Sodium-induced rise in blood pressure is suppressed by androgen receptor blockade

Flutamide increases aldosterone levels in gonadectomized male but not female Wistar rats

BACKGROUND

Sex-specific differences in blood pressure (BP) suggest an important modulating role of testosterone in the kidney. However, little is known about the interaction between androgens and the mineralocorticoid aldosterone. Our objective was to determine the effects of testosterone in gonadectomized male and female rats on a low-salt diet, and to determine the effect of androgen receptor (AR) blockade by flutamide on BP and on aldosterone levels.

METHODS

Normotensive male and female Wistar rats were gonadectomized and put on a low-salt diet. They were treated for 16 days with testosterone or placebo. In addition, the animals received the AR antagonist flutamide or placebo, respectively. BP was measured by tail-cuff method, 24-h urine samples were collected in metabolic cages and blood was collected for hormonal measurements.

RESULTS

Testosterone increased BP in males and females, and this effect could be blocked by flutamide. Flutamide treatment itself significantly increased aldosterone levels in male but not in female rats. These elevated aldosterone levels could be lowered by testosterone treatment during AR blockade. Accordingly to aldosterone levels, flutamide increased in males the serum sodium/potassium to urinary sodium/potassium ratio, an in vivo indicator of renal aldosterone action.

CONCLUSIONS

Testosterone regulates BP in male and female gonadectomized rats via the AR. Flutamide by itself exerts influence over aldosterone in the absence of gonadal steroid replacement suggesting AR involvement in renal sodium handling. These flutamide effects were sex-specific and not seen in female rats.

Testosterone increases: sodium reabsorption, blood pressure, and renal pathology in female spontaneously hypertensive rats on a high sodium diet

Estrogen (E) and testosterone (T) are important in the sexually dimorphic pattern of blood pressure (BP) development. The goal was to examine the effects of endogenous E and exogenous T in the development of hypertension in female spontaneously hypertensive rats (SHR) on a high sodium diet. Female SHR (N = 27, 5-week) were divided into four groups: (1) control (n = 8), (2) ovariectomized (OVX, n = 26), (3) testosterone implants with intact ovaries (T, n = 6), and (4) ovariectomized + testosterone implants (OVX+T, n = 7). T was given immediately after OVX and replaced every two weeks and they were fed a 3% NaCl diet. BP was measured weekly and plasma norepinephrine (NE) analyzed by HPLC. OVX+T females exhibited the greatest elevation in BP (190 ± 4.0 mmHg) compared to controls at 15 weeks of age (140 ± 3.4 mmHg, P < .001) and a pattern of hypertension development similar to that of male SHR. Females with T treatment showed evidence of glomerulosclerosis. In conclusion, T accelerated the development of hypertension similar to the BP pattern observed in males; the presence of ovaries attenuated the T induced increase in BP; T increased renal sodium reabsorption, and T increased glomerulosclerosis.

Colony social stress differentially alters blood pressure and resistance-sized mesenteric artery reactivity in SHR/y and WKY male rats

Increased sympathetic nervous system (SNS) activity, testosterone, and spontaneously hypertensive rat Y chromosome (SHR Yc) play a role in a genetic model of hypertension. Male rats with the SHR Yc and Wistar-Kyoto (WKY) autosomes (denoted SHR/y) exhibit these characteristics when compared to rats with the WKY Yc and WKY autosomes (denoted WKY). We hypothesized that chronic social stress will increase blood pressure and SNS activity more in SHR/y males compared to WKY males, resulting in increased myogenic reactivity along with decreased vasoconstriction of small mesenteric arteries. SHR/y and WKY males were housed in strain- specific colonies (10 males with 10 females) or as controls (10 males). Systolic blood pressure (SBP) and blood samples were collected prior to termination. Second-order mesenteric arteries were studied using a pressure arteriograph in which myogenic reactivity and phenylephrine (PE) responsiveness were measured. SHR/y colony SBP, and circulating norepinephrine and testosterone concentrations were elevated compared to control and WKY colony males (p < 0.05). Mesenteric artery myogenic reactivity was increased in SHR/y colony males (p < 0.001). Mesenteric arteries from SHR/y colony males exhibited a significant decrease in PE-induced constriction. Colony social stress elevated both SNS activity and testosterone level which may be responsible for the increased mesenteric artery myogenic reactivity, and SBP as noted in SHR/y males.

Antihypertensive effects of flutamide in rats that are exposed to a low-protein diet in utero

OBJECTIVE

We investigated whether gestational age of in utero low-protein diet played a role in the subsequent development of adult hypertension and whether it is gender dependent and examined whether flutamide (a specific, nonsteroidal competitive antagonist of the androgen receptor) reduces blood pressure in rat offspring that are exposed to in utero low-protein diet (6%).

