Abstract
The effects of different calcium concentrations on the twitch-inhibitory potency of clonidine and of guanethidine have been examined in the rat isolated vas deferens. Vasa deferentia did not respond to field stimulation at 0.3 Hz in Krebs solution containing 0.325 mmol/1 of calcium. Increasing the calcium concentration to 5.2 mmol/1 caused a concentration-dependent increase in size of the twitch response. The twitch inhibitory potency of clonidine was inversely proportional to the calcium concentration. The inhibitory effect of guanethidine was not influenced by changes in calcium concentration. The results show that the modulation of motor function by presynaptic alpha-adrenoceptors in the rat vas deferens is calcium-dependent.
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