Frailty is associated with long-term outcome in patients with sepsis who are over 80 years old: results from an observational study in 241 European ICUs

BACKGROUND

Sepsis is one of the most frequent reasons for acute intensive care unit (ICU) admission of very old patients and mortality rates are high. However, the impact of pre-existing physical and cognitive function on long-term outcome of ICU patients ≥ 80 years old (very old intensive care patients (VIPs)) with sepsis is unclear.

OBJECTIVE

To investigate both the short- and long-term mortality of VIPs admitted with sepsis and assess the relation of mortality with pre-existing physical and cognitive function.

DESIGN

Prospective cohort study.

SETTING

241 ICUs from 22 European countries in a six-month period between May 2018 and May 2019.

SUBJECTS

Acutely admitted ICU patients aged ≥80 years with sequential organ failure assessment (SOFA) score ≥ 2.

METHODS

Sepsis was defined according to the sepsis 3.0 criteria. Patients with sepsis as an admission diagnosis were compared with other acutely admitted patients. In addition to patients' characteristics, disease severity, information about comorbidity and polypharmacy and pre-existing physical and cognitive function were collected.

RESULTS

Out of 3,596 acutely admitted VIPs with SOFA score ≥ 2, a group of 532 patients with sepsis were compared to other admissions. Predictors for 6-month mortality were age (per 5 years): Hazard ratio (HR, 1.16 (95% confidence interval (CI), 1.09-1.25, P < 0.0001), SOFA (per one-point): HR, 1.16 (95% CI, 1.14-1.17, P < 0.0001) and frailty (CFS > 4): HR, 1.34 (95% CI, 1.18-1.51, P < 0.0001).

CONCLUSIONS

There is substantial long-term mortality in VIPs admitted with sepsis. Frailty, age and disease severity were identified as predictors of long-term mortality in VIPs admitted with sepsis.

Effect of cholera toxin on passive transepithelial transport of 51 Cr-ethylenediaminetetraacetic acid and 14 C-mannitol in rat jejunum

Intestinal fluid secretion, mainly derived from the crypts, induced, for example, by cholera toxin, decreases the passive transport of small hydrophilic molecules into the lumen. However, the effect of the fluid secretion on the passive absorption of these substances and thus on the permeability of the villus absorptive area is not known. Therefore, the transport rates of 51Cr-ethylenediaminetetraacetic acid (EDTA) and 14C-mannitol from lumen to plasma and from plasma to lumen were recorded in jejunal loops of anaesthetized rats during cholera toxin-induced fluid secretion in the absence and presence of glucose in the intestinal lumen and expressed as clearance (microL (min g)(-1)). The results showed that the cholera toxin induced fluid secretion and abolished the passive absorption of 51Cr-EDTA both in the absence and presence of luminal glucose during a high perfusion rate (0.5 mL min(-1)). The clearance of mannitol was also inhibited at the low perfusion rate (0.2 mL min-1) with the glucose-free perfusate but only reduced with the glucose perfusate. The results show that mechanisms activated by cholera toxin inhibit the passive absorption of inert hydrophilic substances. This is proposed to be mainly caused by a reduction in the accessibility of the villus epithelium to the luminal content. Furthermore, the secretion seems predominantly to inhibit the passive absorption at the basal parts of the villus while the absorption rate at the villus tips is better preserved. The results also show that the intestinal absorption and secretion of fluid takes place at different locations (villus and crypts, respectively).

Involvement of enteric nerves in permeability changes due to deoxycholic acid in rat jejunum in vivo

AIM

Stress and Clostridium difficile toxin A increase epithelial permeability in the small intestine via vagus and visceral afferents, in turn activating mucosal mast cells. Bile acids also increase epithelial permeability but it is not known if nerves or mast cells are involved in this effect in the small intestine.

METHOD

In jejunum of anesthetized rats, the effects of hexamethonium and atropine on deoxycholic acid (DCA) induced fluid secretion and increase in epithelial permeability was therefore studied by determining the appearance and disappearance rates of 14C-mannitol and 51Cr-EDTA into and from a perfusion system containing 4 or 8 mm DCA and expressed as clearance.

RESULTS

DCA increased net fluid transport and appearance and to a less extent disappearance rates of the probes. Hexamethonium but not atropine, chronic denervation or the NO synthase inhibitor L-NNA did significantly decrease the appearance rate and net fluid secretion. The levels of the mast cell protease II (RMCP II) in perfusate and plasma were not increased by DCA. The clearance ratio Cr-EDTA/mannitol indicates that the plasma clearance of the permeability probes is partly secondary to net fluid transport only at higher DCA concentrations.

CONCLUSION

We conclude that the DCA effect on epithelial permeability is to a large part induced by intramural reflex(es) containing nicotinic receptors. The results also suggest that mast cell degranulation and NO release are not involved in the mechanism. This indicates that the nerve effect on intestinal paracellular permeability is not mediated by the mechanisms described for stress or Clostridium difficile toxin A.

Water absorption enhances the uptake of mannitol and decreases Cr-EDTA/mannitol permeability ratios in cat small intestine in situ

BACKGROUND

Recently, we hypothesized that mannitol absorption in human intestinal permeability tests is a reflection of small intestinal water absorption and is dependent mainly on the efficiency of the countercurrent multiplier in the villi. This may affect the outcome of clinical double-sugar permeability tests. We tested the hypothesis in cats, another species with an efficient countercurrent multiplier.

