Kathryn Sandberg

Sex differences in primary hypertension

Men have higher blood pressure than women through much of life regardless of race and ethnicity. This is a robust and highly conserved sex difference that it is also observed across species including dogs, rats, mice and chickens and it is found in induced, genetic and transgenic animal models of hypertension. Not only do the differences between the ovarian and testicular hormonal milieu contribute to this sexual dimorphism in blood pressure, the sex chromosomes also play a role in and of themselves. This review primarily focuses on epidemiological studies of blood pressure in men and women and experimental models of hypertension in both sexes. Gaps in current knowledge regarding what underlie male-female differences in blood pressure control are discussed. Elucidating the mechanisms underlying sex differences in hypertension may lead to the development of anti-hypertensives tailored to ones sex and ultimately to improved therapeutic strategies for treating this disease and preventing its devastating consequences.

Ovariectomy Augments Hypertension in Aging Female Dahl Salt-Sensitive Rats

The ovariectomized (OVX) Dahl salt-sensitive (DS) rat fed a low-salt diet is a model of postmenopausal hypertension. In addition to estrogen loss, aging can also contribute to postmenopausal hypertension. We hypothesized that: (1) female DS rats on a low-salt diet become hypertensive with age; (2) ovariectomy accelerates age-dependent hypertension in the DS rat caused by estrogen depletion; and (3) this hypertension correlates with increased type 1 angiotensin receptor (AT1R) number (Bmax). Blood pressure was monitored by telemetry from 3 to 12 months and AT1R Bmax was determined by Scatchard analysis in glomeruli and adrenal cortex. Three groups of DS rats were studied: intact, OVX, and 17&bgr;-estradiol–replaced OVX (OVX+E). In intact rats, aging to 12 months resulted in hypertension (159±6 mm Hg) and an 82% decrease in estrogen. Blood pressure in OVX was significantly higher than OVX+E through 12 months of age (173±4 versus 150±8 mm Hg). At 4 months, OVX increased AT1R Bmax compared with intact and OVX+E in both glomeruli and adrenal cortex. Aging also increased AT1R Bmax in these tissues in intact rats. In summary, female DS rats fed a low-salt diet have hypertension develop with age, that is accelerated by OVX and attenuated by estrogen replacement. Concurrently, AT1Rs are upregulated by age and OVX, which is prevented by estrogen replacement. This study suggests that an increased activity of the renin angiotensin system contributes to the development of hypertension, and estrogen protects against this process.

Glomerulosclerosis and Tubulointerstitial Fibrosis are Attenuated with 17β-Estradiol in the Aging Dahl Salt Sensitive Rat

This study examined the effects of estrogen deficiency by ovariectomy (OVX) and 17beta-estradiol (E(2)) replacement (OVX+E(2)) on glomerulosclerosis and tubulointerstitial fibrosis and the mechanisms contributing to these changes, including expression of collagen type IV and laminin, transforming growth factor-beta (TGF-beta), and activity of matrix metalloproteinases (MMP) in the kidneys of young (4 mo [4M]) and aged (12 mo [12M]) Dahl salt-sensitive (DSS) rats maintained on a low-salt (0.1% NaCl) diet. While normal renal morphology was observed in the 4M rats in all treatment groups, moderate to severe glomerulosclerosis (glomerulosclerotic index [GSI]: 4M, 0.22 +/- 0.09 versus 12M, 1.43 +/- 0.17; P < 0.001) and cortical tubulointerstitial fibrosis (CTIFI: 4M, 0 versus 12M, 57.1 +/- 4.9; P < 0.01) was observed in the 12M rats. The severity of glomerulosclerosis and cortical tubulointerstitial fibrosis in the 12M group was augmented with OVX (GSI, 3.27 +/- 0.34; CTIFI, 74.4 +/- 9.2; P < 0.01 versus Intact at 12M) and attenuated with E(2) replacement ([GSI], 1.09 +/- 0.09; CTIFI, 49.2 +/- 6.8). In the 12M animals, OVX was also associated with increased deposition and expression of laminin (Intact, 228.1 +/- 6.7; OVX, 277.4 +/- 9.6 AU; P < 0.01), increased expression of TGF-beta (Intact, 85.0 +/- 23.0; OVX, 178.0 +/- 20.5 AU; P < 0.001), and decreased activity of cortical MMP-9 (Intact, 3.8 +/- 0.8; OVX, 2.4 +/- 0.6 AUC; P < 0.01). E(2) replacement opposed these effects (laminin, 229.9 +/- 6.2 AU; TGF-beta, 101.3 +/- 25.2 AU; MMP-9, 5.2 +/- 0.2 AUC). The severity of the disease in the 12M rats correlated with a modest decrease in creatinine clearance (Intact, 0.26 +/- 0.01; OVX, 0.22 +/- 0.01; OVX+E(2), 0.28 +/- 0.01 mg/min per 100 g) and increase in BUN (Intact, 20.3 +/- 2.1; OVX, 32.6 +/- 5.1; OVX+E(2), 24.3 +/- 2.4 mg/dl). The authors conclude that E(2) is renoprotective in the aging DSS rat by attenuating glomerulosclerosis and tubulointerstitial fibrosis.

