Actin and myosin isoforms in gallbladder smooth muscle following cholesterol feeding in prairie dogs

Gallbladder smooth muscle contractility decreases after high-cholesterol feeding in prairie dogs. This decrease is not associated with alterations in the total amounts of the contractile proteins actin and myosin. The present study was designed to determine if cholesterol feeding results in alterations in the isoforms of actin and/or myosin heavy chain in gallbladder smooth muscle. Control prairie dogs were fed a trace-cholesterol diet and test animals were fed a high (1.2%)-cholesterol diet for 8 days. Although the proportion of beta-actin was unchanged, the proportion of alpha-actin in the gallbladder was less in the animals fed the high-cholesterol diet (32.6% +/- 1.5% in the control animals and 24.6% +/- 0.4% in the diet animals). On the other hand, the proportion of gamma-actin was significantly greater in the cholesterol-fed animals. There were no significant differences in the proportions of the myosin heavy-chain isoforms between the two groups. Also, there was no change in the volume fraction of smooth muscle in the gallbladders from the two groups. Thus, cholesterol feeding induces a shift in actin isoforms at the same time that there is a decrease in contractility. Whether the altered pattern of actin isoforms is related to the functional changes remains to be determined.     

Ketamine inhibits lipopolysacharide (LPS) induced gastric luminal fluid accumulation

INTRODUCTION: Lipopolysacharide (LPS) causes gastrointestinal ileus and gastric luminal fluid accumulation. Ketamine, an anti-inflammatory anesthetic agent attenuates accumulation of luminal fluid. However, its effects on gastrointestinal transit induced by endotoxemia are unknown. The purpose of this study was to determine if the anti-inflammatory properties of ketamine improve impaired gastric emptying and gastrointestinal transit because of LPS. MATERIALS AND METHODS: Rats were given ketamine (70 mg/kg i.p.) or saline 1 h before LPS (20 mg/kg, i.p.) or saline injection. Five hours after LPS injection, rats were gavaged with 1 cc consisting of 0.1 ml of 5 mm FITC Dextran added to 0.9 ml of saline. After 30 min, rats were sacrificed, and gastric emptying, gastrointestinal transit, and gastric fluid accumulation determined. Gastric and ileal mucosa were harvested for analysis of inducible nitric oxide synthase (iNOS) (Western immunoblot). Results are reported as mean +/- SE (n > or = 5 per group; ANOVA). RESULTS: Ketamine did not prevent LPS induced gastrointestinal ileus, nor did it improve gastric emptying. More importantly, it did not worsen gastrointestinal function or gastric emptying when compared to saline controls. However, it did decrease LPS induced gastric luminal fluid accumulation and blunted iNOS expression in both the stomach and ileum. CONCLUSION: These data indicate that the ability of ketamine to attenuate gastric fluid accumulation is not because of improved gastric emptying or improved gastrointestinal transit. Moreover, while iNOS may play a role in LPS induced gastric luminal fluid accumulation, it does not appear to be a major mediator of the gastrointestinal ileus caused by LPS.     

Resuscitation-induced gut edema and intestinal dysfunction

BACKGROUND: Mesenteric venous hypertension and subsequent gut edema play a pivotal role in the development of intra-abdominal hypertension. Although gut edema is one cause of intra-abdominal hypertension, its impact on gut function is unknown. The purpose of this study was to create a model of acute hydrostatic gut edema and to evaluate its effect on gut motility and barrier function. METHODS: The first study, group A, evaluated the effect of gut edema on transit over time using 20 mL/kg 0.9% saline. The second study, group B, focused on the 12-hour time period using 80 mL/kg 0.9% saline. Rats were randomized to superior mesenteric vein partial occlusion (venous hypertension) or sham surgery. At 6, 12, and 24 hours, group A underwent intestinal transit and tissue water weight measurements. At 12 hours, group B underwent tissue water, transit, ileal permeability and resistance, lactate and myeloperoxidase activity, and mucosal injury measurements. RESULTS: Venous hypertension with fluid resuscitation caused acute hydrostatic gut edema, delayed intestinal transit, increased mucosal permeability to macromolecules, and decreased tissue resistance over time. Mucosal injury was minimal in mesenteric venous hypertension. CONCLUSION: Acute mesenteric venous hypertension and resuscitation-induced gut edema, in the absence of ischemia/reperfusion injury, is associated with delayed intestinal transit and altered gut barrier function.     

Functional and structural changes in intestinal smooth muscle after jejunoileal bypass in rats

Active stress and cross-sectional area of intestinal muscle were assessed in tissues taken from unoperated rats, from rats that had undergone bypass of 70% of the small bowel, and from rats that had undergone transection and anastomosis of the bowel. Thirty-five days after operation, muscle from the intestine of transected and bypassed animals elicited active stresses that were equal to or greater than those developed by muscle taken from unoperated animals. The total cross-sectional areas of the in-continuity segment and the area and thickness of the muscle layers of both the in-continuity and bypassed segments were greater when compared with unoperated animals. Significant differences also existed among tissues taken from bypassed and transected animals. Additionally, transection induced increases in active stress, area of muscle in the distal intestine, and circular muscle thickness in the mid- and distal intestine when compared with tissues from unoperated animals. These findings support the hypothesis that intestinal bypass induces increases in functioning smooth muscle tissue.     

