The action of morphine, pethidine, and amidone upon the intestinal motility of conscious dogs

Observations concerning the action of 5-hydroxytryptamine on the peristaltic reflex

In isolated guinea-pig intestine 5-hydroxytryptamine increased the longitudinal muscle contractions in response to acetylcholine while the ganglionic action of nicotine was first facilitated and then blocked. Phenyldiguanide, veratrine, veratridine and protoveratrine, like 5-hydroxytryptamine, depressed the response to nicotine, leaving that to acetylcholine unaffected.The sensory stimulants, like 5-hydroxytryptamine, facilitated the peristaltic reflex when applied to the mucosa, and abolished it when applied to the serosa. Preceding the block, the initial effect of low concentrations of 5-hydroxytryptamine applied to the serosa was a short stimulation of peristalsis.Concentrations of 5-hydroxytryptamine which had an approximately equal stimulant action (mucosal 1 to 4 x 10(-6), serosal 2 to 8 x 10(-8)) were tested when various parts of the reflex arc were blocked. During block by procaine introduced into the lumen, mucosal application of 5-hydroxytryptamine re-established peristalsis, but serosal application of 5-hydroxytryptamine had no effect. During block by hexamethonium or atropine present in the bath, 5-hydroxytryptamine restored peristalsis more effectively by serosal application than by mucosal application. During block by serosal application of 5-hydroxytryptamine, morphine, phenoxybenzamine or dihydroergotamine, mucosal application of 5-hydroxytryptamine restored the peristaltic reflex while serosal application had no effect. During block by 2-bromo-lysergic acid diethylamide or lysergic acid diethylamide acting from the serosal surface, 5-hydroxytryptamine had no effect whether acting on the mucosal or on the serosal surface.It is concluded that 5-hydroxytryptamine facilitates the peristaltic reflex at two sites: when introduced into the lumen it stimulates mucosal sensory receptors; when acting from the serosal surface it sensitizes the muscle to the transmitter acetylcholine. There is also a transient stimulant action on the ganglia which is soon followed by inhibition; this indicates that 5-hydroxytryptamine applied to the serosa abolishes peristalsis by ganglion block.

Comparative effects of analgesics on pain threshold, respiratory frequency and gastrointestinal propulsion

In the rat, the ratio of the analgesic to the respiratory depressant potency was the same for morphine, codeine, diamorphine, methadone, dipipanone, piperidylisomethadone, phenadoxone, dextromoramide, and propoxyphene. The relative respiratory depressant activity of pethidine tended to be less, but the difference was not significant. The ratio of the analgesic dose to the dose preventing transport of a charcoal meal in the rat was about the same for morphine, codeine, pethidine, methadone, phenadoxone, dimethylthiambutene, and propoxyphene; the relative activities of these compounds in inhibiting the peristaltic reflex of the isolated guinea-pig ileum were also similar. However, because of differences in the slopes of regression lines in the charcoal meal test, some compounds (for example, morphine) had a greater effect on gastrointestinal propulsion than others (for example, pethidine) when given at moderate analgesic dose levels.In studies of the effects of intracisternal morphine in the rat, effects on the spinal reflex of the tail were to some extent dissociated from effects on the threshold for a squeak response. Further, the delaying of transport of a charcoal meal paralleled depression of respiratory rate, and this is evidence for the participation of a central as well as a peripheral action in the effect of morphine on the gastrointestinal tract. The delay in propulsion was reduced by nalorphine and increased by atropine and two general anaesthetic substances, but was unaffected by a number of other pharmacological agents.

The calcium channel antagonist, verapamil, potentiates the inhibitory action of morphine on intestinal and biliary motility

The effects of morphine and verapamil have been assessed on the gastrointestinal propulsion of charcoal meal and egg yolk-induced gall bladder emptying in mice. Each drug significantly inhibited these functions. In combination, an additive effect was seen on the inhibition of gastrointestinal transit, whilst verapamil potentiated the morphine-induced inhibition of gall bladder emptying. It is concluded that calcium ion channel antagonists may potentiate the activity of opiate drugs.

Opioid action of the intestine: the importance of the intestinal mucosa

Drug effects on the intestine are traditionally explained in terms of action on the muscle layers and the nerves that control them. This is particularly true in the case of the opioids but research starting two decades ago has identified the intestinal mucosa as the site of action of the antidiarrhoeal opioids. Continued research using the intestinal mucosa offers a fresh approach to solving some old problems. For example it could lead to more confident predictions to be made about the wanted and unwanted effects of opioid drugs on the intestine and may help to find better drug treatments for alleviating withdrawal diarrhoea in addicts. Eventually it may help to explain how the general process of opioid dependence occurs at a cellular level.

