Increased sympatho-adrenomedullary activity in young patients with borderline hypertension: hyperresponses to isometric stress and glucagon injection

The purpose of this study was to estimate the sympatho-adrenomedullary activity in young patients with borderline hypertension (BHT, n=23), compared with age-matched normotensive subjects (NT, n=9), so that two studies were performed as follows: they were subjected to isometric stress, by maintaining handgrip at the 30% level of maximal voluntary contraction for three minutes. With the exercise blood pressure and pulse rate increased to the same degree in BHT as in NT. In contrast, the response of plasma total catecholamine (plasma epinephrine plus norepinephrine) at the end of this isometric exercise was greater in BHT than in NT (93.0 +/- 12.6 in BHT vs. 47.1 +/- 15.4pg/ml in NT). Moreover, the effects of intravenous glucagon injection (1 USP unit) were studied in twelve subjects of BHT (n = 12) and all of NT (n = 9). The injection of glucagon induced a transient increase in pulse rate, but there was no significant difference in the elevation of pulse rate with glucagon between BHT and NT. Plasma epinephrine also increased temporarily, and returned to the baseline within ten minutes after injection. The increments of plasma epinephrine at two and three minutes after injection were significantly greater in BHT than those in NT: 44.1 +/- 12.3 vs. 5.1 +/- 4.4pg/ml, and 68.9 +/- 13.2 vs. 32.1 +/- 8.9 pg/ml, respectively. Thus, patients with borderline hypertension had the augmented response of plasma catecholamine to both isometric exercise and glucagon stimulation. Evidence presented suggests that the responses of sympathetic nervous system and adrenal medulla to stress are increased in young patients with borderline hypertension. Moreover, the augmented response of sympatho-adrenomedullary system to stress may be involved in the development of essential hypertension.