The renin-aldosterone response to stimulation and suppression during normal pregnancy

Physiological Changes in Pregnant Women Due to Hormonal Changes

Pregnancy affects many organ systems and causes significant physiological changes that are mainly caused by changes in hormone levels. This review explores the complex interactions between pregnancy-related hormonal changes and renal function, providing insights into the practical applications of these relationships. Extensive literature searches were conducted, combining data from several sources to produce thorough knowledge. Essential discoveries include changes in renal hemodynamics, calcium/phosphorus level variations, thyroid gland hypertrophy, changed function, and cardiovascular adaptations. The review also addresses how sex hormones affect immunological responses, emphasizing their importance for conditions like multiple sclerosis. Additionally impacted is the gastrointestinal tract, which results in symptoms like nausea and heartburn. Comprehending these physiological changes is essential for proficient therapeutic handling, guaranteeing the best possible health for both the mother and the fetus. The study emphasizes the importance of specialized medical treatment during pregnancy and calls for more investigation to clarify the intricacies of these physiological changes.

Association of Elevated Serum Aldosterone Concentrations in Pregnancy with Hypertension

Emerging evidence indicates a previously unrecognized, clinically relevant spectrum of abnormal aldosterone secretion associated with hypertension severity. It is not known whether excess aldosterone secretion contributes to hypertension during pregnancy. We quantified aldosterone concentrations and angiotensin peptides in serum (using liquid chromatography with tandem mass spectrometry) in a cohort of 128 pregnant women recruited from a high-risk obstetrics clinic and followed prospectively for the development of gestational hypertension, pre-eclampsia, superimposed pre-eclampsia, chronic hypertension, or remaining normotensive. The cohort was grouped by quartile of aldosterone concentration in serum measured in the first trimester, and blood pressure, angiotensin peptides, and hypertension outcomes compared across the four quartiles. Blood pressures and body mass index were greatest in the top and bottom quartiles, with the top quartile having the highest blood pressure throughout pregnancy. Further stratification of the top quartile based on increasing (13 patients) or decreasing (19 patients) renin activity over gestation revealed that the latter group was characterized by the highest prevalence of chronic hypertension, use of anti-hypertensive agents, pre-term birth, and intrauterine growth restriction. Serum aldosterone concentrations greater than 704 pmol/L, the 75th percentile defined within the cohort, were evident across all categories of hypertension in pregnancy, including normotensive. These findings suggest that aldosterone excess may underlie the development of hypertension in pregnancy in a significant subpopulation of individuals.

Activation of the Renin-Angiotensin-Aldosterone System Is Attenuated in Hypertensive Compared with Normotensive Pregnancy

Hypertension during pregnancy increases the risk of adverse maternal and fetal outcomes, but the mechanisms of pregnancy hypertension are not precisely understood. Elevated plasma renin activity and aldosterone concentrations play an important role in the normal physiologic adaptation to pregnancy. These effectors are reduced in patients with pregnancy hypertension, creating an opportunity to define the features of the renin-angiotensin-aldosterone system (RAAS) that are characteristic of this disorder. In the current study, we used a novel LC-MS/MS-based methodology to develop comprehensive profiles of RAAS peptides and effectors over gestation in a cohort of 74 pregnant women followed prospectively for the development of gestational hypertension and pre-eclampsia (HYP, 27 patients) versus those remaining normotensive (NT, 47 patients). In NT pregnancy, the plasma renin activity surrogate, (PRA-S, calculated from the sum of Angiotensin I + Angiotensin II) and aldosterone concentrations significantly increased from the first to the third trimester, accompanied by a modest increase in the concentrations of angiotensin peptide metabolites. In contrast, in HYP pregnancies, PRA-S and angiotensin peptides were largely unchanged over gestation, and third-trimester aldosterone concentrations were significantly lower compared with those in NT pregnancies. The results indicated that the predominant features of pregnancies that develop HYP are stalled or waning activation of the RAAS in the second half of pregnancy (accompanied by unchanging levels of angiotensin peptides) and the attenuated secretion of aldosterone.

