Biochemical changes in two subjects succumbing to syncope.

Biochemical data are presented of two subjects who fainted during a psychophysiologic experiment. Both subjects showed similar postfaint reactions for heart rate, noradrenaline, glucose, human growth hormone, and cortisol. Heart rates showed rather low values, returning to the normal range after about 45 min. Noradrenaline plasma levels were also very low. However, levels of human growth hormone, cortisol, and glucose were very high in comparison to the control values. Taking into account psychologic prefaint data of previous studies and the present biochemical findings, it is argued that the onset of fainting involves the rapid succession of two stress reactions: the fight--flight reaction and the conservation--withdrawal reaction.