METHODS

The lumen-to-tissue transport of [14C]mannitol and [51Cr]EDTA was studied in in situ perfused jejunum of eight anaesthetized cats using four isotonic perfusion solutions with varying sodium and glucose content. The transport of water was monitored, and the absorption rate of the probes was calculated by their disappearance from the perfusate.

RESULTS

There was a significant positive correlation between water absorption and [14C]mannitol clearance from the different perfusates (r = 0.99; P < 0.01), whereas this correlation was absent for [51Cr]EDTA clearance (r = 0.05; P = 0.95). There was also a significant negative correlation between water absorption and [51Cr]EDTA/[14C]mannitol clearance ratios (r = 0.98; P < 0.02).

CONCLUSIONS

The results show a prominent effect of water absorption on mannitol uptake through pores which, also during glucose transport, exclude Cr-EDTA. The difference in water absorption from the solutions used in cat small intestine is dependent on the effectiveness of the countercurrent multiplier; we conclude that the capability of this mechanism influences mannitol absorption in vivo. Qualitatively comparable results were obtained using oral test solutions with varying NaCl and glucose concentrations in human volunteers. We propose that the functioning of the countercurrent multiplier is essential for the interpretation of double-sugar tests in clinical studies.

Permeability of the rat small intestinal epithelium along the villus-crypt axis: effects of glucose transport

BACKGROUND & AIMS

The aim of this study was to elucidate the permeability characteristics of the epithelium along the villus-crypt axis and investigate the effect of glucose transport on these characteristics along this axis.

METHODS

The disappearance rates of (14)C-mannitol and (51)Cr-EDTA or (3)H-inulin were determined as clearance (Cl(x)) from a recirculating perfusion system of the jejunal lumen in anesthetized rats. Net fluid transport was varied over a large range by exchanging mannitol with glucose in the perfusate solution and by inhibition of nervously mediated secretory processes with hexamethonium. The perfusion rate was 0.5 or 0.2 mL/min.

RESULTS

Cl(Man) enhanced significantly with increasing net fluid transport (secretion 8.50+/-1.88, to absorption 16.72+/-1.75 microL x min(-1) x g(-1)) and with glucose perfusates. Cl(Cr-EDTA) was constant irrespective of net fluid transport and was reduced to insignificant values at a perfusion rate of 0.2 mL/min. Cl(In) was not different from zero.

CONCLUSIONS

The absorbing apical part of the villus contains small pores (radius, <6 A) allowing passive transport via solvent drag of, e.g., monosaccharides, whereas the pores in the crypts are large (50-60 A) and inaccessible to the luminal content. The basal part of the villus contains medium-sized pores (10-15 A) through which no solvent drag occurs. Active glucose transport in the rat mainly increases the number of small pores accessible for passive transport, whereas the size of these pores seems to stay constant.

Somatic nerve stimulation and cholera-induced net fluid secretion in the small intestine of the rat: evidence for an opioid effect

The effects of somatic nerve stimulation on cholera toxin induced secretion was investigated in vivo in anaesthetised rats. Small intestinal secretion was induced with cholera toxin and measured by a gravimetric technique. Afferent stimulation (pulse frequency within train; 100 Hz; train duration: 50 ms; train frequency: 3 Hz) of the sciatic nerve over 30 min significantly reduced the net fluid secretion both during (P < 0.05) and after cessation of the stimulation (P < 0.01). The greatest effect was obtained immediately after the termination of the nerve stimulation when the secretion was reversed to net fluid absorption. The opioid receptor antagonist naloxone (10 mg kg(-1) i.v.) administrated during the stimulation, significantly inhibited the antisecretory effect seen after the stimulation, thus no significant difference was seen between the control period and the periods after cessation of the stimulation. The opioid receptor antagonist naloxone methiodide (10 mg kg(-1) i.v.), which does not cross the blood-brain barrier, partly inhibited the antisecretory effects but not with the same magnitude as naloxone, thus the net fluid secretion was still significantly inhibited after the stimulation (P < 0.05). We conclude that afferent stimulation of the sciatic nerve strongly inhibits the cholera toxin induced secretion in the small intestine. This inhibition involves primarily a central opioid mechanism and to a lesser extent peripheral opioid mechanism.

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)

Influence of pH on reservoir mucosal absorption/-secretion and tubular and glomerular function. Studies in patients with a continent ileal reservoir for urinary diversion

Ten patients with a continent ileal reservoir for urinary diversion were studied regarding transmucosal fluxes of water and electrolytes at different pH. The urine was by-passed the reservoir via a Foley catheter. The experiment set-up was designed to exclude urine from reservoir mucosa exposition during the study. Test solutions of pH 4 and pH 7 with electrolytes and a non-absorbable volume marker (PEG MW 4000) were instilled into the empty reservoir. The influence of altered pH on the flow of water and Na,+K+ and Cl- across the reservoir mucosa was analysed. The maximal concentration ability after intranasal desmopressin (Minirin), the creatinine and Na-clearance as well as the fractional Na-excretion were calculated from measurements on the by-passed urine. The results showed a secretion of water, Na+ and Cl- into the reservoir while the K+ content was constant. The mucosal flows of water and electrolytes were not affected by alterations in reservoir pH. Maximal concentration ability appeared to be reduced compared to normals. Fractional Na excretion was within normal limits.