Characterization of [3H]hemicholinium-3 binding associated with neuronal choline uptake sites in rat brain membranes.

Hemicholinium-3 (HCh-3) is a potent and specific inhibitor of the high-affinity choline transport process (HAChT) localized on cholinergic neurons. In this study, the specific binding of [3H]HCh-3 (120 Ci/mmol) was characterized in crude synaptic membranes prepared from rat brain. The binding of [3H]HCh-3 to forebrain membranes was saturable, reversible and specific with an apparent Kd under optimal conditions of 35 nM and a Bmax of 56 fmol/mg protein. The potency of various HAChT inhibitors correlated with their apparent affinities for the specific [3H]HCh-3 binding site. The specific binding of [3H]HCh-3 exhibited an uneven regional distribution in the adult rat brain that corresponded to the activity of the HAChT in these regions. Transsection of the fornix, which causes a degeneration of the septal hippocampal cholinergic pathway, resulted in comparable reductions of the specific [3H]HCh-3 binding and the specific activity of choline acetyltransferase, a presynaptic marker for cholinergic terminals in the hippocampal formation; the lesion did not affect the specific activity of glutamic acid decarboxylase, a presynaptic marker for GABAergic neurons within the hippocampus. Maximal binding occurred in the presence of 200 mM NaCl: potassium, lithium, rubidium and calcium substituted poorly for sodium; and bromide, fluoride, iodide, sulfate and phosphate were less effective anions than chloride. Increasing concentrations of NaCl increased the affinity of the site for [3H]HCh-3 with no significant effect on the maximal number of sites; the enhancement of affinity was due to a selective slowing of the rate of dissociation of the ligand from its binding site. These findings indicate that [3H]HCh-3 binds to the carrier site mediating the HAChT on cholinergic neurons; thus, this radioligand may be a useful probe for investigating this presynaptic component (HAChT) of cholinergic neurons.

Sex chromosome effects unmasked in angiotensin II-induced hypertension

Sex differences in mean arterial pressure (MAP) are reported in many experimental models of hypertension and are ascribed to gonadal sex based on studies showing that gonadectomy and gonadal hormone replacement affect MAP. The interpretation of these studies, however, has been confounded by differences in the sex chromosome complement (XX versus XY). To investigate the sex chromosome complement independent of gonadal sex, we used the 4 core genotype mouse model in which gonadal sex is separated from the sex chromosome complement enabling comparisons among XX and XY females and XX and XY males. We found that, in the gonadectomized (GDX) 4 core genotype, MAP after 2 weeks of angiotensin II infusion (200 ng/kg per minute) was greater in XX than XY (MAP [in millimeters of mercury]: GDX-XX-female, 148±4.5; GDX-XY-female, 133±4.4; GDX-XX-male, 149±9.4; GDX-XY-male, 138±5.5; P<0.03, XX versus XY; n=8 to 9 per group). In contrast, no sex chromosome effects were found on heart rate, body weight, or plasma angiotensin II 2 weeks after angiotensin II infusion. This study suggests that, in addition to effects of gonadal hormones on blood pressure, X- or Y-linked genes, parental imprinting, or X mosaicism contributes to sex differences in hypertension. Furthermore, the finding that MAP was greater in XX mice compared with XY mice in the GDX state suggests that adverse sex chromosome effects encoded within the XX sex chromosome complement could contribute to hypertension in women with ovarian hormone deficiency, such as postmenopausal women and women with premature ovarian failure.

Ontogeny of angiotensin II receptors.

Aside from the well known role of angiotensin II (Ang II) in blood pressure regulation and fluid homeostasis, accumulating evidence suggests that the octapeptide hormone also plays a role in growth and development. There are two major classes of Ang II receptors (AT1and AT2) which mediate Ang II action. Both classes are members of the large superfamily of seven transmembrane domain spanning receptors. Fetal tissue express high levels of AT receptors. Throughout fetal and postpartum life, the AT1and AT2tissue distribution changes dramatically. The evolution of each receptor type is distinct and varies according to the organ. Thus, the different patterns of temporal expression of each receptor class could be related to various roles that Ang II may play during development.

Vasopressin V2 Receptor Binding Is Down-Regulated during Renal Escape from Vasopressin-Induced Antidiuresis1

This study evaluated whether renal escape from vasopressin-induced antidiuresis is associated with alterations of vasopressin V2 receptor binding in the kidney inner medulla. A radioligand binding assay was developed using a novel iodinated vasopressin V2 receptor antagonist to analyze vasopressin V2 receptor binding in kidney inner medullary tissue from three groups of rats: normal rats maintained on ad libitum water intake, rats treated with 1-deamino-[8-d-arginine]vasopressin (DDAVP), and rats treated with DDAVP that were also water loaded to induce renal escape from antidiuresis. Analysis of the binding data showed that DDAVP treatment reduced vasopressin V2 receptor binding to 72% of normal levels. Water loading induced a marked further down-regulation of vasopressin V2 receptor binding. This receptor down-regulation began by day 2 of water loading, which correlated with the initiation of renal vasopressin escape; by day 3 of water loading, vasopressin V2 receptor expression fell to 43% of DDAVP-trea...

