Blood Concentrations Of Aldosterone Research Articles

Immunological, hormonal and hemostasis parameters in cosmonauts’ blood after long-term orbital missions

The extreme factors associated with space flight influence pronouncedly various physiological systems of the human body. The current study focuses on the impact of factors associated with prolonged space missions lasting up to 6 months on cellular innate immunity, hormonalregulation, and hemostasis in Russian cosmonauts. Immune system adaptation to the conditions of long-term space flight was shown to be accompanied by a significant increase in the level of monocytes and granulocytes, along with a decreased number of cells expressing adhesion molecules. The coagulation cascade, main anticoagulant and fibrinolysis proteins were also evaluated. The early post-flight period was characterized by elevated D-dimer levels compared to baseline values, indicative of blood clotting and fibrinolysis activation caused by a damage of endothelium during landing. aAlterations in blood rheology during re-adaptation to Earth conditions was also observed. The blood concentrations of aldosterone, cortisol, estradiol, testosterone, osteocalcin, and erythropoietin were analyzed, and their correlation with the parameters of hemostasis was assessed.The summary findings indicate an adaptive physiological reaction in cosmonauts associated with 6 months duration of spaceflight. The observations may be related to endothelium damage, which manifested in the activation of certain components of the immune system, along with the activation of fibrin clot formation and subsequent fibrinolysis.

Effect of Anti-Hypertensive Medication on Plasma Concentrations of Lysyl Oxidase: Evidence for Aldosterone-IL-6-Dependent Regulation of Lysyl Oxidase Blood Concentration.

Lysyl oxidase (LOX) is a secretory protein that catalyzes elastin and collagen cross-linking. Lowering LOX expression and activity in endothelial cells is associated with a high risk of aneurysms and vascular malformation. Interleukin-6 (IL-6), elevated in hypertension, is known to suppress LOX expression. The influence of anti-hypertensive medication on the plasma LOX concentration is currently unknown. In a cohort of 34 patients diagnosed with resistant hypertension and treated with up to nine different drugs, blood concentration of LOX was analyzed to identify drugs that have an impact on plasma LOX concentration. Key findings were confirmed in a second independent patient cohort of 37 patients diagnosed with dilated cardiomyopathy. Blood concentrations of aldosterone and IL-6 were analyzed. In vitro, the effect of IL-6 on LOX expression was analyzed in endothelial cells. Patients receiving aldosterone antagonists had the highest plasma LOX concentration in both cohorts. This effect was independent of sex, age, blood pressure, body mass index, and co-medication. Blood aldosterone concentration correlates with plasma IL-6 concentration. In vitro, IL-6 decreased the expression of LOX in endothelial cells but not fibroblasts. Aldosterone was identified as a factor that affects blood concentration of LOX in an IL-6-dependent manner.

АНАЛИЗ ПОКАЗАТЕЛЕЙ СИСТЕМЫ АЛЬДОСТЕРОН-РЕНИН У ПАЦИЕНТОВ С ХРОНИЧЕСКОЙ БОЛЕЗНЬЮ ПОЧЕК И ВТОРИЧНЫМ ГИПЕРПАРАТИРЕОЗОМ

In 207 patients with different stages of CKD and 60 individuals in the comparison group, the parameters of the renin-angiotensin-aldosterone system and their relationship with renal function and PTH levels were determined. It was found that patients with CKD are characterized by a tendency towards a lower level of aldosterone in the blood serum, up to the terminal stage of CKD, as well as hyperreninemia in the early stages of CKD and its decrease with the progression of the disease. The highest incidence of hyperaldosteronism was recorded in dialysis and transplant patients. A weak correlation was found between PTH and aldosterone levels in patients with CKD. At the same time, multidirectional changes in the medians of blood concentrations of aldosterone and renin were revealed in subgroups of patients with the presence and absence of SHPT.

