A role for muscarinic receptors or rho-kinase in hypertension associated rat bladder dysfunction?

Purpose: Essential arterial hypertension is a frequent condition. Spontaneously hypertensive rats (SHRs) show bladder dysfunction similar to that seen in patients with overactive bladder. Since muscarinic receptors and rho-kinase have a key role in the regulation of bladder contractility, we determined whether alterations of either one might contribute to hypertension associated bladder dysfunction. Materials and Methods: The bladders of SHRs and normotensive Wistar Kyoto rats (WKYs) were compared in in vitro radioligand binding and contractility studies. Results: The mean total number of muscarinic receptors +/- SEM (181 +/- 14 vs 191 +/- 22 fmol/mg protein) and the relative roles of their subtypes were similar in SHRs and WKYs. Contractile responses to the muscarinic agonist carbachol (maximum effect 2.04 +/- 0.24 vs 2.05 +/- 0.14 mN/mm strip length and -log EC50 5.61 +/- 0.07 vs 5.64 +/- 0.04) and to KCl in a receptor independent manner were similar in the 2 strains. The M-3 selective antagonist darifenacin inhibited carbachol responses much more potently than the M-2 selective antagonist methoctramine but the potency of the 2 drugs was similar in each strain. The rho-kinase inhibitor Y27,632 attenuated carbachol induced contraction in a quantitatively similar manner in SHRs and WKYs. Conclusions: An altered function of muscarinic receptor subtypes or rho-kinase does not appear to contribute to bladder dysfunction in SHRs.