The properties of the β₁- and β₂-adrenoceptor partial agonist (±)-carteolol were investigated against the β₂- and β₃-adrenoceptors of the taenia caecum of the guinea pig. (−)-Isoprenaline and (±)-carteolol induced concentration-dependent relaxation in this tissue. The non-selective β₁- and β₂-adrenoceptor antagonist (±)-propranolol (10-100 nM), the selective β₂-adrenoceptor antagonist ICI 118, 551 (10-100 nM) and the non-selective β₁, - β₂- and β₃-adrenoceptor antagonist (±)-bupranolol (10-100n M), caused a concentration-dependent rightward shift of the concentration-response curves for (−)-isoprenaline and (±)-carteolol. Schild regression plot analyses carried out for (±)-propranolol against (−)-isoprenaline and (±)-carteolol gave pA₂ values of 8.35 and 8.24, respectively. Schild plot analyses of ICI 118, 551 against (−)-isoprenaline and (±)-carteolol gave pA₂ values of 8.47 and 8.41, respectively Schild plot analyses of (±)-bupranolol against (−)-isoprenaline and (±)-carteolol gave pA₂ values of 8.47 and 8.53, respectively. Slopes of the Schild plots were not significantly different from unity. These results suggest that the relaxant effects of (±)-carteolol in the guinea pig taenia caecum are mediated by β₂-adrenoceptors but not by β₃-adrenoceptors.

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The aquaporins (AQ-s) are a group of intrinsic membrane proteins which facilitate movement of water across cell membranes ; their recent identification in the kidney has led to the reappraisal of the mechanisms and pathways of water movement across epithelia. Aquaporin-1, (CHIP-28) is reported distributed in cardiac myocytes and vascular smooth muscle cells of large arteries. A related protein, AQ-4, has been identified in the sarcolemma of skeletal muscle fibres. We report aquaporin expression in the cell membrane of smooth muscle cells of the rat genital tract ; fluorescence immunohistochemistry of rat uterine (fallopian) tube and vagina demonstrated AQ-1 in visceral smooth muscle of these tissues. In the uterine tube, AQ-1 labelling is most pronounced in the innermost longitudinal and the inner cells of the circular muscle layer and is absent from the outer longitudinal muscle layer of the myosalpinx. The possibility of a specific role for AQ-1 in tubal transport by altering the tubal luminal diameter during the estrus cycle is suggested.

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We have evaluated the role of adrenergic components in the pelvic splanchnic nerve on the erectile function in the dog. Electrical stimulation of pelvic splanchnic nerves increased blood flow in the internal pudendal artery and also elevated the cavernous pressure. These increases were blocked in part by phentolamine or methylene blue, but not by propranolol or atropine. The effects of cholinergic and adrenergic agonists and antagonists on mechanical responses were also examined in muscle strips obtained from various arteries in the intrapelvic region including the internal pudendal artery Norepinephrine induced contraction in the iliac artery and relaxation in the internal pudendal artery, and both the contraction and relaxation responses were blocked by phentolamine but not by propranolol. These findings suggest that in the dog, α-adrenergic components projected through the pelvic splanchnic nerve may contribute to penile erection, together with cyclic GMP-mediated mechanisms.

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