SECRETION RATE OF ALDOSTERONE IN NORMAL PREGNANCY

Pregnancy-specific transcriptional changes upon endotoxin exposure in mice

Objectives Pregnant women are more susceptible to certain infections; however, this increased susceptibility is not fully understood. Herein, systems biology approaches were utilized to elucidate how pregnancy modulates tissue-specific host responses to a bacterial product, endotoxin. Methods Pregnant and non-pregnant mice were injected with endotoxin or saline on 16.5 days post coitum (n=8-11 per group). The uterus, cervix, liver, adrenal gland, kidney, lung, and brain were collected 12 h after injection and transcriptomes were measured using microarrays. Heatmaps and principal component analysis were used for visualization. Differentially expressed genes between groups were assessed using linear models that included interaction terms to determine whether the effect of infection differed with pregnancy status. Pathway analysis was conducted to interpret gene expression changes. Results We report herein a multi-organ atlas of the transcript perturbations in pregnant and non-pregnant mice in response to endotoxin. Pregnancy strongly modified the host responses to endotoxin in the uterus, cervix, and liver. In contrast, pregnancy had a milder effect on the host response to endotoxin in the adrenal gland, lung, and kidney. However, pregnancy did not drastically affect the host response to endotoxin in the brain. Conclusions Pregnancy imprints organ-specific host immune responses upon endotoxin exposure. These findings provide insight into the host-response against microbes during pregnancy.

Origin of deoxycorticosterone sulfate (DOC-SO4) in plasma of pregnant women: pregnenolone-3,21-disulfate is a placental precursor of DOC-SO4

The plasma levels of deoxycorticosterone sulfate (DOC-SO4) in near-term pregnant women are approximately 100 times those in plasma of men or non-pregnant women. Yet, neither the tissue site of synthesis nor the precursor of DOC-SO4 that enters maternal plasma is known. Several potential sources have been excluded: plasma DOC-SO4 is not derived from plasma DOC; and the secretion of C21-steroids (other than aldosterone) from the maternal adrenals during human pregnancy is not increased. Similarly, the transfer of DOC-SO4 from fetal plasma cannot account for the high level of DOC-SO4 in the maternal compartment, and a reduced clearance of plasma DOC-SO4 during pregnancy cannot account for the high levels of DOC-SO4. Indeed, the rate of clearance of DOC-SO4 from plasma is 10-100 times that of most other steroid sulfates. To address this question further, we evaluated the possibility that fetal plasma pregnenolone-3,21-disulfate serves as a precursor for DOC-SO4 formation in the placenta. The preferential hydrolysis of the 3beta-sulfate of pregnenolone-3,21-disulfate in placenta would give rise to pregnenolone-21-monosulfate, which, if acted upon by placental 3beta-hydroxysteroid dehydrogenase/delta5 --> 4 isomerase, could give DOC-SO4. [3H]Pregnenolone-3,21-disulfate was incubated with minces of human placental tissue for 5, 20, 60 and 120 min. Radiolabelled DOC-SO4, DOC, and pregnenolone-21-monosulfate were isolated from the incubation media and quantified. After a 5 min incubation, 7.5% of substrate was converted to DOC-SO4; and after 20, 60 and 120 min approximately 30% of the [3H]pregnenolone-3,21-disulfate was recovered from the media of these incubations as [3H]DOC-SO4. [3H]DOC was also present in the incubation media and the concentrations of this product increased as a function of incubation time. Therefore, pregnenolone-3,21-disulfate, which is present in very high concentrations in fetal plasma (approximately 1000 ng/ml), is metabolized in the placenta to DOC-SO4. Because of the fetal and maternal vascular arrangements of the hemochorioendothelial placenta of human pregnancy, steroids produced in syncytiotrophoblasts preferentially enter the intervillous space; thus, fetal plasma pregnenolone-3,21-disulfate may serve as a placental precursor of maternal plasma DOC-SO4.

