Sex differences in the sympatho-adrenal response to isometric exercise

The effects on heart rate, blood pressure, and plasma catecholamines (epinephrine, norepinephrine, dopamine) of sustained isometric contraction (SIC) were studied in six women and nine men. Each subject held a tension equivalent to 30% of maximal handgrip strength until exhaustion. There were no significant differences between women and men in the duration of handgrip. Rise of heart rate and blood pressure were similar for women and men. Considering the absolute plasma levels of each catecholamine, no sex differences was observed at rest and at any time during SIC, except for epinephrine whose concentration was higher in men at first min of SIC. On the other hand, women and men exhibited different adrenergic patterns in response to SIC: in the first min of exercise the plasma level of the three catecholamines increased in men whereas for women plasma catecholamines levels were essentially unaffected. Thus, epinephrine seems to play a minor role in the regulation of heart rate and blood pressure during SIC for women. Another interesting result of our study is that SIC is able to induce an increase in dopamine plasma level for women as well as for men.