Abstract
The intrinsic innervation of the bovine forestomach was investigated by analyzing the responses of isolated smooth muscle preparations to transmural electrical stimulation. Transmural stimulation (TMS) caused a contraction or a contraction followed by relaxation in longitudinal muscle (LM) strips prepared from the anterior (ras) and dorsal (rds) sacs of the rumen, and from the greater curvature of the reticulum (ret), and the omasum (oma). The excitatory component of the biphasic response elicited by TMS was enhanced by anticholinesterases. After atropine treatment, it was converted into an inhibitory one. The relaxation was predominantly obtained in the LM of rds and the circular muscle (CM) of oma. It was entirely resistant to adrenergic α- and β-blockers or a combination of them and guane-thidine. Tetrodotoxin and cocaine inhibited or abolished reversibly both excitatory and inhibitory responses evoked by TMS, while hexamethonium had little effect on them. Stimulation began to cause the contraction at the frequency of 2-5 Hz and response reached a maximum between 40 and 80 Hz with the supramaximum intensity. This relaxation in response to TMS appeared at 2 Hz and reached a maximum at 10 Hz or less. Adrenaline caused a contraction followed by a relaxation in the LM of rds and a contraction in the CM of oma, but they were inhibited almost completely by phenoxybenzamine and propranolol, Tespectively. These results suggest that the smooth muscle of the bovine forestomach was supplied by postganglionic excitatory cholinergic nerves and nonadrenergic inhibitory nerves.
