Report of the National Heart, Lung, and Blood Institute Working Group on epigenetics and hypertension

Hypertension, defined as a condition associated with 65140-mm Hg systolic blood pressure or 6590-mm Hg diastolic blood pressure, affects >1 billion people worldwide,1 and in 2009 it cost the US healthcare system more than $73 billion.2 Despite the availability of many antihypertensive therapies, individual responses vary, and efficacy remains a concern. Current treatments have yielded only modest reductions in the overall disease risk even in countries where therapeutics are available and affordable. The initiating causes and the pathogenic mechanisms for disease and its comorbidities remain largely unknown, and prognostic markers for adult hypertension that could improve its diagnosis, prevention, and, ultimately, its management are not yet available. As a result, 4828$3.6 trillion more over the next 10 years.

Effects of long-term captopril treatment on endotheliumdependent relaxation in the spontaneously hypertensive rats (SHR)

Genetic hypertension in the SHR is associated with endothelium dysfunction. The purpose of this study was to evaluate the effects of long-term treatment with captopril (ACE inhibitor) on endothelium dependent relaxation. Experimental male SHRs were divided into three groups: SHRCAP received oral captopril from in-utero to 6-7 months of age; OFFCAP were treated like SHRCAP but taken off captopril at 2 months of age and then maintained on tap water, and untreated SHR were given tap until experimentation. Age-matched WKYs were used as normotensive controls. The average MAP after 6 months of treatment with captopril were t23±3 mmHg (SHRCAP), as compared to 134±3 mmHg (OFFCAP), 169±3 mmHg (SHR), and 130±2 (WKY). Isolated aortic rings (2-3 mm) with functional endothelium were suspended in tissue chambers for measurement of isometric force. Indomethacin IbuM) treated rings were contracted by accumulative addition of phenylephnne (3x10° M - 3x 10° M). Acetylcholine-induced relaxation was markedly impaired in untreated SHRs. In contrast, endothelium dependent relaxation responses was significantly enhanced by captopril treatment. Maximum relaxation to acetylcholine was 8.6±5.61% of phenylephrine contraction in the SHRCAP group versus 35±8% in the untreated SHR (p\u3c0.05). Additionally, EC50 values for acetylcholine-induced relaxation was significantly lower in SHRCAP 2 x 10° M versus SHR 107 M (p\u3c0.05). Further, our data shows that 5 months after cessation of captopril treatment, aortic rings prepared from OFFCAP animals exhibited greater maximum acetylcholine-induced relaxation (11 ±9%) than that of the untreated SHRs (p\u3c0.05). These data suggest that early application of captopril can prevent alterations in endothelial function observed in SHR even after ACE inhibitory therapy has been stopped

Responsiveness of locus ceruleus neurons in hypertensive rats to vasopressin

We studied the actions of vasopressin administered microiontophoretically onto neurons of the locus ceruleus in rats with deoxycorticosterone-acetate (DOCA)-salt hypertension and in control (normotensive) rats. Rats were studied at 3 days (prehypertensive stage) and 4 to 6 weeks after DOCA-salt treatment (chronic hypertensive stage). Experiments were performed in anesthetized rats using conventional microiontophoretic and single-cell recording techniques. Three days after DOCA-salt administration, the treated rats showed no rise in arterial pressure in comparison with control rats, but 4 to 6 weeks later, the treated rats had significantly greater pressures (p less than 0.01) than controls. Vasopressin administered with currents of 10 to 90 nA for 1 minute produced a current-dependent increase in the firing rate of noradrenergic neurons in all rats. Increases in the firing rate of noradrenergic neurons in DOCA-salt-treated rats, whether in the prehypertensive or the chronic stage, were significantly greater than increases in control rats. These findings indicate that 1) vasopressin can affect neuronal activity in the locus ceruleus and 2) noradrenergic neurons in the locus ceruleus of DOCA-salt-treated rats have an increased responsiveness to the excitatory effects of vasopressin in both prehypertensive and chronic stages of hypertension

Captopril treatment and its withdrawal prevents impairment of endothelium-dependent responses in the spontaneously hypertensive rat