Control of vascular resistance in the maternal and feto-placental arterial beds

This review aims to provide a comprehensive summary of the mechanisms involved in the physiological adaptation of the vasculature to pregnancy. Profound changes occur both systemically and in discrete circulations in the mother, but it is debatable which factors are responsible. Similarly, whilst the feto-placental circulation must be substantially controlled by humoral mechanisms, the exact role of each potential contributor is not known. In view of the hitherto unappreciated and very important role of the endothelium-derived vasodilator, nitric oxide, in the control of peripheral vascular resistance, considerable emphasis will be placed on the many recent investigations in this area.

Corticostatins

Corticostatic (anti-ACTH) peptides were first isolated from rabbit fetal and adult lung and from rabbit neutrophils. They have now been isolated from human, rat, and guinea pig tissues. They have several biologic activities that include inhibition of ACTH binding, stimulation of L-type Ca(2+) channels, monocyte chemotaxis, and degranulation of mast cells with the release of histamine. Rabbit corticostatin I (CSI) is widely distributed in maternal and fetal rabbit tissues and is localized to neutrophils, macrophages, and monocytes, and the changing concentration of CSI with advancing gestation indicates a possible physiologic role during pregnancy.

Effect of plasma sodium on aldosterone secretion during angiotensin II stimulation in normal humans

Studies were carried out in normal male subjects (n = 6, age 20-35 years) to determine the interaction of angiotensin II and plasma sodium on aldosterone secretion. These relations were quantified by elevation of plasma sodium with an infusion of 5% sodium chloride (4 ml/kg/30 min i.v.) with measurements of plasma aldosterone, atrial natriuretic factor (ANF), and arginine vasopressin (AVP) over 3 hours. Two hours before sodium chloride infusion, an intravenous infusion of angiotensin II was begun at 0.5 or 5.0 ng/kg/min and continued throughout the study. Plasma potassium was maintained constant by the addition of potassium to the infusate. NaCl/KCl infusion raised plasma sodium 4 meq/l with no decreases of plasma potassium. Plasma aldosterone averaged 7 +/- 1.8 ng/dl before NaCl infusion in subjects infused with 0.5 ng angiotensin II and was not significantly reduced with sodium chloride infusion. Angiotensin II infused at 5 ng/kg/min resulted in average plasma aldosterone levels of 31 +/- 3.6 ng/dl, which sodium chloride infusion decreased to 16.6 +/- 1.3 ng/dl (p less than 0.05) in 60 minutes. Plasma aldosterone remained depressed for the remaining period of study. Plasma ANF increased from 40 to 60 pg/ml with sodium chloride infusion. We conclude that small physiological elevations of plasma sodium concentrations can signal substantial decreases of plasma aldosterone in normal human subjects in situations where plasma angiotensin II is moderately elevated. The precise mechanisms of these responses remain to be determined.

Sodium-renin-aldosterone relations in normal and hypertensive pregnancy

To examine the short-term regulation of sodium excretion, plasma volume, and the renin-aldosterone system in pregnancy, women in their first pregnancy received either a high-salt (HS) (250 mmol/day) or a low-salt (LS) (20 mmol/day) diet for 7 days during the second and third trimester and after delivery (total 213 studies). Twenty women, studied while normotensive during mid-pregnancy, developed pregnancy-induced hypertension (PIH) in the third trimester. There was slightly greater difficulty adapting to sodium depletion (LS diet) during normal pregnancy compared with postpartum. The final mean values for sodium excretion were 27 (SE 2), 28 (SE 3) and 14 (SE 4) mmol/day in the second and third trimester and postpartum respectively. Sodium excretion with the HS diet was similar at all stages and plasma volumes were maintained as effectively during pregnancy as after delivery following both diets. Plasma renin activity (PRA) and aldosterone concentration rose and fell significantly following the LS and HS diets but the sensitivity of renin response to changes in salt intake was blunted during normal pregnancy. Women who later developed PIH, when studied whilst normotensive, failed to stimulate plasma aldosterone after salt depletion in their second trimester and did not exhibit the 'sodium-independent' component of PRA seen in continuously normotensive subjects at this stage.

