The role of gender in salt-induced hypertension

Sex differences in blood pressure regulation and hypertension: renal, hemodynamic, and hormonal mechanisms

The teleology of sex differences has been argued since at least as early as Aristotle's controversial Generation of Animals more than 300 years BC, which reflects the sex bias of the time to contemporary readers. Although the question "why are the sexes different" remains a topic of debate in the present day in metaphysics, the recent emphasis on sex comparison in research studies has led to the question "how are the sexes different" being addressed in health science through numerous observational studies in both health and disease susceptibility, including blood pressure regulation and hypertension. These efforts have resulted in better understanding of differences in males and females at the molecular level that partially explain their differences in vascular function and renal sodium handling and hence blood pressure and the consequential cardiovascular and kidney disease risks in hypertension. This review focuses on clinical studies comparing differences between men and women in blood pressure over the life span and response to dietary sodium and highlights experimental models investigating sexual dimorphism in the renin-angiotensin-aldosterone, vascular, sympathetic nervous, and immune systems, endothelin, the major renal sodium transporters/exchangers/channels, and the impact of sex hormones on these systems in blood pressure homeostasis. Understanding the mechanisms governing sex differences in blood pressure regulation could guide novel therapeutic approaches in a sex-specific manner to lower cardiovascular risks in hypertension and advance personalized medicine.

Sex differences in preclinical models of hypertension

Hypertension remains the primary contributor in the development of cardiovascular disease which is rapidly increasing worldwide. High blood pressure affects men and women differently and understanding these sex differences is the ultimate unmet need for researchers in this field. Due to the inherent differences in hypertension prevalence, control and outcomes between men and women, novel research needs to be carried out to tackle these disparities and improve targeted treatment. Animal models of hypertension have provided valuable insights into the sexual dimorphism of blood pressure mechanisms. The availability of genetic and non-genetic hypertensive strains allows the opportunity to study diverse environmental and genetic factors that affect blood pressure, therefore presenting a valuable tool for researchers. Sex differences are present before birth and throughout life, which presents a challenge for the study of disease development in humans, but these complexities can be resolved with the use of in vivo models that display similarities to human disease. The aim of the present review is to provide an overview of the different available animal models of hypertension that present sexual dimorphisms and to discuss their relevance to humans.

Hypertension after the Menopause: What Can We Learn from Experimental Studies?

Hypertension is the most prevalent cardiovascular disease of the adult population and is closely associated with serious cardiovascular events. The burden of hypertension with respect to vascular and other organ damage is greater in women. These sex differences are not fully understood. The unique feature in women is their transition to menopause accompanied by profound hormonal changes that affect the vasculature that are also associated with changes of blood pressure. Results from studies of hormone replacement therapy and its effects on the cardiovascular system are controversial, and the timing of treatment after menopause seems to be important. Therefore, revealing potential sex- and sex hormone-dependent pathophysiological mechanisms of hypertension in experimental studies could provide valuable information for better treatment of hypertension and vascular impairment, especially in postmenopausal women. The experimental rat models subjected to ovariectomy mimicking menopause could be useful tools for studying the mechanisms of blood pressure regulation after menopause and during subsequent therapy.

Short exposure to high salt in drinking solution leads to a cardiovascular phenotype of hypertension without changes in the blood volume of rats

NEW FINDINGS

What is the central question of this study? Is the cardiovascular phenotype of high blood pressure observed in rats salt loaded with 2% NaCl in drinking solution a blood volume-dependent hypertension? What is the main finding and its importance? Animals exposed to 2% NaCl drinking solution develop hypertension, with dominance of sympathetic outflow and high [Na+ ] in the cerebrospinal fluid, but without changes in the blood volume. The phenotype of salt-dependent hypertension might be related to accumulation of [Na+ ] in the cerebrospinal fluid, which makes it an interesting animal model in which to study the neuronal pathways involved in control of the circulation in osmotic challenge conditions.

ABSTRACT

Evidence suggests that hypertension induced by high salt intake is correlated with an autonomic imbalance that favours sympathetic hyperactivity and an increase in vascular resistance, indicating a neurogenic component to this pathology. Although there are several animal models in which to study salt-induced hypertension with prolonged exposure to a high-sodium diet, here we sought to investigate whether the increase in arterial blood pressure of rats subjected to a short exposure to high salt, with 2% NaCl drinking solution instead of water, relies on changes in the circulating blood volume. Male Wistar rats were divided randomly into three groups: euhydrated (EU, n = 10), salt loaded (SL, n = 13) and water deprived (WD, n = 6). The SL rats exhibited a significant increase in mean arterial blood pressure, with a large low-frequency component of systolic arterial blood pressure variability, when compared with the EU group. Circulating blood volume did not differ between SL and EU rats, but it was lower in WD rats. Compared with EU rats, the [Na+ ] in cerebrospinal fluid was higher in SL rats and similar in magnitude to the WD rats. Plasma [Na+ ] did not differ between SL and EU rats, but it was higher in WD rats. Collectively, our data suggest that the hypertension induced by a short exposure to high salt intake closely resembles a neurogenic mechanism, but not a blood volume-dependent mechanism, with cumulative [Na+ ] in the cerebrospinal fluid that could be associated with changes in the neurochemistry of autonomic nuclei, which are highly susceptible to osmotic stress related to high salt consumption.

The Effect of Biological Sex on Arterial Stiffness and Renin-Angiotensin-Aldosterone System Activity in Response to Cyclooxygenase-2 (COX-2) Inhibition

Background

Cardiovascular disease is the leading cause of death globally. Cyclooxygenase (COX)-derived prostaglandins play an important role in cardiovascular health regulation. Animal studies suggest a greater vascular dependence on prostaglandins in female subjects, but whether this extends to humans is unknown. We aimed to assess the effect of COX-2 inhibition on blood pressure and arterial stiffness, validated markers of cardiovascular risk, in human adults.

Methods

Healthy premenopausal females and males were studied in high-salt balance before and after 14 days of daily oral celecoxib, 200 mg ingestion, on 2 identical study days. Blood pressure (BP) and pulse-wave velocity (PWV) were measured at baseline and in response to an Angiotensin II (AngII) challenge, a validated marker of renin-angiotensin-aldosterone system activity.

