularly and constitutively secreted an inactive form of renin (prorenin). One of these cell lines was cloned to homogeneity. This line maintained high level expression of renin mRNA throughout 3 months of continuous culture. Although the cells contained an equal proportion of active and inactive renin, the species constitutively secreted into the media was predominantly (95%) prorenin. However, active renin secretion was stimulated 2.3- and 4.6-fold by treatment with 8-bromo-cAMP after 4 and 15 h, respectively. In addition, the presence of multiple secretory granules was confirmed by ultrastructural analysis. These cells, which express renin mRNA and can regulate secretion of active renin, should provide an excellent tool for studying renin gene regulation and secretion. Furthermore, these mice should provide a useful source for the establishment of renin-expressing cell lines from a variety of renin-expressing tissues.

Disproportional release of differently glycosylated forms of human renin by furosemide

Concanavalin A (con A) chromatography of human plasma revealed the presence of three differently glycosylated forms of active renin (AR) and prorenin (PR), including the con A unbound forms (AR-I and PR-I), the loosely-bound forms (AR-II and PR-II), and the tightly-bound forms (AR-III and PR-III). These three forms of AR and PR were observed in human renal extracts. Normal male volunteers were intravenously given the diuretic furosemide (20 mg), kept standing for one hr and the effect on each form of renin was examined. These treatments elevated the plasma concentrations of AR-I, II and III by 2.1 ± 0.2, 2.6 ± 0.5, and 6.3 ± 1.1-fold, respectively (n=12), thereby indicating that the increase in AR-III was significantly larger than that in the other two forms (P < 0.01). This disproportional increase was accompanied by a significant increase in the relative percent of AR-III in plasma from 21.6 ± 2.5 to 42.2 ± 3.0 % (P<0.01). On the other hand, increase in the plasma levels of PR-I, II, and II was small (1.4 ± 0.1, 1.0 ± 0.1, and 1.1 ± 0.2-fold, respectively). These results provide evidence for the presence of differently glycosylated forms of AR and PR in human plasma and suggest the preferential release of AR-III with the acute stimulation of renin, by furosemide.

Ren-2 as well as Ren-1 renin exists in the kidney and plasma of a two-renin gene mouse.

Ren-1 renin is synthesized in the kidney of every mouse. Ren-2 renin has been observed in the submandibular gland (SMG) of male mice carrying two renin genes. However, it is not known if Ren-2 renin is in the kidney and blood of the two-renin gene mice. In this study, a direct ELISA for Ren-2 renin (SMG renin) was established by a sandwich method. This ELISA could measure the Ren-2 active renin in the range from 1 to 100 ng and distinguish Ren-2 active from not only Ren-1 renin but also Ren-2 prorenin. By a combination of this assay system and conventional methods, the pro-form as well as the active form of Ren-2 renin was found in the kidney and plasma of male AKR mice carrying two-renin genes.

Calciotropic Hormones in Human and Experimental Hypertension

Although altered cellular calcium handling plays a critical role in the pathophysiology of hypertension, little attention has been focused on the impact of calcium regulating hormones on this process. Recent research provides evidence that parathyroid hormone, calcitonin, 1,25-dihydroxyvitamin D, as well as newly described factors such as calcitonin gene-related peptide (CGRP), exert target-organ-specific actions in cardiac and peripheral vascular tissues, are linked to the renin-aldosterone system, and thus to the control of sodium metabolism, and may directly participate in the hypertensive process, especially in low renin and salt sensitive forms of hypertensive disease. The metabolic set-point of these linked renin and calcium hormone systems, which serve to transduce environmental dietary mineral signals at the cellular level, determines the blood pressure consequences of sodium and calcium loading and/or restriction, and helps to explain the heterogeneous and seemingly inconsistent effects of these dietary maneuvers on blood pressure. Measurement of renin and calcium factors in hypertension thus provides a physiological basis for individualized therapeutic recommendations in human hypertension.

Stimulation of plasma inactive renin by dexamethasone in the cat

An inactive form of renin in human plasma is the biosynthetic precursor, prorenin. The cat is a good animal model for studies of inactive renin. The gene for human renin contains sequences homologous to the glucocorticoid consensus sequence. The response of cat plasma (active and inactive renin) and of angiotensinogen to administration of dexamethasone (0.5 mg/kg im, daily) was studied in ketamine-sedated cats (20 mg/kg im). Inactive renin increased by twofold after 7 days of dexamethasone (P less than 0.01). After a 7-day recovery period, it returned to base line. Active renin did not change. Angiotensinogen fell by 35% (P less than 0.01). The time course of the selective increase of plasma inactive renin showed that inactive renin began to rise after 2 days, peaking after 5 days. Ketamine alone induced inactive renin to rise slightly but significantly (P less than 0.05), although the magnitude of the increment was much less than that observed in ketamine-sedated cats receiving dexamethasone (P less than 0.01). Active renin did not change, whereas angiotensinogen was reduced by 25% (P less than 0.01). Our findings support the hypothesis that glucocorticoids might have a selective role in the synthesis and/or secretion of the precursor of renin, at least in the cat.

Incorporation of labeled renin into the tissues of the rabbit.

