An investigation of α‐adrenoceptor responsiveness in the vas deferens of spontaneously hypertensive rats

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Abstract
1 α-Adrenoceptor-mediated responses were investigated in isolated vasa deferentia from spontaneously hypertensive rats (SHR) and normotensive Wistar rats (NWR). 2 There was no significant difference between NWR and SHR in the inhibition of the isometric contraction to single pulse field stimulation by α2-selective agonists in prostatic portions, nor by α2-selective agonists and the α1-selective agonist, amidephrine in epididymal portions in the presence of nifedipine to prevent postjunctional actions of α-1-selective agonists. 3 There was no significant difference between NWR and SHR in the potency of amidephrine in causing a postjunctionally mediated potentiation of the isometric contraction to single pulse field stimulation in prostatic portions but the maximum potentiation was significantly reduced in SHR. However, the maximum potentiation of the isometric contraction by the calcium entry facilitator, Bay K 8644, was not significantly different between NWR and SHR. The maximum direct contraction to amidephrine, but not to Bay K 8644, was also significantly reducd in SHR. 4 The irreversible α1-adrenoceptor antagonist, phenoxybenzamine was more potent in SHR than NWR in reducing the maximum potentiation by amidephrine of the stimulation-evoked isometric contraction and in reducing the maximum direct contraction to amidephrine. 5 It is concluded that there is a reduced postjunctional α1-mediated responsiveness in the vas deferens of SHR due probably to a reduction in receptor number.