Results

Thirteen females (age [mean ± standard deviation], 38 ± 13 years) and 11 males (age, 34 ± 9 years) were studied. Pre-COX-2 inhibition, resting measures of systolic (S)BP (P = 0.2) and diastolic (D)BP (P = 0.1) were similar between sexes. Post-COX-2 inhibition, resting SBP (P < 0.001) and DBP (P = 0.02) were significantly lower in females than in males. COX-2 inhibition was not associated with changes in arterial parameters by sex (change in DBP: P = 0.54; change in PWV: P = 0.55; females vs males). COX-2 inhibition was associated with increased SBP (P = 0.039 vs pre-COX-2 inhibition), but no change in DBP (P = 0.16) or PWV (P = 0.52) response to AngII challenge in females. Measures did not differ in response to AngII pre- vs post-COX-2 inhibition in males (SBP: P = 0.88; DBP: P = 0.93; PWV: P = 0.97).

Conclusions

The effects of COX-2 inhibition on arterial function may differ by sex, but further studies are needed. Given the association between nonsteroidal anti-inflammatory drugs (NSAIDs) and cardiovascular risk, increased attention regarding sex-specific pathophysiology is warranted.

The Role of Macula Densa Nitric Oxide Synthase 1 Beta Splice Variant in Modulating Tubuloglomerular Feedback

Abnormalities in renal electrolyte and water excretion may result in inappropriate salt and water retention, which facilitates the development and maintenance of hypertension, as well as acid-base and electrolyte disorders. A key mechanism by which the kidney regulates renal hemodynamics and electrolyte excretion is via tubuloglomerular feedback (TGF), an intrarenal negative feedback between tubules and arterioles. TGF is initiated by an increase of NaCl delivery at the macula densa cells. The increased NaCl activates luminal Na-K-2Cl cotransporter (NKCC2) of the macula densa cells, which leads to activation of several intracellular processes followed by the production of paracrine signals that ultimately result in a constriction of the afferent arteriole and a tonic inhibition of single nephron glomerular filtration rate. Neuronal nitric oxide (NOS1) is highly expressed in the macula densa. NOS1β is the major splice variant and accounts for most of NO generation by the macula densa, which inhibits TGF response. Macula densa NOS1β-mediated modulation of TGF responses plays an essential role in control of sodium excretion, volume and electrolyte hemostasis, and blood pressure. In this article, we describe the mechanisms that regulate macula densa-derived NO and their effect on TGF response in physiologic and pathologic conditions. © 2023 American Physiological Society. Compr Physiol 13:4215-4229, 2023.

Beyond the Gastrointestinal Tract: Oral and Sex-Specific Skin Microbiota Are Associated with Hypertension in Rats with Genetic Disparities

Current knowledge of the link between microbiota and hypertension is limited to the gut. Besides the gut, oral cavity and skin are other locations where sodium chloride (NaCl) is in direct contact with microbiota. While oral nitrate reducing-bacteria generate nitric oxide, which lead to vasodilation and lowering of blood pressure (BP), the skin excretes sodium via sweat glands and is an important site for sodium and BP homeostasis. However, knowledge on the contributions of oral and skin microbiota to BP regulation, is limited. Therefore, the current study was conducted to compare the tripartite relationship between site, sex, and genetic effects on the composition of oral, skin and gut microbiota impacting hypertension. Microbiota were profiled from the oral cavity, skin and feces of both male and female hypertensive Dahl salt-sensitive (S) and congenic rats with genomic substitutions on rat chromosomes (RNO) 1, 5, 9 and 10, demonstrating disparate BP effects. Sex-specific differences in β-diversity were observed only in skin microbiota. The most abundant taxa of the oral and skin microbiota were Actinobacteria and Cyanobacteria, respectively. Oral Actinobacteria were inversely associated with BP. While the abundance of oral Actinobacteria was upregulated by the BP locus on RNO10 in both sexes, depletion of skin Cyanobacteria decreased the protection from hypertension in the RNO5 female, but not male, congenic strain. In conclusion, this is the first study to identify specific microbiota in sites other than gut as contributors to BP regulation. Notably, both oral Actinobacteria and skin Cyanobacteria were beneficial for lowering BP.

Endothelial Cullin3 Mutation Impairs Nitric Oxide-Mediated Vasodilation and Promotes Salt-Induced Hypertension

Human hypertension caused by in-frame deletion of CULLIN3 exon-9 (Cul3∆9) is driven by renal and vascular mechanisms. We bred conditionally activatable Cul3∆9 transgenic mice with tamoxifen-inducible Tie2-CRE^ERT2 mice to test the importance of endothelial Cul3. The resultant mice (E-Cul3∆9) trended towards elevated nighttime blood pressure (BP) correlated with increased nighttime activity, but displayed no difference in daytime BP or activity. Male and female E-Cul3∆9 mice together exhibited a decline in endothelial-dependent relaxation in carotid artery. Male but not female E-Cul3∆9 mice displayed severe endothelial dysfunction in cerebral basilar artery. There was no impairment in mesenteric artery and no difference in smooth muscle function, suggesting the effects of Cul3∆9 are arterial bed-specific and sex-dependent. Expression of Cul3∆9 in primary mouse aortic endothelial cells decreased endogenous Cul3 protein, phosphorylated (S1177) endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) production. Protein phosphatase (PP) 2A, a known Cul3 substrate, dephosphorylates eNOS. Cul3∆9-induced impairment of eNOS activity was rescued by a selective PP2A inhibitor okadaic acid, but not by a PP1 inhibitor tautomycetin. Because NO deficiency contributes to salt-induced hypertension, we tested the salt-sensitivity of E-Cul3∆9 mice. While both male and female E-Cul3∆9 mice developed salt-induced hypertension and renal injury, the pressor effect of salt was greater in female mutants. The increased salt-sensitivity in female E-Cul3∆9 mice was associated with decreased renovascular relaxation and impaired natriuresis in response to a sodium load. Thus, CUL3 mutations in the endothelium may contribute to human hypertension in part through decreased endothelial NO bioavailability, renovascular dysfunction, and increased salt-sensitivity of BP.

High-fat and high-sodium diet induces metabolic dysfunction in the absence of obesity

OBJECTIVE

Excess dietary fat and sodium (NaCl) are both associated with obesity and metabolic dysfunction. In mice, high NaCl has been shown to block high-fat (HF) diet-induced weight gain. Here, the impact of an HF/NaCl diet on metabolic function in the absence of obesity was investigated.

METHODS

Wild-type mice were administered chow, NaCl (4%), HF, and HF/NaCl diets. Metabolic analysis was performed by measuring fasted blood glucose and insulin levels and by glucose tolerance test and insulin tolerance test.