Undetectably low blood aldosterone concentrations are prevalent in COVID-19 patients but poorly quantified by chemiluminescent immunoassay

Undetectably low blood aldosterone concentrations are prevalent in COVID-19 patients but poorly quantified by chemiluminescent immunoassay

On the consistency of different methods for detecting aldosterone concentration in blood

Objective To evaluate the consistency of different methods for detecting aldosterone concentration in blood and to establish a reference interval of serum aldosterone concentration by liquid chromatography-tandem mass spectrometry(LC-MS/MS). Methods Concentrations of blood aldosterone were measured by LC-MS/MS, chemiluminescent assays (Diasorin, Domestic A and B systems) and radioimmunoassay (RIA) in 138 healthy adults, 67 patients with essential hypertension and 23 patients with primary aldosteronism. Results Aldosterone concentrations measured by various methods were quiet different(P 0.05) between CLIA(Domestic B) and LC-MS/MS, 0.338(P<0.01) as well as between RIA and LC-MS/MS. Bland-Altman analysis for the measurements showed poor consistency among methods for aldosterone concentrations. The reference interval was 15.2-222.2 pg/ml for serum aldosterone concentrations by LC-MS/MS. Conclusions There are significant differences of blood aldosterone concentrations determined by different methods. Clinically, a specified reference interval might be needed while using different methods. Key words: Aldosterone; Liquid chromatography-tandem mass spectrometry; Chemiluminescent assays; Radioimmunoassay

Association of aldosterone and arginine vasopressin concentrations and clinical markers of hypoperfusion in neonatal foals.

Critically ill foals often present to veterinary hospitals with impaired organ perfusion which can be demonstrated by increased blood L-lactate concentrations. As a compensatory mechanism to low blood pressure and electrolyte abnormalities, aldosterone and arginine vasopressin (AVP) are released to restore organ perfusion and function. Several studies have investigated the ability of blood L-lactate concentrations to predict severity of disease and outcome in critically ill human patients, adult horses and foals. However, information on the aldosterone and AVP response to hypoperfusion and its association with L-lactate concentrations in neonatal foals is limited. To determine the association between clinical hypoperfusion and endocrine markers of reduced tissue perfusion in normo- and hypoperfused foals. Prospective, multicentre, cross-sectional observational study. Blood samples were collected on admission from 72 clinically hypoperfused, 110 normoperfused (73 hospitalised and 37 healthy) foals of ≤4 days of age. Foals were considered clinically hypoperfused if they had L-lactate concentrations ≥2.5 mmol/l and one of the 3 following findings: heart rate >120 beats/min, packed cell volume (PCV) >0.44 l/l or azotaemia (increased creatinine and blood urea nitrogen [BUN]). Blood concentrations of aldosterone and AVP were determined by radioimmunoassays. Aldosterone, AVP, creatinine and BUN concentrations and heart rate, PCV and blood osmolality were higher in clinically hypoperfused compared with normoperfused foals (P<0.05). Risk of hypoperfusion increased with the presence of hypothermic extremities (OR = 5.26) and with each one unit increase in albumin concentrations (OR = 3.5) (P<0.05). The proposed admission L-lactate cut-off value above which nonsurvival could be reliably predicted in hospitalised foals was 10.6 mmol/l with 82% of sensitivity and 74% of specificity. Hyperaldosteronaemia and hypervasopressinaemia as well as hypothermic extremities and increased albumin concentrations are potent predictors of hypoperfusion in hospitalised foals.

Rationale and Design of the Double-Blind, Randomized, Placebo-Controlled Multicenter Trial on Efficacy of Early Initiation of Eplerenone Treatment in Patients with Acute Heart Failure (EARLIER)

Aldosterone is one of the major factors to cause organ damage during an acute phase of heart failure (HF), and many reports have demonstrated that patients with acute decompensated HF (ADHF) have high blood aldosterone concentrations, and the high aldosterone concentrations predict poor prognosis in patients with HF. These findings suggest that eplerenone, an antagonist of aldosterone receptors may provide a new concept and strategy for the treatment of ADHF, protecting the heart and other organs during chronic phases, depending on the restoration of hemodynamic abnormalities. EARLIER is an event-driven clinical trial with an estimated enrolment of 300 patients hospitalized with ADHF with reduced left ventricular ejection fraction. ADHF includes ischemic or non-ischemic HF, and patients can be enrolled within 72 h after the visit to the hospital. We randomize the patients taking standard therapies for ADHF to the eplerenone and placebo groups. Eplerenone, either 25 or 50 mg, is administered for 6 months in the eplerenone group, and the corresponding placebo is administered in the placebo group on top of the standard care. We set the primary endpoint as the incidence of the composite endpoint (cardiac death or first re-hospitalization due to cardiac disease) 6 months after the enrollment, and also check the quality of life, i.e., exercise capacity and safety features of eplerenone. EARLIER is a clinical trial of eplerenone targeting ADHF and also the first multicenter investigator-initiated phase III trial in the cardiovascular field in Japan, funded by the Japanese government.

