Ileal and colonic contractions by endothelin-1 in experimentally induced paralytic ileus in rats

DO ANTIBIOTICS CONTRIBUTE TO POSTOPERATIVE ILEUS? CONTRACTILE RESPONSES OF ILEUM SMOOTH MUSCLE IN GUINEA PIGS TO LONG-TERM PARENTERAL CEFTRIAXONE AND AMPICILLIN

BACKGROUND

Antibiotics may impair small bowel smooth muscle contractility and contribute to postoperative ileus. The aim of this study was to compare the contractile responses of ileum smooth muscle to different agonists in guinea pigs treated with ceftriaxone (Rocephin; F. Hoffman-La Roche, Kaiseraugst, Switzerland) or ampicillin (Ampisina; Mustafa Nevzat Ilaç Sanayii AS, Istanbul, Turkey).

METHODS

Twenty-four adult guinea pigs were randomly divided into three groups. Whereas eight of these received ceftriaxone sodium (100 mg/kg per day, i.m.) for 10 days, another eight guinea pigs received ampicillin (50 mg/kg per day, i.m.) for 10 days and the remaining eight served as the control group receiving 1 mL distilled water during 10 days as placebo. By the end of 10 days, the animals were killed and their ilea were excised. Ileum segments were placed in an organ bath; concentration-response relationship for carbachol and histamine were obtained by adding the reagent cumulatively to the bath.

RESULTS

pD(2) values being the same, maximum contractile responses (E(max)) to carbachol and histamine were significantly reduced in the ceftriaxone sodium group compared with the control group. No significant differences in E(max) and pD(2) values to carbachol and histamine were observed between the ampicillin group and the control group.

CONCLUSION

These data indicate that whereas ceftriaxone may impair small bowel smooth muscle contractility, ampicillin does not. There are implications for the long-term use of parenteral antibiotics in the postoperative period.

Pharmacological characterization of endothelin receptors-mediated contraction in the mouse isolated proximal and distal colon

The study investigated the role of endothelin (ET) and the ET receptor subtypes ET(A) and ET(B) in mediating longitudinal contraction in the mouse proximal and distal colon. Cumulative concentration-response curves to a range of ET agonists (ET-1, ET-2, ET-3, (Ala(1,3,11,13)) ET and IRL 1620) were established by administering concentrations ranging from 0.01 nM to 0.3 microM. Concentration-response curves to ET-1, which exhibits a high affinity for both ET(A) and ET(B) receptor subtypes, were also established in the presence of the ET(A) antagonist BMS 182874 and the ET(B) antagonist IRL1038. The addition of the selective ET(A) receptor antagonist BMS 182874 caused a rightward shift of the concentration-response curve to ET-1 in both sections of the colon. The ET(B) receptor antagonist IRL1038 (0.3-1 microM) did not significantly effect the response to ET-1 in the proximal colon but caused a significant decrease in response towards higher concentrations ranges (>or=3 nM) in the distal colon. A comparison of the concentration-response curves to ET-1, ET-2 and ET-3 showed a rank order of potency ET-1>or=ET-2>>ET-3 in the proximal colon and ET-1>or=ET-2>or=ET-3 in the distal colon. The selective ET(B) receptor agonists, (Ala(1,3,11,13)) ET and IRL 1620 did not produce any response in the proximal sections of the colon but produced a smaller contraction in the distal segments. The data indicate that ET can contract the proximal tissues of the mouse colon predominantly via ET(A) receptors and in the distal tissues via ET(A) and ET(B) receptors.

Endothelin-1 stimulates sphincter of Oddi motility and decreases trans-sphincteric flow: a possible mechanism contributes to cholestasis in disease states

Endothelin-1 (ET-1) is a potent stimulator of gallbladder contractility. Its role in modulation of sphincter of Oddi (SO) motility and trans-sphincteric flow (TSF) has not been evaluated. To characterize the effects of ET-1 on SO motility and TSF, 10 anaesthetized Australian possums (in vivo, n = 6) were given graded doses of ET-1 (5-200 pmol kg-1) via closed intra-arterial injection. Blood pressure, TSF and SO motility (basal pressure, phasic amplitude, contraction frequency) were analysed. For in vitro studies, eight SO rings were subjected to 10-12-10-7 mol L-1 cumulative concentrations of ET-1 in organ bath and SO motility was measured. Data are expressed as mean +/- SEM. Statistical analysis used anova. ET-1 induced a dose-related increase in blood pressure with a maximal increase of 37.5 +/- 2.5 mmHg at 200 pmol kg-1, (P < 0.001). ET-1 also increases SO basal pressure (P < 0.001) and contraction frequency (P < 0.0001). However, the contraction amplitude was not significantly affected. ET-1 decreased TSF in a dose-related manner (P < 0.001) with cessation of TSF at the highest dose (P < 0.001). In vitro studies showed a significant increase in mean SO motility index, and frequency of contractions at higher ET-1 concentrations (10-9-10-7 mol L-1). ET-1 is a potent stimulator of SO motility resulting in a reduction in TSF.

Effects of trout endothelin on the motility of gastrointestinal smooth muscle from the trout and rat

Trout endothelin (ET), previously isolated from the kidney of the rainbow trout Oncorhynchus mykiss, contains four amino acid substitutions at residues 4-7 compared with rat ET-1. Trout ET produced sustained and concentration-dependent contractions of strips of longitudinal smooth muscle from trout stomach (pD(2) = 7.52 +/- 0.06) and proximal small intestine (pD(2) = 7.80 +/- 0.10) and from rat fundus (pD(2) = 7.78 +/- 0.14). Rat ET-1 was equipotent with trout ET for contraction of rat fundus and 2- to 3-fold more potent for contraction of trout gastrointestinal tissues. In contrast, rat ET-1 was 10- to 20-fold more potent than trout ET in constricting isolated rings of vascular tissue from trout efferent branchial artery and cardinal vein and from rat aorta (Y. Wang et al., 1999, Am. J. Physiol. 277, R1605-R1611). It is known that the contractile effects of ET-1 on rat fundus are mediated through the ET(B) receptor and effects on the rat aorta are mediated through the ET(A) receptor. We propose, therefore, that trout gastrointestinal tissues express an ET(B)-type receptor that differentiates poorly between trout ET and rat ET-1, whereas trout vascular tissues express an ET(A)-type receptor that is preferentially activated by rat ET-1. The rat ET-1-induced contractions of the trout gastrointestinal tissues are in part indirect, involving a serotoninergic neuronal pathway in the intestine and a noncholinergic, nonserotoninergic pathway in the stomach.