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.

On the involvement of tachykinin neurons in the secretory nervous reflex elicited by cholera toxin in the small intestine

The possible involvement of tachykinins in the nervous reflex activated by exposing the intestinal mucosa to cholera toxin was investigated in cats and rats. Three types of experiments were performed. In cats the release of tachykinins into blood was followed after placing cholera toxin in the intestinal lumen. In rat experiments a tachykinin receptor antagonist (Spantide II) was given close i.a. and its effect on cholera toxin-evoked fluid secretion was studied. Finally, in rats the effect of cholera toxin on the SP contents in the intestinal mucosa was studied. No release of tachykinins could be demonstrated. Spantide II did not change the rate of cholera toxin induced secretion. The SP content in the intestinal mucosa was not influenced by placing the toxin in the intestinal lumen. Hence, no experimental evidence was obtained for the involvement of a tachykinin neuron in the intestinal secretory nervous reflex activated by cholera toxin. Based on observations reported in the literature the involvement of an acetylcholine/tachykinin neuron in the reflex is tentatively discussed.

Transcellular fluid secretion induced by cholera toxin and vasoactive intestinal polypeptide in the small intestine of the rat

The permeation of intravenously administered 51Cr-EDTA and [14C]mannitol to the perfused intestinal lumen was measured in anaesthetized rats together with the net intestinal fluid. Net fluid secretion was induced by cholera toxin or by intravenous infusion of vasoactive intestinal polypeptide (VIP). The plasma clearance of Cr-EDTA and mannitol was 0.9 +/- 0.1 and 1.4 +/- 0.2 microliters min-1 g-1 intestine during the control period prior to the secretion and the net fluid absorption was about 7 +/- 5 microliters min-1 g-1. Cholera toxin induced a net fluid secretion of about 30 +/- 7 microliters min-1 g-1 but the clearance did not rise but decreased significantly. The findings for VIP-induced secretion were similar. No indication of solvent drag was seen. Thus it is concluded that the fluid was secreted in channels which were smaller than the probes and we propose that the secreted fluid entered the intestinal lumen through the epithelial cells and not by the paracellular route. The decreased permeation of Cr-EDTA and mannitol from plasma to lumen during volume secretion suggest that there was a decreased mucosal permeability during the secretion. The decrease in permeability was consistent with a decrease in pore size. One explanation of the data is that the pore radius contracted from about 35 to 15 A during cholera if we assume a homogenous pore population. However, the data indicated that there was not a uniform size of the pore.(ABSTRACT TRUNCATED AT 250 WORDS)

Difference between the antisecretory mechanisms of opioids and the somatostatin analogue octreotide in cholera toxin-induced small intestinal secretion in the rat

The antisecretory effect of morphine and the somatostatin analogue octreotide was studied on cholera toxin-induced secretion in anaesthetized rats. Small intestinal secretion was induced with cholera toxin. Morphine (6 mg/kg b.wt.) and the somatostatin analogue octreotide (3 micrograms/kg b.wt.) reduced the cholera secretion in rats whose intestines had been subjected to sympathetic denervation. This was in contrast to the secretion elicited by helodermin which was unaffected by octreotide and morphine in the presence of nicotinic ganglionic blockade. The alpha-adrenergic receptor blocker phentolamine (1-2 mg/kg b.wt. i.v.) and the inhibitor of sympathetic transmitter release guanethidine (5 mg/kg b.wt. i.v.) abolished the antisecretory effect of morphine on the cholera secretion in contrast to the antisecretory effect of somatostatin which was unaffected by the alpha-blockade. It is proposed that the antisecretory effect of morphine and octreotide on cholera toxin-induced secretion was conducted at a step prior to the activation of the secretory epithelium and that the antisecretory effect of morphine was mediated indirectly by interaction with sympathetic nerve terminals in the intestine. The findings are consistent with a model where octreotide and morphine inhibit the nervous secreto-motor reflex activated by the cholera toxin.

Actions of serotonin antagonists on cholera-toxininduced intestinal fluid secretion

The effects of several 5-hydroxytryptamine (5-HT) receptor antagonists were tested in rats in vivo on the intestinal fluid secretion evoked by cholera toxin. Five receptor antagonists were used, namely 2-bromolysergic acid diethylamine (2-bromo-LSD), granisetron, ketanserin, methysergide and ondansetron. The drugs were used in doses that inhibited the arterial hypertension and/or bradycardia evoked by 5-HT given i.v. Granisetron and ondansetron markedly diminished cholera-toxin-evoked secretion, whereas ketanserin was without any effect. Methysergide also diminished cholera-toxin-induced fluid secretion particularly when the drug was given as an i.v. infusion. The results are considered in relation to the pathophysiology of cholera secretion and to the current views of receptor subtypes for 5-HT. It is proposed that the receptor involved is a 5-HT3 receptor, possibly also a receptor of the 5-HT1 type. Results from experiments in which 5-HT (20 mM) was placed in the intestinal lumen to evoke an intestinal secretion suggest that the 5-HT3 receptor is located in the villus tissue. It was also demonstrated that zimeldine, an inhibitor of presynaptic 5-HT reuptake, diminished choleraic secretion, an effect that may be ascribed to a 5-HT tachyphylaxis caused by an accumulation of 5-HT in a synaptic cleft.

