Beta-adrenergic receptors and catecholamines in the rat heart during tourniquet trauma.

Tourniquet trauma produced a decrease in the noradrenaline content in the heart of the rats through the period of tourniquet application (up to 4 hr). In the same period, the content of adrenaline was significantly increased. This relationship between noradrenaline and adrenaline remained the same in the posttraumatic period. Parallel to the observed changes in the catecholamine content of the heart, a significant decrease in the number of the beta-adrenergic receptors (Bmax) and an increase in their affinity (a decrease in KD) was also found in the hearts of rats exposed to tourniquet trauma. These changes remained throughout the posttraumatic period, with one exception: no change 30 min after trauma has been observed. Reapplication of tourniquet was associated with a restoration of the beta-adrenergic receptors and complete survival of the animals. The decrease in the beta-receptors density after trauma might be due to down-regulation produced by increased concentration of adrenaline, a beta-receptor agonist. Meanwhile, some other factors, particularly ischaemia, might also contribute to the observed changes in the beta-adrenergic binding sites.