Time-response curves for barium and noradrenaline in vas deferens of castrated rat.

Time-response curves for barium chloride and noradrenaline were obtained in the isolated vas deferens of 30-day castrated rats. The contractions induced by a maximal dose of barium chloride reached a peak after about 20-30 sec and then decreased to a lower level (fade). 5 min after drug addition the response had faded to about 20% of the peak contraction while in normal preparations it decreased to about 55%. When calcium was removed from the nutrient solution, both peak and 5-min effects of sequential doses were reduced, and fell progressively at a faster rate than in normal preparations. When Ca2+ concentration was increased from 1.8 mM up to 36.0 mM, fading was abolished. The data were analyzed on the basis of receptor changes involving the translocation of calcium in smooth muscle.