[Action of morphine on periodic gastric motor activity in dogs after selective distal vagotomy].

Chronic experiments on 9 dogs with gastric fistulas (with preliminary selective vagotomy in 5) were made to examine the action of morphine on periodic gastric motility (PGM). Morphine was injected subcutaneously at rest, selecting the minimal threshold vomitive dose (TVD) that provoked a series of contractions with a single vomiting attack, and the maximal dose that produced only an extra period of contractions. Clear-cut differences were discovered in the dogs' sensitivity to morphine (the groups with high and low sensitivity, the TVD 35 and 110 micrograms/kg on the average, respectively). Three consecutive stages were defined on the part of PGM in the response to morphine injection. After vagal denervation the sensitivity to morphine (as evaluated from the TVD magnitude) remained unchanged, the second stage (the alternating accelerated cycles) was lost, while the third stage involved continuous contractions. It is inferred that the primary reaction to morphine occurs as a result of eliminating the central inhibitory effects on PGM, the second stage is effected according to the mechanism of the enterogastric reflex, whereas the third stage reflects complete loss of the central and peripheral inhibitory mechanisms that regulate PGM.