Role of the adrenal medullae in male and female DOCA-salt hypertensive rats

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.

Dexamethasone Causes Hypertension in Rats Even Under Chemical Blockade of Peripheral Sympathetic Nerves

Synthetic glucocorticoids (GCs) are widely used to treat inflammatory conditions. However, chronic use of GCs can lead to hypertension. The cause of this undesired side effect remains unclear. Previously, we developed an in vivo rat model to study the mechanisms underlying hypertension induced by the chronic administration of the potent synthetic GC, dexamethasone (DEX) and found that the catecholamine biosynthetic pathway plays an important role. In the current study, we used this model to investigate the role of the adrenal medulla, renal nerves, and other peripheral sympathetic nerves in DEX-induced hypertension. After 5 days of baseline telemetric recording of mean arterial pressure (MAP) and heart rate (HR), rats were subjected to one of the following treatments: renal denervation (RDNX), adrenal medullectomy (ADMX), 6-hydroxydopamine (6-OHDA, 20 mg/kg, i.p.) to induce chemical sympathectomy, or a combination of ADMX and 6-OHDA. On day 11, the animals received vehicle (VEH) or DEX in drinking water for 7 days, with the latter causing an increase in MAP in control animals. ADMX and RDNX by themselves exacerbated the pressor effect of DEX. In the chemical sympathectomy group, DEX still caused a rise in MAP but the response was lower (ΔMAP of 6-OHDA/DEX < VEH/DEX, p = 0.039). However, when ΔMAP was normalized to day 10, 6-OHDA + DEX did not show any difference from VEH + DEX, certainly not an increase as observed in DEX + ADMX or RDNX groups. This indicates that sympathetic nerves do not modulate the pressor effect of DEX. TH mRNA levels increased in the adrenal medulla in both VEH/DEX (p = 0.009) and 6-OHDA/DEX (p = 0.031) groups. In the 6-OHDA group, DEX also increased plasma levels of norepinephrine (NE) (p = 0.016). Our results suggest that the activation of catecholamine synthetic pathway could be involved in the pressor response to DEX in animals even under chemical sympathectomy with 6-OHDA.

Female C57BL/6J mice lacking the circadian clock protein PER1 are protected from nondipping hypertension

The circadian clock is integral to the maintenance of daily rhythms of many physiological outputs, including blood pressure. Our laboratory has previously demonstrated the importance of the clock protein period 1 (PER1) in blood pressure regulation in male mice. Briefly, a high-salt diet (HS; 4% NaCl) plus injection with the long-acting mineralocorticoid deoxycorticosterone pivalate (DOCP) resulted in nondipping hypertension [<10% difference between night and day blood pressure (BP) in Per1-knockout (KO) mice but not in wild-type (WT) mice]. To date, there have been no studies that have examined the effect of a core circadian gene KO on BP rhythms in female mice. The goal of the present study was to determine whether female Per1-KO mice develop nondipping hypertension in response to HS/DOCP treatment. For the first time, we demonstrate that loss of the circadian clock protein PER1 in female mice does not significantly change mean arterial pressure (MAP) or the BP rhythm relative to female C57BL/6 WT control mice. Both WT and Per1-KO female mice experienced a significant increase in MAP in response to HS/DOCP. Importantly, however, both genotypes maintained a >10% dip in BP on HS/DOCP. This effect is distinct from the nondipping hypertension seen in male Per1-KO mice, demonstrating that the female sex appears to be protective against PER1-mediated nondipping hypertension in response to HS/DOCP. Together, these data suggest that PER1 acts in a sex-dependent manner in the regulation of cardiovascular rhythms.

