SEX-DIFFERENCES IN CATECHOLAMINE RESPONSE TO CLONIDINE

Sex-related differences both in the basal secretion of catecholamines and in the adrenergic reactivity to various stimuli have been describe d. We studied the responses of catecholamines and arterial blood press ure to clonidine (0.3 mg per os) in 31 normotensive subjects (10 men ( M), aged 18-42 years, and 21 women (W), aged 20-48 years). Plasma cate cholamines were determined by HPLC at -30, -15, 0, 120, 130, 140 min a fter clonidine. The basal levels of plasma norepinephrine were similar in men and in women (M = 1.16 +/- 0.26 vs. W = 0.87 +/- 0.07 nmol/l). Basal plasma epinephrine levels were not different in the two sexes ( M = 0.21 +/- 0.03 vs. W = 0.14 +/- 0.03 nmol/l). The mean arterial pre ssure decrease after clonidine was similar in the two groups (M = 13 /- 3 vs. W = 15 +/- 2 mmHg). The decrease in plasma epinephrine after clonidine was similar in men and women (M = 0.06 +/- 0.04 vs. W = 0.09 +/- 0.02 nmol/l). In contrast, the plasma levels of norephinephrine a fter clonidine were reduced more in women than in men either when expr essed as absolute values (W = 0.63 +/- 0.07 vs. M = 0.3 +/- 0.1 nmol/l ; F = 7.6, P < 0.02) or as percentage change (W = 71 +/- 3 vs. M = 34 +/- 8; P < 0.002). The present study demonstrates that an elevated alp ha2-adrenergic activity in women may be responsible for the sexual dim orphism in catecholamine secretion.