Sympathetic Nerve Activity in Patients with Essential Hypertension : A Comparison of the Activity among Patients with Labile and Stable, or Low, Normal and High Renin Essential Hypertension : VII CONFERENCE ON THE PATHOGENESIS OF HYPERTENSION

In order to compare sympathetic nerve activity among subgroups in essential hypertensives, with reference to labile or stable hypertension and to level of plasma renin activity (PRA), the urinary excretion of catecholamines, serum dopamin-beta-hydroxylase (DBH) activity and pressor response to infused noradrenaline (NA-response) were estimated in the patients with essential hypertension. The measurements were performed during the first and the last four days of two weeks of rest after admission to the hospital, during which the patients were kept at rest with neither medication nor salt-restriction. Patients were divided into two groups with a reduction of mean arterial pressure (MAP) by more than 10 mmHg (Responder) and less then 9 mmHg (Non-Responder) following two weeks of rest, or into three renin subgroups, i.e., low, normal and high PRA. From the measurements during the first four days of two weeks, the following results were obtained. In the Responder, a 24 hour urinary excretion of noradrenaline (NA) and the increase of urinary NA during two hours of 60° head-up tilt were significantly augmented (p < 0.01 and p < 0.05, respectively) and NA-response was suppressed (p < 0.05) as compared with the Non-Responder. In addition, a significantly negative correlation was found between the increase of urinary NA by the tilt during this period and the changes in MAP following two weeks of rest. However, a significant difference between the Responder and the Non-Responder did not exist in age, values of heart rate (HR), MAP, cardiac index (CI), total peripheral resistance index (TPRI), plasma volume (PV), extracellular fluid volume (ECFV), total exchangeable sodium (Nae) and serum DBH. Comparison among low, normal and high PRA patients revealed significantly lower urinary NA excretion (p < 0.001) and serum DBH activity (p < 0.05) in the low PRA patients. NA-response was significantly higher (p < 0.001) in the low PRA patients than in the normal PRA patients, both of which were significantly higher than in the high PRA patients or the normotensive subjects. PV, ECFV and Nae of the low PRA patients were significantly more elevated than those of both the normal and high PRA patients, whereas no significant difference was found in HR, MAP, CI and TPRI among these three patient groups. These findings suggest that an augmentation of sympathetic nerve activity exists, and it possibly plays a role in blood pressure rise in the patients with labile type of essential hypertension. The patients with low renin essential hypertension exhibited a suppressed sympathetic nerve activity, which might be not primary but rather secondary as the results of changes in water-sodium balance.