Involvement of platelet activating factor in the endotoxin-induced effects on gastrointestinal electrical activity and some haematological parameters in the conscious miniature pig.

In conscious miniature pigs the influence of intravenous dose of lipopolysaccharide (LPS), 10 microg/kg over 10 min, with and without pretreatment with a platelet activating factor (PAF) antagonist, SAH 63-675 10 mg/kg, on gastrointestinal electrical activity, arterial pressure and clinical and haematological parameters was studied. Dose of LPS provoked mild clinical signs and hypotension, which were prevented by PAF antagonism. The LPS induced leukocytosis and increase in mature neutrophils, however, were PAF independent. Pretreatment with the PAF antagonist attenuated the LPS-provoked inhibition of electrical activity in the antrum, jejunum, ileum and caecum. These results suggest a beneficial effect of PAF antagonism in porcine endotoxaemia.

[Animal experiments: legal, scientific and ethical aspects]. / Dierexperimenten: wettelijke, wetenschappelijke en ethische aspecten.

Among the legal aspects the following topics are treated: the definitions of an experimental animal, an animal experiment and alternative methods with special reference to the 3 R's (replacement, reduction and refinement of animal experiments); the qualifications, education and training of researchers and animal technicians; the licence for animal experimentation; the control on animal welfare; the origin and identification of experimental animals; statistical data on the number of experimental animals; ethics committees and their structure and functions in The Netherlands and Flanders. Extrapolation, species specificity and variability are the most important scientific limitations of animal experimentation. After a short historical survey on the man-animal relation, the following ethical aspects are discussed: the instrumental versus intrinsic value of an experimental animal; the hybrid status of the animal; the objectives of animal rights movements; the balance between the human benefit of an animal experiment and the discomfort for the animal; the problem of animal rights and animal suffering and pain.

Influence of platelet activating factor on gastrointestinal electrical activity and some haematological and clinical parameters in the conscious miniature pig.

The effects of intravenous (i.v.) infusion of platelet-activating factor (PAF), 100 ng/kg/min for 10 min, with and without pretreatment with a selective PAF-antagonist on gastrointestinal electrical activity, arterial pressure and clinical and haematological parameters were studied. Conscious miniature pigs with electrodes implanted in the wall of the antrum pylori and small and large intestine were used. Platelet-activating factor induced restlessness or depression, shivering, tachypnoea and coughing, retching and vomiting, hypotension and a delayed and sustained increase in leucocyte count with an increase in percentage of segmented neutrophils. The PAF-antagonist, SAH 63-675, administered at 10 mg/kg intravenously, inhibited these effects. Platelet-activating factor resulted in a decrease in electrical activity in the antrum and large intestine, whereas small intestinal activity was not significantly influenced. Pretreatment with the antagonist suppressed these inhibitory effects.

Effect of some gastrointestinal hormones on antral, small intestinal and caecal myoelectrical activity in the conscious miniature pig.

The effect of i.v. infusion of gastrin (CCK-4), cholecystokinin (CCK-8) and pancreatic polypeptide (PP), 20 and 200 ng/kg/min for 1 h, on gastrointestinal electrical activity and arterial pressure was studied in conscious miniature pigs. During infusion of CCK-8 a transient hypertension was observed. In the antrum, the 3 peptides provoked an increase in slow wave activity and a decrease in spike activity. In the intestine, CCK-8 induced an increase in ileal spiking activity, whereas infusion of PP resulted in an increased frequency of long spike bursts in the caecum.

Effect of cisapride on myoelectrical activity of the gastrointestinal tract in the conscious miniature pig.

In conscious miniature pigs with electrodes implanted in the wall of the antrum pylori, duodenum, jejunum, ileum and caecum, the influence of intravenous injection of cisapride, 0.5 and 1 mg/kg, on gastrointestinal myoelectrical activity, was examined. Cisapride, 1 mg/kg, induced a delayed and sustained increase in antral myoelectrical activity. The studied intestinal segments were rather insensitive to the stimulating effect of the benzamide, since only the jejunum and the caecum revealed an increase in myoelectrical activity with the higher dose studied.

Effect of the C-terminal tetrapeptide amide of gastrin (CCK-4) and pancreatic polypeptide on gastrointestinal electrical activity in the conscious miniature pig.