Relaxin alters rat uterine myosin light chain phosphorylation and related enzymatic activities

Uteri from estrogen-primed rats were suspended isometrically, contracted by 0.28 microM prostaglandin F2 alpha, and exposed to 1 microgram/ml purified porcine relaxin for 1 and 10 min. Relaxin treatment for 10 min, but not for 1 min, resulted in a significant decrease in the activity of myosin light chain kinase (MLCKase). Calcium-activated ATPase activity of a crude actomyosin fraction was also decreased by treatment with relaxin for 10 min. Relaxin treatment (10 min) also decreased the relative amount of phosphorylated myosin 20,000 dalton light chains. These effects were consistent with the degree of inhibition of uterine contractions by relaxin. The data suggest that relaxin may inhibit uterine contractile activity by decreasing MLCKase activity and, in turn, myosin phosphorylation and ATPase activity.     

Helminth regulation of host IL-4Ralpha/Stat6 signaling: mechanism underlying NOS-2 inhibition by Trichinella spiralis

Gastrointestinal nematode infection is known to alter host T cell activation and has been used to study immune and inflammatory reactions in which nitric oxide (NO) is a versatile player. We previously demonstrated that Trichinella spiralis infection inhibits host inducible NO synthase (NOS-2) expression. We now demonstrate that (i) an IL-4 receptor alpha-subunit (IL-4Ralpha)/Stat6-dependent but T cell-independent pathway is the key for the nematode-induced host NOS-2 inhibition; (ii) endogenous IL-4 and IL-13, the only known IL-4Ralpha ligands, are not required for activating the pathway; and (iii) treatment of RAW264.7 cells with parasite-cultured medium inhibits NOS-2 expression but not cyclooxygenase 2 expression. We propose that a yet-unidentified substance is released by the nematode during the host-parasite interaction.     

Actomyosin, Collagen, and Succinate Dehydrogenase Determinations in Opossum Esophageal Muscles

The contractile activities of the lower esophageal sphincter (LES), esophageal body smooth muscle (SM), and esophageal body striated muscle (ST) of the opossum differ in their dependence on oxygen. One possible explanation for this difference in oxygen dependence is that the muscles differ in their oxidative capacities. The purpose of this study was to estimate the oxidative. capacity of these muscles by measuring the activity of succinate dehydrogenase (SDH). Since the muscles are structurally as well as functionally distinct, we also determined the amount of actin, myosin, collagen, and total protein in the tissues. LES contained less total protein and more collagen than SM and ST. The actin contents per unit of total protein of all three tissues were similar. The myosin contents and the actin: myosin ratios, however, were significantly different among all three muscles. The interpretation of the values of the SDH activity depended on the manner in which the data were expressed. When SDH activity was expressed relative to the tissue content of myosin, the values were different among all three muscles. These findings support the hypothesis that there is biochemical variability in these three esophageal muscles that may account in, part for their differences in contractile behavior.     

Abdominal compartment syndrome: the cause or effect of postinjury multiple organ failure

Abdominal compartment syndrome (ACS) has emerged to be a significant problem in patients who develop postinjury multiple organ failure (MOF). Current laboratory research suggests that ACS could be a second hit for the development of MOF. Recent studies demonstrate that ACS is an independent predictor of MOF and that the prevention of ACS decreases the incidence of MOF. The Trauma Research Centers at the University of Colorado and the University of Texas-Houston Medical School are focused on defining the role of the gut in postinjury MOF. Because ACS is a plausible modifiable risk factor, our interest has been to 1) describe the epidemiology of ACS, 2) build prediction models, 3) provide strategies for prevention and treatment of ACS, and 4) develop relevant laboratory models. This review summarizes our findings.     

Excess adenosine in murine penile erectile tissues contributes to priapism via A2B adenosine receptor signaling

Priapism, abnormally prolonged penile erection in the absence of sexual excitation, is associated with ischemia-mediated erectile tissue damage and subsequent erectile dysfunction. It is common among males with sickle cell disease (SCD), and SCD transgenic mice are an accepted model of the disorder. Current strategies to manage priapism suffer from a poor fundamental understanding of the molecular mechanisms underlying the disorder. Here we report that mice lacking adenosine deaminase (ADA), an enzyme necessary for the breakdown of adenosine, displayed unexpected priapic activity. ADA enzyme therapy successfully corrected the priapic activity both in vivo and in vitro, suggesting that it was dependent on elevated adenosine levels. Further genetic and pharmacologic evidence demonstrated that A2B adenosine receptor-mediated (A2BR-mediated) cAMP and cGMP induction was required for elevated adenosine-induced prolonged penile erection. Finally, priapic activity in SCD transgenic mice was also caused by elevated adenosine levels and A2BR activation. Thus, we have shown that excessive adenosine accumulation in the penis contributes to priapism through increased A2BR signaling in both Ada -/- and SCD transgenic mice. These findings provide insight regarding the molecular basis of priapism and suggest that strategies to either reduce adenosine or block A2BR activation may prove beneficial in the treatment of this disorder.