Our previous work has shown that pure hog renin, when injected into one-kidney, one-clip hypertensive rabbits elicits not only antirenin antibodies but also antibodies to what appears to be an altered form of renin (antigen M). Antiantigen M stains the cytoplasm of smooth muscle cells and certain other cells in tissues of normal and hypertensive rabbits. We now report studies in which pure 125I hog and rabbit renin have been infused into hypertensive rabbits for seven-day periods and the tissues subsequently examined for nondegraded radioactive components. The concentration and the distribution of radioactivity found in different tissues of six rabbits that received hog renin and six that received rabbit renin showed enormous variation, for which there is no reasonable explanation. A very significant amount of radioactivity was found to be incorporated into a high molecular weight or insoluble form that may be antigen M. A major portion of the radioactivity has a molecular weight of about 40,000 and has been assumed to be unaltered 125I renin. In plasma there was a very high molecular weight radioactive component that was capable of binding to antirenin or antiantigen M antibodies to a limited degree. In addition there was a major component with a molecular weight of 68,000 that is not formed in vitro but is produced in vivo. It resembles prorenin in human plasma in that it does not adsorb on pepstatin-Sepharose and does adsorb on Cibacron Blue. However, it differs from prorenin in that it does not bind to antirenin antibodies nor can it be activated by trypsin.

Blood pressure and acidic renin forms in stroke-prone hypertensive rats.

Six forms of renin, distinguishable by their isoelectric focusing characteristics, are found in rat kidney and plasma (forms 1-6, form 1 having the most basic pI). To test the hypothesis that high blood pressure in stroke-prone spontaneously hypertensive rats (SHRSP) is associated with a particular fraction of the renin forms, systolic blood pressure (SBP) and renin profile were measured in SHRSP, normotensive Wistar-Kyoto rats (WKY), and their genetic crosses (F1). Adult SHRSP showed an increase in the proportion of forms 4, 5, and 6 compared with WKY. F1 showed values between SHRSP and WKY. A strong positive correlation was noted between the fraction of the acidic forms of renin and SBP. The mean blood pressure and the fraction of the acidic renin forms in SHRSP and WKY pups also fitted the same regression line. However, no correlation existed between renal renin content (RRC) and SBP. SHRSP pups had a higher RRC than age-matched WKY or F1. RRC in normal adult SHRSP was lower than that in WKY or F1 of the same age. In old animals, SHRSP again showed the highest RRC, and microangiography of the kidney of old SHRSP revealed a loss of fine vascularity with few visible glomeruli. These results indicate that the established phase of hypertension in SHRSP is associated with an increased proportion of the acidic forms of renin, which may have a unique role in the establishment or maintenance of hypertension. It is also suggested that high RRC in the early developmental stage plays a role in the developing phase of hypertension.

Modification of glycosylation of renin in sodium-depleted and captopril-treated rats.

Concanavalin A (con A) chromatography of rat plasma revealed the presence of three differently glycosylated forms of renin, including the con A unbound form (renin C), the loosely bound form (renin A), and the tightly bound form (renin B). Rat renal cortical slices in vitro secreted all these forms. They had a different half-life in the plasma after ligation of both renal artery and vein (half-life of 21 +/- 1, 14 +/- 3, and 35 +/- 4 min for renin A, B, and C, respectively). Thus differently glycosylated forms of renin are released from the kidney into the blood circulation and disappear, with a different half-life. Rats were sodium-depleted and captopril-treated (40-60 mg.kg-1.day-1) for 2 wk, and the effects of these treatments on relative proportions of renin A, B, and C were investigated. These treatments elevated plasma renin concentration approximately 60-fold (from 24 +/- 3 to 1,406 +/- 128 ng angiotensin I.h-1.ml-1; P less than 0.01), in association with an increase in the relative percent of renin C in the plasma from 22 +/- 2 to 39 +/- 3% (P less than 0.01). Moreover, the relative proportion of renin C released from the renal cortical slices was significantly higher in the treated than in the control rats (42 +/- 9 vs. 16 +/- 3% of secreted renin, respectively; P less than 0.02). These results show that the predominant release of renin C, with the longest half-life (35 min) in the plasma, contributes to the increased plasma renin concentration in sodium-depleted and captopril-treated rats.

Human decidua is a major source of renin.

Plasma prorenin levels are elevated in normal pregnant women. Current evidence suggests renin production by tissues of the uteroplacental unit contribute to this elevation. The purpose of this investigation was to define the source of renin biosynthesis within the human uteroplacental unit and to characterize the renin produced. RNA extraction and Northern blot analysis consistently demonstrated renin mRNA expression in uterine lining both in the pregnant (decidua) and nonpregnant states (endometrium) and in fetal chorion laeve, which is inseparable from the decidua. In contrast, renin mRNA expression was not detected in basal plate and intertwin chorion (which is separate from decidua), amnion, myometrium, or placental villi. The total renin content in decidual homogenates was two- to threefold greater than in endometrial homogenates, and cultured human decidual cells produced significantly more total renin than cultured human endometrial cells, suggesting that pregnancy enhanced renin production by the cells lining the uterus. Immunoblot analysis and [3H]leucine incorporation identified 47,000-mol wt prorenin as the major form of renin produced by cultured human decidual cells. These studies indicate that maternal decidua is the major source of prorenin in the uteroplacental unit.