The effect of IV infusion of CCK-4, 33.2 and 332 pM/kg/min, and pancreatic polypeptide (PP), 4.8 and 48 pM/kg/min, on gastrointestinal electrical activity was studied in conscious miniature pigs with electrodes implanted in the wall of the antrum pylori and small intestine. In the antrum pylori infusion of the higher dose of both peptides provoked an increase in frequency of the basic electrical rhythm together with a decrease in frequency of spike bursts. In the studied dose range CCK-4 and PP were without influence on small intestinal electrical activity.

Effect of CCK-8 on myoelectrical activity of the gastrointestinal tract in the conscious miniature pig.

In conscious miniature pigs, with implanted electrodes in the wall of the antrum pylori, duodenum, jejunum, and ileum, the influence of IV infusions of CCK-8 (17.5 and 175 pM/kg/min) on gastrointestinal myoelectrical activity was measured. Although both doses under study induced a decrease in antral spike activity. only the higher dose resulted in an overall decrease in integrated myoelectrical activity. In the ileum both doses augmented spiking activity during the infusion, but inhibited electrical activity after the end of the infusion. No response was observed in the duodenum and jejunum. The experiments demonstrate the overall inhibitory effect of CCK-8 on antral electrical activity and its stimulatory influence on ileal smooth muscle.

Are muscarinic receptors involved in the effect of serotonin on gastrointestinal electrical activity in the conscious piglet?

In conscious piglets provided chronically with electrodes in the wall of the antrum pylori, duodenum, jejunum and ileum, the effect of intravenous infusion of 5-HT, 4 micrograms/kg/min for 2 h, with and without pre-treatment with atropine, 0.5 mg/kg, on gastrointestinal myoelectrical activity was studied. In the antrum, fast oscillations were partially inhibited by 5-HT and nearly completely blocked by the atropine/5-HT combination and by atropine alone. In the small intestine 5-HT induced a decrease in MMC interval, an increase in phase III activity in duodenum and jejunum and an acceleration of propagation velocity as measured for the jejunum. These effects were not influenced by atropine. Following atropine, phase II activity in the jejunum was significantly inhibited by 5-HT. The ileum was rather insensitive to 5-HT. It is concluded that the inhibitory effect of 5-HT on antral electrical activity is enhanced by atropine, and that 5-HT has a stimulatory effect on small intestinal activity which is not dependent on a muscarinic action.

Effect of vasoactive intestinal polypeptide on porcine gastrointestinal electrical activity.

The influence of intravenous infusion of VIP, 150 and 300 pmol/kg/min, on gastrointestinal electrical activity was studied in conscious piglets with electrodes implanted in the wall of the antrum pylori, duodenum, jejunum, and ileum. Both doses resulted in a decrease in antral electrical activity. In the small intestine, only the lower dose caused a shortening of the irregular spiking activity phase in the jejunum and ileum. In the jejunum this resulted in a reduction of the MMC interval. It may be concluded that the prevailing effect of VIP is an inhibition of gastrointestinal electrical activity in the piglet.

Effect of serotonin on gastrointestinal electrical activity in the conscious piglet.

In conscious piglets with electrodes implanted in the wall of the antrum pylori, duodenum, jejunum and ileum, the influence of intravenous infusion of serotonin (5-HT), 4 micrograms/kg/min for 2 hours, on gastrointestinal electrical activity and arterial pressure was examined. 5-HT was without significant influence on antral electrical activity and arterial pressure. In the small intestinal parts 5-HT provoked a shortening of the interval of the migrating myoelectrical complex (MMC) by reducing the duration of phase I and phase II activities, and an increase in propagation velocity. 5-HT also induced an increase in phase III activity. A possible involvement of 5-HT in the initiation and propagation of the MMC is suggested.

Influence of motilin on gastrointestinal electrical activity in the conscious piglet.

In conscious just-weaned piglets, fed ad libitum, with electrodes implanted in the wall of the antrum pylori, duodenum, jejunum, ileum and caecum, infusion of motilin (2 and 20 ng/kg/min for 2h) induced a transient increase in the frequency of the fast oscillations in the antrum followed by a delayed decrease. The polypeptide, however, was unable to induce a premature or extra phase III activity or to change the frequency of the migrating myoelectrical complexes.

Comparison of the in vitro adhesion of K88, K99, F41 and P987 positive Escherichia coli to intestinal villi of 4- to 5-week-old pigs.