The chemerin knockout rat reveals chemerin dependence in female, but not male, experimental hypertension

Measures of the adipokine chemerin are elevated in multiple cardiovascular diseases, including hypertension, but little mechanistic work has been done to implicate chemerin as being causative in such diseases. The chemerin knockout (KO) rat was created to test the hypothesis that removal of chemerin would reduce pressure in the normal and hypertensive state. Western analyses confirmed loss of chemerin in the plasma and tissues of the KO vs. wild-type (WT) rats. Chemerin concentration in plasma and tissues was lower in WT females than in WT males, as determined by Western analysis. Conscious male and female KO rats had modest differences in baseline measures vs. the WT that included systolic, diastolic, mean arterial and pulse pressures, and heart rate, all measured telemetrically. The mineralocorticoid deoxycorticosterone acetate (DOCA) and salt water, combined with uninephrectomy as a hypertensive stimulus, elevated mean and systolic blood pressures of the male KO higher than the male WT. By contrast, all pressures in the female KO were lower than their WT throughout DOCA-salt treatment. These results revealed an unexpected sex difference in chemerin expression and the ability of chemerin to modify blood pressure in response to a hypertensive challenge.-Watts, S. W., Darios, E. S., Mullick, A. E., Garver, H., Saunders, T. L., Hughes, E. D., Filipiak, W. E., Zeidler, M. G., McMullen, N., Sinal, C. J., Kumar, R. K., Ferland, D. J., Fink, G. D. The chemerin knockout rat reveals chemerin dependence in female, but not male, experimental hypertension.

DOCA-Salt Hypertension: an Update

Hypertension is a multifaceted disease that is involved in ∼40% of cardiovascular mortalities and is the result of both genetic and environmental factors. Because of its complexity, hypertension has been studied by using various models and approaches, each of which tends to focus on individual organs or tissues to isolate the most critical and treatable causes of hypertension and the related damage to end-organs. Animal models of hypertension have ranged from Goldblatt's kidney clip models in which the origin of the disease is clearly renal to animals that spontaneously develop hypertension either through targeted genetic manipulations, such as the TGR(mRen2)27, or selective breeding resulting in more enigmatic origins, as exemplified by the spontaneously hypertensive rat (SHR). These two genetically derived models simulate the less-common human primary hypertension in which research has been able to define a Mendelian linkage. Several models are more neurogenic or endocrine in nature and illustrate that crosstalk between the nervous system and hormones can cause a significant rise in blood pressure (BP). This review will examine one of these neurogenic models of hypertension, i.e., the deoxycorticosterone acetate (DOCA), reduced renal mass, and high-salt diet (DOCA-salt) rodent model, one of the most common experimental models used today. Although the DOCA-salt model is mainly believed to be neurogenic and has been shown to impact the central and peripheral nervous systems, it also significantly involves many other body organs.

Antihypertensive and antioxidant effects of protocatechuic acid in deoxycorticosterone acetate-salt hypertensive rats

Protocatechuic acid (PCA) is a natural antioxidant with beneficial cardiovascular properties. In this study, the effect of supplementation with PCA was investigated in deoxycorticosterone acetate (DOCA)-salt hypertension. Male Wistar rats received DOCA (25 mg/kg, s.c.) twice weekly and 1% NaCl in drinking water and simultaneously treated with PCA (50, 100 and 200 mg/kg, p.o.) for 4 weeks. Systolic blood pressure (SBP) was detected using tail-cuff method. Electrolytes including Na⁺, K⁺ and chloride, catalase activity, glutathione, total antioxidant capacity, malondialdehyde (MDA) and hydroperoxides concentration were measured in serum samples. Body and organs weight, water intake and, kidney and heart histopathology were also evaluated. Administration of PCA reversed the changes caused by DOCA-salt approximately at all doses. At the lowest dose, PCA significantly decreased SBP (132.5 ± 4.0 vs 152.3 ± 4.5 mmHg, P < .05), serum sodium (138.5  ± 1.52 vs 141 ± 1.50, P < .05) and chloride level (101.6 ± 1.47 vs 110 ± 1.39, P < .01) and raised serum potassium level (3.8 ± 0.09 vs 3.1 ± 0.17, P < .05) compared with DOCA-salt hypertensive rats. PCA increased serum catalase activity, total antioxidant capacity and glutathione concentration and reduced MDA and hydroperoxides levels. PCA also improved organ weight changes, reduced water intake and moderately prevented histopathological changes of kidney and heart upon DOCA-salt administration. The present study indicates the antihypertensive and antioxidant effects of PCA against DOCA-salt hypertension.