Ghrelin and obestatin inhibit enucleation-induced adrenocortical proliferation in the rat

Studies involving the role of ghrelin (GHREL) in regulating the proliferative activity of various cell types have obtained variable results depending primarily on the experimental model applied. It was recently reported that neither GHREL nor obestatin (OBS) affected the proliferative activity of cultured rat adrenocortical cells. In view of the conflicting results, we investigated the effects of GHREL and OBS on the proliferative activity of rat adrenocortical cells in a model of bilateral enucleation-induced adrenocortical regeneration in the rat. Rats were sacrificed 5 or 8 days after surgery. Twenty-four hours before being sacrificed, the appropriate groups were infused with 3 nmol GHREL or OBS/100 g. The mitotic index was assessed using the stachmokinetic method with vincristine. In comparison with intact rats, expression levels of ppGHREL, BAX, JUN-B and JUN-C genes were notably higher in regenerating adrenals, and neither GHREL nor OBS infusion affected these levels. Expression levels of the GHS-R, GPR39v2 and FOS genes were affected neither by adrenal enucleation nor GHREL or OBS infusion. Expression of only two studied genes, GPR39v1 and EGR1, was regulated by OBS. In the regenerating adrenal glands, GPR39v1 and EGR1 mRNA levels were higher than the levels in intact animals. GHREL infusion had no effect while OBS infusion notably stimulated GPR39v1 mRNA levels in the regenerating adrenal gland and evoked an opposite effect on EGR1 mRNA. OBS administration resulted in a potent decrease in the mitotic index of the studied cells, an effect found at both days 5 and 8 of the experiment. GHREL exerted a similar effect only at day 5 of adrenocortical regeneration. Neither GHREL nor OBS had an effect on blood aldosterone concentrations. GHREL infusion lowered plasma corticosterone concentration at day 5 but not 8 of the experiment, while OBS administration was ineffective. Thus, this study is the first to demonstrate that, in vivo, both GHREL and OBS inhibit the growth of the regenerating adrenal cortex. Moreover, the data suggest that the effect of OBS might be, at least in part, mediated by the EGR1 pathway known to be critical in cell proliferation.

Genistein-Induced Histomorphometric and Hormone Secreting Changes in the Adrenal Cortex in Middle-Aged Rats

The soybean phytoestrogen, genistein, is increasingly consumed as an alternative therapeutic for age-related diseases, namely cardiovascular conditions, cancer and osteoporosis. Besides estrogenic/antiestrogenic action, this isoflavone exerts a prominent inhibitory effect on tyrosine kinase and the steroidogenic enzyme families, thus affecting hormonal homeostasis. The aim of this study was to examine the effects of genistein on: histomorphometric features of the adrenal cortex, blood concentrations of aldosterone, corticosterone and dehydroepiandrosterone (DHEA) and adrenal tissue corticosterone content in orchidectomized middle-aged male rats. Sixteen-month-old Wistar rats were divided into sham-operated (SO), orchidectomized (Orx) and genistein-treated orchidectomized (Orx+G) groups. Genistein (30 mg/kg/day) was administered subcutaneously for three weeks, while the control groups received the vehicle alone. The adrenal cortex was analysed histologically and morphometrically. Circulating concentrations of aldosterone, corticosterone and DHEA, as well as adrenal tissue corticosterone levels, were determined by immunoassay. When compared to the SO group, orchidectomy decreased the ZG and ZR cell volume by 43% and 29%, respectively (P<0.05). Serum concentrations of aldosterone and DHEA were markedly lower [13% and 41%, respectively (P<0.05)], while serum and adrenal tissue levels of corticosterone did not change after orchidectomy. Orchidectomy followed by genistein treatment increased the ZG, ZF and ZR cell volume by 54%, 34% and 77%, respectively (P<0.05), compared to the untreated orchidectomized group. Histological analysis revealed noticeable vacuolization of the ZG and ZF cells in the Orx+G group. Serum aldosterone and corticosterone concentrations together with adrenal tissue corticosterone were 47%, 31% and 44% lower, respectively (P<0.05), whereas serum DHEA concentration was 342% higher (P<0.05) in this group in comparison with the Orx group. This study shows that in orchidectomized middle-aged rats, genistein can cause the shunting of metabolic pathways in the adrenals, supporting DHEA secretion and inhibiting corticosterone and aldosterone secretion.