The new world primates as animal models of glucocorticoid resistance

Many New World primate species have greatly increased plasma cortisol concentrations, decreased plasma cortisol binding globulin capacity and affinity, marked resistance of the hypothalamic-pituitary-adrenal axis to suppression by dexamethasone, and no biological evidence of glucocorticoid excess. These primates also have high levels of circulating progesterone, estrogen, mineralocorticoid, androgen and vitamin D. The glucocorticoid target tissues that have been examined (circulating mononuclear lymphocytes and cultured skin fibroblasts) have normal concentrations of glucocorticoid receptors with decreased affinity for dexamethasone. Transformation of B-lymphocytes with the Epstein-Barr virus leads to glucocorticoid receptor induction that is less than that observed with cells from Old World primates. The receptor in these cells has a low affinity for dexamethasone. The low affinity leads to an increased loss of specific bound ligand during thermal activation. Meroreceptor generation is normal. The molecular weight of the receptor, determined by SDS-PAGE, is similar to that of Old World primates (approximately 92,000) and the activation pattern per se, examined in vitro by heating cytosol and performing phosphocellulose chromatography, appears similar to that of human controls. The ratios of nuclear to cytosolic hormone-receptor-complexes and of cytosolic activated to unactivated receptor complexes in intact cells are similar to Old World primates. Results from mixing studies do not support the hypothesis that a binding inhibitor(s) or a deficient cytosolic positive modifier(s) of binding underlies the findings in these primates. The New World primates, unlike men with the syndrome of primary cortisol resistance, have compensated for their condition with intra-adrenal and mineralocorticoid receptor adaptations. Thus, unlike Old World primates, cortisol in New World primates has only weak sodium-retaining potency because the aldosterone receptor has a low affinity for cortisol. The common element that would explain the apparent resistance to six steroid hormones in New World primates remains unknown.

The origin of and metabolic fate of deoxycorticosterone and deoxycorticosterone sulfate in pregnant women and their fetuses

DOC and DOC-SO4, which are present in large amounts in the blood of pregnant women, are derived from sources other than maternal adrenal. Other investigators demonstrated that treatment of near-term pregnant women with ACTH or dexamethasone did not cause alterations in the blood levels of DOC. To define the source(s) of DOC and DOC-SO4 in plasma of pregnant women, we evaluated the conversion of plasma progesterone (P) to DOC in extraadrenal sites. DOC is formed from plasma P and, provided that the pregnancy is one characterized by the usual large production of estrogen, DOC production in a given woman is proportional to the level of P in plasma. Unlike other steroid conversions or interconversions, however, the fractional conversion of P to DOC among apparently normal persons varied widely 0.011 +/- 0.003 (mean +/- SEM, n = 40, range = 0.001 to 0.030). In women pregnant with a normal living fetus, the product of the production rate of P and the fractional conversion of P to DOC is sufficient to account for the majority of DOC produced in the mother. There may be a second source of DOC, i.e. the transfer of DOC from the fetal to the maternal compartment in a manner that involves (a) direct transfer of DOC by way of trophoblast and (b) by desulfurylation of DOC-SO4 from fetal umbilical arterial plasma in trophoblast and thence transfer of DOC liberated in trophoblast to the maternal compartment. Presently, it is clear that DOC-SO4 in blood of pregnant women is not derived from plasma DOC; and there is little or no evidence in support of the proposition that DOC-SO4 (as a sulfoconjugate) is transferred from the fetal to the maternal compartment because of placental hydrolysis to DOC. Among the extraadrenal tissue sites identified as those in which 21-hydroxylation of plasma P could be effected are some also believed to be tissue sites of mineralocorticosteroid action, viz, kidney, aorta, thymus, and spleen. Quantitatively, the origin of DOC in the fetus is not as clear as in the maternal compartment; yet, many tissues of the fetus have been identified in which both steroid 21-hydroxylase and 21-hydroxysteroid sulfotransferase activity are present. Thus, in the human fetus, extraadrenal as well as adrenal production of DOC and DOC-SO4 are possible.