RESULTS

After 10 weeks on diets, male and female mice on the HF diet gained weight, and HF/NaCl mice had significantly reduced weight gain similar to chow-fed mice. In the absence of obesity, HF/NaCl mice had significantly elevated fasting blood glucose and impaired glucose control during glucose tolerance tests. Both NaCl and HF/NaCl mice had decreased pancreas and β-cell mass. Administration of NaCl in drinking water did not protect mice from HF-diet-induced weight gain and obesity. Further analysis revealed that longer administration of HF/NaCl diets for 20 weeks resulted in significant weight gain and insulin resistance.

CONCLUSIONS

The data demonstrate that despite early inhibitory effects on fat deposition and weight gain, an HF/NaCl diet does not prevent the metabolic consequences of HF diet consumption.

Treatment With Gemfibrozil Prevents the Progression of Chronic Kidney Disease in Obese Dahl Salt-Sensitive Rats

Recently, we reported that Dahl salt-sensitive leptin receptor mutant (SS^LepRmutant) rats exhibit dyslipidemia and renal lipid accumulation independent of hyperglycemia that progresses to chronic kidney disease (CKD). Therefore, in the current study, we examined the effects of gemfibrozil, a lipid-lowering drug (200 mg/kg/day, orally), on the progression of renal injury in SS and SS^LepRmutant rats for 4 weeks starting at 12 weeks of age. Plasma triglyceride levels were markedly elevated in the SS^LepRmutant strain compared to SS rats (1193 ± 243 and 98 ± 16 mg/day, respectively). Gemfibrozil treatment only reduced plasma triglycerides in the SS^LepRmutant strain (410 ± 79 mg/dL). MAP was significantly higher in the SS^LepRmutant strain vs. SS rats at the end of the study (198 ± 7 vs. 165 ± 7 mmHg, respectively). Administration of gemfibrozil only lowered MAP in SS^LepRmutant rats (163 ± 8 mmHg). During the course of the study, proteinuria increased to 125 ± 22 mg/day in SS rats. However, proteinuria did not change in the SS^LepRmutant strain and remained near baseline (693 ± 58 mg/day). Interestingly, treatment with gemfibrozil increased the progression of proteinuria by 77% in the SS^LepRmutant strain without affecting proteinuria in SS rats. The renal injury in the SS^LepRmutant strain progressed to CKD. Moreover, the kidneys from SS^LepRmutant rats displayed significant glomerular injury with mesangial expansion and increased renal lipid accumulation and fibrosis compared to SS rats. Treatment with gemfibrozil significantly reduced glomerular injury and lipid accumulation and improved renal function. These data indicate that reducing plasma triglyceride levels with gemfibrozil inhibits hypertension and CKD associated with obesity in SS^LepRmutant rats.

Identifying Interactions between Dietary Sodium, Potassium, Sodium-Potassium Ratios, and FGF5 rs16998073 Variants and Their Associated Risk for Hypertension in Korean Adults

Hypertension is affected by both genetic and dietary factors. This study aimed to examine the interaction between dietary sodium/potassium intake, sodium–potassium ratios, and FGF5 rs16998073 and link these with increased risk for developing hypertension. Using data from the Health Examinee (HEXA) Study of the Korean Genome and Epidemiologic Study (KoGES), we were able to identify a total of 17,736 middle-aged Korean adults who could be included in our genome-wide association study (GWAS) to confirm any associations between hypertension and the FGF5 rs16998073 variant. GWAS analysis revealed that the FGF5 rs16698073 variant demonstrated the strongest association with hypertension in this population. Multivariable logistic regression was used to examine the relationship between dietary intake of sodium, potassium, and sodium–potassium ratios and the FGF5 rs16998073 genotypes (AA, AT, TT) and any increased risk of hypertension. Carriers with at least one minor T allele for FGF5 rs16998073 were shown to be at significantly higher risk for developing hypertension. Male TT carriers with a daily sodium intake ≥2000 mg also demonstrated an increased risk for developing hypertension compared to the male AA carriers with daily sodium intake <2000 mg (adjusted odds ratio (AOR) = 2.41, 95% confidence intervals (CIs) = 1.84–3.15, p-interaction < 0.0001). Female AA carriers with a daily potassium intake ≥3500 mg showed a reduced risk for hypertension when compared to female AA carriers with a daily potassium intake <3500 mg (AOR = 0.75. 95% CIs = 0.58–0.95, p-interaction < 0.0001). Male TT carriers in the mid-tertile for sodium–potassium ratio values showed the highest odds ratio for hypertension when compared to male AA carriers in the lowest-tertile for sodium–potassium ratio values (AOR = 3.03, 95% CIs = 2.14–4.29, p-interaction < 0.0001). This study confirmed that FGF5 rs16998073 variants do place their carriers (men and women) at increased risk for developing hypertension. In addition, we showed that high daily intake of sodium exerted a synergistic effect for hypertension when combined with FGF5 rs16998073 variants in both genders and that dietary sodium, potassium, and sodium–potassium ratios all interact with FGF5 rs16998073 and alter the risk of developing hypertension in carriers of either gender among Koreans.

New Mechanism for the Sex Differences in Salt-Sensitive Hypertension: The Role of Macula Densa NOS1β-Mediated Tubuloglomerular Feedback

Females are relatively resistant to salt-sensitive hypertension than males, but the mechanisms are not completely elucidated. We recently demonstrated a decisive role of macula densa neuronal NOS1β (nitric oxide synthase β)-mediated tubuloglomerular feedback (TGF) in the long-term control of glomerular filtration rate, sodium excretion, and blood pressure. In the present study, we hypothesized that the macula densa NOS1β-mediated TGF mechanism is different between male and female, thereby contributing to the sexual dimorphism of salt-sensitive hypertension. We used microperfusion, micropuncture, clearance of fluorescein isothiocyanate-inulin, and radio telemetry to examine the sex differences in the changes of macula densa NOS1β expression and activity, TGF response, natriuresis, and blood pressure after salt loading in wild-type and macula densa-specific NOS1 knockout mice. In wild-type mice, a high-salt diet induced greater increases in macula densa NOS1β expression and phosphorylation at Ser 1417, greater nitric oxide generation by the macula densa, and more inhibition in TGF response in vitro and in vivo in females than in males. Additionally, the increases of glomerular filtration rate, urine flow rate, and sodium excretion in response to an acute volume expansion were significantly greater in females than in males. The blood pressure responses to angiotensin II plus a high-salt diet were significantly less in females than in males. In contrast, these sex differences in TGF, natriuretic response, and blood pressure were largely diminished in knockout mice. In conclusion, macula densa NOS1β-mediated TGF is a novel and important mechanism for the sex differences in salt-sensitive hypertension.

