Responses of rat isolated intestinal segments to stimulation of perivascular mesenteric nerve fibres

Abstract

1. Isolated preparations of segments of rat jejunum were set up for isotonic recording of the activity of the longitudinal smooth muscle and the extrinsic nerve supply running with the mesenteric blood vessels was stimulated for 30-s periods at 0.5-20 Hz. 2. Contractions were regularly elicited during periods of stimulation at 0.5-2 Hz, and were usually elicited during stimulation at 5 Hz, but relaxations were usually elicited during stimulation at 10 and 20 Hz. On cessation of the period of stimulation, a secondary contraction occurred in most preparations regardless of whether the primary response during the period of stimulation had been a contraction or a relaxation. 3. Tetrodotoxin (0.9 microM) abolished responses during periods of stimulation and the secondary contraction. 4. The relaxations were mimicked by noradrenaline and were abolished by blockade of alpha- plus beta-adrenoceptors but were not affected by hexamethonium, indicating that they are attributable to stimulation of postganglionic noradrenergic fibres. 5. The contractions were mimicked by acetylcholine and were abolished by atropine and hexamethonium, suggesting that they are attributable to stimulation of preganglionic cholinergic nerves: they were also abolished in the presence of capsaicin, indicating that sensory neuropeptide-containing nerve fibres may be involved. 6. The secondary contraction that usually occurred on cessation of stimulation was still present after blockade by atropine or capsaicin of the contractions occurring during stimulation. It was also present after blockade by propranolol and phentolamine of the relaxations occurring during stimulation, and was not affected by indomethacin.