Influence of sex on cardiovascular drug responses: role of estrogen

In this review we discuss the sex/estrogen-specific modulation of cardiovascular function and responses to current therapeutics. We discuss how anatomical differences such as a smaller kidney size, and lower glomerular filtration rate in females, reduce the clearance and increase the toxicity of some drugs in females. Other important sex differences include the dampening effect of estrogen on central sympathetic and renin angiotensin systems. Further, we discuss how a shift in myocardial redox status leads to paradoxical transformation of estrogen into a pro-inflammatory hormone. Finally, the review, along with cited recent publications, identify some areas that need further investigation to advance our understanding of the sex differences in cardiovascular disease outcomes to help develop female specific interventions for these anomalies.

Mineralocorticoid receptors and the heart, multiple cell types and multiple mechanisms: a focus on the cardiomyocyte

MR (mineralocorticoid receptor) activation in the heart plays a central role in the development of cardiovascular disease, including heart failure. The MR is present in many cell types within the myocardium, including cardiomyocytes, macrophages and the coronary vasculature. The specific role of the MR in each of these cell types in the initiation and progression of cardiac pathophysiology is not fully understood. Cardiomyocyte MRs are increasingly recognized to play a role in regulating cardiac function, electrical conduction and fibrosis, through direct signal mediation and through paracrine MR-dependent activity. Although MR blockade in the heart is an attractive therapeutic option for the treatment of heart failure and other forms of heart disease, current antagonists are limited by side effects owing to MR inactivation in other tissues (including renal targets). This has led to increased efforts to develop therapeutics that are more selective for cardiac MRs and which may have reduced the occurrence of side effects in non-cardiac tissues. A major clinical consideration in the treatment of cardiovascular disease is of the differences between males and females in the incidence and outcomes of cardiac events. There is clinical evidence that female sensitivity to endogenous MRs is more pronounced, and experimentally that MR-targeted interventions may be more efficacious in females. Given that sex differences have been described in MR signalling in a range of experimental settings and that the MR and oestrogen receptor pathways share some common signalling intermediates, it is becoming increasingly apparent that the mechanisms of MRs need to be evaluated in a sex-selective manner. Further research targeted to identify sex differences in cardiomyocyte MR activation and signalling processes has the potential to provide the basis for the development of cardiac-specific MR therapies that may also be sex-specific.

Involvement of protein kinase C-CPI-17 in androgen modulation of angiotensin II-renal vasoconstriction

AIMS

Previous studies suggested that androgens augmented renal vascular responses to angiotensin II (Ang II). The protein kinase C (PKC)-CPI-17 pathway is involved in vascular constriction. We tested the hypothesis that this pathway may contribute to androgenic amplification of Ang II-renal vasoconstriction in the New Zealand genetically hypertensive (NZGH) rat.

METHODS AND RESULTS

NZGH underwent sham operation, castration, or castration with testosterone replacement at 5 weeks of age. When the rats were 16-17 weeks of age, mean arterial pressure (MAP) and renal vascular resistance (RVR) responses to intravenous Ang II infusion (20, 40, and 80 ng/kg/min) were recorded before and after treatment with a PKC inhibitor, chelerythrine. mRNA expression of PKC isoforms and CPI-17 protein expression were analysed in renal cortex. MAP and RVR responses to Ang II were enhanced in androgen-replete NZGH. The Ang II-induced increase in RVR was significantly lower in castrated NZGH (ranged from 100 +/- 8% to 161 +/- 9% of baseline) than in sham-operated NZGH (ranged between 123 +/- 3% and 237 +/- 19% of baseline). Testosterone treatment restored RVR responses to Ang II in castrated rats. Chelerythrine treatment markedly reduced the MAP and RVR responses to Ang II in each group and attenuated the differential MAP and RVR responses to Ang II amongst the three groups. PKCdelta and PKCepsilon mRNA levels were significantly reduced by castration and increased by testosterone treatment. In contrast, no significant differences in protein expression were detected for these PKC isoforms. Castration decreased while testosterone treatment increased CPI-17 and phospho-CPI-17 expression.

