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.