Sympathoadrenergic regulation and the adrenoceptor system.

We investigated the effects of endurance and high-intensity training periods on the plasma catecholamine (CA) concentration at rest; on the basal alpha- and beta-adrenoceptor density, regulation, and function on circulating cells; and on the cardiovascular adaptation in long-distance runners and swimmers. The findings of each period were compared with those of untrained men. Endurance training of the long-distance runners and the swimmers led both to a reduced sympathetic activity at rest, indicated by lower CA values, and to a lower beta-receptor density and responsiveness on circulating lymphocytes and an increased alpha 2-receptor sensitivity on circulating platelets. During the high-intensity training period beta-receptor density and responsiveness increased, alpha 2-receptor sensitivity normalized, and heart rate as well as blood pressure values increased in both trained groups. The basal sympathetic activity remained reduced, but the norepinephrine-to-epinephrine (NE/EPI) ratio increased. The NE/EPI ratio might play an important part in the regulation of adrenoceptor density during these different training periods. Swimming-specific characteristics caused different physiological impacts compared with running training, but an attenuated baroreceptor sensitivity might be indicated in both intensively trained groups.