Mobilization of colonic kallikrein following pelvic nerve stimulation in the atropinized cat

The role of chemical mediators in the pathogenesis of inflammation with emphasis on the kinin system

In recent years, numerous agents have been recognized as inflammatory mediators. In this review, however, we discuss only those having direct relevance to human inflammatory diseases These mediators are clinically important due to their proinflammatory properties such as vasodilatation, increased vascular permeability, pain and chemotaxis. They may lead to the fifth cardinal sign, loss of function in inflammatory diseases. Agonists and non-specific antagonists are used as pharmacological tools to investigate the inflammatory role of PGs, LTs, PAF, IL-1, histamine, complement, SP, PMN-leukocytes, and kallikrein-kininogen-kinin systems. Unfortunately, no compound is known which concurrently abolishes all actions and interactions of inflammatory mediators. Therefore it would be highly useful to promote efforts in developing selective and competitive antagonists against proinflammatory actions of these chemical mediators. This may help to a better understanding of the pathogenesis of inflammatory reactions, and it may also be useful for the therapy of inflammatory diseases.

Plasma kinin-precursor levels in clinical intestinal inflammation

Plasma kinin-precursor (kininogen) concentrations were measured in the peripheral venous blood of 7 untreated patients with inflammatory bowel diseases, 12 healthy subjects, and 5 uncomplicated fracture cases. The mean plasma kininogen levels were significantly raised (P less than 0.025) in patients with intestinal inflammation (7.0 +/- 1.0 micrograms BK Eq/ml), as compared with the value found in healthy subjects (5.7 +/- 0.7 micrograms BK Eq/ml), and in fracture cases (5.0 +/- 1.2 micrograms BK Eq/ml). The packed cell volume did not differ (P greater than 0.05) between patients and control groups. Thus, the raised plasma kininogen levels observed in patients were not the result of nonspecific changes in plasma volume. It is suggested that raised plasma kininogen might be due to increased synthesis to provide substrate for excessive kinin-formation, to a potent inflammatory agent, or to high synthesis of acute-phase reactants. The possible significance of this observation is discussed.

Bradykinin releases acetylcholine from myenteric plexus by a prostaglandin-mediated mechanism

Release of [3H]acetylcholine (ACh) under the influence of bradykinin was measured from myenteric plexus-longitudinal muscle strips taken from guinea pig small intestine. Bradykinin stimulated the efflux of [3H]ACh in a dose-dependent manner. This stimulation by bradykinin was resistant to the effect of [Des-Arg9-Leu8]-bradykinin but not to indomethacin, indicating that the ACh-releasing action of bradykinin was mediated indirectly by a prostaglandin mechanism. Direct evidence for a stimulation of ACh release by prostaglandin E1 was obtained. Prostaglandin was able to stimulate ACh release in a dose-related fashion. The inhibition of bradykinin-induced ACh release by indomethacin was partly reversed by exogenous prostaglandin E1. These results suggest a neuromodulatory role for bradykinin in the enteric nervous system.

Intestinal kallikrein activity is reduced in a bypassed segment of the small intestine in the rat

The possible pancreatic origin of intestinal kallikrein was studied in a jejuno-ileal bypass model in the rat. The bypassed loops were made of variable lengths (2-72 cm) and samples were taken at 10 cm intervals to relate enzyme activities to adaptive changes caused by local and systemic stimulus. The kallikrein activity was dramatically reduced (mean 92.3%) in the bypassed loops while only moderately reduced (mean 35.8%) activities were found in the intestine remaining in continuity. Kallikrein was uniformly distributed throughout the functional small intestine in normal and bypass operated animals. The longitudinal distribution profiles obtained for brush border enzymes in normal animals were almost absent in the bypassed loops, but were apparent in the remaining intestine. The main adaptive growth was observed in the remaining small intestine, Both here and in the loop, the growth depended on the amount of bypassed tissue. Our observations are strongly in favour of a pancreatic origin of the glandular kallikrein activity found in the small intestine in the rat.