Steroid 21-sulfatase activity in human placenta

Intravenously administered [3H]-deoxycorticosterone sulfate is not metabolized by way of deoxycorticosterone in men or non-pregnant women. Thus, it can be implied that steroid 21-sulfatase is not active in human tissues. On the other hand, evidence has accrued that deoxycorticosterone sulfate is hydrolyzed in human placenta. In the present investigation, we sought to ascertain if steroid 21-sulfatase activity were present in placenta and, if so, to characterize the enzyme activity in this tissue. Steroid 21-sulfatase activity was found to be present in microsome-enriched fractions prepared from human placental tissue; conditions of linearity of the reaction with time and protein concentration were established and the apparent KM of the enzyme for deoxycorticosterone sulfate was 100 microM. Thus, deoxycorticosterone sulfate, which is present in high concentration in plasma of the human fetus, may enter trophoblast wherein it could be hydrolyzed; the deoxycorticosterone formed could be secreted into the maternal circulation. Such a process, together with deoxycorticosterone formation from plasma progesterone in extraadrenal sites, could account for the high concentrations of deoxycorticosterone that are present in plasma of near-term pregnant women.

Urinary free 18-hydroxycorticosterone, plasma aldosterone, and urinary aldosterone metabolites in normal pregnancy

The final steps in aldosterone biosynthesis are unclear. Undecided is whether 18-hydroxycorticosterone is a precursor of aldosterone or an end product. 18-Hydroxycorticosterone is secreted in close relationship to aldosterone. To get adequate information on the status of aldosterone in pregnancy, determination of more than one parameter of aldosterone seems to be necessary. Urinary excretion of free 18-hydroxycorticosterone, tetrahydroaldosterone, aldosterone-18-glucuronide, free aldosterone, and the plasma concentration of aldosterone were measured by radioimmunoassay in 16 primigravid women in the last trimester of normal pregnancy and in 13 healthy nonpregnant women. All steroids measured were significantly increased in pregnancy. The ratios of aldosterone-18-glucuronide to tetrahydroaldosterone in the two groups were not significantly different, so that significant changes in renal or hepatic aldosterone metabolism could not be demonstrated in pregnancy. When pregnant women with ankle edema (n = 7) were compared to pregnant women without edema (n = 9), no differences in steroid patterns could be found. The increased excretion of 18-hydroxycorticosterone in pregnancy confirms the state of hyperaldosteronism in normal pregnancy which is associated with an increase in biologically active, free aldosterone. Dissociation in the excretion of the two aldosterone metabolites and free aldosterone was found in three pregnant women, in whom excretion of aldosterone-18-glucuronide was increased but excretion of tetrahydroaldosterone and free aldosterone was in the normal nonpregnant range.

Hormonal adaptation to the stresses imposed upon sodium balance by pregnancy and lactation in the Yanomama Indians, a culture without salt

The Yanomama Indians of northern Brazil and southern Venezuela have been identified as a "no-salt" culture. In this study, data were obtained to determine in this population the adjustments of sodium-related hormones to the stresses imposed upon sodium balance by pregnancy and prolonged lactation. Controls against the possibility that findings in the Yanomama were ethnic rather than dietary were provided by similar observations in the Guaymi Indians of Panama, who have free access to salt. Urinary concentrations of sodium were approximately 1 mEq/l in male and female Yanomama, with 24-hour excretion rates in the males averaging 1 mEq, similar to our prior observation. The pregnant Yanomama had exceeding high urinary concentrations of aldosterone. These were associated with higher plasma renin activities and serum aldosterone concentrations than in all other subjects. Although pregnant Guaymi had elevations of serum and urinary aldosterone, these were significantly lower (p < 0.001) than those of the Yanomama. Prolonged lactation in the Yanomama was associated with elevation of plasma renin activity and serum and urinary aldosterone concentration compared with the Guaymi, but were not higher than those in nonlactating Yanomama females. The findings suggest that pregnancy in a salt-poor environment is associated with an exaggerated augmentation of hormonal responses that enhance positive sodium balance.