Sex Differences in Renal Inflammation and Injury in High-Fat Diet-Fed Dahl Salt-Sensitive Rats

We examined the impact of sex on high-fat diet (HFD)-induced renal alterations in Dahl salt-sensitive and Sprague Dawley rats. In Dahl rats, HFD (60% kcal from fat for 24-26 weeks starting at weaning) significantly and equally increased blood pressure in males and females when compared with rats fed a control diet (10% kcal from fat). Male Dahl rats on HFD exhibited progressive renal histological injury and moderately increased renal macrophage infiltration at 10 and 24 weeks of feeding when compared with males on control diet. Female Dahl rats had lower grade renal injury and less macrophage infiltration (except at 17 weeks) than males regardless of diet. Male Dahl rats on both diets showed progressively increasing numbers of renal T-cells, a pattern not observed in females. HFD per se did not significantly affect renal T-cell number. Male Dahl rats had lower renal regulatory T-cells cell ratio than females at 24 weeks. Renal macrophage and T-cell infiltrations were highly correlated to final mean arterial pressure levels in males but not in females. Sprague Dawley rats fed HFD were normotensive without significant renal injury/inflammation after 24 weeks of feeding. In summary, HFD feeding fails to increase arterial blood pressure in Sprague Dawley rats but strongly promotes hypertension in both male and female Dahl salt-sensitive rats. Only Dahl males, however, exhibited blood pressure-associated renal inflammation and injury. Maintenance of regulatory T-cells ratio may protect against hypertension-associated renal injury/inflammation but not HFD-induced hypertension.

Influence of the selective COX-2 inhibitor celecoxib on sex differences in blood pressure and albuminuria in spontaneously hypertensive rats

We previously reported that female spontaneously hypertensive rats (SHR) have greater cyclooxygenase-2 (COX-2) expression in the renal medulla and enhanced urinary excretion of prostaglandin (PG) E₂ (PGE₂) metabolites compared to male SHR. Based on the role of COX-2-derived prostanoids in the regulation of cardiovascular health, the aim of the current study was to test the hypothesis that blood pressure (BP) in female SHR is more sensitive to COX-2 inhibition than in males. Seven week old male and female SHR were implanted with telemetry transmitters for continuous BP recording. After one week of baseline BP recording, male and female SHR were randomized to receive the selective COX-2 inhibitor celecoxib (10 mg/kg/day) or vehicle for six weeks (from 9 to 14 weeks of age). Female SHR had lower BP and albuminuria compared to male SHR as well as enhanced urinary excretion of PGE metabolite (PGEM), 6-keto PGF_1α and thromboxane B₂, indicators of PGE₂, PGI₂ and TXA₂, respectively. Treatment with celecoxib did not significantly alter BP or albuminuria in either female or male SHR. Celecoxib did not change PGs metabolites excretion in male SHR; however, excretion levels of PGEM and 6-keto PGF_1α were reduced in female SHR. COX-2 derived PG can also induce oxidative stress. Markers of oxidative stress (thiobarbituric acid reactive substances (TBARs) and H₂O₂ excretion) were lesser in female SHR versus male SHR. Celecoxib treatment did not significantly change markers of oxidative stress in female SHR, however, urinary TBARs excretion was significantly reduced in male SHR after 6 weeks of treatment with celecoxib. Therefore, although celecoxib treatment appears to have distinct effects on prostanoids levels in female SHR vs. males, it is unlikely that COX-2 contributes to established sex differences in BP in SHR.

Distinct effects of dietary flax compared to fish oil, soy protein compared to casein, and sex on the renal oxylipin profile in models of polycystic kidney disease

Oxylipins are bioactive lipids derived from polyunsaturated fatty acids (PUFA) that are important regulators of kidney function and health. Targeted lipidomic analyses of renal oxylipins from four studies of rodent models of renal disease were performed to investigate the differential effects of dietary flax compared to fish oil, soy protein compared to casein, and sex. Across all studies, dietary fish oil was more effective than flax oil in reducing n-6 PUFA derived oxylipins and elevating eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) derived oxylipins, whereas dietary flax oil resulted in higher α-linolenic acid (ALA) oxylipins. Dietary soy protein compared to casein resulted in higher linoleic acid (LA) derived oxylipins. Kidneys from females had higher levels of arachidonic acid (AA) oxylipins, but similar or lower levels of oxylipins from other PUFA. Modulation of the oxylipin profile by diet and sex may help elucidate their effects on renal physiology and health.

Efficacy of naproxen with or without esomeprazole for pain and inflammation in patients after bilateral third molar extractions: A double blinded crossover study

Background

Using a double-blinded randomized crossover design, this study aimed to evaluate acute postoperative pain management, swelling and trismus in 46 volunteers undergoing extractions of the two lower third molars, in similar positions, at two different appointments who consumed a tablet of either NE (naproxen 500 mg + esomepraz ole 20 mg) or only naproxen (500 mg) every 12 hours for 4 days.

Material and Methods

Parameters were analyzed: self-reported pain intensity using a visual analog scale (VAS) pre- and postoperative mouth opening; incidence, type and severity of adverse reactions; total quantity consumed of rescue medication; and pre- and postoperative swelling.

Results

Female volunteers reported significantly more postoperative pain at 1, 1.5, 2, 3 and 4hrs after surgery while also taking their first rescue medication at a time significantly earlier when consuming NE when compared to naproxen (3.7hrs and 6.7hrs). Conversely, no differences were found between each drug group in males.

Conclusions

In conclusion, throughout the entire study, pain was mild after using either drug in both men and women with pain scores on average well below 40mm (VAS), although in women naproxen improved acute postoperative pain management when compared to NE.

Key words:Oral surgery, third molar, pain, naproxen, esomeprazole, NSAIDs.

The Importance of Biological Sex and Estrogen in Rodent Models of Cardiovascular Health and Disease

Nearly one-third of deaths in the United States are caused by cardiovascular disease (CVD) each year. In the past, CVD was thought to mainly affect men, leading to the exclusion of women and female animals from clinical studies and preclinical research. In light of sexual dimorphisms in CVD, a need exists to examine baseline cardiac differences in humans and the animals used to model CVD. In humans, sex differences are apparent at every level of cardiovascular physiology from action potential duration and mitochondrial energetics to cardiac myocyte and whole-heart contractile function. Biological sex is an important modifier of the development of CVD with younger women generally being protected, but this cardioprotection is lost later in life, suggesting a role for estrogen. Although endogenous estrogen is most likely a mediator of the observed functional differences in both health and disease, the signaling mechanisms involved are complex and are not yet fully understood. To investigate how sex modulates CVD development, animal models are essential tools and should be useful in the development of therapeutics. This review will focus on describing the cardiovascular sexual dimorphisms that exist both physiologically and in common animal models of CVD.