Bradykinin-stimulated electrolyte secretion in rabbit and guinea pig intestine. Involvement of arachidonic acid metabolites

Bradykinin (BK) increases short-circuit current (Isc) when added to the serosal side of rabbit or guinea pig ileum or rabbit colon. Significant effects on Isc are seen at concentrations as low as 10(-10) M. Anion substitution experiments and unidirectional 36Cl flux measurements indicate that this effect of BK on Isc is due to Cl secretion. The effect of BK on Isc can be partially blocked (60-70% inhibition) by cyclooxygenase inhibitors (indomethacin and/or naproxen) and completely blocked by the phospholipase inhibitor, mepacrine. The combined cyclooxygenase/lipoxygenase inhibitors BW 755 and eicosa-5,8,11,14-tetraynoic acid (ETYA) also completely block the effect of BK on Isc but the slow-reacting substance of anaphylaxis (SRS-A) antagonist FPL 55712 has no effect. None of the above inhibitors diminish the effect on Isc of other exogenously added secretory stimuli such as vasoactive intestinal peptide (VIP), theophylline, or prostaglandin E2 (PGE2). Prior desensitization of rabbit ileum to PGE2 blocks the effect on Isc of BK but not those of VIP or theophylline. Conversely, prior desensitization of rabbit ileum to BK greatly reduces the effect of PGE2 on Isc. BK also stimulates the synthesis of PGE2 in rabbit ileal and colonic mucosa and this effect can be blocked by prior addition of either indomethacin or mepacrine. These effects of BK are similar to those of exogenously added arachidonic acid (AA). AA also stimulates Cl secretion and increases PGE2 synthesis and its effect on Isc can be inhibited by prior desensitization to PGE2 or by prior addition of indomethacin. The above results indicate that BK stimulates active Cl secretion in both small and large intestine and suggest that this effect is due to the intracellular release of AA. Although the prostaglandins appear to be the major products of AA metabolism contributing to the secretory response, lipoxygenase products may also play a role.

Angiotensin I converting enzyme of rat intestinal and vascular surface membrane

High levels of angiotensin I converting enzyme are present in rat intestinal mucosa and in intestinal arteries. Homogenates of both tissues were subfractionated and fractions enriched in vascular plasma membrane or intestinal brush border were prepared. The preparations were identified and their purities established by marker enzyme enrichment and/or electron microscopy. Converting enzyme activity was highly enriched on both the vascular plasma membrane and the intestinal brush border. Subsequently the properties of these membrane-bound enzymes were compared. Both surface membrane-bound enzymes were highly sensitive to inhibition by captopril (SQ 14225) and teprotide (SQ 20881). Similar to converting enzyme isolated from other sources, they were also inhibited by bradykinin, angiotensin I, EDTA and o-phenanthroline. Finally, both membrane-bound enzymes were relatively resistant to activation by sonication, freezing and thawing or detergent. These results demonstrate significant similarities between surface membrane-bound converting enzyme from vascular and non-vascular sites. In addition, in view of the possible relationship of kinins and angiotensins to gastrointestinal function and blood flow, inhibition of gastrointestinal converting enzyme by captopril may affect some aspects of intestinal physiology.

Changes in colonic tissue levels of inflammatory mediators in a guinea-pig model of immune colitis

An immune colitis based on a delayed-type hypersensitivity reaction was induced in dinitrochlorobenzene (DNCB)-sensitized guinea-pigs by intrarectal challenge with DNCB. A low challenge dose (0.25% DNCB) induced mild inflammatory changes in the distal colon and rectum characterized by goblet cell depletion. A higher challenge concentration (5% DNCB) resulted in severe colonic ulceration with crypt abscess formation. The inflammatory mediators, histamine, 5-hydroxytryptamine (5HT), glandular kallikrein and PGE2 were measured in freeze-dried colonic mucosae. Histamine content was three times control (p less than 0.01) in 0.25% DNCB induced colitis, although no significant change was observed in 5% DNCB challenged animals. Mucosal 5HT content was significantly reduced (p less than 0.01) after both challenges. Glandular kallikrein content did not differ from control, while PGE2 was significantly (p less than 0.05) increased at both challenge doses. The possible significance of these changes with respect to severity of inflammation and aetiology of colitis is discussed.

