1. Dose-response curves for noradrenaline, phenylephrine and clonidine were determined isometrically on the mouse vas deferens at 26 degrees C, 15 degrees C and compared to the one obtained at 37 degrees C. 2. In the presence of noradrenaline, reducing temperature induced an increase of both maximal developed tension and sensitivity to the drug. Reduction by 50% of the extracellular calcium concentration abolished the maximal contraction potentiation. 3. When reducing temperature to 26 degrees C, the maximal contraction was increased and depressed in the presence of phenylephrine and clonidine respectively. 4. The results suggest (a) that cooling increases the reactivity of mouse vas deferens by activation of alpha 1 adrenoceptors and depresses it by activation of alpha 2 adrenoceptors (b) that calcium ions could play an important role in the potentiation of the maximal contraction.
