EXTROVERSION AS A MODIFYING FACTOR IN CATECHOLAMINE AND BEHAVIORAL-RESPONSES TO ETHANOL

Individual differences in catecholamine response to stress and ethanol were tested in extraverts and introverts on the basis of Eysenck's dr ug postulate claiming that introverts would be less susceptible to sed ative drugs like ethanol. Forty-four healthy males received either 0.8 g/kg ethanol mixed into a drink of caffeine-free cola or a respective placebo and were tested with a stressful mental arithmetic task befor e and 40 min after the intake of the drink. Plasma catecholamines were determined from blood samples drawn at five defined intervals from an indwelling cannula and self-ratings on deactivation, relaxation, and anxiety were obtained as well as quality and quantity of performance i n the arithmetic task. Results showed that there was no difference in catecholamine stress responses between introverts (Ex -) and extravert s (Ex +) before the drink, but that the intake of the fluid (both etha nol and placebo) resulted in higher norepinephrine (NE) increases in E x - than in Ex +. The combined effects of ethanol and stress yielded l arger responses of longer durations in Ex- than in Ex +. The concomita nt psychological changes showed larger reductions in anxiety and incre ases in relaxation as well as larger decrements in quality of performa nce (% errors) in introverts in spite of their higher catecholamine in creases. Thus, the predictions on the basis of arousal theory could no t be verified experimentally and the drug postulate has to be modified in the sense that introverts probably have a higher depletion of NE i n the central nervous system under physical but not under mental stres s which is reflected by higher levels in the plasma and respective dec reases in performance and activation.