Effect of moderate cooling on endogenous noradrenaline release from the mesenteric vasculature of rats

1. Experiments were performed to investigate whether moderate cooling can reduce exocytotic noradrenaline release in the deep circulation of rats. 2. The release of endogenous noradrenaline from the entire mesenteric vasculature of the isolated intestine of rats was determined along with the perfusion pressure response to transmural field stimulation (TFS) (4-14 Hz) at 37 degrees C or 24 degrees C. 3. Although moderate cooling significantly augmented the perfusion pressure responses to TFS, it markedly depressed TFS-induced endogenous noradrenaline release. Moderate cooling also significantly reduced the perfusion pressure responses to exogenous noradrenaline. 4. Treatment of mesenteric vascular preparations with cocaine (10(-6) M) plus corticosterone (4 x 10(-5) M) to inhibit neuronal and extraneuronal noradrenaline uptake, respectively, significantly increased the TFS-induced pressor response at 37 degrees C, but not at 24 degrees C. 5. However, treatment with cocaine in combination with corticosterone significantly increased the TFS-induced release of noradrenaline at both temperatures. The enhancement produced by these uptake inhibitors on the TFS-induced noradrenaline release at 37 degrees C was significantly smaller than that observed at 24 degrees C. 6. These results indicate that moderate cooling can depress the exocytotic noradrenaline release in the mesenteric vasculature. However, it appears that reduced re-uptake by moderate cooling probably overcomes the inhibitory effect of cooling on the release of noradrenaline. 7. Thus, it is suggested that the increased pressor responses to TFS by moderate cooling are due, at least in part, to reduced uptake at lower temperatures.