Comparative Pharmacology of the Male and Female Rabbit Bladder Neck and Urethra: Involvement of Nitric Oxide

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Abstract
The present study compared the contractile and relaxant responses of male and female rabbit bladder neck and urethra to field stimulation (FS) and various contractile and relaxant agents, with special attention paid to the involvement of nitric oxide (NO) in the mediation of field-stimulated relaxation. FS at basal tension elicited a frequency-dependent contractile response in all preparations. The maximal response to high frequency FS was significantly greater in the bladder neck strips isolated from male rabbits than in those from female rabbits. There were no significant differences in the response to bethanechol or phenylephrine between strips isolated from males and females. Field-stimulated responses of the strips from male bladder neck and urethra were greater than the response to phenylephrine. The responses of all strips to FS were greater than those to bethanechol. In addition, the response to phenylephrine was generally greatere than that to bethanechol. Phentolamine was a significantly more effective inhibitor of the response of the female bladder neck and urethral strips to FS than of the response of the male strips. The contractile response of all strips to phenylephrine was generally greater than that to bethanechol for both sexes and for both bladder neck and urethral strips. NG-nitro-L-arginine methylester (L·NAME) inhibited totally the field-stimulated relaxation of all strips. Isoproterenol stimulated a slowly developing but significant inhibition of phenylephrine prestimulated contractions. In conclusion, significant differences exist in the magnitude of field-stimulated relaxation between the bladder neck and urethra of both male and female rabbits, and, for all tissues, field-stimulated relaxation could be completely inhibited by pretreatment with L·NAME, an NO synthesis inhibitor.

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