The adhesion of K88ab, K88ac, K88ad, P987, K99, F41 and K99/F41 positive Escherichia coli strains to duodenal, jejunal and ileal villi was studied using an in vitro adhesion assay. The villi were harvested from 4- to 5-week-old pigs. The K88+ strains adhered in large numbers (42 +/- 5 to 81 +/- 4 E. coli/250 microns villous length) to the villi from most pigs and in low to moderate numbers (5 +/- 2 to 24 +/- 7 E. coli/250 microns villous length) or not to villi of some pigs. The K99+ and F41+ strains either adhered in low numbers (1 +/- 1 to 11 +/- 2 E. coli/250 microns villous length) or did not adhere, whereas the P987+ and K99/F41+ strains always adhered in low to moderate numbers (2 +/- 1 to 26 +/- 2 E. coli/250 microns villous length). The number of bacteria adhering to the villi was the highest for the K88ab+ and K88ac+ strains (55 +/- 5 to 81 +/- 4 E. coli/250 microns villous length) and decreasing in the following order: K88ad > P987 > K99/F41 > K99 > F41 (= 1 +/- 1 to 4 +/- 1 E. coli/250 microns villous length). There was no difference in the adhesion of the villi of the different small intestinal segments for the P987+ and F41+ strains. The K99+ strains adhered significantly more to the villi of the caudal half of the small intestine, the K99/F41+ strain to jejunal and ileal and the K88+ strains to jejunal villi in comparison to duodenal ones.

Influence of substance P on gastrointestinal myoelectrical activity in the conscious piglet.

In conscious piglets with electrodes implanted in the wall of the antrum pylori, the small intestine and the caecum, the influence of intravenous infusion of substance P (SP) (0.1 and 1 micrograms/kg/min for 2 hours) on gastrointestinal myoelectrical activity and arterial pressure was studied. SP was without significant influence on electrical activity of the antrum. However, intestinal myoelectrical activities were significantly stimulated. In the small intestine SP infusion resulted in an increase in frequency of migrating myoelectrical complexes and in irregular spiking activity, resulting in an augmentation of the integrated total activity. In the caecum SP provoked a prolongation of complexes of long spike bursts (LSB) as well as an increase in number of LSB/complex. In the studied doses SP had no significant effect on arterial pressure.

Influence of leukotriene D4 on arterial pressure and gastrointestinal electrical activity in the conscious piglet.

In 6 conscious weaned piglets with implanted electrodes in the corpus and antrum of the stomach, the duodenum, jejunum, ileum and caecum the influence of intravenous infusion of leukotriene (LT)D4, 0.1 and 1 microgram kgmin for 10 min, on mean arterial pressure and gastrointestinal electrical activity was examined. LTD4 induced a significant increase in arterial pressure. Gastrointestinal electrical activity, however, was little influenced, since only the antrum pylori revealed a transient decrease.

Influence of indomethacin on endotoxin-induced changes in gastrointestinal myoelectrical activity and some haematological and clinical parameters in the conscious piglet.

The effect of indomethacin, administered intravenously at 5 mg/kg, on the changes in gastrointestinal myoelectrical activity, rectal body temperature, clinical appearance and some haematological parameters induced by intravenous bolus injection of endotoxin, at 10 micrograms/kg, was examined in conscious piglets with electrodes implanted in the antrum pylori, duodenum, jejunum and ileum. Indomethacin inhibited the endotoxin-induced febrile response and the accompanying clinical signs. However, it was without influence on the induced leukopenia and shift to the left. Indomethacin both delayed the onset of and shortened the endotoxin-induced increase in the duration of the antral inhibitory phase and the duodenal phase I activity. It therefore appears that prostanoids are probably not the main factors involved in the endotoxin-induced haematological and gastrointestinal myoelectrical activity changes in the piglet.

Effect of infusion of a diarrheogenic dose of PGE2 on gastrointestinal electrical activity in the conscious piglet.