Antisecretory effect of splanchnic nerve stimulation on choleratoxin-induced secretion in the cat, an effect mediated at the crypts

The experiments were performed on cats anaesthetized with alpha-chloralose. Segments of the small intestine were perfused with sodium-free hypotonic choline-mannitol solution and intestinal net fluid transport was recorded with a volumetric technique. The content of sodium and chloride in the lamina propria of the small intestinal villus was measured with an electron microprobe in freeze-dried paraffin embedded tissue. In absorbing control intestine, there was an even distribution of electrolytes along the villi. Sympathetic nerve stimulation (5 Hz, 5 ms, 5 V) did not significantly affect electrolyte distribution and net fluid transport. Intestinal secretion was elicited by pretreatment of the intestine with cholera toxin. The concentration of sodium and chloride was elevated in the apical third of the villi in intestines during the secretion since secreted sodium from the crypts was reabsorbed into the villi. Sympathetic nerve stimulation decreased the cholera secretion significantly in intestines pretreated with cholera-toxin. Furthermore, the apical gradients of sodium and chloride in the villi, caused by the reabsorbed sodium and chloride, disappeared during sympathetic nerve stimulation. It is concluded that, in the used experimental model, the antisecretory effect of sympathetic nerve stimulation was caused by inhibition of crypt secretion and not by augmented villus absorption.

Interaction between antisecretory opioid and sympathetic mechanisms in the rat small intestine

The putative existence of an endogenous opioid antisecretory mechanism in the small intestine was tested in anaesthetized Sprague-Dawley rats. Cholera secretion was elicited with cholera toxin and net fluid secretion was measured in vivo using a gravimetric technique allowing on line registrations. Opioid blockade with naloxone (10 mg kg-1 i.v.) increased the cholera secretion significantly but had no effect on control absorption. Pretreatment with phentolamine (2 mg kg-1 i.v.) eliminated the effect of opioid blockade indicating an interaction between the opioid and the adrenergic mechanisms. The effect of naloxone on cholera secretion was unchanged after acute division of the sympathetic nerves to the intestine and removal of the adrenals. Chronic sympathetic denervation of the small intestine, on the other hand, abolished the effect of opiate blockade on the secretion. The antisecretory effect of sympathetic nerve stimulation was unchanged by opiate blockade.

CONCLUSION

An intrinsic antisecretory opioid mechanism has been demonstrated in the small intestine of the rat. This endogenous opioid mechanism seems to decrease secretion indirectly via peripheral activation of the sympathetic antisecretory system.

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.

Villus and crypt electrolyte and fluid transport during intestinal secretion

The apical parts of jejunal villi of net-absorbing intestine have been shown to contain sodium chloride concentration gradients which are associated with water absorption (Sjöqvist & Beeuwkes 1989). To determine whether these gradients are different in states of intestinal net secretion, jejunal segments of chloralose-anaesthetized cats were perfused with modified Krebs-Henseleit solutions while secretion was elicited by cholera toxin or vasoactive intestinal polypeptide (VIP). The segments were then rapidly frozen and freeze-dried, and sodium and chloride contents of the lamina propria of single villi were measured by X-ray microanalysis. The apical third of the villus was found to contain a concentration gradient of sodium and chloride when the lumen contained sodium, with no difference between secreting intestine and absorbing control intestine. When the intestine was perfused with hypotonic choline-mannitol solution, no sodium or chloride gradient was found. In this state, treatment of the intestines with secretagogues allowed development of an apical concentration gradient. This demonstrated that the absorptive function of the villus tip was unimpaired during secretion and that secretion from the crypt could supply sufficient electrolyte to allow formation of an apical gradient.

Villous sodium gradient associated with volume absorption in the feline intestine: an electron-microprobe study on freeze-dried tissue

Water transport in biological tissue is driven by local osmotic gradients created by accumulation of actively transported ions in tissue compartments. To localize and measure such gradients, jejunal segments from the small intestine of anaesthetized cats were perfused with modified isotonic Krebs-Henseleit electrolyte solution, and net fluid transport was measured with a volumetric technique. The segments were then rapidly frozen, freeze-dried, and prepared for X-ray micro-analysis of elemental content. Whenever the lumen perfusate contained sodium, the apical third of the villus was found to have a sodium gradient rising to a tip concentration more than twice that at the base of the villus. This sodium gradient was associated with a chloride gradient and fluid absorption. No similar potassium gradient was found. When choline replaced sodium in the intestinal lumen, no gradient of sodium chloride was found and no net fluid absorption occurred. Absorption of fluid was thus apparently coupled to absorption of sodium through creation of a local osmotic gradient in the tip of the intestinal villus.

