Origin of adenosine released from rat vas deferens by nerve stimulation

Abstract

After labelling of vasa deferentia from intact rats with [ 3H]adenine there was a spontaneous outflow of labelled purines, mainly as adenosine, inosine and hypoxanthine. There was a spontaneous outflow of endogenous adenosine and inosine amounting to 6 and 2 pmol/min from a single vas. The uptake inhibitor dipyridamole increased the rate of outflow to 27 and 28 pmol/min, respectively. Transmural nerve stimulation of vasa from intact and castrated rats increased the rate of purine release but with a different time course than for the release of [ 3H]noradrenaline ([ 3H]NA). Phentolamine (3 μM) increased [ 3H]NA release, suggesting the presence of presynaptic α-adrenoceptors in castrated vasa, but almost abolished purine release. Adenosine (1 μM) decreased [ 3H]NA release without affecting [ 14C]purine overflow. Dipyridamole (1 μM) had the opposite effect. The inhibitory effect of adenosine on noradrenaline release was similar in intact and castrated vasa. In the subcellular distribution studies ATP was detected in the small, dense-cored vesicle fraction, but the ratio ATP: NA was only 1.20–1.60. Labelling of the vesicle fraction by [ 3H]adenine was usually found, but the degree of labelling was small. The results indicate that endogenous adenosine is released from rat vas deferens in amounts that may be sufficient to cause pre- and postjunctional effects. In particular the amounts of ATP released together with NA are suggested to be quantitatively insignificant.