Spontaneously hypertensive rats exhibit an enhanced mydriatic response to clonidine. Evidence for enhanced sensitivity of central α2-adrenoceptors

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Abstract
Comparisons among spontaneously hypertensive (SHR), Kyoto Wistar (KW), and Wistar (W) rats were made of the functional states of central nervous system (CNS) α2-adrenoceptors (clonidine-induced mydriasis) and nonvascular peripheral presynaptic α2-adrenoceptors (clonidine-induced inhibition of the neurogenic twitch of the isolated vas deferens). While there were no differences among the strains of rats in the concentration of clonidine required to produce a 50% inhibition of the electrically evoked contractile response of the vas deferens, there was a signficant reduction in the mean effective concentration (ED50) of clonidine to induce mydriasis in SHR as compared with KW and W rats. These observations indicate that CNS α2-adrenoceptors may be functionally more sensitive in SHR. The data also suggest that the sensitivity of nonvascular presynaptic α2-adrenoceptors, at least in the vas deferens, is not altered in hypertensive animals.

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