Severe Headache or Migraine History is Inversely Correlated With Dietary Sodium Intake: NHANES 1999-2004

Objective

We investigated whether dietary sodium intake from respondents of a national cross‐sectional nutritional study differed by history of migraine or severe headaches.

Background

Several lines of evidence support a disruption of sodium homeostasis in migraine.

Design

Our analysis population was 8819 adults in the 1999–2004 National Health and Nutrition Examination Survey (NHANES) with reliable data on diet and headache history. We classified respondents who reported a history of migraine or severe headaches as having probable history of migraine. To reduce the diagnostic conflict from medication overuse headache, we excluded respondents who reported taking analgesic medications. Dietary sodium intake was measured using validated estimates of self‐reported total grams of daily sodium consumption and was analyzed as the residual value from the linear regression of total grams of sodium on total calories. Multivariable logistic regression that accounted for the stratified, multistage probability cluster sampling design of NHANES was used to analyze the relationship between migraine and dietary sodium.

Results

Odds of probable migraine history decreased with increasing dietary sodium intake (odds ratio = 0.93, 95% confidence interval = 0.87, 1.00, P = .0455). This relationship was maintained after adjusting for age, sex, and body mass index (BMI) with slightly reduced significance (P = .0505). In women, this inverse relationship was limited to those with lower BMI (P = .007), while in men the relationship did not differ by BMI. We likely excluded some migraineurs by omitting frequent analgesic users; however, a sensitivity analysis suggested little effect from this exclusion.

Conclusions

This study is the first evidence of an inverse relationship between migraine and dietary sodium intake. These results are consistent with altered sodium homeostasis in migraine and our hypothesis that dietary sodium may affect brain extracellular fluid sodium concentrations and neuronal excitability.

Lipid mediators are critical in resolving inflammation: a review of the emerging roles of eicosanoids in diabetes mellitus

The biosynthesis pathway of eicosanoids derived from arachidonic acid, such as prostaglandins and leukotrienes, relates to the pathophysiology of diabetes mellitus (DM). A better understanding of how lipid mediators modulate the inflammatory process may help recognize key factors underlying the progression of diabetes complications. Our review presents recent knowledge about eicosanoid synthesis and signaling in DM-related complications, and discusses eicosanoid-related target therapeutics.

Moderate inappropriately high aldosterone/NaCl constellation in mice: cardiovascular effects and the role of cardiovascular epidermal growth factor receptor

Non-physiological activation of the mineralocorticoid receptor (MR), e.g. by aldosterone under conditions of high salt intake, contributes to the pathogenesis of cardiovascular diseases, although beneficial effects of aldosterone also have been described. The epidermal growth factor receptor (EGFR) contributes to cardiovascular alterations and mediates part of the MR effects. Recently, we showed that EGFR is required for physiological homeostasis and function of heart and arteries in adult animals. We hypothesize that moderate high aldosterone/NaCl, at normal blood pressure, affects the cardiovascular system depending on cardiovascular EGFR. Therefore we performed an experimental series in male and female animals each, using a recently established mouse model with EGFR knockout in vascular smooth muscle cells and cardiomyocytes and determined the effects of a mild-high aldosterone-to-NaCl constellation on a.o. marker gene expression, heart size, systolic blood pressure, impulse conduction and heart rate. Our data show that (i) cardiac tissue of male but not of female mice is sensitive to mild aldosterone/NaCl treatment, (ii) EGFR knockout induces stronger cardiac disturbances in male as compared to female animals and (iii) mild aldosterone/NaCl treatment requires the EGFR in order to disturb cardiac tissue homeostasis whereas beneficial effects of aldosterone seem to be independent of EGFR.

Age-dependent salt hypertension in Dahl rats: fifty years of research

Fifty years ago, Lewis K. Dahl has presented a new model of salt hypertension - salt-sensitive and salt-resistant Dahl rats. Twenty years later, John P. Rapp has published the first and so far the only comprehensive review on this rat model covering numerous aspects of pathophysiology and genetics of salt hypertension. When we summarized 25 years of our own research on Dahl/Rapp rats, we have realized the need to outline principal abnormalities of this model, to show their interactions at different levels of the organism and to highlight the ontogenetic aspects of salt hypertension development. Our attention was focused on some cellular aspects (cell membrane function, ion transport, cell calcium handling), intra- and extrarenal factors affecting renal function and/or renal injury, local and systemic effects of renin-angiotensin-aldosterone system, endothelial and smooth muscle changes responsible for abnormal vascular contraction or relaxation, altered balance between various vasoconstrictor and vasodilator systems in blood pressure maintenance as well as on the central nervous and peripheral mechanisms involved in the regulation of circulatory homeostasis. We also searched for the age-dependent impact of environmental and pharmacological interventions, which modify the development of high blood pressure and/or organ damage, if they influence the salt-sensitive organism in particular critical periods of development (developmental windows). Thus, severe self-sustaining salt hypertension in young Dahl rats is characterized by pronounced dysbalance between augmented sympathetic hyperactivity and relative nitric oxide deficiency, attenuated baroreflex as well as by a major increase of residual blood pressure indicating profound remodeling of resistance vessels. Salt hypertension development in young but not in adult Dahl rats can be attenuated by preventive increase of potassium or calcium intake. On the contrary, moderate salt hypertension in adult Dahl rats is attenuated by superoxide scavenging or endothelin-A receptor blockade which do not affect salt hypertension development in young animals.

Sex-specific associations of nutrition with hypertension and systolic blood pressure in Alaska Natives findings from the GOCADAN study

OBJECTIVES

To examine sex-specific associations of nutritional factors with prevalent hypertension (HTN) and systolic blood pressure (SBP) in Alaska Natives. Diet is known to affect SBP, a major risk factor for cardiovascular disease.

STUDY DESIGN

Cross-sectional analysis of participants without diabetes in the Genetics of Coronary Artery Disease in Alaska Natives study.

METHODS

Macronutrients such as fat, carbohydrate and protein and micronutrients such as sodium were investigated. HTN was defined as SBP≥140 mmHg, diastolic blood pressure≥90 mmHg and/or taking anti-HTN medication. Analyses were stratified by sex and covariates included age, body mass index (BMI), energy intake, smoking and physical activity.