Studies on the atropine-resistant sacral parasympathetic vascular and motility responses in the cat colon

1. Pelvic nerve stimulation in atropinized cats elicits a sustained contraction of the proximal colon and a relaxation of the rectum. Concomitantly there is an immediate but transient vasodilatation which is followed by recurrent increases and a slight post-stimulatory hyperaemia. Direct stimulation of the pelvic nerve produces secretion of colonic kallikrein and activation of the plasma kinin system. The present study examines whether Trasylol, which inhibits the kinin system, affects the atropine-resistant responses observed on pelvic nerve stimulation. 2. After I.V. or close I.A. administration of Trasylol, the initial vasodilatation on pelvic nerve stimulation was markedly reduced and in a few experiments completely blocked. The recurrent blood flow increases and the post-stimulatory hyperaemia observed on prolonged stimulation were completely abolished. In contrast the proximal colonic contraction and the rectal relaxation appeared unchanged after Trasylol. 3. The reactivity of the vascular bed after Trasylol injection was studied by recording the changes of vascular resistance following sympathetic vasoconstrictor fibre activation and infusion of bradykinin before and after Trasylol injection. The responses were quantitatively unchanged excluding an unspecific interference with nervous transmission or vascular smooth muscle reactivity. 4. The results show that the atropine-resistant vasodilatation in the cat colon as elicited by pelvic nerve stimulation is partly abolished by a kallikrein inhibitor. This observation lends further support to the hypothesis that kinins might be involved in this response. The motor response, however, appears not be dependent on such a mechanism.

A comparison between ATP and bradykinin as possible mediators of the responses of smooth muscle to non-adrenergic non-cholinergic nerves

The effects of ATP, bradykinin (BK) and electrical stimulation of intramural non-adrenergic non-cholinergic nerves (NS) were compared in four smooth preparations. In the guinea-pig taenia caeci and rat duodenum, ATP (10(-7)-5 x 10(-5) M) and BK (5 x 10(-10)-10(-7) M) closely mimicked the response to NS. The relaxations to BK, but not to ATP or NS, were inhibited by carboxypeptidase B (3-15 U/ml) and apamin (10(-8)-5 x 10(-8) M) prevented the relaxations to all three stimuli. BK contracted the guinea-pig distal colon whereas ATP and NS caused inhibition. In the guinea-pig bladder, ATP and NS induced rapid phasic contractions whereas BK caused tonic contractions. In the latter two preparations, incubation with indomethacin failed to reveal any BK relaxation. In view of its failure to mimic the nerve-mediated response in two of the tissues, and of its selective inhibition by carboxypeptidase B in the other two, BK is less likely to be the transmitter in non-adrenergic non-cholinergic nerves supplying smooth muscle.

