The two portions of rat vas deferens differed in the postjunctional sensitivity to noradrenaline. Alpha1-adrenoceptor-linked phosphoinositide breakdown was analysed in this tissue. The noradrenaline-induced [3H]inositol phosphate accumulation was similar in both ends although the pEC50 was higher in the epididymal (5.97+/-0.07) than in the prostatic (5.47+/-0.15, P<0.01) portion. [3H]Prazosin showed similar density of binding sites in both portions. Tissue pretreated with pertussis toxin did not change [3H]inositol phosphate accumulation. Finally, Western blot analysis indicated a smaller concentration of Gq/11 protein in the prostatic half (-29+/-5%, P<0.01). These results suggest that the different sensitivity to noradrenaline could be due to the higher availability of this sort of G protein in the epididymal portion.