CONCLUSION

Collectively, these results suggest that androgens modulate renal vascular responses to Ang II in part via an effect on the PKC-CPI-17 signalling pathway.

Down-regulation of adrenal neuronal nitric oxide synthase mRNAs and proteins after deoxycorticosterone acetate-salt treatment in rats

The aim of this study was to evaluate the possible changes of adrenal neuronal nitrite oxide synthase (nNOS) messenger RNA (mRNA) and protein of rats after deoxycorticosterone acetate (DOCA)-salt treatment. We determined adrenal nNOS expression in 12 vehicle-treated and 13 DOCA-salt-treated rats by in situ hybridization, immunohistochemistry, and multiplex RT-PCR methods. Adrenal nNOS was also detected by Western blot in five vehicle-treated and five DOCA-salt-treated rats. The results showed that adrenal nNOS mRNA and nNOS immunoreactivities were mainly localized in the medulla and some in the regions of zona glomerulosa. DOCA-salt treatment inactivated nNOS mRNA and peptide expression prominent in the adrenal medulla and slight in the zona glomerulosa. The relative quantities of nNOS mRNA in the adrenals of the DOCA-salt-treated group was 8.8-fold decreased. At the same time, the relative quantities of steroid acute regulatory protein mRNA and phenylethanolamine N-methyltransferase mRNA in the adrenals of the DOCA-salt-treated group were significantly decreased. Western blots showed that total adrenal nNOS were 3.7-fold down-regulated after DOCA-salt treatment. Our results indicated that the down-regulation of adrenal nNOS synthesis might be associated with the inactivation of adrenal function in face of volume expansion.

Deletion of the neuropeptide Y (NPY) Y1 receptor gene reveals a regulatory role of NPY on catecholamine synthesis and secretion

The contribution of neuropeptide Y (NPY), deriving from adrenal medulla, to the adrenosympathetic tone is unknown. We found that in response to NPY, primary cultures of mouse adrenal chromaffin cells secreted catecholamine, and that this effect was abolished in cultures from NPY Y(1) receptor knockout mice (Y(1)-/-). Compared with wild-type mice (Y(1)+/+), the adrenal content and constitutive release of catecholamine were increased in chromaffin cells from Y(1)-/- mice. In resting animals, catecholamine plasma concentrations were higher in Y(1)-/- mice. Comparing the adrenal glands of both genotypes, no differences were observed in the area of the medulla, cortex, and X zone. The high turnover of adrenal catecholamine in Y(1)-/- mice was explained by the enhancement of tyrosine hydroxylase (TH) activity, although no change in the affinity of the enzyme was observed. The molecular interaction between the Y(1) receptor and TH was demonstrated by the fact that NPY markedly inhibited the forskolin-induced luciferin activity in Y(1) receptor-expressing SK-N-MC cells transfected with a TH promoter sequence. We propose that NPY controls the release and synthesis of catecholamine from the adrenal medulla and consequently contributes to the sympathoadrenal tone.

Castration reduces blood pressure and autonomic venous tone in male spontaneously hypertensive rats

OBJECTIVE

The development of arterial hypertension is sexually dimorphic. Venous tone is elevated in the spontaneously hypertensive rat model of hypertension. This study tested the hypothesis that endogenous androgens exacerbate venous tone in the developmental stages of spontaneous hypertension.