Evidence for a dual pelvic nerve influence on large bowel motility in the cat

1. The effects of efferent electric pelvic nerve stimulation on colorectal motility and blood flow with emphasis on the motor responses in consecutive colonic and rectal segments were studied in anaesthetized cats. It was considered of particular interest to explore whether selective pharmacological blockade and graded nerve stimulations might reveal the presence of functionally differentiated efferent fibres controlling colonic motility.2. Pelvic nerve stimulation induced immediate and sustained colorectal contractions and a simultaneous increase of the over-all colonic blood flow. The excitatory responses declined immediately on cessation of a shortlasting stimulation (< 2 min); after a longlasting one, however, the rectal contraction was maintained for several min.3. The colonic contraction on pelvic nerve stimulation remained unchanged after atropine but was delayed in onset. Moreover, in the transverse and distal colon it was preceded by a relaxation which was most pronounced in the distal part. The vasodilator response was unchanged.4. After atropine the rectal segment showed a purely relaxatory response. Despite continuous pelvic nerve stimulation the relaxation vanished, however, and rectal volume returned to resting level with 3-5 min. On cessation of such a prolonged stimulation there was a marked rectal ;after-contraction'.5. The excitation thresholds for the efferent nerve fibres eliciting these different responses could not be separated. The motility and the vasodilator responses were not influenced by adrenergic or by serotoninergic blockade.6. The results indicate that direct preganglionic stimulation of the cat pelvic nerves activates intramural cholinergic excitatory neurones as well as non-cholinergic excitatory neurones and furthermore, non-adrenergic non-cholinergic inhibitory neurones, which together result in most complex colonic and rectal motor responses. From a functional point of view these centrally controlled responses may well be independently controlled by separate preganglionic neurones though they do not differ concerning excitation thresholds.7. The effects are consistent with a dual function of the distal colon and rectum. Such a dual parasympathetic influence on the large bowel simulates the vagal control of the stomach, where specific vagal relaxatory fibres convey a reflex widening of the corpus-fundus reservoir during food intake.

The effect of diet on tissue levels of kinin-forming enzyme in blood-free rat gastro-intestinal tract

1. Kallikreins, kinin-forming enzymes, are present in the wall of the gastro-intestinal tract. The role of the kinin-forming system in the gut is unknown. In the present study, a modified bio-assay technique was used to detect the presence of tissue concentration gradients of kinin-forming enzyme (KFE) at different levels of the rat gastro-intestinal tract and the effect on them of diet.2. Segments of rat gut, perfused free of blood, were homogenized in 0.1 N-HCl and activated by autolytic processes. Total KFE content was then determined by incubation of extract with standard kinin-forming substrate, followed by bio-assay of the released kinin using superfused oestrous rat uterus. Acid extraction of the KFE gave a recovery of 127.4% when compared with simple water extraction.3. Tissue concentrations of KFE were determined in stomach, duodenum, jejunum, terminal ileum, caecum and proximal and distal colon. Concentrations were determined after (A) normal diet, (B) water ad libitum for 24 hr and (C) isotonic glucose ad libitum for 60 hr.4. All the gut tissues contained KFE. After diet A there was least (19.5 +/- 1.0 ng bradykinin equivalent formed per minute (KU) per gram wet weight) in the stomach and a single large peak (504 +/- 92 KU .g(-1) wet weight) in the caecum.5. The different dietary states produced changes only in the duodenum, the caecum and the distal colon. The duodenal level was raised when the organ was empty after diet B (140 +/- 29 KU .g(-1)) and fell when filled with solid or fluid after diets A (57 +/- 14 KU .g(-1)) and C (80 +/- 17 KU .g(-1)) respectively. The caecal KFE level, which was high when the lumen was full after diet A, fell progressively as it was increasingly emptied after diets B (213 +/- 41 KU .g(-1)) and C (105 +/- 42 KU .g(-1)) respectively. The KFE concentration in the distal colon was low when the lumen was full after diets A (58 +/- 10 KU .g(-1)) and B (66 +/- 17 KU .g(-1)) and rose when the lumen was nearly empty after diet C (118 +/- 17 KU .g(-1)).6. Kinin-forming activity in rat intestinal extracts had a pH optimum at pH 8.5 and formed a bradykinin-like spasmogen. The increased activity in the fasted rat duodenum was not significantly inhibited by soybean trypsin inhibitor (100 mug/ml.) while that in caeci from fed rats was inhibited by 17% (P < 0.05).7. These changes may indicate physiological involvement of the kallikrein-kinin system in these organs.