Miguel Luján

PHARMACOLOGICAL CHARACTERIZATION OF OPIATE PHYSICAL DEPENDENCE IN THE ISOLATED ILEUM OF THE GUINEA-PIG

1 Physical dependence was produced in ilea from naive guinea‐pigs by exposure of the tissues to different opiates for logarithmically‐spaced periods of time (20–320 min). The responsiveness of the tissue to naloxone, as indicated by a strong contracture of the ileum, was enhanced in contrast to that found in intestines not exposed to opiates. 2 The dose‐response curves to naloxone obtained in tissues individually exposed to different opiates showed that their relative potency in increasing sensitivity to naloxone was as follows: levorphan > morphine > Met‐enkephalin > nalorphine > pentazocine. 3 The naloxone‐induced response was dose‐dependent and was directly related to the opiate concentration and length of exposure. 4 Dextrorphan, the inactive isomer of levorphan, did not increase the responsiveness of the tissues to the narcotic antagonist, indicating that the phenomenon is stereospecific. 5 The naloxone‐induced contraction in ilea exposed for 320 min to morphine (1 × 10−6 m) was not prevented or suppressed by the administration of a large dose of morphine (1 × 10 −5 m) before or immediately after the naloxone challenge. 6 The evidence presented here shows that a phenomenon resembling in vivo opiate physical dependence can be acutely produced in vitro with pharmacological characteristics similar to other naloxone‐induced abstinence effects.

Pertussis toxin blocks the action of morphine, norepinephrine and clonidine on isolated guinea-pig ileum

Administration of pertussis toxin (60 micrograms/kg i.p.) to guinea-pigs blocked the ability of morphine, norepinephrine and clonidine to inhibit electrically stimulated contractions in the isolated ileum. The toxin reached its maximum effect 6 days after its administration. The effect of the toxin was reversible; a slow but full recovery of the response to morphine was observed in ilea from guinea-pigs treated with toxin 18 days before the experiment. It is suggested, based on the known action of pertussis toxin, that inhibition of adenylate cyclase through Ni (guanine-nucleotide regulatory protein) is involved in the acute action of morphine, norepinephrine and clonidine in the motoneurons of the myenteric plexus of the ileum.

Morphine-theophylline interaction: antagonism or facilitation?

1 Morphine‐theophylline interactions were investigated in both acute and narcotic‐dependent preparations, in vitro and in vivo, using four different experimental models: LD50 doses of morphine and naloxone in the mouse; naloxone‐induced contractions in the electrically‐stimulated and opiate‐dependent isolated ileum of the guinea‐pig; naloxone‐induced jumps in the mouse; and calcium uptake in synaptosomal preparations. 2 The LD50 of morphine was significantly increased by theophylline. 3 The lethal effect of theophylline was potentiated by pretreatment of the animals with naloxone. 4 Theophylline displayed protective effects in the inhibitory response to morphine and antagonism to the withdrawal response induced by naloxone in the electrically‐stimulated isolated ileum of the guinea‐pig. 5 The number of jumps induced by naloxone in morphine‐dependent mice was significantly diminished by theophylline. 6 The inhibitory effect of morphine on the synaptosomal uptake of calcium was decreased by theophylline. 7 The effects of both morphine and theophylline on the cyclic nucleotides and the possible role of calcium in these actions are discussed.

Morphine dependence in the isolated guinea-pig ileum and its modification by p-chlorophenylalanine

Abstract Experiments were performed to quantitatively determine morphine physical dependence in the isolated guinea-pig ileum and to assess the influence of p-chlorophenylalanine (PCPA) on its development. Ileum segments taken from animals treated with 10 s.c. injections of 100 mg/kg of morphine, given at intervals of 8 hr without interruption, responded with intense, prolonged, dose-dependent contractions to the in vitro administration of naloxone, although contractions guinea-pigs also responded to naloxone, although contractions were smaller and of short duration. The sensitivity to naloxone on segments isolated from morphinized animals was compared to that of controls. Ilea from morphine-treated guinea-pigs were 8 to 32 times more sensitive to naloxone, as determined by a shift in the naloxone concentration-response curve to the left. There was also a three-fold increase in the maximum response. This phenomenon was taken as evidence of narcotic dependence. PCPA, given before morphine administration, at doses producing only a slight (11%) decrease in intestinal serotonin (5-HT) levels, partially reduced the sensitivity of the morphine-treated ileum to naloxone. However, high doses of PCPA, decreasing intestinal 5-HT by 40%, enhanced the abstinence-like effects of naloxone in the morphine pretreated ileum. PCPA by itself changed the responsiveness of the non-morphinized ileum to naloxone. The direction and magnitude of the change produced by PCPA alone was roughly equivalent to that produced by the serotonin depletor in the morphinized ileum. This finding indicates that PCPA has no effect upon the development of physical dependence in the isolated ileum. It remains to be determined whether or not the increased sensitivity to naloxone induced by high doses of PCPA has something in common with the changes in responsiveness to the antagonist induced by narcotics.