STUDY DESIGN

Pregnant rats were fed either with 20% protein (control) or 6% protein (low-protein diet) from day 1 or day 12 of gestation. Fetoplacental weights and mortality rates of pups were assessed. Systolic blood pressure, mean arterial blood pressure, and circulatory hormone levels in offspring were determined. In addition, male and female hypertensive offspring were treated with flutamide, and their blood pressure was monitored.

RESULTS

After delivery, pup weights were reduced, and pup mortality rates increased in the low-protein diet-day 1 group. Systolic blood pressure and mean arterial blood pressure were elevated in low-protein diet-day 1 males and females and low-protein diet-day 2 males. Significant (P < .05) reduction in blood pressure was achieved with flutamide in low-protein diet-day 1 females. Serum estradiol levels were decreased (P < .05) in low-protein diet-day 1 females; flutamide attenuated this effect.

CONCLUSION

The day of in utero insult by low-protein diet is critical in the induction of adult hypertension; the severity is gender dependent. Flutamide was found to protect against hypertension only in females.

The change in blood pressure during pubertal growth

Blood pressure (BP) in children may increase more during puberty. Using a cohort of children where BP and body size had been closely monitored, we compared the rates of change in BP during the 3-yr period before puberty, during puberty ( approximately 4.5-yr period), and the 3-yr period after puberty. Because there was no specific staging information with respect to puberty, we used pubertal growth (PG) as a surrogate of puberty. The latter was determined from serial measurements of height. All subjects (n = 151) were followed from before the period of PG to the period after PG; none were related. An age-dependent increase in systolic BP in the pre-PG period was similar regardless of sex or race. During PG, systolic BP in males increased three to six times faster than in the pre-PG period. In females, systolic BP increased less than in males during PG but still increased two to four times faster than in the pre-PG period. The increase in males was significantly greater than in females (P < 0.001). Post-PG changes in BP were similar to changes in pre-PG BP. In summary, PG was associated with profound increases in systolic BP. There were noticeably greater increments in males than in females consistent with the emergence of the well known sexual dimorphism in BP.

Patterning of renal cGMP production by the natriuretic peptide receptor type A and blood pressure in spontaneously hypertensive rats

Although important advances have been made over past decades in studying the mechanisms of hypertension, the nature of cellular signaling patterns involved and their relationship remain unclear. High cGMP production rates in isolated renal glomeruli have been presented as a characteristic of spontaneously hypertensive rat (SHR) even before the development of hypertension, which suggests that this event might be a cause of the increase in blood pressure. Using cross-breeding between SHR and WKY parental strains to obtain F1 and F2 hybrids, we have investigated the patterning of high blood pressure and cGMP production rates. We have found that, in the F2 population, the mean blood pressure and both basal and ANP(1-28)-stimulated cGMP production are similar to the parental SHR. In addition, we have found a positive correlation between blood pressure and high cGMP production rates in the F2 population. The higher cGMP production was not a consequence of hypertension, since in DOCA-salt hypertensive rats cGMP production was similar to that observed in normotensive WKY rats. These observations suggest that high cGMP production is a characteristic linked to hypertension. Finally, reciprocal crosses between the SHR and WKY parental strains showed that in the F1 population blood pressure but not cGMP production are associated with the Y chromosome.

Abolition of hypertension-induced end-organ damage by androgen receptor blockade in transgenic rats harboring the mouse ren-2 gene

A sexual dimorphism in hypertension has been observed in both human and laboratory animal studies. The mechanisms by which male sex hormones regulate cardiovascular homeostasis are still not yet fully understood and represent the subject of this study. The possible involvement of androgen receptors in the development of hypertension and end-organ damage in transgenic rats harboring the mouse Ren-2 renin gene [TGR(mREN2)27] was studied. Male TGR(mREN2)27 rats were treated with the androgen receptor antagonist Flutamide starting at 4 wk of age. Also, an androgen receptor mutation (testicular feminization mutation [tfm]) was introduced in these rats by crossbreeding male TGR(mREN2)27 rats with tfm rats. The resulting offspring male rats that contain the tfm mutation are insensitive to androgens. Flutamide treatment or tfm mutation produced a significant attenuation of the development of hypertension. Besides a reduction in cardiac hypertrophy, urinary albumin excretion was blunted and no histologic characteristics of end-organ damage were observed in the kidney after Flutamide treatment. Testosterone levels increased 15-fold after Flutamide treatment and 2.7-fold by the tfm mutation. Also, plasma estrogens and luteinizing and follicle-stimulating hormones were significantly increased. Plasma renin concentrations and activity but not plasma angiotensinogen were reduced. Our results indicate that androgens contribute not only to the development of hypertension, but even more importantly to end-organ damage in TGR(mREN2)27 rats.