Evidence for increased sympatho-adrenomedullary activity in young subjects with borderline hypertension

Three different studies were performed to estimate the sympatho-adrenomedullary activity in young subjects with borderline hypertension (BHT, n = 40), compared with age-matched normotensive subjects (NT, n = 24). In the first study, 23 BHT and 9 NT were subjected to isometric stress by maintaining handgrip at the 30% level of maximal voluntary contraction for 3 min. The response of plasma total catecholamines at the second and third min during the isometric exercise were greater in BHT than in NT (98.9 +/- 24.3 vs. 18.0 +/- 30.7 and 93.0 +/- 12.6 vs. 47.1 +/- 15.4 pg/ml, respectively, p less than 0.05). In the second study, the effects of intravenous glucagon injection (1 USP unit) were studied in 12 BHT and 9 NT. The increments of plasma epinephrine (E) at 2 and 3 min after injection were significantly greater in BHT than those in NT: 44.1 +/- 12.3 vs. 5.1 +/- 4.4 pg/ml, and 68.9 +/- 13.2 vs 32.1 +/- 8.9 pg/ml, respectively, p less than 0.05. In the last study, the pressor effects of intravenous norepinephrine (NE) infusion (100 and 200 ng/kg/min for 15 min) were examined in 17 BHT and 15 NT under three different sodium balances: regular customary diet, treatment with diuretics and high-sodium diet. Treatment with diuretics decreased and high-sodium diet increased the pressor response to NE in both groups, but there were no significant differences in NE reactivity between 2 groups throughout the study.(ABSTRACT TRUNCATED AT 250 WORDS)