METHODS

Male spontaneously hypertensive rats (SHRs) were subjected to sham operation, castration or castration + testosterone treatment. Ten-week-old SHR rats were instrumented for the measurement of arterial and venous pressure. A balloon catheter was advanced into the right atrium. Mean circulatory filling pressure (MCFP), an index of venous tone, was calculated. Mean arterial pressure (MAP) and MCFP were recorded from conscious rats. Postsynaptic adrenergic responsiveness was assessed by constructing cumulative dose-response curves to norepinephrine (NE). Baseline values and responsiveness to NE were obtained before and after autonomic blockade.

RESULTS

MAP and MCFP were significantly reduced in castrated (MAP, 130 +/- 4 mmHg; MCFP, 5.5 +/- 0.2 mmHg) versus sham-operated SHRs (MAP, 149 +/- 5 mmHg; MCFP, 6.7 +/- 0.3 mmHg) or castrated + testosterone-treated SHRs (MAP, 145 +/- 6 mmHg; MCFP, 7.1 +/- 0.4 mmHg). Ganglion blockade abolished these differences in MAP and MCFP. Infusion of NE caused dose-dependent increases in MAP and MCFP. The MAP responses in castrated SHRs were displaced to the right of those for sham and castrated + testosterone-treated SHRs. This was not evident in the venous circulation, where there were no marked differences in the NE dose-MCFP response curves.

CONCLUSION

Accordingly we conclude that endogenous male sex steroids contribute to the elevated arterial and venous pressures observed in the SHR.

Sexual dimorphism in angiotensin II-induced hypertension and vascular alterations

Sex differences in the degree of high blood pressure have been described in several forms of experimental animal models of hypertension. However, the influence of sex on angiotensin II-induced hypertension has not been studied. In the present study, we investigated and compared the effects of chronic angiotensin II treatment on blood pressure and vascular function in male and female rats. Chronic treatment with angiotensin II (0.7 mg/kg daily for 10 d) significantly raised arterial blood pressure in male but not female Sprague-Dawley rats; it upregulated the NAD(P)H oxidase gp67 phox subunit in the aorta of male but not female rats; and it exaggerated the vasoconstrictor responses to norepinephrine and serotonin in the mesenteric vascular bed (MVB) of male but not female rats. Vasodilator responses to acetylcholine (ACh) but not papaverine (PPV) or isoprenaline (ISO) were reduced in the MVB of angiotensin II-treated male but not female rats. ACh, but not PPV or ISO dilatory responses were potentiated in the MVB of angiotensin II-treated female rats. The present findings demonstrate that exogenous angiotensin II upregulates aortic NAD(P)H oxidase gp67 phox subunit, and induces hypertension and mesenteric vascular dysfunction only in male rats.

Noradrenergic content and turnover rate in kidney and heart shows gender and strain differences

The objective of this study was to compare strain and gender differences in kidney and heart norepinephrine (NE) content and turnover rate in normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR, SHR/a, and SHR/y). Our laboratory has shown that the Y chromosome has a significant effect on blood pressure in the SHR model of hypertension through the use of two new rat stains, SHR/a and SHR/y, to study the Y chromosome. SHR/a have a SHR autosomal genetic background with a WKY Y chromosome, whereas the SHR/y rats have a WKY autosomal genetic background with a SHR Y chromosome. Tissues were homogenized after alpha-methyl-DL-p-tyrosine injection and analyzed for NE. The male kidney NE content was significantly lower in the WKY compared with the SHR, SHR/y, and SHR/a. Kidney and heart NE content was significantly higher in females compared with males in all strains except the SHR/y. The WKY and SHR/y females had significantly lower kidney NE turnover rates, and the SHR and SHR/a females had significantly higher kidney NE turnover rates than strain-matched males. This study suggests both a strain and gender difference in sympathetic nervous system activity through noradrenergic neurotransmission.

gamma-Aminobutyric acid (GABA)--A function and binding in the paraventricular nucleus of the hypothalamus in chronic renal-wrap hypertension

