Relation of renin status to neurogenic vascular resistance in borderline hypertension

Abstract

The relation of renin-angiotensin status to general hemodynamics and to neurogenic vascular resistance was studied in patients with border-line hypertension. Plasma renin activity during standing was referred to a standard renin-urinary sodium nomogram derived from 18 normal subjects. Among 22 patients with borderline hypertension the renin level was high in 8, low in 4 and within normal limits in the remaining 10. In patients with borderline hypertension and high or normal levels of plasma renin activity, the blood pressure elevation was due to increased total peripheral vascular resistance. In contrast, in patients with low renin borderline hypertension, total peripheral resistance was not significantly elevated; the blood pressure elevation reflected a cardiac index 12 percent higher than that in normal subjects. The neurogenic contribution to total peripheral vascular resistance was assessed by studying the effects of alpha adrenergic blockade with phentolamine, after prior autonomic blockade of the heart with atropine (0.04 mg/kg body weight) and propranolol (0.2 mg/kg). Phentolamine (15 mg) produced an immediate reduction in total peripheral resistance of 12.0 +/- 6.7 percent in patients with high renin borderline hypertension (P less than 0.01) but no change in normal subjects or those with borderline hypertension and normal or low renin levels. Normalization of the blood pressure followed "total" autonomic blockade with atropine, propranolol or phentolamine only in patients with high renin borderline hypertension. It is concluded from these preliminary data that in high renin borderline hypertension the blood pressure elevation is sustained by neurogenic mechanisms. The elevated renin level in these patients is probably an expression of increased sympathetic nervous activity. Although the elevated plasma renin level may possibly be contributing to the generation of higher sympathetic tone, or data do not support a direct role of circulating angiotensin in the maintenance of the elevated vascular resistance.

Pressor factors and cardiovascular pressor responsiveness in borderline hypertension.

“…6 e Nevertheless, it is conceivable that plasma renin or norepinephrine levels could vary with the duration of borderline BP elevations. Known duration in our patients ranged from 2 weeks to 72 months (mean, 21 ± 6 months), but no information on this factor has been provided in the previous reports of frequently altered plasma renin 7 -" or norepinephrine 51 8 levels in borderline hypertension.…”

“…1 ' 2 Whether and to what extent borderline BP elevations may depend on abnormalities in major endocrine pressor factors, such as the sympathetic and/or renin-angiotensin systems, are still controversial. In borderline hypertensive patients who were grouped according to BP and age, blood levels and urinary excretion of norepinephrine as an approximate index of adrenergic activity were reported to be normal 3 ' * or mildly increased; 8 '" plasma renin activity (PRA) was found to be either low, 7 normal, 3 or high. 8 The pressor effect of any vasoactive factor depends not only on its concentration but also on cardiovascular response.…”

Mechanism of increased alpha adrenergic vasoconstriction in human essential hypertension.

“…sive patients with high-renin and increased plasma norepinephrine, arterial pressure was normalized when autonomic cardiac blockade was followed by phentolamine (7,8).…”

Psychosomatic factors in borderline hypertensive subjects and offspring of hypertensive parents.

“…50 - 51 It has been found especially in high renin established hypertension 52 -53 and borderline hypertension. 54 Neurogenic mechanisms have been shown to be responsible for blood pressure elevation in patients with high renin borderline hypertension 55 and mild established essential hypertension.…”