Somatostatin and methionine-enkephalin inhibit cholera toxin-induced jejunal net fluid secretion and release of vasoactive intestinal polypeptide in the cat in vivo

A major part of the net fluid secretion that is elicited by cholera toxin in the small intestine of the cat has been shown to be mediated by intramural nervous reflex(es). The release of vasoactive intestinal polypeptide (VIP) from the small intestine is increased by cholera toxin. We report that close intra-arterial infusions of methionine-enkephalin (met-enk) and somatostatin cause a parallel reduction in cholera toxin-induced net fluid secretion and in VIP release from the small intestine of the cat. Intestinal blood flow was slightly, but significantly increased by met-enk and not influenced by somatostatin. These results strengthen the hypothesis that VIP is involved as a neurotransmitter in the nervous reflex mediating cholera toxin-induced secretion.

Involvement of opioid and nicotinic receptors in rectal and anal reflex inhibition of urinary bladder motility in cats

The present study was performed to investigate mechanisms involved in urinary bladder relaxation during reflex activation of the pelvic nerves in the cat. Electrical stimulation of the pelvic nerves produced a contraction of the urinary bladder (P less than 0.05) and colon (P less than 0.05). Reflex activation of the pelvic nerves by rectal distension or mechanical stimulation of the anus induced relaxation of the bladder (P less than 0.05), while a colonic contraction was elicited (P less than 0.05). Naloxone (1.5 mg kg-1, i.v.) abolished the reflex inhibition of bladder motility elicited by rectal distension or mechanical stimulation of the anus (P less than 0.05). However, the urinary bladder and colonic contraction produced by electrical stimulation of the pelvic nerves were not affected. Hexamethonium (10 mg kg-1, i.v.) or severing of the pelvic nerves completely abolished the responses of the urinary bladder and colon to electrical stimulation or reflex activation of the pelvic nerves. The results indicate that inhibitory reflexes from the rectum and anal canal to the urinary bladder are conveyed via efferents of the pelvic nerves, and involve both nicotinic and opioid receptor mechanisms.

The effect of splanchnic nerve stimulation and neuropeptide Y on cholera secretion and release of vasoactive intestinal polypeptide in the feline small intestine

The effect of sympathetic nerve stimulation and intra-arterial infusion of neuropeptide Y (NPY) on net fluid secretion and release of vasoactive intestinal polypeptide (VIP) was studied in the cat small intestine during a secretion due to cholera toxin. Activation of the splanchnic nerves (4 Hz, 5 ms, 5 V) decreased net fluid secretion to 57 +/- 10% of control. Concomitantly, the release of VIP was reduced to less than 50%. Furthermore, close i.a. infusion of NPY (estimated increase in plasma concentration 75 nmol l-1) reduced the net fluid secretion and VIP release to 27 +/- 5 and 28 +/- 4% of the pre-stimulatory value. The correlation between the decrease in net fluid secretion and reduction in VIP release showed a strong positive correlation (r = 0.83). These results strongly indicate that the antisecretory effect of sympathetic nerve stimulation during cholera diarrhoea is mediated by inhibition of secretory VIP neurons in the intestinal mucosa. A similar mechanism is also proposed for the intravascularly administered NPY.

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.

Release of vasoactive intestinal polypeptide anally of a local distension of the feline small intestine

The peristaltic reflex is elicited by a local distension of the intestine and consists of an ascending contraction and a descending inhibition of the smooth muscle layer. The transmitter mediating the inhibition of the smooth muscle cells is not known but vasoactive intestinal polypeptide (VIP) has, among others, been proposed to mediate the descending inhibition of a distension. An in vivo preparation of a segment of the feline intestine was designed to allow collection of the venous effluent and determination of the VIP release orally and anally of a distension. The release of VIP rose significantly more on the anal side of the intestinal distension, and so did the blood flow. Division of the myenteric plexus prevented the asymmetry of the VIP release to a large extent. These effects of distension on the release of VIP are consistent with the hypothesis that VIP mediates the descending inhibition of the peristaltic reflex.

Reflex sympathetic inhibition of colonic motility in the cat

Sympathico-adrenergic mechanisms involved in the reflex inhibition of colonic motility were investigated in anaesthetized cats. Reflex inhibition of spontaneous motility of the colon was induced by application of hydrochloric acid onto the serosal surface of the small intestine and the peritoneum of the abdominal wall. This inhibition was reduced by propranolol and phentolamine. The spontaneous colonic motility was also reduced by administration of isoproterenol, noradrenaline, and clonidine. It is concluded that the sympathetic reflex inhibition of colonic motility is mediated by alpha- and beta-adrenergic mechanisms in the cat.

Mechanisms of neurotensin-induced fluid secretion in the cat ileum in vivo

Neurotensin (NT) is released from N cells in the small intestinal epithelium. Among other effects NT is known to elicit fluid secretion in the small intestine. This study was carried out in order to elucidate the mechanism by which NT elicits this secretion. Neurotensin infusions at two rates (4.5 and 45 pmol min-1 kg-1 body wt) to isolated segments of cat ileum in vivo, caused a steady rate of net fluid secretion and a release of vasoactive intestinal polypeptide into the mesenteric vein. The secretion was totally inhibited by tetrodotoxin. Hexamethonium, a nicotinic receptor antagonist, inhibited the secretion elicited by the lower but not by the higher dose of NT. Met-enkephalin also inhibited the induced secretion while pyrilamine, a histamine-I receptor antagonist had no effect. No significant change in enteric blood flow was caused by the NT infusion. These results indicate that NT elicits a nervous reflex in the enteric nervous system which, accordingly, turns the transport of the enterocytes into net fluid secretion.