Effects of pregnancy on glucose handling by rat kidneys

1. Glomerular filtration rate (g.f.r.), and renal reabsorption and excretion of glucose, sodium and potassium were measured in 7-8 day pregnant rats and age-matched (12-13 week old) virgin controls undergoing saline and glucose infusions. 2. Pregnancy was associated with an increased g.f.r. and a decreased urine flow rate during both infusions. 3. During saline infusion, more glucose was excreted in pregnant animals than in virgins but with no significant difference in fractional reabsorption. During glucose infusion, pregnant animals excreted less glucose than virgins, owing to a decrease in the filtered load but with no significant difference in fractional reabsorption. 4. During both saline and glucose infusion, pregnant animals excreted less sodium than virgin controls. 5. During saline infusion, pregnant animals excreted more potassium. During glucose infusion, pregnant animals excreted less potassium than control animals.

Factors controlling plasma renin and aldosterone during pregnancy

The response of plasma renin activity (PRA) and plasma aldosterone (PA) to change in sodium intake was evaluated in pregnant women during the third trimester. After 7 days on a 10 mEq sodium diet, PRA rose from 20.6 +/- 6.2 to 59.6 +/- 11.6 ng/ml/hr and PA from 47 +/- 11 to 127 +/- 27 ng% in pregnant women compared to PRA from 5 +/- 1.2 to 18.9 +/- 5.2 ng/ml/hr and PA from 7.7 +/- 1 to 42 +/- 3 ng% in nonpregnant controls. Pregnant women conserved sodium normally with urinary sodium excretion and weight loss similar to nonpregnant women. After 6 days on a 300 mEq sodium intake, PRA and PA in pregnant women were significantly higher, 10.2 +/- 1.4 ng/ml/hr and 22 +/- 3 ng%, respectively, compared to 1.5 +/- 0.3 ng/ml/hr and 7.3 +/- 1 ng% in controls. On both low- and high sodium intake there was a positive correlation between PRA and PA in pregnant women. Plasma prostaglandin E (PGE) was 0.45 +/- 0.06 ng/ml in pregnant women compared to 0.1 +/- 0.01 ng/ml in control women (p less than 0.01) and urinary PGE excretion was 2780 +/- 357 ng/24 hr in 28 pregnant women compared to 1191 +/- 142 ng/24 hrs (p less than 0.01) in 14 nonpregnant controls. These findings indicate that although renin and aldosterone secretion respond to change in sodium intake in pregnancy, the cause of the increased renin secretion of pregnancy may be secondary to the increase that occurs in prostaglandin synthesis.

Plasma renin and aldosterone in pregnancy complicated by adrenal insufficiency

Serial measurements of plasma renin and plasma aldosterone were made throughout pregnancy in two women with adrenal insufficiency. The values were compared with levels obtained in eight normal primigravidae. Aldosterone levels were low or undetectable in adrenal insufficiency and plasma renin levels were grossly elevated in one patient with adrenal insufficiency but within the normal range in the other.

