Changes in plasma cyclic nucleotides levels during various acute physical stresses.

Studies were performed with healthy volunteers to determine the effects of various stresses known to increase sympathetic nerve activity on the plasma concentration of cyclic AMP and cyclic GMP. Plasma cyclic AMP rose promptly in response to exercise; the elevation was completely abolished by a simultaneous injection of propranolol. Plasma cyclic GMP rose slightly after exercise; the elevation was completely abolished by a simultaneous injection of atropine. No significant changes occurred during tilting and cold pressor stress. The increase in plasma concentrations of cyclic AMP and cyclic GMP may serve as putative indices for beta-adrenergic, and cholinergic functions respectively during exercise of humans.