Role of angiotensin‐converting enzyme 2 and angiotensin(1–7) in 17β‐oestradiol regulation of renal pathology in renal wrap hypertension in rats

17β‐Oestradiol (E2)‐mediated inhibition of angiotensin‐converting enzyme (ACE) protects the E2‐replete kidney from the progression of hypertensive renal disease. Angiotensin‐converting enzyme 2 (ACE2), a homologue of ACE, counters the actions of ACE by catalysing the conversion of angiotensin II (Ang II) to angiotensin(1–7) [Ang(1–7)]. We investigated E2 regulation of ACE2 in the renal wrap (RW) model of hypertension in rats. After 6 weeks on a high‐sodium diet (4% NaCl), the activity of ACE2 was reduced in the renal cortex by 31%, which was mirrored by similar decreases in ACE2 protein (30%) and mRNA expression (36%) in the ovariectomized RW rat (RW‐OVX); E2 replacement prevented these effects. The RW‐OVX rats exhibited greater renal injury, including 1.7‐fold more tubulointerstitial fibrosis and 1.6‐fold more glomerulosclerosis than E2‐replete females (RW‐Intact and RW‐OVX+E2). Angiotensin(1–7) infusion prevented these exacerbating effects of ovariectomy on renal pathology; no differences in indicators of renal injury were observed between RW‐OVX‐Ang(1–7) and RW‐Intact rats. These renal protective effects of Ang(1–7) infusion were not attributable to increased ACE2 activity or to changes in heart rate or body weight, since these parameters were unchanged by Ang(1–7) infusion. Furthermore, Ang(1–7) infusion did not attenuate renal injury by reducing mean arterial pressure (MAP), since infusion of the peptide did not lower MAP but rather caused a slight increase during a 6 week chronic treatment for Ang(1–7). These results suggest that E2‐mediated upregulation of renal ACE2 and the consequent increased Ang(1–7) production contribute to E2‐mediated protection from hypertensive renal disease. These findings have implications for E2‐deficient women with hypertensive renal disease and suggest that therapeutics targeted towards increasing ACE2 activity and Ang(1–7) levels will be renal protective.

Cholinergic lesion of the striatum impairs acquisition and retention of a passive avoidance response.

Significant impairments in the acquisition and retention of a step-down passive avoidance task were found in rats with striatal lesions induced by the cholinergic neurotoxin AF64A. No significant differences between control and AF64A-injected rats were found in sensitivity to electric shock or in various measures of spontaneous locomotor activity. Striatal choline acetyltransferase (CAT) activity was significantly decreased in AF64A-treated rats compared with controls, whereas glutamic acid decarboxylase (GAD) activities were not. Furthermore, there were no significant differences between groups in activities of CAT and GAD in either the cortex or the hippocampus, results that support the specificity of the lesion to the striatum. The passive avoidance deficits found in these rats after intrastriatal injection of AF64A support a role for the striatal cholinergic system in complex behavioral processes.

Sex Differences in T-Lymphocyte Tissue Infiltration and Development of Angiotensin II Hypertension

There is extensive evidence that activation of the immune system is both necessary and required for the development of angiotensin II (Ang II)–induced hypertension in males. The purpose of this study was to determine whether sex differences exist in the ability of the adaptive immune system to induce Ang II–dependent hypertension and whether central and renal T-cell infiltration during Ang II–induced hypertension is sex dependent. Recombinant activating gene-1 (Rag-1)–/– mice, lacking both T and B cells, were used. Male and female Rag-1–/– mice received adoptive transfer of male CD3+ T cells 3 weeks before 14-day Ang II infusion (490 ng/kg per minute). Blood pressure was monitored via tail cuff. In the absence of T cells, systolic blood pressure responses to Ang II were similar between sexes (&Dgr;22.1 mm Hg males versus &Dgr;18 mm Hg females). After adoptive transfer of male T cells, Ang II significantly increased systolic blood pressure in males (&Dgr;37.7 mm Hg; P<0.05) when compared with females (&Dgr;13.7 mm Hg). Flow cytometric analysis of total T cells and CD4+, CD8+, and regulatory Foxp3+-CD4+ T-cell subsets identified that renal lymphocyte infiltration was significantly increased in males versus females in both control and Ang II–infused animals (P<0.05). Immunohistochemical staining for CD3+-positive T cells in the subfornical organ region of the brain was increased in males when compared with that in females. These results suggest that female Rag-1–/– mice are protected from male T-cell–mediated increases in Ang II–induced hypertension when compared with their male counterparts, and this protection may involve sex differences in the magnitude of T-cell infiltration of the kidney and brain.