Oral contraceptives--induced hypertension--nine years later

Nine years have gone by since oral contraceptive hypertension was first recognized as a clinical entity. In that time it has become apparent that what at first was thought to be a rare disorder is extremely common. Indeed, overt hypertension develops, in time, in about 5 per cent of Pill users. Increases in blood pressure, albeit within the normal range, are still more common. Pill hypertension may develop gradually. It is sometimes quite severe, and it is characteristically reversible within a few months after therapy is stopped. Oral contraceptives produce changes in the renin-angiotensin-aldosterone system, particularly a consistent marked increase in the plasma renin substrate concentration which may be associated with increases in plasma renin activity and aldosterone excretion. The estrogenic component of contraceptive pills appears to be the more important factor in producing abnormalities in the renin system. The mechanisms for the hypertensive response are not entirely clear since normotensive women using the pill may exhibit similar or even more marked changes in the renin axis. The pressor response could have both volume and vasoconstrictor components mediated by the sodium-retaining effects of the estrogen in the presence of a relatively, if not an absolutely, higher plasma renin activity, with the latter being held abnormal by the high plasma renin-substrate levels. A failure of the kidneys to fully suppress renal renin secretion could thus be an important predisposing factor. Our in vitro experiments support the idea that the increased substrate is involved in pathogenesis because they indicate that in normal subjects plasma renin substrate is not present in "excess". Thus, a doubling of the physiologic levels of substrate by oral contraceptives leads to an almost twofold increase in the capacity for angiotensin production as indicated by studies of the initial reaction velocity. These observations define certain guidelines for applying oral contraceptive therapy. At least one base-line blood pressure measurement should be obtained, and blood pressure and weight should be followed a two- or three-month intervals during treatment. Furthermore, oral contraceptive therapy may be contraindicated in women with a history of hypertension, renal disease, toxemia, or fluid retention. Others in whom oral contraceptives are relatively contraindicated include those with a positive family history of hypertension, younger women in whom a longer term commitment is likely, and groups, such as blacks, especially prone to hypertensive phenomena.

Effects of ADH on the activity and function of the renin-angiotensin-aldosterone system in infants and in children

In babies ranging in age from 1 to 25 weeks and in children between 1 and 14 years, plasma renin activity and urinary aldosterone activity were determined in relation to urinary sodium excretion. A reciprocal correlation was found demonstrating that the hyperactivity of the renin-angiotensin-aldosterone system is stimulated in infants by a low sodium intake. A second stimulus was observed in the influence of the hypothalamo-neurohypophyseal system, when the plasma renin activity was suppressed by administration of antidiuretic hormone and sodium excretion increased due to a decreased aldosterone activity. Our study suggests that there exists a feedback between the renin-angiotensin-aldosterone system and ADH release and that this feedback plays an important role in the regulation of water and electrolyte balance in the young infant.

The effect of pregnancy on mineralo- and gluco-corticoid secretion in the sheep

1. The peripheral blood concentrations of aldosterone, corticosterone and cortisol were measured during pregnancy in conscious, undisturbed sheep. 2. Aldosterone levels did not change during pregnancy and the mean pregnant value, 1-2 s.d. 1-4 ng/100 ml(n = 12) was not significantly different from the non-pregnant value, 2-1 s.d. 1-7 (n = 16). 3. Cortisol levels likewise were unchanged by pregnancy-non-pregnant values were 0-56 s.d. 0-50 mug/100 ml (n = 12) compared with 0-46 s.d. 0-40 mug/100 ml (n = 16) in pregnant sheep. 4. Sheep of 110-140 days gestation had a 400 mmol greater total exchangeable sodium than non-pregnant sheep. Plasma volume and plasma renin concentration tended to be elevated near to term. 5. Very high aldosterone secretion rates and peripheral blood levels could be produced in pregnant sheep by stress, intravenous ACTH or angiotensin II infusions, and by sodium deficiency. It is suggested that the pregnant sheep may show increased sensitivity in contrast to non-pregnant sheep to these stimuli and the enlarged size of their adrenals may be a contributing factor.