Angiotensin converting enzyme inhibitors (ACE-I) have been shown to prevent impairment of endothelial cell function in Spontaneous Hypertensive rats (SHR). The purpose of this study was to examine the effects of early, long-term captopril (ACE-I) treatment and its withdrawal on vascular reactivity in SHR. Three groups of male SHR were studied: 1) untreated SHR; 2) SHR treated with captopril in-utero and maintained on oral treatment post- weaning (SHRCAP); and 3) SHR treated with captopril in-utero followed by withdrawal of drug therapy at two months of age (OFFCAP). All rats were studied at six months of age. Isolated aortic ring segments were suspended in tissue chambers for measurement of isometric force. Ring segments were exposed to cumulative concentrations of serotonin or phenylephrine (3x10-9-3x10-5 M). SHR demonstrated an enhanced sensitivity to serotonin induced contraction. EC50 value were: SHR 3.6 ± 1.4 x 10-7M, SHRCAP 9.5 ± 0.5 x 1017 and OFFCAP 8.1±0.9 x 10-7. Endothelium-dependent relaxation to acetylcholine (ACh) was markedly impaired in the SHR. Maximum relaxation (R(max)) to ACh was 61.1 ± 1.6% of serotonin induced contraction versus 91.4 ± 1.2% and 90.7 ± 1.8% relaxation in SHRCAP and OFFCAP, respectfully (p\u3c0.05). These data suggest that early, long-term treatment with captopril can prevent alterations in endothelial function observed in SHR even after ACE-inhibitor therapy has been stopped

Cardiovascular effects of intracerebroventricular injection of vasopressin in unanaesthetized normotensive and DOCA-salt hypertensive rats

The mean arterial pressure (MAP) and heart rate (HR) responses to intracerebroventricular (i.c.v.) administration of arginine vasopressin (AVP) in unanaesthetized normotensive control and DOCA-salt hypertensive rats were studied. Intracerebroventricular administration of AVP (0.25-1000 ng) to control rats produced dose-dependent long-lasting increases in MAP (5-45 mmHg) and HR (35-110 beats/min). Peripheral treatment of rats with an antipressor AVP antagonist had no effect on i.c.v. AVP-induced increases in MAP and HR, whereas the responses were blocked by i.c.v. administration of the antagonist. Peripheral administration of phentolamine and propranolol also completely blocked the changes in MAP and HR. DOCA-salt hypertensive rats showed significantly greater increases in MAP and HR in response to i.c.v. AVP and a tenfold lower threshold for stimulation. The results demonstrate that AVP acting on central neural structures can produce increases in MAP and HR by stimulating sympathetic outflow. Increased sensitivity and responsiveness to i.c.v. AVP in hypertensive rats suggest a potential mechanism of action of AVP in hypertension

Alterations in responsiveness of noradrenergic neurons of the locus coeruleus in deoxycorticosterone acetate (DOCA)-salt hypertensive rats

Locus coeruleus may have a function in central blood pressure regulation and possibly in the pathogenesis of hypertension. In keeping with this notion, we have recently shown that deoxycorticosterone acetate (DOCA)-salt hypertensive rats demonstrate a greater increase in blood pressure induced by locus coeruleus stimulation than control animals. In an attempt to elucidate the underlying mechanisms leading to this alteration in responsiveness of the locus coeruleus, the sensitivity of noradrenergic neurons of the locus coeruleus to the transmitter candidates, epinephrine and glutamate, was investigated in DOCA-prehypertensive (3 days post-DOCA), DOCA chronic hypertensive (6-8 weeks post-DOCA) and control rats using conventional microiontophoretic and single cell recording techniques. Iontophoretically applied epinephrine produced a current-dependent decrease in spontaneous firing rate of all noradrenergic neurons in both DOCA-treated and control rats. Locus coeruleus neurons of DOCA-treated rats at 3 days and 6-8 weeks were less sensitive to epinephrine than those of control rats and the magnitude of the depression in spontaneous firing rate was less. By contrast, iontophoretic applications of glutamate produced an increase in activity of all noradrenergic locus coeruleus neurons. However, there was minimal difference in glutamate sensitivity between neurons of DOCA and control rats. Since the changes in epinephrine sensitivity are apparent not only in the chronic stage but also in the prehypertensive stage, our findings suggest a potential role of the adrenergic input to the locus coeruleus in the pathogenesis of DOCA-hypertension