Electrically induced narcotic-like dependence in the isolated guinea-pig ileum

Abstract Segments of guinea-pig ileum stimulated at 10 Hz (0.5 msec, supramaximal voltage) for periods of 15 min respond with an intense, dose-dependent contraction to the in vitro administration of naloxone. The antagonist produced only a very modest contraction in control segments (0.1 Hz stimulation). Comparison of dose-response curves for naloxone indicated that the sensitizing effect of electrical stimulation at 10 Hz was on the order of 100-fold. The addition of naloxone to the bath immediately before the stimulatory period at 10Hz completely prevented the development of this effect. Moreover, atropine produced a dose-dependent inhibition of the contraction. It was also found that the magnitude of the naloxone-induced contraction is a function of the duration of the stimulatory period and is maximal after about 15 min. The data presented indicate that the contraction induced by naloxone in ilea stimulated at 10 Hz has many similarities to the response produced by the same antagonist in narcotic-dependent preparations. Thus, it is possible that electrical stimulation at high frequencies induces a state of narcotic-like dependence in this tissue. Acetylcholine may be the mediator of the naloxone-induced contraction.

Behavioral and biochemical correlates of chronic administration of quipazine

In Experiment 1 groups of rats received single injections of 1, 3, 10, 20 or 40 mg/kg quipazine, and their total 24-hr food and water intake after a 24-hr deprivation period was recorded; there was a dose-related reduction of both food and water intake. In Experiment 2 a group of 15 rats received 5 mg/kg/day, SC quipazine during 29 days, and a control group received saline injections. During treatment, all animals were exposed to a 24-hr food and water deprivation schedule, alternated with 24 hr of free access. Food and water consumption was measured 2 and 24 hr after drug injection; regional 5-HT concentrations were determined at 1 and 13 treatment days by fluorometric assay. Beginning the first treatment day, food and water intake decreased, but by the 13th day the quipazine group had returned to normal ingestion levels. 5-HT concentrations were increased in cerebellum and cortex in acute conditions, but after 13 days they had decreased in cerebellar samples. In Experiment 3 we found that the effects of quipazine on food and water ingestion were recovered after 14 days of discontinuing chronic drug administration.

Kindling-like phenomenon in the isolated ileum of the guinea-pig.

Repeated bursts of low voltage electrical stimulation of the isolated ileum of the guinea-pig gradually leads to the development and progressive intensification of the tissue basal activity, culminating in spontaneous, sudden strong contractions of the preparation, which persist for several hours after the stimulation has been discontinued. The magnitude of these alterations are determined by the parameters of the stimulation, mainly by the number of electrical stimulations, the frequency of stimulation, and the interstimulus interval. Maximal alterations are obtained with periods of stimulation of 20 Hz for 10 sec, pulses of 3.0 msec, repeated every 20 min for 15 times. Phenytoin, flunitrazepam, diazepam, phenobarbital and carbamazepine effectively inhibited the fully developed phenomenon in the tissues. The effect described in this report may be related to kindling in the brain.

Adipsic, but not anorectic, effect of fluprazine hydrochloride in rats

The present experiment explored the anorectic and adipsic effects of fluprazine hydrochloride, a phenylpiperazine compound. Thirty-eight albino rats were randomly assigned either to a control saline group (six rats) or to groups (eight subjects each) receiving an IP dose of fluprazine in saline (1.25, 2.5, 5 or 10 mg/kg). No anorectic effect of the drug doses was observed 30, 60, 90, 120, 180 and 240 min, and 24 h after drug injection. However, water drinking was significantly decreased 30 min after drug administration, with 5 and 10 mg/kg, compared to saline.

Electrocardiographic alterations induced by repeated electrical stimulation of the heart at low intensity

Repeated, low-intensity electrical stimulation of the heart gradually leads to the development of electrocardiographic abnormalities that culminate in cardiac arrhythmias, mainly A-V block in the isolated heart frog and ventricular and supraventricular tachyarrhythmias in the canine heart in situ. The pattern of development of these alterations shows some characteristics similar to the kindling phenomenon. Blockade of adrenergic influences on the heart offered complete protection against the development of cardiac arrhythmias. These results support the idea that a kindling-like effect can be induced by the periodic electrical stimulation of structures other than the CNS.