A study of angiotensin II pressor response throughout primigravid pregnancy

The present study was designed to ascertain sequentially the pressor response to angiotensin II in young primigravid patients throughout pregnancy in order a) to define when in pregnancy resistance to the pressor effects of angiotensin II develops; b) to define the physiologic sequence of events leading to this resistance; and c) to ascertain whether sensitivity to infused angiotensin II could be detected before the onset of clinical signs of pregnancy-induced hypertension. With this prospective approach, two separate groups of patients were defined. The first group of patients remained normal throughout pregnancy. The second group consisted of those patients who, while clinically normotensive during the initial phase of the study, ultimately developed hypertension of pregnancy.192 patients were studied; of these, 120 patients remained normotensive and 72 developed pregnancy-induced hypertension. In both groups, vascular resistance to infused angiotensin II (more than 8 ng/kg/min required to elicit a pressor response of 20 mm Hg in diastolic pressure) was demonstrated as early as the 10th wk of pregnancy. In the group that remained normotensive, maximum mean vascular resistance occurred at 18-30 wk of pregnancy, (mean pressor dose required being 13.5 to 14.9 ng/kg/min). In those subjects who developed pregnancy-induced hypertension, the mean maximum dose required was 12.9 ng/kg/min, which was observed at the 18th wk of pregnancy. By the 22nd wk there was a clear separation of the two groups, with the mean dose requirement of the subjects destined to develop hypertension being progressively less than that of those who remained normal. The difference between the two groups became significant (P < 0.01) by 23-26 wk of pregnancy. Among patients requiring more than 8 ng/kg/min on one or more tests done between wk 28-32, 91% remained normotensive. Conversely, during the same time period among patients requiring less than 8 ng/kg/min, on at least one occasion, 90% developed pregnancy-induced hypertension.

Uterine blood flow and uterine renin secretion

Experiments were carried out in pregnant nephrectomized rabbits to determine the relationship between uterine blood flow and uterine renin secretion. Uterine blood flow was measured by the percentage distribution of radioactive microspheres injected into the left ventricle which lodged in uterus and placenta, and cardiac output was measured by dye dilution. In 40 animals, 24 hr after nephrectomy, uterine blood flow was 4.7+/-0.4% of cardiac output and absolute flow 32.4+/-3 ml/100 g per min. Plasma renin activity (PRA) in uterine vein, 994+/-182 ng/100 ml per hr, was higher than in carotid artery, 832+/-143 (P < 0.025). With reduction of uterine blood flow from 4.7+/-0.5 to 1.95+/-0.3% of cardiac output and absolute flow from 30.8+/-4.6 to 8.8+/-2 ml/100 g per min, uterine vein PRA rose from 1434+/-234 to 4430+/-300 (P < 0.001), and carotid artery PRA from 1009+/-200 to 2300+/-350 (P < 0.01). Hemorrhagic hypotension caused uterine vein PRA to increase from 913+/-293 to 3638+/-1276 (P < 0.001) and carotid artery PRA from 774+/-252 to 1730+/-433 (P < 0.01). Uterine blood flow expressed as a percentage of cardiac output remained constant after hemorrhage, 5.5+/-0.9 and 6.3+/-0.8%, although absolute flow fell from 37+/-7.7 to 29+/-3.6 ml/100 g per min because of the large fall in cardiac output which occurred.Angiotensin, 10 ng/kg per min, caused no significant change in blood pressure or cardiac output but increased uterine blood flow from 4.1+/-0.6 to 8.4+/-1% (P < 0.005) of cardiac output with absolute flow increasing from 37.4+/-7 to 73.2+/-10 ml/100 g per min (P < 0.001). The increase in uterine blood flow during angiotensin was abolished by the prior administration of propranolol. Isoproterenol, 0.5 mu/min, increased uterine blood flow from 3.5+/-0.6 to 6.4+/-1.2% of cardiac output (P < 0.02) with absolute flow increasing from 25+/-5 to 51+/-12 ml/100 g per min (P < 0.05). Norepinephrine, 500 ng/min, caused no significant change in uterine blood flow. These findings suggest that uterine renin might be involved in regulating uterine blood flow, secretion being increased in response to a reduction in flow with the resultant rise in circulating or local angiotensin, through beta adrenergic stimulation, increasing uterine blood flow.

