Bilal O. Al-Jiffry

Endothelin-1 induces contraction of human and Australian possum gallbladder in vitro.

BACKGROUND Endothelin-1 (ET-1) stimulates guinea pig gallbladder (GB) muscle strip contractility; however, the role and source of ET-1 in the GB remains to be elucidated. AIMS To determine the effect of ET-1 on human and possum GB muscle strip contractility and evaluate whether ET-1 is present in GB tissue. METHODS GB muscle strips were mounted in organ baths to measure isometric tension. ET-1 was added cumulatively with and without pretreatment with the neural blocker tetrodotoxin (TTX) or the ET receptor antagonists BQ-123, BQ-788, and tezosentan. Immunohistochemical localization of ET was performed on freshly fixed and cultured GBs. RESULTS ET-1 induced concentration-dependent increases in tone in human and possum GB strips (p<0.05). This response was unaffected by BQ-123, BQ-788, and TTX but antagonized by BQ-123+BQ-788 in the human tissue only. Tezosentan (10(-4) mol/l) blocked the ET-1-induced response in human and possum GB strips (p<0.001). Although ET immunoreactivity was absent in freshly fixed possum GB, immunoreactivity was observed in the GB epithelium of freshly fixed human tissue and in both possum and human tissue following 24 h of organ culture. CONCLUSION ET-1 acts directly on human and possum GB smooth muscle producing contractions, possibly via ET-B receptors. ET may be present under pathophysiological conditions altering GB function.

Inhibitory motor innervation of the gall bladder musculature by intrinsic neurones containing nitric oxide in the Australian Brush-tailed possum (Trichosurus vulpecula)

BACKGROUND Gall bladder functions are modulated by neurones intrinsic to the organ. Data are available on the neurochemical composition of intrinsic and extrinsic nerves innervating the gall bladder but are lacking on specific functional classes of gall bladder neurones. AIMS To characterise the intrinsic motor neurones of the gall bladder and identify their roles using pharmacological techniques. METHODS Retrograde tracing from the possum gall bladder muscle in vitro allowed identification of intrinsic motor neurones. Subsequently, their content of choline acetyltransferase and nitric oxide synthase, markers of acetylcholine and nitric oxide containing neurones, was established using immunohistochemical techniques. Organ bath pharmacology was used to evaluate neurotransmission by acetylcholine and nitric oxide in gall bladder muscle strips. RESULTS Innervation of the gall bladder musculature by neurones of both the muscular and serosal plexuses was demonstrated. A large proportion (62%) of these motor neurones were immunoreactive for nitric oxide synthase. All gall bladder neurones showed immunoreactivity for choline acetyltransferase. Organ bath pharmacology confirmed the neuroanatomical data, showing acetylcholine and nitric oxide mediating neurotransmission to the gall bladder musculature. CONCLUSIONS Neurones containing acetylcholine and nitric oxide, located within the muscular and serosal plexuses, provide excitatory and inhibitory motor innervation of the gall bladder, respectively. The large inhibitory innervation suggests active relaxation of the gall bladder during filling, mediated by intrinsic nerves.

Secretin induces variable inhibition of motility in different parts of the Australian possum sphincter of Oddi

The sphincter of Oddi (SO) may not function as a single structure. We aimed to determine the response of the proximal and distal segments of the bile duct (BD‐SO) and pancreatic duct (PD‐SO) components of the SO to secretin, with and without neural blockade with tetrodotoxin (TTX). In anaesthetized Australian possums, separate manometry catheters were placed in the proximal and distal BD‐SO or PD‐SO segments to record motility. Secretin, 50–1000 ng kg–1, was administered, followed by TTX, and re‐administration of secretin, 500 and 1000 ng kg–1. Changes in the motility index (MI, frequency × mean amplitude) were determined. Statistical analysis utilized repeated‐measures ANOVA. Secretin produced a dose‐dependent decrease in MI from the proximal and distal BD‐SO and PD‐SO (all P < 0.001). The maximum inhibition, at 1000 ng kg–1, was 21 ± 4%, 33 ± 6% and 42 ± 5% of control (mean ± SEM), for proximal and distal BD‐SO, and distal PD‐SO, respectively. The proximal PD‐SO MI, however, was inhibited to 62 ± 6% of control, at 1000 ng kg–1. TTX enhanced the secretin‐induced response to the same level at the four sites (P < 0.02). We conclude that secretin inhibits the motility of the possum SO in a nonuniform manner and is modulated by neural activity.