In 5 conscious piglets with electrodes implanted on the antrum pylori and small intestine, phasic and integrated electrical activity was daily recorded. PGE2, 10 micrograms/kg/min, was infused intravenously during 1.5 h and the induced changes in electrical activity were analyzed. Clinical appearance was also studied. PGE2 induced an inhibition in both antral and intestinal activity. In the antrum this inhibition was characterized by a decrease in the frequency of electrical control activity and fast oscillations, and an increase in the duration of the inhibitory phase. Small intestinal recordings revealed an increase in the quiescence phase for the duodenum and a decrease in the integrated total activity for the duodenum, jejunum and ileum, induced by a decrease in phase II activity. PGE2 was without influence on phase III activity and the recycling of the migrating myoelectrical complexes. All piglets developed a severe diarrhea. Vomiting, sedation, fever and shivering were observed in most animals. These data suggest that the diarrheogenic effect of PGE2 is not provoked by an increase in small intestinal motility. Moreover, the direct effect of this PG is a partial inhibition of gastrointestinal electrical activity.

Influence of PGF2 alpha on gastrointestinal activity in the conscious piglet.

In 5 conscious piglets with electrodes implanted on the antrum pylori, duodenum, jejunum and ileum, the effect of intravenous infusion of PGF2 alpha, 1 and 10 micrograms/kg/min during 2 h, on gastrointestinal electrical activity was studied. The influence of the PG, 10(-8) to 10(-4) M, on longitudinal tissue strips from the same segments was also examined. The in vitro results demonstrate that PGF2 alpha has only a weak contractile effect on duodenal and jejunal strips. This effect was enhanced in the presence of atropine and indomethacin. In the in vivo part of the study PGF2 alpha induced an inhibition of antral electrical activity as evidenced by a prolongation of the inhibitory phases and a reduction of the frequency of the fast oscillations. In the small intestine only ileal activity was changed significantly. PGF2 alpha provoked an increase in the phase II or irregular spiking activity and an increase in the interval of the migrating myoelectrical complexes in this segment.

Experimental induction of diarrhoea in newly-weaned piglets.

To induce diarrhoea and hypovolaemia, newly-weaned conventionally bred piglets (3- to 4-weeks-old), were either given secretagogues or were inoculated with enterotoxigenic Escherichia coli (ETEC). Choleratoxin (n = 2), E. coli heat-labile enterotoxin (n = 2) or castor oil (n = 2) were given intragastrically or piglets were intraperitoneally injected with DL 5-hydroxytryptophan (n = 3). These substances induced a transient diarrhoea without clinical symptoms of dehydration. Therefore, a combination of castor oil and DL 5-hydroxytryptophan was given two times a day during 3 consecutive days to 3 piglets. Although diarrhoea lasted for 5 days, still no hypovolaemia occurred. Probably the secretagogues have to be given continuously to mimic the continuous release of enterotoxins during secretory colibacillary diarrhoea. It was, therefore, tried to reproduce colibacillosis in the just-weaned piglets. Animals were inoculated with K88ac fimbriae producing ETEC strains (O149:K91:K88ac; LT, STa and STb positive) (n = 7), or pretreated with chloramphenicol followed by the ETEC inoculation (n = 8), or pretreated with the antibiotic, inoculated with an enteropathogenic coronavirus, transmissible gastroenteritis virus (TGEV), and subsequently inoculated with ETEC (n = 18). Only the last procedure induced a reproducible diarrhoea (93%) and dehydration resulting in a mortality of 80%. It was concluded that the latter experimental procedure could be used to study diarrhoea and hypovolaemia in newly-weaned piglets and to evaluate the effect of potentially antisecretory drugs on postweaning diarrhoea in piglets.

Influence of prostaglandin E2 infusion on gastrointestinal electrical activity in the conscious piglet.

In 5 conscious piglets with implanted electrodes in the antrum pylori, duodenum, jejunum and ileum, electromyographic activity was recorded daily on a multichannel recorder with a time constant of 0.03 s for intestinal and of 1 s for gastric recordings, and simultaneously integrated at 20 s intervals. PGE2 was infused for 2 h in relatively low doses of 0.1 and 1 microgram/kg/min, to avoid excessive hypersecretion, which would disguise direct effects. Each dose was tested once in each animal with a 1 week interval. Infusion of 0.1 microgram/kg/min revealed no significant changes in antral and small intestinal electrical activity. One microgram/kg/min however induced a strong depression of fast oscillations until the end of the infusion and prolongation of the inhibitory phase in the antrum following a duodenal phase of regular spiking activity. Intestinal segments displayed a prolongation of the quiescent phase and a decrease in the integrated area curve of the phase of irregular spiking activity. Recurrence of the phase of regular spiking activity was unaltered in either segment. These data suggest that the direct effect of PGE2 on gastrointestinal motility in the piglet is a partial inhibition of intestinal contractions.