Modulation of adrenergic receptors and adrenergic functions in cold adapted humans

To specify the role of adrenoceptors in mediating adrenergic functions after adaptation of humans to cold, effect of administration of increasing concentrations of beta 1 and beta 2 adrenomimetics (Dobutamine, Bricanyl) on resting metabolic rate, heart rate, systolic blood pressure, rectal and skin temperatures of control humans and of cold adapted winter swimmers was studied. Increase in metabolic rate, mediated by beta 1 and beta 2 adrenomimetics, was attenuated after cold adaptation, indicating downregulation of beta 1 and beta 2 adrenoceptors. Since cold adapted humans have greater capacity of nonshivering thermogenesis, than that mediated by both beta 1 and beta 2 adrenoceptors, the role of other subtypes of adrenoceptors in mediating nonshivering thermogenesis is anticipated. Heart rate increased after administration of the beta 2 agonist, but was not influenced by the beta 1 agonist. The significance of beta 2 adrenoceptors in mediating heart rate was depressed after cold adaptation. Data indicate that modifications of activity of beta adrenoceptors play crucial role in mechanisms responsible for adaptation of humans to cold.