Salt Sensitivity of Blood Pressure in Women

Several clinical and large population studies indicate that women are more salt-sensitive than men, yet the precise mechanisms by which the sexually dimorphic onset manifests remains incompletely understood. Here, we evaluate recent epidemiological data and highlight current knowledge from studies investigating sex-specific mechanisms of salt-sensitive blood pressure (SSBP). Emerging evidence indicates that women of all ethnicities are more salt-sensitive than men, at all ages both premenopausal and postmenopausal. However, menopause exacerbates severity and prevalence of SSBP, suggesting that female sex chromosomes predispose to and female sex hormones mitigate SSBP. Results from both human and rodent studies support the contribution of enhanced and inappropriate activation of the aldosterone-ECMR (endothelial cell mineralocorticoid receptor) axis promoting vascular dysfunction in females. Increases in adrenal response to angiotensin II, in association with higher ECMR expression and activation of endothelial ENaC (epithelial sodium channel) in females compared to males, are emerging as central players in the development of endothelial dysfunction and SSBP in females. Female sex increases the prevalence and susceptibility of SSBP and sex hormones and sex chromosome complement may exert antagonistic effects in the development of the female heightened SSBP.

Establishing Reference Ranges for Aldosterone, Renin and Aldosterone-to-Renin Ratio for Women in the Third-Trimester of Pregnancy

OBJECTIVE

Diagnosis of primary hyperaldosteronism in pregnancy is complicated due to lack of reference ranges for aldosterone, renin and aldosterone-to-renin ratio. We have endeavoured to establish third-trimester reference ranges for the above-mentioned parameters.

DESIGN & PATIENTS

We performed postural tests for aldosterone and renin (chemiluminescence immunoassay Liason® DiaSorin Inc., Italy) in 70 healthy pregnant women (age 30.53±4.51 years), at 32.38±4.25 weeks of gestation and in 22 non-pregnant healthy women (age 33.08±8.72 years).

RESULTS

Aldosterone reference ranges were 6.51-73.97 ng/dl and 12.33-86.38 ng/dl, for supine and upright positions, respectively and that for renin were 6.25-59.36 µIU/ml and 11.12-82.55 µIU/ml, respectively. Aldosterone and renin concentrations were higher in an upright position (p=0.000459 and p=0.00011, respectively). In contrast, aldosterone-to-renin ratio was not affected by posture (i. e. 0.497-3.084 ng/dl/µIU/ml versus 0.457-3.06 ng/dl/µIU/ml, p=0.12), but was higher (p=0.00081) than in non-pregnant controls. In comparison to manufacturer-provided non-pregnant reference range, supine aldosterone concentrations increased by 556% (lower cut-off) and 313% (upper cut-off), while upright aldosterone concentrations increased by 558% (lower cut-off) and 244% (upper cut-off). The reference range for supine renin concentrations increased by 223% (lower cut-off) and 48.7% (upper cut-off), while upright renin concentrations increased by 253% (lower cut-off) and 79% (upper cut-off).

CONCLUSIONS

There is an upward shift in aldosterone and renin reference ranges in the third-trimester of pregnancy accompanied by an increase in an aldosterone-to-renin ratio, that is not influenced by posture. It remains to be established whether the aldosterone-to-renin ratio may be used as a screening tool for primary hyperaldosteronism in pregnancy.

Physiological changes in pregnancy and their influence on the endocrine investigation

BACKGROUND

Physiological changes in pregnancy may result in significant alterations in endocrine hormone profiles, serum and urine electrolytes and endocrine gland morphology on imaging. Pregnancy-specific pathophysiological processes may also affect the results for endocrine tests. Investigation of endocrine disorders in pregnancy requires knowledge of these changes and awareness of the safety of dynamic hormone testing and imaging for the mother and foetus.

OBJECTIVE

This review seeks to outline the important physiological changes in pregnancy affecting reference intervals of basal and dynamic endocrine tests in pregnancy and the scenarios in which these changes are clinically significant, the pregnancy-specific disorders that may affect the investigation of endocrine disorders, and the safety of dynamic testing and imaging.

CONCLUSION

Awareness of the effect of physiological changes, and the potential impact of pregnancy-specific disorders of endocrine tests, and the safety of imaging is crucial to the management of endocrine disorders in pregnancy.

