Characterization of alpha-adrenoceptors in the preprostatic urethra of sexually immature male lambs.
Strips of preprostatic urethra from immature male lambs (3-4 months old) were used to study alpha-adrenoceptor-mediated contractions in vitro. The rank order of potency of the agonists was noradrenaline = phenylephrine greater than adrenaline. B-HT 920 was ineffective and clonidine behaved as a weak partial agonist. The rank order of efficacy was found to be noradrenaline greater than phenylephrine greater than adrenaline. Prazosin (10(-9)-10(-6) M) and rauwolscine (10(-6)-10(-4) M) antagonized noradrenaline-induced contractions. The pA2 values were 7.89 and 5.38 for prazosin and rauwolscine, respectively. Phenoxybenzamine reduced the maximal response to noradrenaline and shifted the concentration-response curve to the right. The dissociation constant (KA) of noradrenaline was calculated to be 4.05 +/- 0.21 x 10(-6) M and the occupancy-response plot for noradrenaline showed a linear relationship. It is concluded that alpha-adrenergic contraction of the preprostatic urethra from immature lambs are mediated by alpha 1-adrenoceptors. It is also suggested that the lack of a receptor reserve may affect the degree of urethral constriction and could be related to hormonal status.
Departamento de Fisiología, Facultad de Veterinaria, Universidad Complutense, Madrid, Spain.
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García-Pascual
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Costa
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Isla
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García-Sacristán
D000316:Adrenergic alpha-Agonists / Q000378:metabolism / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure; D009638:Norepinephrine / Q000378:metabolism; D010643:Phenoxybenzamine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D012741:Sexual Maturation / Q000502:physiology; D012756:Sheep; D014521:Urethra / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D010643:Phenoxybenzamine; D009638:Norepinephrine