Sympathetic nerve activation decreases the release of vasoactive intestinal polypeptide from the feline intestine

The splanchnic nerves to the small intestine were stimulated in anaesthetized cats. Activation of the sympathetic nerves caused vasoconstriction, increased net fluid absorption and decreased release of vasoactive intestinal polypeptide (VIP) in the small intestine. In the colon, parasympathetic nerve stimulation elicited vasodilatation and increased release of VIP. Additional stimulation of the sympathetic lumbar colonic nerves decreased the colonic blood flow and inhibited the release of VIP. These effects of the stimulation of the lumbar colonic nerves were blocked by phentolamine. It is concluded that, in the feline intestine, sympathetic nerve stimulation presynaptically decreased the release of VIP via an alpha-adrenergic mechanism.

The effects of phorbol esters on fluid transport and blood flow in the small intestine

Studies were designed to examine the effects of phorbol esters on intestinal fluid transport and blood flow in the anesthetized cat and enteropooling in the conscious rat. Intraluminal administration of phorbol ester into a segment of isolated small bowel produced a copious intestinal secretion and a concomitant mesenteric hyperemia in the cat. Net fluid movement in the intestine was converted from absorption in the control state to secretion following phorbol ester administration. Intravenous atropine reduced the phorbol ester-induced secretion by 56%; clonidine abolished the remaining secretory response. In the rat, intragastric administration of phorbol ester produced enteropooling comparable to that of other potent intestinal secretagogues. Since phorbol esters are known to activate protein kinase C, these studies suggest that activation of protein kinase C in the small intestine may lead to a full secretory response. The evidence suggests that this secretion is accompanied by a metabolic hyperemia. These results suggest that protein kinase C plays an important role in the regulation of intestinal fluid transport.

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.

Reflex adrenergic inhibition of colonic motility in anesthetized rat caused by nociceptive stimuli of peritoneum. An alpha 2-adrenoceptor-mediated response

Nociceptive stimulation of the peritoneum inhibits colonic motility via a sympathoadrenergic reflex. This sympathetic reflex most probably induces the inhibition indirectly via a presynaptic blockade of cholinergic transmission. To further clarify this reflex, colonic motility was continuously recorded by a volume method in rats exposed to nociceptive abdominal stimulation and intravenous drug administration. Intraabdominally applied HCl inhibited colonic motility, which was unaffected by nonselective beta-adrenoceptor blockade (propranolol). However, the nonselective alpha-adrenoceptor antagonist phentolamine and the selective alpha 2-adrenoceptor antagonist yohimbine restored motility. Spontaneous colonic motility was unaffected by the nonselective beta-adrenoceptor agonist (isoproterenol) and the selective alpha 1-adrenoceptor agonist (L-phenylephrine). On the other hand, a nonselective alpha-agonist (noradrenaline) and a selective alpha 2-adrenoceptor agonist (clonidine) inhibited spontaneous colonic motility. It is suggested that in the rat sympathetic reflex inhibition of colonic motility caused by abdominal nociception is mediated via presynaptic alpha 2-adrenoceptors inhibiting the excitatory cholinergic neurons.

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

Intestinal net fluid transport was measured in vivo continuously with a gravimetric method. Chemical stimulation of the jejunal serosa with hydrochloric acid (0.1 M), ethanol (20%), cat bile or 7-deoxycholic acid (10 mM) evoked an intestinal fluid secretion. Hexamethonium (10 mg/kg b.wt.i.v.) or serosal application of lidocaine (1% solution) partially blocked this secretory response. Bradykinin and prostaglandin E1, two important inflammatory mediators, elicited fluid secretion when applied to the serosal surface at a concentration of 10(-4) M. This secretion was also partly inhibited by hexamethonium. Furthermore indomethacin (10 mg/kg b.wt. i.v.) or pyrilamine (10 mg/kg b.wt. i.v.), a H1-receptor blocker, partly inhibited the secretory response caused by chemical stimulation of the serosa while cimetidine (1 mg/kg b.wt. i.v.), a H2-receptor blocker, had no effect. Freeze sectioned samples from chemically stimulated intestines were examined by fluorescence microscopy. A leakage of i.v. administrated Evans blue labelled albumin into the interstitial space of the serosa and the outer layer of the muscularis was found. It is concluded: The intestinal fluid secretion studied is mainly elicited by nociceptive stimulation of nerves in the serosa or the outer muscularis. The reflex may be activated by the local release of histamine, kinins and prostaglandins. The reflex studied is part of an inflammatory response.