Kidney Physiology in Pregnancy

A woman's body undergoes a myriad of changes throughout the course of a normal gestation. The kidneys play a central role in driving adjustments that guarantee maternal and fetal well-being, including a dramatic increase in glomerular filtration rate, alterations in tubular function, and changes in electrolyte and acid/base handling. Early in gestation, systemic vasodilation, driven by both a change in quantity of and response to various hormones, leads to increased renal blood flow and glomerular filtration rate. Vasodilation also results in activation of the renin-angiotensin-aldosterone axis, which combined with changing tubular handling causes alterations in total body stores of electrolytes and total body water, resulting in a lower serum sodium concentration. In addition, mild proteinuria, glucosuria, and a decrease in serum calcium and magnesium are common. The primary acid/base change seen in pregnancy is a mild respiratory alkalosis due to progesterone effects. This article provides an overview of the current understanding of the healthy response of the kidneys to pregnancy, an understanding of which is key to caring for the pregnant patient, and early identification of alterations that may indicate underlying kidney pathology in pregnancy.

High aldosterone, hypertension and adrenal adenoma in a 36-year-old pregnant patient: Is this primary aldosteronism?

A 36-year-old woman presented at 16 weeks' gestation with severe hypertension. In comparison to the non-pregnant reference normal ranges, potassium was 3.1-3.9 mmol/L, aldosterone 2570-3000 pmol/L (N 250-2885) renin was unsuppressed (24-76.4 ng/L (N1.7-23.9)), with aldosterone to renin ratios in the reference range. An adrenal MRI scan demonstrated a 1.8 × 1.4 cm left adrenal adenoma. Primary aldosteronism was strongly suspected and surgery considered. However, she was managed conservatively with labetalol and modified-release nifedipine with no obstetric complications. Post-partum blood pressures remained elevated with normal aldosterone (539 pmol/L), unsuppressed renin (5.2 ng/L) and normal aldosterone-to-renin ratio (104 (N < 144)). Suspected primary hyperaldosteronism is challenging to investigate and manage in pregnancy. The accepted screening and confirmatory tests are either contraindicated or not validated in pregnancy. Pregnancy has significant effects on the renin-angiotensin-aldosterone pathway leading to physiologic elevations in both aldosterone and renin. While primary hyperaldosteronism has been associated with poor pregnancy outcomes, optimal management in pregnancy is not clearly established.

Progesterone Predisposes Females to Obesity-Associated Leptin-Mediated Endothelial Dysfunction via Upregulating Endothelial MR (Mineralocorticoid Receptor) Expression

Compelling clinical evidence indicates that obesity and its associated metabolic abnormalities supersede the protective effects of female sex-hormones and predisposes premenopausal women to cardiovascular disease. The underlying mechanisms remain poorly defined; however, recent studies have implicated overactivation of the aldosterone-MR (mineralocorticoid receptor) axis as a cause of sex-specific cardiovascular risk in obese females. Experimental evidence indicates that the MR on endothelial cells contributes to obesity-associated, leptin-induced endothelial dysfunction in female experimental models, however, the vascular-specific mechanisms via which females are predisposed to heightened endothelial MR activation remain unknown. Therefore, we hypothesized that endogenous expression of endothelial MR is higher in females than males, which predisposes them to obesity-associated, leptin-mediated endothelial dysfunction. We found that endothelial MR expression is higher in blood vessels from female mice and humans compared with those of males, and further, that PrR (progesterone receptor) activation in endothelial cells is the driving mechanism for sex-dependent increases in endothelial MR expression in females. In addition, we show that genetic deletion of either the endothelial MR or PrR in female mice prevents leptin-induced endothelial dysfunction, providing direct evidence that interaction between the PrR and MR mediates obesity-associated endothelial impairment in females. Collectively, these novel findings suggest that progesterone drives sex-differences in endothelial MR expression and predisposes female mice to leptin-induced endothelial dysfunction, which indicates that MR antagonists may be a promising sex-specific therapy to reduce the risk of cardiovascular diseases in obese premenopausal women.

