Physiological responses to catecholamine infusions in type A and type B men.

To determine whether there are basic biological differences between Type A and Type B men, we compared hemodynamic, electrophysiologic and neuroendocrine responses to equipotent doses of isoproterenol (ISO) and norepinephrine (NE) in 10 Type A and 10 Type B men ages 18 to 29. Results showed equal hemodynamic and neuroendocrine responses to graded ISO doses in Type A and Type B individuals. In contrast, Type A men showed a more prolonged decrease in electrocardiographic T-wave amplitude (TWA) than did Type B men. Post hoc analyses of the correlates of TWA recovery during high-dose ISO infusion provide preliminary evidence for a more robust parasympathetic antagonism of sympathetic nervous system effects in Type B men, especially those with low scores on the Cook-Medley Ho scale. These findings suggest that, in addition to cognitively mediated increases in sympathetic nervous system reactivity, Type As may also be placed at increased risk of developing coronary heart disease by reduced levels of parasympathetic antagonism of sympathetic effects.