Role of neuronal and extraneuronal factors in temperature mediated responsiveness of adrenoceptors

Abstract

Changes in bath temperature caused changes in the adrenergic responsiveness of rabbit iris dilator muscle as indicated by shifts in dose-response curves along the log axis and changes in maximum responses. Responses of control tissues to an alpha agonist (norepinephrine) were increased at lower temperatures and responses to a beta agonist (isoprenaline) were increased at higher temperatures. Responses of control tissues were compared with responses of tissues pretreated with cocaine or with responses of adrenergically denervated tissues (chemical and surgical). Changes in ED50 values with temperature change are similar in control, cocaine pretreated or denervated muscles. In contrast, changes in maximum response with temperature change are reversed by cocaine pretreatment or denervation. Pretreatment of tissues with an inhibitor of catechol-o-methyl transferase (tropolone) or an inhibitor of monoamine oxidase (iproniazid) did not affect the temperature sensitivity of adrenoceptors. Also, responses to terbutaline, a beta agonist not susceptible to catechol-o-methyl transferase, changed with temperature. These data indicate that for rabbit iris dilator muscle both a neuronal and an extraneuronal component are involved in adrenoceptor response changes induced by temperature change and that changes in rates of activity of metabolizing enzymes are not involved.