Estimation of 24-h aldosterone secretion in the dog using the urine aldosterone:Creatinine ratio

Objectives One potential method of evaluating renin–angiotensin–aldosterone system (RAAS) activation involves the quantification of urinary aldosterone excretion. While blood concentrations of aldosterone are easily obtained, results may be misleading because of minute-to-minute variation in aldosterone secretion and subsequent blood concentrations. Urinary aldosterone concentration measurement represents a more consistent “pooled” index of aldosterone secretion, but obtaining 24-h urine samples is time-consuming, difficult, and fraught with potential error. We postulated that the urinary aldosterone:creatinine ratio, measured from spot urine samples, would correlate well with 24-h urinary aldosterone excretion, and would provide a simple index of aldosterone excretion that would eliminate the need for 24-h urine collection. Animals, materials and methods After validating an assay for aldosterone in canine urine, 24-h urinary aldosterone excretion was determined by radioimmunoassay from 8 normal, male beagle dogs under control conditions, after RAAS stimulation with amlodipine administration, and after RAAS attenuation with the addition of enalapril to amlodipine administration. Spot urine samples, each obtained at the same time of day, were used to determine the aldosterone:creatinine ratio during control conditions, RAAS stimulation, and RAAS attenuation. Results The aldosterone:creatinine ratio from spot-checked urine samples correlated well with 24-h urinary aldosterone excretion ( r = 0.77, P < 0.0001). Conclusions A spot urinary aldosterone:creatinine ratio might be substituted for 24-h urinary aldosterone determination.

Effects of the endothelin-1 receptor antagonist tezosentan on renal blood flow and diuresis during prolonged increased intra-abdominal pressure

Background.It has earlier been shown that increased intra-abdominal pressure (IAP) reduces renal blood circulation and urine output both clinically and experimentally. The aim of this study was to investigate the effect of endothelin-1 inhibition by the endothelin-1 receptor antagonist tezosentan on renal blood circulation and diuresis in pigs subjected to prolonged increased intra-abdominal pressure. Material and methods.The IAP in domestic pigs was maintained at 30 mmHg for 3 h. One group of 10 animals was pre-treated with the endothelin-1 receptor antagonist tezosentan, and then received continuous infusion of tezosentan throughout the experiment. Another group of 10 animals served as control. We measured renal cortex blood flow, plasma renin activity, blood concentrations of endothelin-1 and aldosterone, and diuresis. Results.The administration of tezosentan to pigs with an IAP of 30 mmHg was followed by reduced arterial pressure, reduced renal cortex blood flow, and reduced diuresis. The plasma renin activity increased markedly, but neither renal vascular resistance nor blood concentration of aldosterone did change significantly. Conclusion.Tezosentan reduced the arterial blood pressure, which resulted in decreased renal cortex blood flow, and aggravation of the oliguria usually observed under increased IAP. The plasma renin activity increased, but this was not followed by changes in renal vascular resistance, or blood concentration of aldosterone. The results indicate that drugs, which reduce the arterial pressure, may be harmful to the kidneys under increased IAP.

The state of the renin-angiotensin-aldosterone system in patients with the neuroendocrine-metabolic form of the hypothalamic syndrome.

1. Normalization of the baseline level of aldosterone in the blood, and of the reaction of the glomerular zone of the cortical substance of the adrenal glands and the juxtaglomerular apparatus of the kidneys, does not take place under the influence of conventional symptomatic treatment in NEMHS patients. 2. Treatment of NEMHS patients with peritol leads to normalization of the concentration of aldosterone in the blood; the reaction of the glomerular zone of the cortical substance of the adrenal glands and of the juxtaglomerular apparatus of the kidneys to both stimulators improves substantially. 3. The blood aldosterone concentration normalizes following the course of treatment with parlodel, while the reaction of the glomerular zone of the cortical substance of the adrenal glands and of the juxtaglomerular apparatus of the kidneys to insulin hypoglycemia does not change, while the reaction to an acute load of furosemide improves.