The goal of this study was to determine whether gamma-aminobutyric acid (GABA)ergic transmission and GABA binding are altered in chronic renal-wrap hypertension. Three groups of hypertensive and sham-operated rats were prepared for separate protocols. Four weeks later, the animals were prepared with femoral artery catheters for the measurement of mean arterial pressure. In all groups, blood pressure was significantly higher in the renal-wrapped animals. In the first study, bilateral microinjection of the GABA-A antagonist, bicuculline (50 pmol/site), into the paraventricular nucleus of the hypothalamus (PVN) caused a greater increase in arterial pressure (21.9+/-1.4 versus 16.7+/-1.8 mm Hg, P<0.05) and heart rate (135+/-15 versus 98+/-12 bpm, P=0.064) in hypertensive rats. [(3)H]Flunitrazepam was used to measure binding to the GABA-A receptor. Magnocellular neurons and the adjacent medial parvicellular neurons had more intense binding compared with the remainder of the PVN. B(max) was greater for the higher density binding area; the K(d) value was less in the high-density region. There were no differences in these parameters between normotensive and hypertensive animals. Competitive reverse transcription-polymerase chain reaction was used to measure the expression of mRNA for the alpha(1) subunit of the GABA-A receptor. No difference was observed in the mRNA between renal-wrapped and sham-operated rats. In summary, inhibition of GABA-A receptors in the PVN is augmented in the chronic phase of hypertension and is unrelated to a change in the expression of the number or affinity to the receptor. These findings suggest that the greater GABAergic activity is the result of an increase in GABA release in the PVN in chronic renal-wrap hypertension.

Deoxycorticosterone acetate-salt hypertensive rats display gender-related differences in ET(B) receptor-mediated vascular responses

1. Male DOCA-salt rats exhibit vasoconstriction upon ET(B) activation. Because hypertension is less severe in female than male DOCA rats, we hypothesized that female DOCA rats would display attenuated ET(B) vasoconstrictor responses. 2. Uninephrectomized Wistar rats received DOCA and drinking water containing NaCl/KCl. Control rats received vehicle and tap water. Systolic blood pressure was higher in male vs female DOCA rats. Responses to endothelin-1 (ET-1), IRL-1620, an ET(B) agonist, and acetylcholine were evaluated in isolated aortas and in vivo in the mesenteric microcirculation. 3. Endothelium-denuded aortas from male, but not female, DOCA rats displayed increased sensitivity to ET-1. IRL-1620 contracted aortas from male DOCA rats, but not control or female DOCA aortas. Noradrenaline-constricted and endothelium-intact aortas from male, but not female, DOCA rats displayed increased relaxation to IRL-1620 compared to control aortas. 4. In vivo, increased vasoconstriction to ET-1 was observed in male and female DOCA rats. IRL-1620 induced vasodilation in control rats, but vasoconstriction in male DOCA rats. There were minimal changes in diameter in vessels from female DOCA rats. 5. The initial fall in blood pressure induced by ET-1 and IRL-1620 was attenuated in male DOCA rats. Bosentan, a mixed ET(A)/ET(B) receptor antagonist, lowered blood pressure in male and female DOCA rats, but a greater and marked decrease occurred in the male DOCA group. 6. The gender-related differences in ET-1/ET(B)-mediated effects both in the vasculature and blood pressure suggest that sex-related functional up-regulation of ET(B) receptors may play a role in the more severe hypertension in male DOCA hypertensive rats.

