FUNCTIONAL REGULATION OF ARTERY ADRENORECEPTORS IN RESPONSE TO NOREPINEPHRINE ADMINISTRATION DURING SYMPATHOLYSIS FOLLOWING A 30-DAY COLD ADAPTATION IN WORKING MUSCLES

Abstract

Aim. This study explores the functional regulation of artery adrenoreceptors in response to norepinephrine administration during functional sympatholysis following a 30-day cold adaptation in working muscles. Materials and methods. Our investigation involved four experimental groups: a control group, a group subjected to electrical muscle stimulation (sympatholysis), a group exposed to 30 days of cold adaptation, and a group combining both sympatholysis and cold adaptation. Using a constant flow pump, the limb muscles of rabbits were perfused with blood through the femoral artery. Following the administ­ration of norepinephrine, the activity of α1-ARs was assessed by measuring changes in perfusion pressure. Sympatholysis was induced through electrical stimulation of the hind limb muscles. Data analysis in Lineweaver–Burk plots (double reciprocal plots) allowed us to determine the sensitivity of adrenergic receptors to norepinephrine (1/K), the number of active α1-ARs (Pm), and the dissociation constant of the mediator-receptor complex (K). Results. Our findings reveal a significant decrease in the reactivity of α1-ARs to norepinephrine after cold adaptation, attributed to a reduction in the number of active α1-ARs. Notably, sympatholysis was more pronounced in rabbits exposed to cold adaptation compared to those without, indicating a heightened responsiveness to sympatholysis under cold stress. Conclusion. The study demonstrates that cold adaptation enhances the effectiveness of sympatholysis in increasing blood flow to working muscles, as evidenced by a more pronounced decrease in the number of active α1-ARs.