INTERRELATIONSHIP BETWEEN CORTISOL AND ATRIAL NATRIURETIC FACTOR IN THE IMMATURE OVINE FETUS

1. In chronically cannulated ovine fetuses (100-130 days of gestation) the infusion of cortisol (86.7 +/- 15 micrograms/h for 4 h) or human atrial natriuretic factor (ANF; 4.4 micrograms for 2 h) resulted in highly significant increases in the excretion of sodium, chloride, potassium and water. 2. Cortisol had no significant effect on fetal plasma ANF concentrations. All values are mean and s.e.m. Plasma immunoreactive ANF was 53 +/- 5 and 67.3 +/- 13 pmol/L in the 4 h saline infused fetuses, and 51.3 +/- 14.3 and 74 +/- 13.3 pmol/L in cortisol-infused fetuses (n = 7). A separate group of fetuses received 2 h infusions of saline or hANF (4.4 micrograms/h), and plasma IR-ANF values were measured (n = 3). The values, at 0, 60, 90 and 120 min were, respectively, 19.7 +/- 3, 17.3 +/- 0.7, 18.7 +/- 3.7 and 20.7 +/- 3.7 pmol/L in the saline infused group, and 25.3 +/- 5.3, 80.7 +/- 32.3, 123.3 +/- 4.3 and 100 +/- 15 pmol/L in the ANF-infused fetuses. 3. Blood cortisol concentrations, in fetuses infused for 4 h with 0.9% NaCl, were 3.1 +/- 0.8 nmol/L (n = 7); in fetuses infused with 0.9% NaCl for 2 h were 3.6 +/- 1 nmol/L (n = 3); in fetuses infused for 4 h with cortisol were 19.9 +/- 1.9 nmol/L (n = 7); and in fetuses infused with hANF for 2 h were 6.0 +/- 3.0 nmol/L (n = 5). 4. There was no effect of fetal hANF infusion on maternal or fetal blood aldosterone concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

The haemodynamic effects of cyclosporin A in sheep.

1. Cyclosporin A (CyA; 12 mg/kg/day) was infused into six conscious sheep over 5 days to examine the haemodynamic effects of the drug in normal animals. 2. Mean arterial pressure was increased from 73(1) mmHg to 90(4) mmHg (P less than 0.001). There was no change in cardiac output but calculated total peripheral resistance was elevated from 16(1) to 21(2) mmHg min/1 (P less than 0.001) on day 4. 3. There was no change in plasma [Na], but a fall in plasma [K]. Urinary Na excretion decreased. Glomerular filtration rate, filtration fraction, renal blood flow, renal vascular resistance, body weight, plasma renin and blood aldosterone concentration were unchanged. 4. CyA produces an increase in blood pressure in sheep associated with an increase in total peripheral resistance on days 1, 3, and 4, in the absence of changes in renal function. This suggests that CyA hypertension is not simply a consequence of nephrotoxicity.

Long-term trophic action of alpha-melanocyte-stimulating hormone on the zona glomerulosa of the rat adrenal cortex.

The effects of alpha-melanocyte-stimulating hormone (alpha-MSH) on the rat adrenal cortex were investigated by coupled morphometric and radioimmunological techniques. Short-term alpha-MSH administration provoked a significant increase in the aldosterone plasma level along with a notable lipid droplet depletion in zona glomerulosa cells. Long-term alpha-MSH treatment induced a notable hypertrophy of zona glomerulosa cells and a further rise in the blood concentration of aldosterone. alpha-MSH did not affect zona fasciculata morphology and corticosterone plasma level. The possibility is discussed that alpha-MSH may be specifically involved in the control of the growth and steroidogenic capacity of rat adrenal zona glomerulosa.

Effects of chronic administration of a methionine-enkephalin analogue on the zona glomerulosa of the rat adrenal cortex.

The effects of D-ala2-met-enkephalinamide (DALA) on the zona glomerulosa of dexamethasone-ACTH-treated rats were investigated by coupled radioimmunologic and morphometric techniques. Short-term DALA administration provoked a significant increase in the aldosterone plasma level along with a notable lipid droplet depletion in zona glomerulosa cells. Long-term DALA treatment induced a striking hypertrophy of zona glomerulosa cells and a further rise in the blood concentration of aldosterone. These findings seem to indicate that DALA is involved not only in the acute enhancement of aldosterone output but also in the stimulation of the growth and steroidogenic capacity of rat adrenal zona glomerulosa.