Cardiovascular and renal effects of central administration of a mineralocorticoid receptor antagonist in conscious female rats

In a previous study we showed that in normotensive male rats brain mineralocorticoid receptor blockade induced a long lasting decrease in blood pressure associated with increased urinary excretion of water and electrolytes. Here, we report the effect of intracerebroventricular injection of a mineralocorticoid receptor antagonist (RU28318; 3,3-oxo-7 propyl-17-hydroxy-androstan-4-en-17yl-propionic acid lactone) on cardiovascular and renal function in female rats. Compared with male rats, females are less sensitive to brain mineralocorticoid receptor blockade. Administration of RU28318 (10 ng, 100 ng) caused a significant decrease in systolic blood pressure (10-12.5%) only at 8 h after injection. An increased urinary excretion of water (about 160%) and electrolytes (about 175%) during the first 8 h after the injection was observed in the 100 ng RU28318 treated group. Heart rate, food intake and water consumption were not affected at either dose. In conclusion, in conscious female rats, brain mineralocorticoid receptors participate in blood pressure and renal function control.

Adrenomedullary function is severely impaired in 21-hydroxylase-deficient mice

Deficiency of 21-hydroxylase (21-OH), one of the most common genetic defects in humans, causes low glucocorticoid and mineralocorticoid production by the adrenal cortex, but the effect of this disorder on the adrenomedullary system is unknown. Therefore, we analyzed the development, structure, and function of the adrenal medulla in 21-OH-deficient mice, an animal model resembling human congenital adrenal hyperplasia. Chromaffin cells of 21-OH-deficient mice exhibited ultrastructural features of neuronal transdifferentiation with reduced granules, increased rough endoplasmic reticulum and small neurite outgrowth. Migration of chromaffin cells in the adrenal to form a central medulla was impaired. Expression of phenylethanolamine-N-methyltransferase (PNMT) was reduced to 27 +/- 9% (P<0.05), as determined by quantitative TaqMan polymerase chain reaction, and there was a significant reduction of cells staining positive for PNMT in the adrenal medulla of the 21-OH-deficient mice. Adrenal contents of epinephrine were decreased to 30 +/- 2% (P<0. 01) whereas norepinephrine and dopamine levels were reduced to 57 +/- 4% (P<0.01) and 50 +/- 9% (P<0.05), respectively. 21-OH-deficient mice demonstrate severe adrenomedullary dysfunction, with alterations in chromaffin cell migration, development, structure, and catecholamine synthesis. This hitherto unrecognized mechanism may contribute to the frequent clinical, mental, and therapeutic problems encountered in humans with this genetic disease.

Gender differences in sympathetic nervous system regulation

1. Females are protected against the development of hypertension. The purpose of the current review is to present the evidence for gender differences in the regulation of the sympatho-adrenal nervous system and to determine if these differences support the hypothesis that, in females, the regulation of the sympathetic nervous system (SNS) is altered such that sympatho-adrenal activation is attenuated or sympatho-adrenal inhibition is augmented. 2. The central control of sympatho-adrenal function is different in females and responses vary during the oestral and menstrual cycles. Pathways regulating the SNS appear to be less sensitive to excitatory stimuli and more sensitive to inhibitory stimuli in females compared with males. 3. Gender differences in arterial baroreflex sensitivity suggest that females may have a greater baroreflex sensitivity, such that alterations in blood pressure are more efficiently controlled than in males. Cardiopulmonary reflex inhibition of sympathetic nerve activity is greater in females, possibly resulting in a greater renal excretory function. 4. An attenuated sensitivity to adrenergic nerve stimulation, but not to noradrenaline (NA), suggests that gender differences in noradrenergic neurotransmission may protect females against sympathetic hyperactivity. Gender differences in the regulation of NA release via presynaptic alpha 2-adrenoceptors, the vasoconstrictor response to the cotransmitter neuropeptide Y and the clearance of catecholamines are consistent with this hypothesis. 5. Similarly, attenuated stress-induced increases in plasma catecholamines in women suggest that females are less sensitive and/or less responsive to adrenal medullary activation. This is supported by findings of gender differences in adrenal medullary catecholamine content, release and degradation. 6. We conclude that there is strong evidence that supports the hypothesis that, in females, the regulation of the SNS is altered such that sympatho-adrenal activation is attenuated or sympatho-adrenal inhibition is augmented.