Plasma Renin Activity, Severity Index and Urinary Catecholamine in Essential Hypertension

Abstract

In 1972, Brunner and coworkers suggested that patients with normal and high renin essential hypertension were at an increased risk of stroke or myocardial infarction as compared with patients with low renin. High PRA level appears to be a risk factor for cardiovascular complications in essential hypertension. But there are many controversies regarding that report.
Several authors reported that urinary or plasma noradrenaline level elevated and correlated slightly positively to PRA level in patients with essential hypertension. It seems that renin-angiotensin system and the sympathetic nervous system may play important roles in maintaining high blood pressure at least in a part of essential hypertension. However, there is no definite evidence that these factors are involved in the pathogenesis of essential hypertension.
In order to investigate interrelations among the renin-angiotensin system, the sympathetic nervous system and the grade of cardiovascular damage in essential hypertension, PRA and severity index were estimated in 105 patients with essential hypertension and urinary noradrenaline was measured in 36 out of 105 patients and in 11 normal subjects. The subjects were either untreated or withheld from any antihypertensive drug for at least one week before the study. Dietary sodium was unristricted.
In the morning under a fasting condition, urine was voided completely at 8: 00 a. m. and blood sample for PRA was taken at 9: 00 a. m. after a one hour rest. Then the subjects took 80 mg of furosemide orally and a second blood sample was taken at 12: 00 a. m. after three hours of ambulation. Urine specimens were collected from 8: 00 a. m. to 9: 00 a. m. and from 9: 00 a. m. to 12: 00 a. m. to estimate the noradrenaline excretion rate at rest and during provocation, respectively.
PRA was measure d by radioimmunoassay and urinary noradrenaline was determined by the trihydroxyindole method. The severity of essential hypertension was estimated according to the severity scoring proposed by three Departments of Internal Medicine of Tokyo University.
The hypertensive subjects were classified into low, normal and high renin g roups depending on their renin responses to the provocation (furosemide plus ambulation) taking into account patients' age. The res ults were as follows:
1) Sixty-six percent of low renin hypertensive subjects was female. Fifty six percent of all hypertensive women belonged to the low renin group.
2) PRA level correlated positively with blood pressure at rest in all essential hypertensives and in the high renin group. However, no correlation was found in low and normal renin groups.
3) There was no significant differnce in the total severity index between low and normal renin groups. The mean value of the index in the high renin group was high as compared with the other groups.
4) There wa s no correlation between age and urinary noradrenaline excretion rate in normal subjects and in all hypertensive patients. Moreover, the urinary noradrenaline excretion rate did not significantly correlate with blood pressure and PRA level in all patients and in each renin subgroup.
5) The urinary noradrenaline excretion rate during provocation in about 25% of essential hypertensive subjects was elevated above Mean+ 2SD of that in normal subjects.
6) There was no marked difference in urinary noradrenaline excretio n rate at rest among renin subgroups. The change in noradrenaline excretion rate by provocation in the low renin group was low as compared with the other groups.
7) The urinary noradrenaline excretion rat e during provocation in the mild essential hypertension (less than 6 point of total severity index) was significantly higher than that in the moderate essential hypertension (from 7 to 10 point).