Suppression der Nebennierenrinde durch Infusion von Etomidat während Allgemeinanästhesie

The effects of anaesthesia with fentanyl and prolonged etomidate infusion (0.8 mg/kg/h) on the peroperative and postoperative change in blood concentrations of aldosterone, cortisol, dehydroepiandrosterone, ACTH, epinephrine, norepinephrine, dopamine, glucose, lactate and free fatty acids (FFA) were investigated in connection with major abdominal surgery. During surgery and anaesthesia with prolonged etomidate infusion no significant alterations in plasma catecholamine concentrations were observed. In contrast, basal plasma levels of ACTH (20.0 +/- 9.5 pg/ml----352.8 +/- 150.8 pg/ml) were elevated in all patients. Despite this endogenous ACTH stimulus, aldosterone (121.8 +/- 19.4 pg/ml----58.4 +/- 10.4 pg/ml) and cortisol (12.3 +/- 2.84 micrograms/dl----5.79 +/- 1.2 micrograms/dl) and dehydroepiandrosterone (2.28 +/- 1.09 ng/ml----1.27 +/- 0.25 ng/ml) levels were markedly depressed in every patient during the perioperative period. Twenty-four hours after surgery the basal steroid values were within or above normal limits.

Inter-relationships between Sodium and Potassium Intake and the Blood Pressure Effects of ACTH in Sheep

These studies examine the effect of sodium (Na) and potassium (K) intake on the pressor and metabolic actions of ACTH (20 micrograms/kg/day) in sheep. After 21 days on each of five regimens in which Na and K intake varied from 0 to 100 mmol/day, no simple relationship between Na and K intake and blood pressure was found. After five days of ACTH treatment, mean arterial pressure (MAP) rose + 5 mmHg in sheep on 0 mmol Na, 0 mmol K (expressed as 0 Na 0 K); + 13 mmHg on 10 Na 100 K; + 5 mmHg on 0 Na 100 K; + 20 mmHg on 100 Na 0 K and + 24 mmHg on 100 Na 100 K. Plasma [K] was unchanged by ACTH on 0 Na 0 K but fell in sheep on the other electrolyte regimens. Water intake increased with ACTH on all regimens except 100 Na 0 K. Blood aldosterone concentration was high in sheep maintained on 0 Na regimens but lower after five days of ACTH treatment in all groups. Blood cortisol and corticosterone concentrations increased with ACTH on all regimens studied.

Dopaminergic modulation of aldosterone secretion?

Metoclopramide (10 mg i.v. injection followed by 10 mg/h i.v. for 2 h) caused a transient rise in blood concentrations of aldosterone in sodium-replete and sodium-depleted sheep. Infusion of metoclopramide into the adrenal artery of sheep with an autotransplanted adrenal gland, at a rate to give a similar concentration of metoclopramide at the adrenal cell level (calculated from rate of infusion and adrenal blood flow), resulted in no alteration in aldosterone secretion rate in either sodium-replete or sodium-deplete animals, even though intravenous metoclopramide caused transient stimulation of aldosterone secretion in the same sheep when sodium replete. Dopamine administered either into the adrenal arterial blood supply or intravenously had no significant effect on aldosterone secretion and did not reverse the stimulatory effects of angiotensin II on aldosterone secretion in the adrenal transplant. The data do not support the suggestion that direct dopaminergic elements play a tonic inhibitory role in aldosterone secretion. It is possible that the agonist effect of metoclopramide on aldosterone secretion may occur by some non-dopaminergic mechanism and it is tempting to speculate that the effect is centrally mediated.

Potassium: aldosterone relationships in pregnant ewes and chronically cannulated ovine fetuses.

As maternal hyperkalemia quickly induces fetal hyperkalemia, it was decided to investigate the effect of small elevations of plasma [K+] on the peripheral blood aldosterone concentration in chronically catheterized ovine fetuses and to compare this response to that obtained in the adult ewe both pregnant and nonpregnant. Fol elevations of plasma [K+] of 0.1 to 0.3 mmole/liter blood aldosterone concentrations were elevated by 6.7 +/- 4.9 (9) ng/dl in nonpregnant sheep, 6.3 +/- 5.0 (6) in pregnant ewes, but only 0.3 +/- 1.7 (4) in fetal sheep. For increments in plasma [K+] of 0.4--1.0 mmole/liter aldosterone increments in nonpregnant ewes were 9.5 +/- 4.5 (4) ng/dl compared with 10.1 +/- 4.7 (5) in pregnant ewes and 1.5 +/- 2.6 (7) in fetuses. There was no obvious correlation between the age of the fetus and the response to increased plasma [K+]. In effect, the blood aldosterone concentration of the fetus was not elevated by increasing plasma plasma [K+]. The ovine fetus is not able to cope with hyperkalemia by increasing blood aldosterone concentration. Until the fetus is close to term, hyperkalemia may jeopardize the pregnancy by causing placental hemorrhages.