Endothelin-3 induces both human and opossum gallbladder contraction mediated mainly by endothelin-B receptor subtype in vitro

Background: Endothelins are produced by gallbladder epithelial cells, suggesting a role in the regulation of gallbladder function.

Endogenous endothelin increases gallbladder tone and leads to acute cholecystitis in the Australian possum

Abstract  Endothelins are bioactive peptides produced by gallbladder epithelial cells. We aimed to determine the role of endothelins in acute cholecystitis. Escherichia coli lipopolysaccharide vs saline (sham) was instilled into the gallbladder lumen of Australian possums. Some animals received the non‐selective endothelin antagonist, tezosentan. At 4 or 24 h, plasma and gallbladder endothelins and white blood cell count (WBCC) were determined. Acute cholecystitis was assessed using a histopathology score. In other animals gallbladder tone was determined. At 4h, a dose‐dependent 60‐fold increase in gallbladder endothelin level occurred (P = 0.001) but other parameters remained comparable with sham animals. Epithelial cells were endothelin‐immunoreactive. At 24 h, the WBCC rose (P < 0.007), and severe cholecystitis developed. Gallbladder but not plasma endothelin levels remained elevated. Tezosentan pre‐treatment resulted in a histologically normal gallbladder, but the WBCC and gallbladder endothelin levels were elevated. Lipopolysaccharide or saline instillation also caused a time‐dependent increase in gallbladder tone over 4 h (P < 0.001), but not in control animals. This increase was reduced by tezosentan treatment. Gallbladder endothelin production is an early event in acute cholecystitis, increases gallbladder tone and plays a crucial role in the inflammatory process.

Endothelins induce gallbladder contraction independent of elevated blood pressure in vivo in the Australian possum.

Endothelin levels are elevated in shock, sepsis, and cholestatic jaundice, and an effect on biliary motility may be postulated. The aim of this study was to determine whether (1) endothelin-1 and endothelin-3 induce gallbladder contraction in vivo, (2) the response is caused by changes in blood pressure, and (3) the response is nerve mediated. Gallbladder pressure and blood pressure were measured in 38 anesthetized possums. Endothelin-1 or endothelin-3 (5 to 200 pmol/kg) was administered by close intra-arterial injection. Tetrodotoxin (9 μg/kg) or the mixed endothelin antagonist tezosentan was infused at a rate of 10 or 100 nmol/kg/min (close intra-arterial injection). Maximum changes in gallbladder pressure (% of carbachol-induced contraction) and blood pressure (mm Hg) were determined. Statistical analysis was carried out by means of repeated-measures analysis of variance and Kruskal-Wallis test. Both endothelin-1 and endothelin-3 induced dose-dependent increases in gallbladder pressure and blood pressure (P < 0.05), which were unaffected by pretreatment with tetrodotoxin. The endothelin-1-induced gallbladder pressure but not blood pressure was reduced by the higher dose of tezosentan (P < 0.03). The lower dose of tezosentan also produced a decrease in the endothelin-3-induced gallbladder pressure (P < 0.02) but not in blood pressure, whereas the higher dose reduced the blood pressure with no further reduction in gallbladder pressure (P < 0.05). Endothelins increase gallbladder motility in vivo, acting directly on the smooth muscle and independent of changes in blood pressure.