Circulatory effects of intraduodenal acidification in the rat

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Abstract
The effect of intraduodenal administration of 0.3 ml/100 g 0.1 N hydrochloric acid and of the i.v. injection of 0.3 U/100 g secretin on the regional circulation was investigated in rats with the radioactive microsphere method. Intraduodenal acid produced a threefold increase in duodenal blood flow, jejunal perfusion was doubled, the perfusion of pancreas increased significantly. There were no significant changes in cardiac output, renal, myocardial, gastric and ileal blood flow. Secretin administration was without effect on the circulation. The same hormone dose produced a tenfold increase in pancreas secretion but was without effect on bile output. It is concluded that in the rat low doses of secretin do not elicit mesenteric flow changes similar to those observed after duodenal acidification. Es wurde an Ratten die Wirkung der intraduodenalen Einführung von 0,3 ml/100 g 0,1 N Salzsäure und der intravenösen Injektion von 0,3 E/100 g Sekretin auf die regionale Blutströmung mit Hilfe der radioaktiven Mikrosphären-Methode untersucht. Die Säuerung des Duodenalinhalts verursachte eine Verdreifachung der Durchblutung im Duodenum und ihre Verdoppelung im Jejunum. Auch die Pankreasdurchblutung nahm signifikant zu. Das Herzminutenvolumen, die Blutströmung des Magens, Ileums, Myocards und der Niere hatten sich nicht signifikant verändert. Sekretinverabreichung führte zu keinen signifikanten Veränderungen der Hämodynamik und der Organdurchblutung. Die gleiche Hormondosis verursachte eine zehnfache Zunahme der Pankreassekretion. Daraus wird geschlossen, daß bei Ratten eine mäßige Sekretindosis keine ähnliche Veränderungen der Mesenterialdurchblutung verursacht als die Säuerung des Duodenalinhalts. Mesenteric blood flow increases after a meal [7, 9, 18, 20, 23] and the reaction may be elicited by the intraduodenal perfusion of digested food [12]. It was assumed that the intestinal hyperaemia is confined to the segment-containing food [12] and is produced by the presence of chyme in the lumen [13]. On the other hand, it was shown by various techniques that intraduodenal introduction of 0.1 N hydrochloric acid increases splanchnic blood flow [2, 3, 5]. In the dog, duodenal acidification increased both hepatic artery and portal venous flow [1] but the localisation of the intestinal hyperaemia is unknown. The mechanism of the splanchnic circulatory changes is not yet fully understood. Vasodilatory responses have been reported after administration of the intestinal hormones gastrin, secretin cholecystokinin or GIP [8, 16, 17, 21]. It was suggested that physiological intraduodenal stimuli may lead to the release of endogenous intestinal hormones in an amount sufficient to account for the observed changes in mesenteric blood flow [9, 16]. It seems, however, that the circulatory changes are not produced by the action of a single intestinal hormone [6]. In the present investigation the effects of intraduodenal acidification on the regional circulation are studied in the rat, and the results are compared with those observed after secretin administration.