Plasma noradrenaline concentration and pressor response to infused noradrenaline in patiens with borderline hypertension, and mild or moderate essential hypertension.

In order to evaluate the significance of sympathetic nerve activity in the pathophysiology and pathogenesis of borderline hypertension or mild or moderate essential hypertension, plasma noradrenaline concentration (PNA) at supine rest and pressor response to infused noradrenaline (NA-R) were evaluated in these in-patients. A significantly positive correlation (r=0.395, p<0.001) between PNA and age was found in normotensive subjects (NT), but not in essential hypertensives (EHT). In the young (below 40 years of age) group, the mean value of PNA in EHT was significantly higher (p<0.05) than that in NT. However no significant difference in PNA between NT and EHT was observed in the middle-age (40-59 years) and old-age (above 60 years) groups. PNA was highest in borderline hypertensives (BHT), second highest in EHT with WHO stage I (WHO-I), third in EHT with WHO stage II (WHO-II), and lowest in NT. Among these age-matched four groups, significant differences in the mean value of PNA were found between NT and BHT (p<0.001) or WHO-I (p<0.05), and between BHT and WHO-II (p<0.05). In a comparison of the age-matched NT, normal renin EHT (NRH) and low renin EHT (LRH), the mean value of PNA in NRH was significantly higher than that in NT (p<0.001) and LRH (p<0.001). Similar differences were observed in the peak value of PNA during 20 minutes when the head was tilted up. A close positive correlation between PNA and simultaneously measured mean arterial pressure (MAP) in the young EHT (r=0.698, p<0.001) and WHO-I (r=0.631, p<0.001), and a weak correlation in the middle-age EHT (r=0.435, p<0.05) and NRH (r=0.311, p<0.05) were demonstrated immediately after hospital admission. In the old-age EHT, WHO-II and LRH, however, no significant correlation was found between PNA and MAP. The mean value of NA-R in young (p<0.005) and middle-aged EHT (p<0.001) was significantly greater than that in respectively age-matched NT. However, no significant difference in NA-R was observed between NT and EHT in old-age subjects. NA-R positively correlated (r=0.239, p<0.005) with age in EHT but not in NT. NA-R was augmented parallel with the development of the stage of hypertension, and that in BHT (p<0.05), WHO-I (p<0.001) or WHO-II (p<0.001) was significantly higher than that in NT, and that in WHO-II as higher (p<0.005) than that in WHO-I. In addition, an inverse correlation between NA-R and PNA was demonstrated in NT (r=-0.472, p<0.01) and all EHT (r=-0.629, p<0.001). This correlation was especially marked in young EHT (r=-0.733, p<0.001), middle age EHT (r=-0.529, p<0.005), WHO-I (r=-0.640, p<0.001), WHO-II (r=-0.699, p<0.001) and NRH (r=-0.548, p<0.001), while no significant correlation was observed in old-age EHT and LRH. The regression line between NA-R and PNA in EHT, particularly in WHO-II, shifted upward as compared with that in NT. From these findings, it may be concluded that the augmentation of sympathetic nerve activity is an important mechanism for maintenance of a high level of blood pressure in borderline and essential hypertensives, particularly in young, mild or renin unsuppressed patients, and that an enhanced pressor response to noradrenaline inversely related to the basal PNA level may play some role in the hypertensive mechanism in middle-age, moderate and low renin essential hypertensives.