Objective: 

Investigation of activation-dependent descending reflex motority of anal canal.

Methods: 

Mechanographic computerized on-line technique, partitioned organ bath, electrical stimulation (EFS, 0.8 ms; 40 V; 5 Hz) or balloon distension were used to evaluate motor responses of anal canal (AC) and recto-anal reflexes. Immunohistochemical and histochemical techniques were used to study the presence and distribution of acetylcholine, substance P and nitric oxide in neuronal structures of the myenteric plexus of the anal canal.

Results: 

Frequency dependent local (14.9±1.35 mN) and descending (5.3±0.7 mN) contractions of AC, elicited by EFS applied to the AC or to the distal part of the rectum were registered and the amplitudes of local responses were more expressed (p<0.05). The descending response of AC induced by balloon distension was a contraction (1.50±0.18 mN) followed by relaxation (3.12±0.34 mN). Atropine (3x10-7 M) suppressed EFS-elicited contractions of AC and a relaxation occurred. The distension-induced contraction was reduced while the relaxation was not altered. In the presence of atropine spantide (10-7 M) augmented contractile response of AC. NG-nito-L-arginine (5x10-4 M) increased the excitatory responses, prevented the atropine-induced relaxation of the EFS-elicited response and inhibited the distension-induced relaxation. L-arginine (5x10-4 M) decreased the contractions and increased the relaxation. ChAT-, substance P- and NADPH-diaphorase-positive nerve fibers were found in myenteric ganglia of the anal canal.

Conclusions: 

The results suggest descending pathways involved in motor activity of anal canal comprising stimulatory cholinergic and tachykininergic, dependent on electrically-induced excitation and inhibitory nitrergic, sensitive to distension of rectal wall.