Binding and Functional Properties of Alpha 1 Adrenoceptors and Area Density of Smooth Muscle in the Canine Prostate

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Abstract
The present study was designed to compare the area density of smooth muscle, and the binding and functional properties of alphai adrenoceptors in 8 different regions of the canine prostate. The area density of smooth muscle, alphai adrenoceptor density, and contractile response to phenylephrine were investigated using immunoenzymatic staining with color assisted computer image analysis, radioligand receptor binding, and isometric tension studies, respectively. The equilibrium dissociation constants (Kd) for 125I-Heat binding and the alphai adrenoceptor densities (Bmax) in the prostatic regions ranged between 138–230 pM and 0.32–0.52 fmol/wet wt., respectively. The maximal tension generated in the presence of phenylephrine (phenylephrine Emax) and phenylephrine EC50s ranged between 0.043–0.129 gm. force/mm.2 CSA and 4.0-11.0 μΜ, respectively. The differences between Kd, Bmax, Emax, and EC50 were not significantly different between the different regions of the prostate. The percent area density of smooth muscle ranged between 10.6-24.4%. A direct relationship was not observed between alphai adrenoceptor density and phenylephrine Emax, or alphai adrenoceptor density and percent area density of smooth muscle. A direct relationship was observed between the phenylephrine Emax and percent area density of smooth muscle (p = 0.003; r = 0.90). The phenylephrine Emax and percent area density of smooth muscle was threefold and 1.6-fold greater in the peripheral prostate relative to the central prostate, respectively. The morphometrical and isometric tension studies provides evidence that the canine prostate is a heterogeneous gland.