Rhythmic Contractions Induced by Vagotomy in the Fundus of Rat Stomach

Abstract

Abstract-Continuous rhythmic contractions were observed in longitudinal muscle strips of fundus obtained from the chronically vagotomized rat stomach. These vagotomy-induced rhythmic contractions (VRC) were not blocked either by tetro dotoxin (3 x 10-6 M) or atropine (3 x 10_1 M), indicating that the VRC was myogenic in origin. It was also found that the VRC had the following characteristics.1) The VRC was blocked either by 10-5 M D600 or by Ca 2+ deprivation from the medium. 2) On replacement of Na+ with sucrose or of K` with Na+, the tone of fundus strips was concomitantly elevated with the cessation of the VRC. 3) 10-5 M ouabain blocked the VRC. 4) The VRC was blocked by cooling. 5) The VRC disappeared under anoxic conditions. Based on these results possible mechanisms of the VRC are dis cussed in relation to an energy dependent activity of the cell membrane.Among the smooth muscle from different tissues which exhibit rhythmic spontaneous contractions in vitro are those from the taenia coli, portal vein, etc. These spontaneous activities seem to be myogenic in origin, since various drugs which interefere with the nervous activity or transmission do not abolish the activities (1-3).On the other hand, rat stomach fundus strips free of mucosa show no spontaneous mechanical activity under usual conditions in vitro (4). In a previous paper, however, we reported that when fLindus strips were prepared from chronically vagotomized rat stomach they exhibited spontaneous rhythmic contractions and that their maximum contractile responses to cholinergic agonists and to serotonin decreased to an appreciable extent. These findings suggest that vagotomy exerts a profound influence on smooth muscle activities (5).This study was undertaken to obtain insight into the mechanisms underlying the spon taneous rhythmic contractions. For this purpose the effects of some agents, of deprivation of ions from the bathing fluid, and also of chronic sympathectomy were investigated. MATERIALS AND METHODSMale rats of Donryu strain weighing from 240 to 300 g were used.Chronic sympa thectomy was performed by excision of celiac ganglion and some length of postganglionic nerve bundle as reported previously (5). Chronic vagotomy was performed by bilateral