TEMPERATURE SENSITIVITY OF THE EXTRANEURONAL UPTAKE AND METABOLISM OF ISOPRENALINE IN THE PERFUSED RAT-HEART

The influence of lowering the temperature (from 37° to either 27° or 20°C) on extraneuronal mechanisms was studied in the rat heart perfused with 3H-isoprenaline. 1. During perfusion at a constant rate, lowering of the temperature increased the resistance to flow. The consequent impairment of the effectiveness of the perfusion of the tissue accounts for most (or all) of the temperature-sensitivity of the non-saturable (probably diffusional) extraneuronal uptake of isoprenaline. 2. For various other extraneuronal mechanisms the effect of lowering the temperature clearly exceeded that attributable to changes in perfusion. This applied to the Vmax (but not to the Kmax) of saturable extraneuronal uptake and extraneuronal O-methylation, as well as to the rate constants for the efflux of isoprenaline and its O-methylated metabolite, OMI. 3. Lowering of the temperature impaired the efflux of isoprenaline from compartment III (characterized by Bönisch et al., 1974, as having a half time of about 10 min) much more than that from compartment IV (characterized by Bönisch et al., 1974, as having a half time of about 25 min). Since these effects are similar to those of an inhibitor of extraneuronal uptake, corticosterone, it is possible that amine efflux from compartment III (but not from compartment IV) is carrier-mediated. 4. It is concluded that the temperature-sensitivity of the extraneuronal accumulation of catecholamines reported in the literature is not solely due to extraneuronal uptake being temperature-sensitive; the intracellular enzyme and the rate constants for the efflux of amine and metabolite are also greatly influenced by temperature. © 1979 Springer-Verlag.