Differential effects of drugs interacting with autonomic transmitters on responses of rat vas deferens to field stimulation

Selective impairment of noradrenergic transmission in the bisected rat vas deferens following photochemically-induced cerebral ischaemia

BACKGROUND

Cerebrovascular disease may impair the autonomic control of peripheral organs including the male urogenital tract. This study investigates the effect of cortico-parietal focal ischaemia on the adrenergic and purinergic transmission in isolated epididymal and prostatic portion of rat vas deferens.

METHODS

Focal brain ischaemia was induced in male rats by photochemical activation following rose bengal intravenous injection. Twenty-four hours following brain ischaemia, cumulative and non-cumulative concentration-response curves were obtained for noradrenaline and alpha,beta-methylene ATP in the right and left epididymal and prostatic portions of the vas deferens. Both portions were also stimulated by single-pulse or pulse trains at 2-30 Hz to produce isometric contractions.

RESULTS

In both portions from ischaemic rats the response to exogenous noradrenaline was markedly depressed compared with controls. Acute cortico-parietal ischaemia almost completely abolished the adrenergic phase of the response to single-pulse stimulation in the epididymal portion of the vas deferens. In addition, brain ischaemia deeply depressed phasic and tonic contractions of the frequency-response curve in both portions of bisected vas deferens.

CONCLUSIONS

Cortico-parietal ischaemia produces a selective noradrenergic impairment at the level of male sexual secondary organs that may contribute to sexual dysfunction after stroke.

Possible role of sildenafil in inhibiting rat vas deferens contractions by influencing the purinergic system

AIM

To evaluate the effect of sildenafil, a selective inhibitor of cyclic guanosine monophosphate (cGMP)-selective type 5 phosphodiesterase, on isolated rat vas deferens and its connections with the purinergic system.

METHODS

Epididymal and prostatic portions of isolated vas deferens were placed in organ baths containing Krebs' solution. Contractions were induced by noradrenaline (NA), adenosine triphosphate (ATP), alpha,beta-methylene ATP and electrical field stimulation (EFS). The effect of sildenafil on the contractions was compared with suramin and Evans blue (EB).

RESULTS

NA, ATP, alpha,beta-methylene ATP and EFS caused contractions in both portions of vas deferens. NA-induced contractions were unaffected by sildenafil and suramin but potentiated by EB. ATP-induced contractions were non-competitively inhibited in both portions by sildenafil and suramin but potentiated by EB. alpha,beta-methylene ATP-induced contractions were unaffected by sildenafil but were inhibited in both portions by suramin and EB. EFS-induced contractions were inhibited by sildenafil and suramin while potentiated by EB.

CONCLUSION

Sildenafil inhibited the contractions in both portions of vas deferens, as did suramin. We have suggested that purinergic system has a role in this antagonism and it seems to be mediated by an ATP-dependent mechanism instead of a receptor interaction.

Effects of Heptanol on Neurogenic Contractions of Vas Deferens: A Comparative Study of Stimulation Frequency in Guinea Pig and Rat

This study examines the role of gap junctional communication in smooth muscle in relation to the frequency of stimulation and the innervation density of the tissue in the generation of neurogenic contractions. Toward this end the effects of heptanol, a gap junctional blocker, on the neurogenic contractions of guinea pig and rat vas deferens at different frequencies of stimulation (single pulse, 5, 10, 20, 40, 60, and 80 Hz) were studied. In both the prostatic and epididymal halves of these tissues, heptanol abolished the neurogenic contractions at the lower frequencies of stimulation. At higher frequencies, contractions were resistant to heptanol action. The effect of heptanol on the neurogenic contractions was found to decrease with increasing stimulation frequency. The neurogenic contractions of rat vas deferens were more resistant to heptanol than those of guinea pig vas deferens. Our data indicate that gap junctional communication is significant in the generation of neurogenic contractions in both guinea pig and rat vas deferens in a frequency-dependent manner, and we discuss the mechanisms underlying these findings.