Mechanisms underlying the intestinal fluid secretion evoked by nociceptive serosal stimulation of the rat

Substance P effects on blood flow, fluid transport and vasoactive intestinal polypeptide release in the feline small intestine

1. Substance P (SP) infusions were given close I.A. to the feline small intestine in vivo in a dose that produced plasma concentrations of 1-5 microM. This infusion regularly evoked a net fluid secretion measured with a gravimetric technique. Concomitantly, the release into blood of vasoactive intestinal polypeptide (VIP), a putative neurotransmitter of the enteric nervous system, increased. 2. The SP-induced fluid secretion was blocked by tetrodotoxin (7 micrograms close I.A.), a blocker of fast sodium channels in excitable tissues, and hexamethonium (10 mg (kg body wt)-1, I.V.), a nicotinic receptor antagonist, suggesting that the SP effect was mediated by the enteric nervous system. In line with this it was shown that the SP-evoked release of VIP was also significantly diminished by hexamethonium. 3. Close I.A. infusions of methionine enkephalin (Met-enkephalin; 7-23 nmol min-1) or electrical stimulation of the sympathetic nerve fibres (6 Hz) to the intestine markedly diminished net fluid secretion and the release of VIP caused by SP given close I.A. 4. The cyclo-oxygenase inhibitor diclofenac (5 mg (kg body wt)-1, I.V.) or the histamine-1 receptor antagonist pyrilamine (10 mg (kg body wt)-1, I.V.) did not influence the fluid secretion caused by SP, indicating that the effects of SP were not due to the actions of prostaglandins or histamine. 5. It is proposed that SP activates a nervous reflex arch that we have shown to be activated by various luminal stimuli, including cholera toxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of the myenteric plexus in the cholera toxin-induced net fluid secretion in the rat small intestine

BACKGROUND

The enteric nervous system is responsible in vivo for most of the change in fluid transport induced by cholera toxin. The aim of the present study was to investigate the importance of the myenteric plexus in the Intramural reflex responsible for this secretion.

METHODS

Long-term ablation of the myenteric plexus was achieved by serosal application of benzalkonium chloride on jejunal segments in rats.

RESULTS

The treated segments without functioning myenteric plexus showed a normal net fluid absorption. Cholera toxin in this segment only induced a reduction of fluid absorption, whereas in a nontreated ileal segment it concomitantly induced a conspicuous net fluid secretion. Intravenous hexamethonium did not change the cholera toxin response in the treated jejunal segments, whereas vasoactive intestinal polypeptide elicited a marked secretion.

CONCLUSIONS

Benzalkonium chloride treatment eliminated the ability of cholera toxin to induce intestinal secretion. Thus, all afferent fibers in the intramural secretory reflex activated by cholera toxin are probably conveyed via the myenteric plexus, which functions as the integrating center in the enteric nervous system. The Ussing chamber technique using stripped intestinal preparations cannot be used when studying effects of luminal secretagogues.

The evolution of postoperative ileus after laparoscopic cholecystectomy. A comparative study with conventional cholecystectomy and sympathetic blockade treatment

Our study is prompted by the arrival of laparoscopic cholecystectomy in connection with the evolution of postoperative ileus (PI) and by its avoidance of the intraabdominal handling implied in conventional cholecystectomy. With this aim a prospective, controlled, randomized, and blind clinical trial was designed using 100 patients divided into five groups (n = 20): I, conventional cholecystectomy (CC): II, CC+injection of 20 ml bupivacaine 0.5% into the mesentery root; III, CC + 7.5 mg propranolol i.v. and 0.5 mg neostigmine s.c., postoperatively until the first defecation; IV, II+III; and V, laparoscopic cholecystectomy. The shortest period of PI was observed in group V. This period increases notably in group IV (53 h), group II (72 h), and group III (84 h) relative to the control group with (89 h). This reduction in PI time runs parallel with an improvement in the patient's general state of well-being. We concluded that after laparoscopic cholecystectomy PI is nonexistent. Furthermore, this study confirms the correlation between the avoidance of intraabdominal manipulation and the evolution of postoperative ileus.

Nerve-mediated effect of ethanol on sodium and fluid transport in the jejunum of the rat

The hypothesis tested in this study is whether a potential harmful substance such as ethanol causes secretion in the small intestine and, if so, whether the secretion is mediated via intestinal nerve reflexes or a direct effect on the epithelium. The jejunum of anaesthetized Sprague-Dawley rats was perfused in vivo with a modified Krebs-Henseleit solution. Three per cent ethanol had no significant effect, whereas 8% ethanol in the perfusate elicited a net secretion of fluid and sodium in the intestine. This secretion was reversed by ganglionic blockade with hexamethonium (10 mg/kg intravenously). The ethanol absorption from the perfusate, on the other hand, was not affected by the ganglionic blockade. We concluded that ethanol dose-dependently caused a nerve-mediated secretion of sodium and fluid in the rat small intestine. Ethanol was probably absorbed by diffusion.

