Excitatory alpha1-adrenergic receptors predominate over inhibitory beta-receptors in rabbit dorsal detrusor.

Purpose: We mapped the regional distribution of alpha1 and beta-adrenergic receptors (ARs) in rabbit ventral and dorsal bladder, and characterized the alpha1-AR subtypes responsible for norepinephrine induced contraction of rabbit dorsal detrusor smooth muscle.
Materials and Methods: Responses to norepinephrine in the absence and presence of adrenergic antagonists were measured in strips taken from clearly defined regions of male rabbit ventral and dorsal bladder.
Results: In the absence of antagonists ventral strips from the bladder body relaxed in response to norepinephrine, while those from the ventral base contracted. Dorsal strips from the bladder dome also relaxed in response to norepinephrine but dorsal strips from the mid and lower body, and the base contracted. All contractile responses were antagonized by incubation with prazosin. Characterization of the alpha-AR subtypes present in dorsal strips from the mid and lower bladder body using BMY 7378 (8-[2-[4 to 2(-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro [4,5] decane-7,9-dione dihydrochloride), chloroethylclonidine, 5-methylurapidil and WB 4101 (2-(2,6-dimethoxyphenoxyethyl)-aminomethyl-1,4-benzodioxane) suggested that the alpha1-AR subtype responsible for the contraction is the alpha1A or alpha1L-AR.
Conclusions: The male rabbit bladder contains at least 4 heterogeneous regions with differing functional responses to adrenergic stimulation, that is 1) the dorsal and ventral dome, where beta-ARs predominate, 2) the ventral detrusor, where beta-ARs predominate, 3) the dorsal detrusor, where alpha1-ARs predominate, and 4) the dorsal and ventral bladder neck, where alpha1-ARs predominate.