RESULTS

Mean age was 42 years for men (n=456) and women (n=602). Men with HTN (n=106) compared to men without HTN consumed a higher proportion of calories from total (p=0.01), saturated (p<0.01) and trans fatty acid (p=0.03) fats. Women with HTN (n=99) compared to women without HTN consumed more total (p=0.03) and monounsaturated (p=0.04) fat, higher protein (p=0.02) and lower total (p<0.01) and simple (p<0.01) carbohydrates. After covariate adjustment, men not on anti-HTN medications (n=407) had significantly higher average SBP with increasing quartiles of trans fatty acid intake (p for linear trend=0.01) and sodium intake (p for linear trend=0.02). For women not on anti-HTN medications (n=528), after covariate adjustment, average SBP decreased with increasing quartiles of omega 3 fatty acid intake (p for linear trend <0.01).

CONCLUSIONS

Prospective evaluation of the sex-specific associations of nutritional factors with HTN and SBP on outcomes is needed along with novel interventions to lower the risk of cardiovascular disease.

Dietary fatty acids in dementia and predementia syndromes: epidemiological evidence and possible underlying mechanisms

Drugs currently used in the treatment of cognitive impairment and dementia have a very limited therapeutic value, suggesting the necessity to potentially individualize new strategies able to prevent and to slow down the progression of predementia and dementia syndromes. An increasing body of epidemiological evidence suggested that elevated saturated fatty acids (SFA) could have negative effects on age-related cognitive decline (ARCD) and mild cognitive impairment (MCI). Furthermore, a clear reduction of risk for cognitive decline has been found in population samples with elevated fish consumption, high intake of monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA), particularly n-3 PUFA. Epidemiological findings demonstrated that high PUFA intake appeared to have borderline non-significant trend for a protective effect against the development of MCI. Several hypotheses could explain the association between dietary unsaturated fatty acids and cognitive functioning, including mechanisms through the co-presence of antioxidant compounds in food groups rich in fatty acids, via atherosclerosis and thrombosis, inflammation, accumulation of b-amyloid, or via an effect in maintaining the structural integrity of neuronal membranes, determining the fluidity of synaptosomal membranes that thereby regulate neuronal transmission. However, recent findings from clinical trials with n-3 PUFA supplementation showed efficacy on depressive symptoms only in non-apolipoprotein E (APOE) epsilon4 carriers, and on cognitive symptoms only in very mild Alzheimer's disease (AD) subgroups, MCI patients, and cognitively unimpaired subjects non-APOE epsilon4 carriers. These data together with epidemiological evidence support a possible role of fatty acid intake in maintaining adequate cognitive functioning and possibly for the prevention and management of cognitive decline and dementia, but not when the AD process has already taken over.

Extracellular signal-regulated kinase 1/2 activation, via downregulation of mitogen-activated protein kinase phosphatase 1, mediates sex differences in desoxycorticosterone acetate-salt hypertension vascular reactivity

Extracellular signal-regulated kinase (ERK)1/2 has been reported to play a role in vascular dysfunction associated with mineralocorticoid hypertension. We hypothesized that, compared with female rats, an upregulation of ERK1/2 signaling in the vasculature of male rats contributes to augmented contractile responses in mineralocorticoid hypertension. Uninephrectomized male and female Sprague-Dawley rats received desoxycorticosterone acetate (DOCA) pellets (200 mg per animal) and saline to drink for 3 weeks. Control uninephrectomized rats received tap water to drink. Blood pressure, measured by telemetry, was significantly higher in male DOCA rats (191+/-3 mm Hg) compared with female DOCA rats (172+/-7 mm Hg; n=5). DOCA treatment resulted in augmented contractile responses to phenylephrine in aorta (22+/-3 mN; n=6) and small mesenteric arteries (13+/-2 mN; n=6) from male DOCA rats versus uninephrectomized male rats (16+/-3 and 10+/-2 mN, respectively; P<0.05) and female DOCA rats (15+/-1 and 11+/-1 mN, respectively). ERK1/2 inhibition with PD-98059 (10 micromol/L) abrogated increased contraction to phenylephrine in aorta (14+/-2 mN) and small mesenteric arteries (10+/-2 mN) from male DOCA rats, without any effects in arteries from male uninephrectomized or female animals. Compared with the other groups, phosphorylated ERK1/2 levels were increased in the aorta from male DOCA rats, whereas mitogen-activated protein kinase phosphatase 1 expression was decreased. Interleukin-10 plasma levels, which positively regulate mitogen-activated protein kinase phosphatase 1 activity, were reduced in male DOCA-salt rats. We speculate that augmented vascular reactivity in male hypertensive rats is mediated via activation of the ERK1/2 pathway. In addition, mitogen-activated protein kinase phosphatase 1 and interleukin 10 play regulatory roles in this process.

Increased blood pressure in mice lacking cytochrome P450 2J5

The cytochrome P450 (CYP) enzymes participate in a wide range of biochemical functions, including metabolism of arachidonic acid and steroid hormones. Mouse CYP2J5 is abundant in the kidney where its products, the cis-epoxyeicosatrienoic acids (EETs), modulate sodium transport and vascular tone. To define the physiological role of CYP2J5 in the kidney, knockout mice were generated using a conventional gene targeting approach. Cyp2j5 (-/-) mice develop normally and exhibit no overt renal pathology. While renal EET biosynthesis was apparently unaffected by the absence of CYP2J5, deficiency of this CYP in female mice was associated with increased blood pressure, enhanced proximal tubular transport rates, and exaggerated afferent arteriolar responses to angiotensin II and endothelin I. Interestingly, plasma 17beta-estradiol levels were reduced in female Cyp2j5 (-/-) mice and estrogen replacement restored blood pressure and vascular responsiveness to normal levels. There was no evidence of enhanced estrogen metabolism, or altered expression or activities of steroidogenic enzymes in female Cyp2j5 (-/-) mice, but their plasma levels of luteinizing hormone and follicle stimulating hormone were inappropriately low. Together, our findings illustrate a sex-specific role for CYP2J5 in regulation of blood pressure, proximal tubular transport, and afferent arteriolar responsiveness via an estrogen-dependent mechanism.