Changes in biochemical tests in pregnancy and their clinical significance

Interpretation of laboratory investigations relies on reference intervals. Physiological changes in pregnancy may result in significant changes in normal values for many biochemical assays, and as such results may be misinterpreted as abnormal or mask a pathological state. The aims of this review are as follows: 1. To review the major physiological changes in biochemical tests in normal pregnancy. 2. To outline where these physiological changes are important in interpreting laboratory investigations in pregnancy. 3. To document the most common causes of abnormalities in biochemical tests in pregnancy, as well as important pregnancy-specific causes.

Salt, aldosterone and extrarenal Na+ - sensitive responses in pregnancy

Outside of pregnancy excessive salt consumption is known to be harmful being linked to increased blood pressure and cardiovascular disease. However, pregnancy represents a major change to a woman's physiology resulting in an intimate adaptation to environmental conditions. It is now becoming apparent that salt is essential for a number of these changes during pregnancy including haematological, cardiac adaptations as well as directly influencing placental development and the uteroplacental immune environment. The present review discusses the important role that salt has during normal pregnancy and evidence will also be presented to show how the placenta may act as a salt sensing organ temporarily, yet substantially regulating maternal blood pressure.

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The placenta may function as an extrarenal regulator of maternal blood pressure.

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Na⁺handling in pregnancy is completely different to the non-pregnant situation.

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Na⁺may actually lower blood pressure in pregnancy affected with pre-eclampsia.

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Aldosterone is an important regulator of placental and fetal development.

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Na⁺ may compensate for aldosterone deficiency in pregnancy.

The peripartum period influenced the serum macromineral profile in mares

Abstract. Changes in metabolic requirements during pregnancy may produce nutritional imbalances predisposing mares to pathological conditions. Therefore, we aimed to examine changes in serum macrominerals during the peripartum period in mares. Fifteen pregnant mares (Group A) were monitored starting at the 263rd day of pregnancy until the 21st day after foaling. Seven non-pregnant and non-lactating mares were used as a control group (Group B). Group A was subjected to blood sampling within 24 ± 12 h after parturition (P) and then 7, 14 and 21 days after foaling (+1, +2, +3 weeks, respectively). Group B was subjected to regular sampling throughout the study to ensure that seasonal changes had no significant effect on studied parameters. Serum samples were analysed for serum electrolytes including sodium (Na+), potassium (K+), calcium (Ca+ + ), phosphorus (P+), chloride (Cl−) and magnesium (Mg+ + ). Two-way repeated measures of analysis of variance (ANOVA) was applied to evaluate significant effects of peripartum on electrolyte concentrations. Group A showed a decrease in Cl− concentrations (P = 0.011) after foaling and lower P+ concentrations (P = 0.015) compared to Group B throughout the study. The linear regression model showed an increase in Na+ concentrations (P = 0.002) and a gradual decrease in serum Ca+ +  (P = 0.001) during pregnancy. Because the most significant changes in serum electrolytes occurred within 2 weeks before and 2 weeks after foaling, monitoring serum electrolyte concentrations would indicate whether the mare needs further mineral supplementation at this stage. The significant changes in a mare's macromineral profile that we observed over the peripartum provide enhanced knowledge about mineral interrelations and their modifications during specific physiological conditions such as late pregnancy and early postpartum.

Pregnancy-associated polyuria in familial renal glycosuria

A pregnant woman presented at gestational week 28 with loss of consciousness and profound polyuria. Further characterization revealed osmotic diuresis due to massive glycosuria without hyperglycemia. Glycosuria reduced substantially postpartum, from approximately 100 to approximately 30 g/1.73 m2 per day. DNA sequencing analysis of the SLC5A2 gene encoding the renal glucose transporter SGLT2 showed a homozygous frame-shift mutation (occurring after the glutamine at amino acid 168 and leading to premature termination of the protein at amino acid 186) diagnostic of familial renal glycosuria. Pregnant women with familial renal glycosuria can be at risk of profound polyuria during pregnancy due to the associated increase in glycosuria. These findings also have implications for the use of SGLT2 inhibitors in clinical practice.