Neurotransmitters involved in the colonic contraction and vasodilatation elicited by activation of the pelvic nerves in the cat

Stimulation of the pelvic nerves causes a contraction of and an increased blood flow in the feline colon. This study was performed to analyze the possible neurotransmitters involved in this response. The colonic contraction and hyperemia caused by pelvic nerve stimulation (5 Hz, 5 ms, 5 V) were not affected by the substance P antagonist (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-substance P, by substance P tachyphylaxis, or by naloxone (0.2-0.3 mg/kg body wt, i.a.). However, after treatment with atropine (0.5 mg/kg body wt, i.v.), naloxone blocked the contraction evoked by pelvic nerve stimulation (p less than 0.01), whereas the vasodilator response was unchanged. Distension of the rectum with a water-filled balloon or mechanical stimulation of the anal wall with a glass rod elicits a pelvo-pelvic reflex with colonic contraction and hyperemia. The contraction elicited by rectal distension was completely abolished by atropine (0.5 mg/kg body wt, i.v.). However, in atropinized animals, mechanical stimulation of the anal wall caused a contraction of the distal colon that was blocked by naloxone (0.2-0.3 mg/kg body wt, i.a.). The hyperemia was not affected by atropine or by naloxone. The results indicate the existence of at least three motor-neuronal systems in the distal colon: one cholinergic and one enkephalinergic system mediating colonic contractions, and one system mediating vasodilatations with another transmitter.

Effect of apamin on release of vasoactive intestinal polypeptide (VIP) from the cat intestines

The effect of apamin, a polypeptide from bee venom, on the release of vasoactive intestinal polypeptide (VIP) during active neurogenic vasodilatation in the intestines was studied in vivo in anesthetized cats. Three non-adrenergic, non-cholinergic mechanisms were investigated, i.e. the vasodilatation seen upon transmural electrical field stimulation, pelvic nerve activation and stimulation of the intramural nerves with 5-hydroxytryptamine (5-HT) infused i.a. Apamin given close i.a. abolished the three vasodilator responses. Concomitantly, the increase of VIP release was also markedly diminished although apamin increased the rate of VIP release seen in the "resting" control period. The results are in agreement with the hypothesis that VIP is the neurotransmitter in the three investigated vasodilator mechanisms.

The effect of apamin on non-adrenergic, non-cholinergic vasodilator mechanisms in the intestines of the cat

The effects of apamin, a polypeptide isolated from bee venom, on different vasodilator mechanisms in the small and large intestines were studied in atropinized cats. In the large intestine vasodilatation in response to pelvic nerve stimulation was either abolished or markedly diminished by I.A. apamin. However, neither the contraction of colonic muscle which occurred under these conditions nor sympathetic vasoconstriction was significantly influenced by apamin, suggesting that the effect of the peptide was not a non-specific effect on nerves or vascular smooth muscle. In the small intestine it was observed that the nervous vasodilatation induced by transmural electrical field stimulation or mechanical mucosal stimulation was either diminished or abolished by apamin. Intestinal vasodilatation, caused by close I.A. infusions of 5-hydroxytryptamine (5-HT), was abolished by apamin. After giving apamin 5-HT infusions induced a vasoconstriction in five out of six experiments. Vasodilatation induced by vasoactive intestinal polypeptide (VIP) was not significantly affected by apamin. In a series of in vitro experiments on rat portal vein, dose-response curves of several putative intestinal neurotransmitters were determined in the presence and absence of apamin. The following substances were tested: VIP, substance P, bradykinin, 5-HT, ATP and adenosine. Apamin had no effect on the dose-response curves of any of these compounds. The results are discussed in relation to the possibility that apamin may act by blocking the release of a putative peptidergic transmitter from nerve terminals.

The effect of intestinal fluid transport of exposing the serosa to hydrochloric acid. A study of mechanisms

Hydrochloric acid (0.1 M) placed on the serosal surface of a jejunal segment evoked an intestinal secretion (rats) or inhibited a net fluid absorption (cats). In rats it was demonstrated that lidocaine (placed on the serosa of periarterially denervated intestinal segments), hexamethonium (given i.v.; innervated or denervated intestines) and indomethacin (given i.v.; denervated intestines) markedly inhibited the acid induced secretion, while atropine (given i.v.) had no effect. In the cat experiments it was shown that tetrodotoxin (given close i.a. to denervated intestines) returned the rate of net fluid absorption to the control value observed before applying acid. It is concluded that exposing the intestinal serosa to an acid solution evokes a fluid secretion that is nervously mediated. Furthermore, it is proposed that prostaglandins are involved in the induction of the fluid secretion probably via a stimulation of nociceptors. It is also suggested that the results may have pathophysiological implications for some types of paralytic ileus.

Evidence for cholera secretion emanating from the crypts. A study of villus tissue osmolality and fluid and electrolyte transport in the small intestine of the cat

Villus tissue osmolality and fluid and electrolyte transport were measured in intestinal segments exposed to cholera toxin. The osmolality of the luminal fluid was kept at about 100, 300, or 600 mOsm X kg-1 by use of appropriate concentrations of mannitol. A net fluid secretion was seen in all experiments, the magnitude being dependent on the osmolality in the lumen. A secretion of sodium, potassium, and chloride was also seen in all experiments but the secretion rate of electrolytes was independent of the osmolality in the intestinal lumen. The hydraulic conductivity of the villus epithelium, calculated from the lumen and tissue osmolality, was the same as that estimated in the normal intestines. A villus tissue osmolality gradient was apparent in all experiments regardless of the mannitol concentration in the lumen, the tip osmolality being hypertonic while the tissue osmolality at the base was isotonic. This was the case also when the luminal fluid was hypotonic, a finding opposite to what we found in an earlier study on the normal feline intestine. A likely explanation for this observation is that the crypts of Lieberkühn secrete fluid containing sodium chloride, which is absorbed by the villus epithelial cells. Hence, a luminal "circulation" of electrolytes between crypts and villi was suggested in the present experimental circumstances.

