Effects and mechanisms of anal electrical stimulation on anorectal compliance and tone in dogs.

Abstract

This study was designed to investigate the changes in rectal compliance and tone during anal electric stimulation and the involvement of the alpha-adrenergic pathway in conscious dogs. Eight healthy dogs were studied in five randomized sessions. Anal sphincter pressure was quantified by using the area under the contractile curve. Rectal compliance and tone were measured in a pressure-controlled phasic and isobaric distention by using an electronic barostat. Anal electric stimulation was performed via a pair of ring electrodes attached to the catheter. The electric stimulation-induced increase in sphincter pressure was lowered by the presence of an alpha(1)-adrenergic receptor antagonist, prazosin (18.6 +/- 7.4 vs. 45.4 +/- 9.7, P < 0.05), or alpha(2)-adrenergic receptor antagonist, yohimbine (10.2 +/- 8.2 vs. 38.3 +/- 7.6, P < 0.05), compared with the control. The threshold volume in rectoanal inhibitory reflex during electric stimulation was significantly higher than during baseline (27.5 +/- 0.9 vs. 22.5 +/- 1.9 ml, P < 0.05). There were no significant differences between the percentage drops in sphincter pressure with and without stimulation at a rectal distention level of 45 ml of air. Anal electric stimulation significantly increased rectal compliance reflected as reduced P(1/2) (11.1 +/- 1.5 vs. 16.7 +/- 1.1, P = 0.027) and reduced kappa (11.6 +/- 2.5 vs. 20.5 +/- 2.6, P = 0.0095), compared with the control session, but did not significantly alter rectal tone. Anal electric stimulation increases anal sphincter pressure, mediated at least partially by the alpha-adrenergic pathway. It also increases rectal compliance but does not alter rectal anal inhibitory reflexes.