Castration induces acute vasoconstriction of blood vessels in the rat prostate concomitant with a reduction of prostatic nitric oxide synthase activity

Purpose: Previous studies demonstrating a rapid and drastic reduction of bl ood flow to the rat prostate gland resulting from castration caused us to c onsider the influence of castration on the state of vascular constriction a nd on the activity of the vascular tone-regulating factors (nitric oxide sy nthase and cyclic GMP) in the rat prostate. Materials and Methods: Sections of ventral prostate glands obtained from in tact and castrated rats were analyzed for the mean areas within smooth musc le-coated blood vessels using a computerized microscopic image analysis sys tem. Nitric oxide synthase (NOS) levels were measured in prostatic extracts from unoperated or castrated rats using an enzyme assay system that measur es conversion of H-3-L-arginine to citruline. Cyclic GMP levels were measur ed in prostatic extracts from unoperated or castrated rats using a competit ive radioimmunoassay system. Results: The mean area within ventral prostate smooth muscle-coated blood v essels was reduced 39% at 24 hours after castration (p = 0.039) and 47.7% a t 48 hours after castration (p = 0.039). NOS activity measured in prostatic extracts was reduced 38% at 24 hours (p = 0.0012) and 51.6% at 36 hours af ter castration (p = 0.0001) compared with the control group of noncastrated rats. Finally, prostatic cGMP levels were reduced 55.8% (p = 0.0018) at 36 hours after castration when compared with controls rats. Conclusion: Within 24 hours after castration, the lumenal areas of smooth m uscle-coated blood vessels in the rat prostate gland were found to be signi ficantly reduced. This vasoconstriction was associated with a significant r eduction of prostatic NOS activity as well as a reduction in the prostatic levels of the NOS co-factor, cGMP. Thus, acute vasoconstriction is a promin ent early event associated with rat prostate regression in response to cast ration and likely contributes to the regression of the tissue.