Dissociation of electrical and mechanical activity caused by vibrations in the spontaneously active smooth muscle of the rat portal vein

The effects of vibrations on the electrical membrane discharge and on the contractile force of the spontaneously active smooth muscle of isolated rat portal vein were studied. The electrical activity was recorded extracellularly and quantitatively related to the mean active force. Sinusoidal vibrations (40 Hz, 2.5--3.0% tissue length peak to peak), applied in the longitudinal direction of the smooth muscle, caused prompt and reversible reduction of active force but neither the pattern of the phasic contractions nor the electrical membrane discharge was altered. The degree of inhibition of mechanical activity increased with vibration amplitude, activity being 50% of control at a vibration amplitude of 12 +/- 4% (mean +/- S.D., n = 8). It is concluded that the induced length changes caused prompt dissociation between electrical membrane discharge and mechanical force development in the vascular smooth muscle. This finding adds support to the previously forwarded hypothesis that vibrations cause inhibition of contracting muscle by direct action on the contractile process.

The effect of Apamin on nonadrenergic, noncholinergic nervous vasodilatations in the cat small intestine

The intestinal vasodilation evoked by mechanical mucosal stimulation or by transmural electrical field stimulation was abolished by close i.a. injection of Apamin, a polypeptide originally isolated from bee venom. Apamin also blocked the vasodilatation induced by close i.a. infusion of vasoactive intestinal polypeptide (VIP). It is suggested that Apamin is a VIP receptor antagonist.

Vasoactive intestinal polypeptide, 5-hydroxytryptamine and reflex hyperaemia in the small intestine of the cat

1. The release of vasoactive intestinal polypeptide (VIP) into venous blood from the small intestine of the cat was studied when mechanically stimulating the intestinal mucosa and during close intra-arterial infusions of 5-hydroxytryptamine (5-HT) or isopropylnoradrenaline. The studies were performed on anaesthetized cats given atropine.2. Mechanical stimulation of the intestinal mucosa induced a vasodilatation and a release of VIP into the intestinal venous blood. Intra-arterial administration of tetrodotoxin was given in doses that blocked the vasoconstrictor effect of the regional sympathetic nerve fibres. This also abolished the vascular response and the release of VIP into blood upon mechanical stimulation.3. Close intra-arterial administration of 2-bromo-lysergic acid diethylamide reduced the VIP release and the intestinal vasodilatation upon mucosal stimulation to largely the same extent.4. Close intra-arterial infusions of 5-HT produced a marked release of VIP from the intestine and a moderate vasodilatation. Close intra-arterial infusions of isopropylnoradrenaline, which caused a pronounced intestinal vasodilatation, evoked only a small release of VIP.5. The results are compatible with the hypothesis that the vasodilatation in the gut, induced by mechanical mucosal stimulation, is mediated via an intramural nervous reflex containing a neurone capable of releasing VIP. It is proposed that the nervous reflex is activated by the release of 5-HT from the enterochromaffin cells evoked by mechanical stimulation of the mucosa.

Villous tissue osmolality and intestinal transport of water and electrolytes

The villous tissue hyperosmolality created by the intestinal countercurrent multiplier has been proposed to be of importance for fluid transport across the intestinal epithelium in vivo. This study was performed to test this hypothesis. Net transport of fluid and electrolytes (sodium, potassium and chloride), as well as unidirectional fluxes of water and sodium were determined in the small intestine of the cat. The villous osmolality was altered by varying the composition of sodium and glucose in the isotonic solutions perfusing the intestinal lumen. Net transport of fluid was correlated to tissue osmolality mainly due to an increase of the unidirectional flux of water from lumen to tissue with augmented tissue osmolality. The results are thus consistent with the view that the intestinal countercurrent multiplier is of essential importance for net water transport. A correlation was found between net water and net sodium intestinal transport. A similar correlation was also demonstrated between net sodium and net chloride absorption rates in the jejunum while in the ileum net loss of sodium into the intestinal lumen was not accompanied by any corresponding loss of chloride ions. This observation suggests the presence of a sodium independent transport mechanism for chloride in the ilium but not in the jejunum.

Effects of vasoactive intestinal polypeptide on blood flow, motility and fluid transport in the gastrointestinal tract of the cat

The effect of close intraarterial infusions of vasoactive intestinal polypeptide (VIP) on gastric motility, intestinal fluid transport and colonic motility were studied in the cat. Regional blood flow was also followed in all experiments. In the stomach VIP produced a gastric relaxation and a blood flow increase. The motility response was similar to that observed when eliciting the vago-vagal reflex relaxation by distending the esophagus. In the small intestine a hyperemia and a decrease of net water uptake was observed. When infusing small amounts of VIP a decrease of net water uptake was seen without any change of intestinal blood flow. Large amounts of VIP produced a transient secretory state in the small intestine. In the colon a hyperemia was seen immediately upon starting the infusion of the drug. After 2-3 min of infusion a contraction of the colon was apparent. The administration of atropine to the animal did not significantly affect any of the responses produced by VIP. The results are discussed in relation to VIP as a possible neurotransmitter in the gastrointestinal tract.