[Pregnancy and kidney diseases]

The prevalence of chronic kidney disease in women of childbearing age reaches approximately 0.2%. Under physiological conditions pregnancy results in important hemodynamic changes on the maternal organism. In the case of chronic kidney disease these adaptations often are only partial. Physiological changes of immune response during pregnancy may contribute to the progress of renal disease. Regardless of the underlying kidney disease, one can assume that the better the glomerular filtration rate and blood pressure are the more favorable the course of pregnancy will be with the chance for a healthy child and stable renal function. To achieve this goal, a close interaction is required between gynecologist, nephrologist, and other specialists in a center with appropriate experience.

Longitudinal study of the renin angiotensin aldosterone system in purebred Spanish broodmares during pregnancy

During pregnancy, the coordinated interaction of the components of the renin-angiotensin-aldosterone system (RAAS) plays a vital role in accommodating the cardiovascular, haemodynamic and haematological needs imposed by foetal development and the placenta. This significantly influences the birth weight of the neonate and foetal viability. Although the evolution of each of the components of this system has been widely described in various species, it has not yet been clarified in the mare. Thus, the objectives of the present research were: 1) to establish reference values for renin (REN), angiotensin II (ANG-II) and aldosterone (ALD) concentrations in Spanish broodmares, and 2) to analyse the evolution of the aforementioned components during pregnancy. Thirty-one Purebred Spanish broodmares aged between 5 and 15 years old were studied for 11 months of pregnancy and compared to a control group composed of 11 non-pregnant Spanish mares. Morning venous blood samples were drawn on a monthly basis during pregnancy and pre-treated to prevent degradation until subsequent analysis. Serum REN, ANG-II and ALD concentrations were analysed by competitive immunoassay. This study found that pregnancy in Purebred Spanish broodmares is characterised by a gradual increase in REN concentrations, variable fluctuations in ALD concentrations, and no significant modifications in ANG-II concentrations. These results could provide potentially valuable information in understanding the physiological basis of the RAAS in mares, since we have been able to establish specific reference ranges for these components, as well as obtaining information on their evolution during pregnancy. As is often the case in other animal species, the increase in RAAS activity is a natural physiological process that occurs during pregnancy in Spanish broodmares. This may also be related to certain metabolic and hormone responses that contribute to the control of homeostasis in pregnant mares.

Relationship between aldosterone and progesterone in the human menstrual cycle

CONTEXT

Aldosterone levels increase during the luteal phase of the menstrual cycle. Prior studies examining relationships between aldosterone and female sex hormones did not control for sodium balance, a major determinant of aldosterone production.

OBJECTIVES

The objectives of this study were 1) to compare aldosterone levels between menstrual phases among cycling women in high- and low-sodium balance; and 2) to examine the relationships between aldosterone and female sex hormones in women and the effects of sex hormones on rat zona glomerulosa (ZG) cell aldosterone production in vitro.

SUBJECTS/INTERVENTIONS

Normotensive, premenopausal women were studied in low- and/or high-sodium balance. Urinary aldosterone, basal serum aldosterone, plasma renin activity (PRA), plasma angiotensin II (AngII), and serum aldosterone after AngII infusion were measured. Isolated rat ZG cells were treated with progesterone, estradiol, or both, and aldosterone was measured.

RESULTS

In high-sodium balance, urinary aldosterone, basal serum aldosterone, and serum aldosterone response to infused AngII were significantly greater (P < 0.05) in the luteal vs. follicular phase. PRA, AngII, and potassium did not differ. Progesterone directly correlated with urinary aldosterone, basal serum aldosterone, and serum aldosterone response to infused AngII. Estradiol did not significantly correlate with aldosterone. In low-sodium balance, no significant differences in aldosterone levels between phases were found. In vitro, progesterone increased ZG cell aldosterone production (P < 0.01), whereas estradiol had no effect.

CONCLUSIONS

In women, urinary and serum aldosterone levels are significantly higher during the luteal phase in high- but not low-sodium balance, whereas PRA and AngII do not differ between phases. Progesterone may directly contribute to increased luteal phase aldosterone production, independent of the renin-angiotensin system.