Salivary electrolyte changes during the normal menstrual cycle

Daily samples of parotid and submaxillary saliva were collected from eight females during a complete menstrual cycle. Findings revealed significant electrolyte changes in the submaxillary saliva. Comparison of menstrual and midcycle concentrations of calcium and sodium demonstrated a notable decrease in calcium and sodium at midcycle, whereas potassium levels increased significantly. Changes were attributed to a probable hormonal effect on salivary composition.

Effect of administered mineralocorticoids or ACTH in pregnant women. Attenuation of kaliuretic influence of mineralocorticoids during pregnancy

The role of augmented aldosterone production in pregnancy is poorly understood. Whereas some consider aldosterone secretion in pregnancy excessive, others suggest that this is a compensatory phenomenon. According to yet another view, mechanisms other than the renin-angiotensin-aldosterone system control sodium homeostasis in pregnancy. Metabolic balance studies were performed on 14 3rd trimester women. Mineralocorticoid activity was experimentally increased by administering desoxycorticosterone acetate, 9alpha-fluorocortisol acetate, or ACTH for 4-12 days. Administration of mineralocorticoid or ACTH consistently caused sodium retention. During this mineralocorticoid-induced volume expansion, aldosterone excretion decreased markedly. Natriuresis, which followed discontinuance of the drug, continued while aldosterone excretion, although greatly diminished compared to control values, was greater than that found in normal, nonpregnant individuals. This saline diuresis did not subside until aldosterone excretion returned to its previously high control values. These observations support the concept of the physiological role of increased aldosterone production in pregnancy. Results further revealed a marked dissociation between antinatriuretic and kaliuretic effects of corticoids. Potassium balance was virtually unaltered during continued mineralocorticoid or ACTH administration, despite initially high or abruptly increased sodium intakes. Finally, mineralocorticoid escape was induced by continued desoxycorticosterone acetate therapy in two male volunteers. Kaliuresis occurred which was subsequently abolished when progresterone was administered. Sodium excretion, however, was virtually unaltered. These data, mimicking results observed in gravidas, suggest that progesterone is an important determinant of potassium homeostasis in pregnant women.

Plasma aldosterone concentration at delivery and during the newborn period

Aldosterone concentrations in plasma of women on normal sodium intake undergoing cesarean section were 3.7+/-1.4 ng/100 ml (mean+/-1 SD). These values were significantly lower (P < 0.001) than those observed in mothers on normal sodium diet, delivered by the vaginal route (14.9+/-7.0 ng/100 ml). A significant elevation (P < 0.001) of the concentrations was found if the mothers had been on sodium restriction and/or diuretics (44.9+/-24.2 ng/100 ml). In supine position, adult nonpregnant subjects have aldosterone concentrations in plasma of 1.7+/-1.4 ng/100 ml on normal sodium intake and of 16.7+/-8.1 ng/100 ml on low sodium diet.Simultaneous determinations of aldosterone levels in cord blood showed that cord values were significantly higher than those of the corresponding mother (P < 0.01 by paired t test). However, values in cord blood of infants born to mothers on a normal sodium intake were significantly lower (P < 0.005) than those of infants whose mothers had required low sodium diet and/or diuretics during their pregnancy. Aldosterone concentrations in plasma of infants 1-72 hr of age and born to mothers on normal sodium intake were 25.9+/-11.7 ng/100 ml (mean +/-1 SD). These values were significantly lower (P < 0.005) than those of infants born to mothers on restricted sodium intake with or without diuretics (80.3+/-54.4 ng/100 ml). The concentrations at birth were not significantly different from those observed during the first 3 days of life (P > 0.6).