Renal hemodynamic effect of cyclooxygenase 2 inhibition in young men and women with uncomplicated type 1 diabetes mellitus

In experimental studies, cyclooxygenase 2 (COX2)-derived vasodilatory prostaglandins play a more prominent role in arterial vasoregulation in females. The gender-dependent effect of COX2 modulation in humans with type 1 diabetes mellitus (DM) is unknown. Accordingly, we examined the renal hemodynamic role of prostaglandins by assessing the response to COX2 inhibition in young men and women with type 1 DM. We also used a graded ANG II infusion to determine whether gender-based differences were mediated by effects of COX2 inhibition on the renin angiotensin system (RAS). We hypothesized that COX2 inhibition would be associated with preferential vasoconstriction in women and would augment their response to ANG II. Baseline renal function and the response to an ANG II infusion were assessed during clamped euglycemia, and again after COX2 inhibition (200 mg celecoxib daily for 14 days) in 12 men and 9 women after 1 wk on a controlled protein and sodium diet. COX2 inhibition was associated with increases in filtration fraction (P = 0.045) and renal vascular resistance and a decline in renal blood flow (P = 0.04) in women compared with men. Before COX2 inhibition, women exhibited a decline in glomerular filtration rate in response to ANG II. COX2 inhibition abolished this effect, whereas the response was not altered in men. In summary, COX2 inhibition was associated with hemodynamic effects that differed based on gender. The ANG II response suggests that with uncomplicated type 1 DM, prostaglandins may contribute to RAS-mediated gender differences. Our results are consistent with experimental data suggesting augmented female prostanoid dependence.

A moderately high fat diet promotes salt-sensitive hypertension in obese zucker rats by impairing nitric oxide production

The objective of this research was to examine the contribution of a moderately high fat (MHF) diet to the development of salt-sensitive hypertension in obese Zucker rats. Lean and obese Zucker rats were fed either a MHF diet or a diet of standard rat chow (control diet) for 10 weeks. From week 4 through week 10, the drinking water was supplemented with 1% NaCl. Blood pressure was measured weekly, and urinary excretion of nitric oxide metabolites (NO(x)) was determined at weeks 4 and 10. At week 10, renal nitric oxide synthase (NOS) activity was assessed in kidney homogenates. Blood pressures of obese, but not lean, rats on the MHF fat diet were significantly increased by salt-supplementation, whereas blood pressures of rats on the control diet were not appreciably affected. NO(x) excretion was increased in response to salt-supplementation in rats on the control diet, with the effect being particularly dramatic in obese rats. After salt-supplementation, NO(x) excretion by rats on the MHF diet was lower than rats on the control diet. In obese rats on the MHF diet, this decrease in NO production was accompanied by a reduction in renal NOS activity. These results indicate that obese rats are more inclined than lean rats to develop diet-induced hypertension in response to a moderately high fat, salt-supplemented diet. Furthermore, they suggest that MHF diet-induced defects in NO production may promote the salt-sensitivity of blood pressure in obese Zucker rats, which appear to require more NO to maintain blood pressure during a salt challenge.

Association between prostaglandin E2 receptor gene and essential hypertension

BACKGROUND

Essential hypertension (EH) is a complex multifactorial polygenic disorder that is thought to result from an interaction between an individual's genetic makeup and various environmental factors. In the kidney, prostaglandins (PGs) are important mediators of vascular tone and salt and water homeostasis, and are involved in the mediation and/or modulation of hormonal action. In previous studies, mice deficient in the prostaglandin E2 (PGE(2)) EP2 receptor had resting systolic blood pressure (BP) that was significantly lower than that of wild-type controls. The BP of those mice increased when they were put on a high-salt diet, suggesting that the EP2 receptor is involved in sodium handling by the kidney. In the present study, we investigated the association between EH and nucleotide polymorphisms in the gene encoding the prostaglandin E2 receptor subtype EP2 (PTGER2).

METHODS

We selected three single-nucleotide polymorphisms (SNP) in the human PTGER2 gene (rs1254601, rs2075797, and rs17197), and we performed a genetic association study of 266 EH patients and 253 age-matched normotensive (NT) controls.

RESULTS

There was no significant difference in overall distribution of genotypes or alleles of any of the SNP between the EH and NT groups. However, among men, the A/A type of the SNP rs17197 (rs17197, A/G in 3'UTR) was significantly more frequent in EH subjects than in NT subjects (P=0.041).

CONCLUSION

The present findings suggest that rs17197 is useful as a genetic marker of EH in men.

Sexual dimorphism in renal production of prostanoids in spontaneously hypertensive rats

Male spontaneously hypertensive rats (SHR) have higher blood pressure, blunted pressure-natriuresis relationship, and accelerated progression of renal injury compared with female SHR. Renal medullary prostanoids mediate vascular tone, salt and water balance, and renin release and, as a result, are involved in the maintenance of renal blood flow and the pathogenesis of hypertension. The aim of this study was to determine whether a gender difference exists in prostanoid production in SHR and whether sex steroids influence prostaglandin (PG) production. Thirteen-week-old intact and gonadectomized male and female SHR rats were placed in metabolic cages for 24-hour urine collection. Prostanoid excretion was determined using enzyme immunoassay. Kidneys were isolated and separated into outer and inner medulla for Western blot analysis. Female SHR had enhanced urinary excretion of PG E2 (PGE2) metabolites and thromboxane B2, an indicator of renal thromboxane production, compared with male SHR. There were no gender differences in excretion of systemic thromboxane or prostacyclin. Correspondingly, female SHR had enhanced microsomal PGE2 synthase protein expression in the renal inner medulla and greater cyclooxygenase-2 (COX-2) expression in the outer medulla. Orchidectomy was associated with increased PGE2 metabolite excretion and microsomal PGE synthase protein expression. Thromboxane B2 excretion was not affected by gonadectomy in either male or female SHR. Protein expressions of COX and cytoplasmic PGE2 synthase in the renal medulla were unchanged by gonadectomy in both sexes. These results demonstrate a sexual dimorphism in renal production of prostanoids in SHR and that PGE production is testosterone sensitive and estrogen insensitive.

Gender differences in the regulation of vascular tone

1. The greater incidence of hypertension and coronary artery disease in men and post-menopausal women compared with premenopausal women has suggested vascular protective effects of the female sex hormone oestrogen. However, vascular effects of the female sex hormone progesterone and the male sex hormone testosterone have also been suggested. 2. Oestrogen, progesterone and testosterone receptors have been identified in the plasmalemma, cytosol and nuclear compartments of vascular cells. The interaction of sex hormones with their specific receptors triggers not only long-term genomic vascular effects, but also acute non-genomic vascular responses. 3. Sex hormones may activate endothelium-dependent vascular relaxation pathways, including the nitric oxide-cGMP and prostacyclin-cAMP pathways and a hyperpolarizing factor pathway. 4. Sex hormones may also inhibit the mechanisms of vascular smooth muscle contraction, such as [Ca2+]i, protein kinase C and other protein kinases. 5. The sex hormone-induced stimulation of endothelium-dependent vascular relaxation and inhibition of vascular smooth muscle contraction may contribute to the gender differences in vascular tone and may represent potential beneficial vascular effects of hormone-replacement therapy during natural and surgically induced deficiencies of gonadal hormones.