The action of loperamide in inhibiting prostaglandin-induced intestinal secretion in the rat

1 The mechanisms by which loperamide inhibits the intestinal secretion induced by prostaglandin E2 were investigated in rat jejunum. 2 In vivo loperamide prevented prostaglandin-induced fluid secretion but did not reduce the associated rise in the transintestinal potential difference. 3 In intestinal sheets the electrical response to prostaglandin E2 was enhanced in the presence of loperamide. 4 The ionic basis of these changes was determined by measuring Na+ and Cl- fluxes across intestinal sheets. Loperamide did not reduce the prostaglandin-induced increase in net Cl- secretion, although it prevented the inhibition of mucosal-to-serosal Na+ movement. 5 Loperamide does not alter cyclic adenosine 3',5'-monophosphate (cyclic AMP) levels by a direct action at the enterocyte, since in isolated enterocytes neither basal nor prostaglandin-stimulated cyclic AMP levels were affected by the drug.

Inhibition by morphine of prostaglandin E1-stimulated secretion and cyclic adenosine 3',5'-monophosphate formation in the rat jejunum in vivo

1 The effects were studied of prostaglandin E1 (PGE1), theophylline and morphine on net water flux and mucosal cyclic adenosine 3',5'-monophosphate (cyclic AMP) levels in the jejunum of anaesthetized rats in vivo. 2 Infusion of PGE1 (3.2 micrograms/min, i.a.) caused a reversal from net water absorption to net secretion and enhanced the mucosal cyclic AMP content by 54%. 3 Theophylline (5 mg/ml, intraluminal) similarly produced a reversal from net water absorption to net secretion and increased mucosal cyclic AMP content by 54%. Additional intra-arterial infusion of PGE1 resulted in a massive increase in net water secretion and an increase in mucosal cyclic AMP content by about 200%. 4 Pretreatment with morphine (10 mg/kg, s.c.) reduced the effect of PGE1 on net water flux and completely inhibited its effect on the mucosal cyclic AMP content. Naloxone (10 mg/kg, s.c.) abolished both effects of morphine. 5 A good correlation (r = 0.99) was demonstrated between mucosal cyclic AMP levels and net water flux. 6 The present results demonstrate that PGE1 stimulates intestinal fluid secretion by increasing mucosal cyclic AMP levels. The antidiarrhoeal effect of morphine can be explained by its inhibition of the PGE-mediated increase in cyclic AMP levels, which, in turn, leads to a reduction in intestinal secretion.

Inhibition of PGE1 induced intestinal secretion by the synthetic enkephalin analogue FK 33-824

1. The effects of the enkephalin analogue, FK 33-824 were compared with those of morphine and naloxone on the prostaglandin E1-induced increase in intestinal fluid volume and unanaesthetized and pithed rats. 2. FK 33-824 inhibits the prostaglandin E1-induced increase in intestinal fluid volume both in unanaesthetized and pithed rats. 3. Naloxone abolished the inhibitory effect of FK 33-824 in both experimental models. 4. It can be concluded from the experiments in pithed rats that the inhibitory effect of FK 33-824, like that of morphine, on prostaglandin E1-induced secretion is caused by a peripheral action. 5. It is assumed that endogenous enkephalins protect against prostaglandin-mediated loss of fluid into the gut lumen. This protective effect can be mimicked by an enkephalin analogue and blocked by naloxone.

Inhibition by morphine of prostaglandin-stimulated fluid secretion in rat jejunum

1 Anesthetized rats (225 to 300 g) were used to study the inhibitory effect of morphine on fluid secreted by the small intestine. 2 Small intestinal fluid secretion was stimulated by infusion of prostaglandin E1 (PGE1) into the aortic arch, the jejunum being more sensitive than the ileum. Infusion of PGE1 2 microgram/min caused maximal net fluid secretion in the jejunum but inhibited net fluid absorption in the ileum. 3 Morphine caused a dose-related inhibition of maximal PGE1-stimulated fluid secretion in the jejunum. At the higher doses of morphine used (5 to 20 mg/kg) the fluid transporting function of the jejunum was restored almost to normal net absorption. 4 The inhibitory effect of morphine on PGE1-stimulated fluid secretion was antagonized by naloxone. Naloxone caused a parallel shift to the right of the dose-response curve for morphine. 5 Two other narcotic analgesics were assayed relative to morphine and their descending order of potency was oxymorphone greater than morphine greater than pethidine. 6 It is suggested that the antisecretory effect of morphine in the small intestine may contribute to its efficacy as an anti-diarrhoeal drug. Further studies on the rat jejunum may show it to be a useful model for predicting narcotic drug activity and as such, may give some insight into the mechanisms of action of these drugs.

The intraluminal pressure patterns in diverticulosis of the colon: Part IV The effect of pethidine and probanthine

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The intraluminal pressure patterns in diverticulosis of the colon: Part II The effect of morphine

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The action of morphine and related substances on contraction and on acetylcholine output of coaxially stimulated guinea-pig ileum

Morphine depresses the twitch and tetanus of stimulated guinea-pig ileum by reducing acetylcholine released from cholinergic nerve endings. Acetylcholine output per shock falls to roughly the same residual amount at varying stimulation rates. Since normal output per shock declines with increasing stimulus frequency, the proportionate effect of morphine diminishes as stimulus frequency rises. Acute "tolerance" to morphine and a state of "morphinedependence" can be produced. Phenadoxone, dihydromorphinone, metopon, methadone, and heroin are more active, codeine and pethidine less active, than morphine. Nalorphine also depresses the twitch and can desensitize the gut both to itself and to morphine.