On the role of vasoactive intestinal polypeptide and tachykinins in the secretory reflex elicited by chemical peritonitis in the cat small intestine

Peritonitis induced by serosal application of 0.1 M hydrochloric acid causes net fluid secretion via the enteric nervous system. The aim of the present study was to investigate the roles of vasoactive intestinal peptide (VIP) and tachykinins in this reflex(es). The release of tachykinins (substance P [SP], neurokinin A [NKA], neuropeptide K [NPK]) and VIP into the mesenteric circulation, net fluid transport, intestinal blood flow and sometimes motility were recorded simultaneously in extrinsically denervated jejunal segments of the cat in vivo. The release of both VIP and NKA was increased upon application of HCl to the cat jejunal serosa. Tetrodotoxin, hexamethonium and methionine enkephalin inhibited both the induced VIP release and the secretory response. The increased release of NKA was unaffected by hexamethonium. We propose that the intramural secretory reflex evoked by acid application of the serosa consists of an 'afferent' tachykinin neuron, a cholinergic interneuron and an 'efferent' VIPergic neuron innervating the secretory enterocytes.

Enteric nerves mediate the fluid secretory response due to Salmonella typhimurium R5 infection in the rat small intestine

Eighteen hours after intragastric inoculation Salmonella typhimurium elicited a net fluid secretion in the jejunum and ileum of rats. The mechanisms behind the secretory response were analysed in vivo. Extrinsic denervation of the experimental intestinal segments had no effect. The nerve-blocking agents hexamethonium (i.v.) and lidocaine (serosally applied) blocked the secretion but atropine had no effect. It was demonstrated that the bacteria were invasive by culturing from the intestinal wall. The presence of inflammatory reactions was supported by the facts that i.v. indomethacin blocked the secretory response and that there was an increased capillary leakage of albumin-bound Evans Blue into the interstitium of the intestinal mucosa. There was also a secretory response upon inoculation of the jejunal and ileal segments by cell-free supernatants of broth where bacteria had been cultured for 24 h and thereafter lysed. This response was, however, blocked by i.v. atropine, which had no effect on the secretion elicited by living bacteria. We could show no presence of E. coli LT, ST or cholera toxin in the cell-free supernatant by means of ELISA-tests. We therefore conclude that (1) S. typhimurium R5 invaded the rat jejunal and ileal mucosa, thereby creating an inflammatory response which in turn activated a nerve reflex(es) within the ENS leading to a net fluid secretion; (2) the presence of prostaglandins was needed for activating the reflex(es); (3) the reflex(es) contained a nicotinergic transmission; (4) enterotoxin was of no importance for the secretory response in the model used.

Mechanisms underlying the small intestinal fluid secretion caused by arachidonic acid, prostaglandin E1 and prostaglandin E2 in the rat in vivo

Prostanoids were given intraluminally (PGE2) or infused close intra-arterially (PGE1 and PGE2) or arachidonic acid was administered intraluminally to denervated jejunal segments of the rat in vivo. These experimental manoeuvres caused a net fluid secretion, although a 1,000-fold higher concentration of the prostanoids was needed from the luminal than from the vascular side. I.v. hexamethonium or serosally applied lidocaine diminished the induced fluid secretion suggesting that the prostanoids act mainly by eliciting local secretory reflexes in the enteric nervous system. This nerve-mediated secretion is not accompanied by any increase in tissue cAMP. However, at higher i.a. concentrations of PGE2 there seems to be a non-neurogenic effect on the enterocytes associated with an increase in tissue cAMP.

Influence of sodium deoxycholate on morphology, net fluid transport and motility in the small intestine of the rat

Intestinal fluid secretion and motility were induced by luminal perfusion of rat small intestine with sodium deoxycholate, a dihydroxy bile salt for 1-3 h. Changes in intestinal morphology were studied simultaneously with the changes in fluid transport and motility. The results suggest that the bile salt causes epithelial lesions which may lead to a reduced fluid absorption in the villi, thereby explaining part of the total change in net fluid transport caused by the bile salt. Pyrilamine and indomethacin did not influence the bile salt-induced secretion. Based on earlier studies, it is proposed that the major part of the bile salt-evoked secretion is mediated via activation of intramural nervous reflex(es), which also stimulate the intestinal smooth muscle cells.

Effect of intra-abdominal bupivacaine instillation on postoperative colonic motility

Effect of intra-abdominal instillation of a local anaesthetic, bupivacaine, on postoperative colonic adynamic ileus was studied in a double blind manner in a randomised series of patients undergoing upper laparotomy. Propulsive colonic activity was studied postoperatively with radio-opaque markers and serial abdominal radiographs. Intra-abdominal instillation of bupivacaine 2 mg/kg bw significantly shortened the period of postoperative colonic inhibition (p less than 0.01), but did not hasten colonic transit. Furthermore, bupivacaine significantly decreased the hyperglycaemic response to surgery. It is suggested that bupivacaine inhibits the inflammatory response within the bowel wall, a response which may maintain the inhibitory spinal reflexes in the postoperative period. Blood concentrations of bupivacaine were shown to be well below toxic levels and no adverse reactions were observed.

Effects of intra-arterially infused adenosine triphosphate (ATP) on release of vasoactive intestinal polypeptide (VIP) from the gastrointestinal tract of the cat

Close i.a. infusions of ATP were made to the stomach, the small intestine or the colon in the cat. The vascular reactions were followed by recording arterial pressure and total venous outflow continuously and the release of VIP was estimated intermittently from arterio-venous concentration differences and blood flow. In all experiments ATP caused a vasodilatation and an increased release of VIP into blood. In control experiments it was shown that evoking a vasodilatation of the same magnitude by close i.a. infusions of isoprenaline or papaverine did not evoke any similar release of VIP. It is concluded that the infused ATP released VIP from the different parts of the gastrointestinal tract. Possible mechanisms underlying this effect are tentatively discussed.