Gender differences in vascular smooth muscle reactivity to increases in extracellular sodium salt

Hypertension is more common in men and postmenopausal women than in premenopausal women, and gender differences in sensitivity to high dietary Na(+) salt have been suggested; however, the vascular mechanisms involved are unclear. We investigated whether increases in the extracellular concentration of Na(+) ([Na(+)](e)) enhance the mechanisms of vascular smooth muscle contraction and whether the vascular effects of [Na(+)](e) exhibit gender differences. Isometric contraction and (45)Ca(2+) influx were measured in endothelium-denuded aortic strips that were isolated from intact male, intact female, castrated male, and ovariectomized (OVX) female Sprague-Dawley rats and incubated in Krebs' solution (2.5 mmol/L Ca(2+)) containing increasing [Na(+)](e) by the addition of 1, 3, 6, 10, 20, and 30 mmol/L NaCl. Increasing [Na(+)](e) for 30 minutes did not increase the resting tone or (45)Ca(2+) influx in any group of rats. Phenylephrine (Phe) caused concentration-dependent increases in contraction and (45)Ca(2+) influx. In vascular strips from intact males, increasing [Na(+)](e) by the addition of 1 to 6 mmol/L NaCl significantly increased the magnitude of Phe contraction and (45)Ca(2+) influx. Further increases in [Na(+)](e) by the addition of 10, 20, and 30 mmol/L NaCl increased Phe-induced (45)Ca(2+) influx but inhibited Phe contraction, possibly because of excessive increases in ionic strength. Preincubation with 2,4-dichlorobenzamil (10(-5) mol/L), inhibitor of the Na(+)-Ca(2+) exchanger, or KB-R7943 (10(-5) mol/L), selective inhibitor of the reverse mode of the Na(+)-Ca(2+) exchanger, abolished the increases in Phe contraction and (45)Ca(2+) influx at increasing [Na(+)](e) obtained by the addition of 1 to 6 mmol/L NaCl. Preincubation in Krebs' solution containing control [Na(+)](e) plus 1 to 6 mmol/L LiCl or N-methyl-D-glucamine did not increase Phe contraction. In intact females, the Phe contraction and Ca(2+) influx were less than those in intact males and were not enhanced with increases in [Na(+)](e). The enhancement of Phe contraction and Ca(2+) influx with increases in [Na(+)](e) were not significantly different between castrated male rats and intact male rats but were greater in OVX female rats than intact female rats. In OVX female rats or castrated male rats treated with 17beta-estradiol (but not 17alpha-estradiol) subcutaneous implants, no significant changes in Phe contraction or Ca(2+) influx with increases in [Na(+)](e) were observed. In OVX female or castrated male rats simultaneously treated with 17beta-estradiol plus the estrogen receptor antagonist ICI 182,780, the Phe contraction and Ca(2+) influx were enhanced with increases in [Na(+)](e). Thus, in intact male rats, small physiological increases in [Na(+)](e) enhance smooth muscle contraction to Phe by a mechanism involving Ca(2+) entry, possibly via the reverse mode of the Na(+)-Ca(2+) exchanger. This mechanism appears to be reduced in the presence of endogenous or exogenous estrogen and thereby protects female rats against excessive increases in vascular reactivity during high dietary Na(+) intake.

1A-779 attenuates angiotensin-(1-7) depressor response in salt-induced hypertensive rats

Chronic infusion of angiotensin-(1-7) [Ang-(1-7)] lowers blood pressure in salt-induced and spontaneously hypertensive (SHR) rats. In the present study, we have examined the acute effect of Ang-(1-7) in salt-induced hypertension using Dahl salt-sensitive rats placed on low (0.3%) or high (8.0% NaCl) salt diets for 2 weeks. Rats fed a high salt diet showed a greater rise in BP than those fed a low salt diet. Ang-(1-7) (24 microg/kg) reduced mean arterial pressure (MAP), enhanced the release of prostacyclin and nitric oxide, and suppressed thromboxane A(2) levels. A-779 (48 microg/kg, i.v), a selective Ang-(1-7) antagonist, partially blocked these effects of Ang-(1-7). The Ang-(1-7)-induced depressor response observed in these animals was related to an increase in vasodilatory prostanoids, a decrease in the constrictor prostanoid thromboxane A(2), and an increase in nitric oxide levels in both plasma and isolated aortic rings.

The calciuric response to dietary salt of Dahl salt-sensitive and salt-resistant female rats

BACKGROUND

We have shown previously that the calciuric response to salt does not differ in Dahl salt-sensitive (S) and salt-resistant (R) male rats. Clinical studies with women, however, suggest an effect of salt sensitivity on the calciuric response to salt. The objective of this study was to determine whether there is an effect of salt sensitivity on the calciuric response to salt of female S and R rats.

METHOD

Dahl S and R female rats were fed high- (8%) or low- (0.3%) salt diets for 3 weeks. The rats were placed in metabolic cages for 24-hour urine collection at baseline and weekly (for sodium and calcium determination).

RESULTS

Blood pressure of female S rats was 177+/-3.0 mm Hg at week 3 of high salt intake compared with 96+/-1 mm Hg for female R rats. Female S rats excreted significantly more calcium than female R rats at baseline (P < 0.001), when fed a nonpurified diet, and during high salt intake (P = 0.004). Salt sensitivity significantly increased calcium excretion, water intake, and urine output when rats were fed a high-salt diet. Calcium excretion, water intake, and urine output of female S rats were time-dependent during high salt intake. Plasma 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D concentrations were markedly lower in female S rats fed a high-salt diet, but not in female R rats. Plasma parathyroid hormone and 1,25-dihydroxyvitamin D concentrations did not significantly differ between female S and R rats, but plasma concentrations of these two hormones at week 3 were significantly higher in S rats fed a high-salt diet compared with S rats fed a low-salt diet.

CONCLUSIONS

Our data indicate that the calciuric response to salt is greater in female S compared with female R rats, thus supporting findings on the effect of salt sensitivity reported in several clinical studies with women. The greater calciuric response to salt of female S rats compared with female R rats, which was not seen in a previous study when male S rats were compared to male R rats, suggest a gender difference in the calciuric response to salt.