Characterization of myenteric neuropathy in the jejunum of spontaneously diabetic BB-rats

Abstract  Decreased gastric expression and function of neuronal nitric oxide synthase (nNOS) has been proposed as a potential mechanism underlying diabetic gastroparesis. As gastric nNOS expression is vagally controlled, these changes might occur secondarily to vagal neuropathy. In addition, it is unclear whether other inhibitory neurotransmitters are also involved. We used the type 1 diabetic BioBreeding (BB)-rat model to study jejunal motor control and nNOS expression, which is independent of the vagus. Jejunal segments were used for in vitro contractility studies, and measurement of nNOS expression after 8 or 16 weeks of diabetes compared with age- and sex-matched controls. Unlike electrical field stimulation and acetylcholine (ACh)-induced contractions, non-adrenergic non-cholinergic (NANC) relaxations were significantly reduced in diabetic rats. In contrast to control rats, NANC relaxations in diabetic rats were N _ω-nitro- l -arginine methyl ester ( l -NAME) insensitive. Jejunal nNOS expression was significantly decreased in diabetic rats. Both in diabetic and in control animals, l -NAME resistant relaxations were sensitive to P₂-receptor antagonists. In the jejunum of spontaneously diabetic rats, decreased nitric oxide responsiveness and decreased nNOS protein expression occur while purinergic transmission is unaffected. These findings indicate that nitrergic enteric neuropathy may be a primary dysfunction in diabetes, independent from vagal dysfunction.     

Endogenous and exogenous ghrelin enhance the colonic and gastric manifestations of dextran sodium sulphate-induced colitis in mice

Abstract Ghrelin is an important orexigenic peptide that not only exerts gastroprokinetic but also immunoregulatory effects. This study aimed to assess the role of endogenous and exogenous ghrelin in the pathogenesis of colitis and in the disturbances of gastric emptying and colonic contractility during this process. Dextran sodium sulphate colitis was induced for 5 days in (i) ghrelin^+/+ and ghrelin^?/? mice and clinical and histological parameters were monitored at days 5, 10 and 26 and (ii) in Naval Medical Research Institute non‐inbred Swiss (NMRI) mice treated with ghrelin (100 nmol kg^?1) twice daily for 5 or 10 days. Neural contractility changes were measured in colonic smooth muscle strips, whereas gastric emptying was measured with the ¹⁴C octanoic acid breath test. Inflammation increased ghrelin plasma levels. Body weight loss, histological damage, myeloperoxidase activity and IL‐1β levels were attenuated in ghrelin^?/? mice. Whereas absence of ghrelin did not affect changes in colonic contractility, gastric emptying in the acute phase was accelerated in ghrelin^+/+ but not in ghrelin^?/? mice. In agreement with the studies in ghrelin knockout mice, 10 days treatment of NMRI mice with exogenous ghrelin enhanced the clinical disease activity and promoted infiltration of neutrophils and colonic IL‐1β levels. Unexpectedly, ghrelin treatment decreased excitatory and inhibitory neural responses in the colon of healthy but not of inflamed NMRI mice. Endogenous ghrelin enhances the course of the inflammatory process and is involved in the disturbances of gastric emptying associated with colitis. Treatment with exogenous ghrelin aggravates colitis, thereby limiting the potential therapeutic properties of ghrelin during intestinal inflammation.     

Influence of ghrelin on the gastric accommodation reflex and on meal-induced satiety in man

Abstract  Ghrelin increases gastric tone in the fasting state and enhances gastric emptying in gastroparesis. The aims of the study were to evaluate the effect of ghrelin on postprandial gastric tone and on meal-induced satiety in health. Ten healthy volunteers underwent a barostat study on two occasions. After determination of intra-abdominal pressure (minimal distending pressure, MDP), isobaric volume measurement was performed for 90 min at MDP + 2 mmHg. After 20 min, ghrelin (40 μg) or saline was administered i.v. over 30 min in a double-blind-randomized cross-over design, followed 10 min later by a liquid meal (200 mL, 300 kcal). Stepwise isobaric distentions (+2 mmHg per 2 min) were performed 60 min after the meal. Data (mean ± SEM) were compared using paired Student's t -test and anova . Separately, a satiety drinking test (15 mL min⁻¹ until satiety score 5) was performed on 10 subjects twice, after treatment with placebo or ghrelin. Ghrelin infusion significantly inhibited gastric accommodation (mean volume increase adjusted means 108.0 ± 50 vs 23.0 ± 49 mL, P  = 0.03, ancova with the premeal postinfusion volume as covariate) and reduced postprandial gastric volumes (197.2 ± 24.6 vs 353.5 ± 50.0 mL, P  = 0.01). Pressures inducing perception or discomfort during postprandial gastric distentions were not altered. During satiety testing, ghrelin did not alter nutrient volume ingested till maximal satiety (637.5 ± 70.9 vs 637.5 ± 56.2 mL, ns). Ghrelin administered during the meal significantly inhibits gastric accommodation in health, but this is not associated with early satiation.     

Effect of peripheral obestatin on gastric emptying and intestinal contractility in rodents

Obestatin has recently been discovered in the rat stomach. It is encoded by the ghrelin gene and has been claimed to be a functional opponent of ghrelin and to be the natural ligand of the GPR39 receptor. The latter could not be confirmed by Holst et al. (Endocrinology, 2006). Yet, in GPR39 knockout mice, gastric emptying is accelerated. We verified the effects of obestatin on gastric emptying and intestinal contractility in rodents. Gastric emptying was measured with the (14)C octanoic breath test in mice. In vitro, the effect of obestatin was studied on electrically stimulated and non-stimulated strips from the fundus and small intestine of mice and rats. Obestatin (60, 125, 250 nmol kg(-1)) did not affect gastric emptying parameters (T(half) and T(lag)) and did not inhibit the prokinetic effects of ghrelin. Mouse and rat intestinal and fundic smooth muscle strips did not respond to obestatin either in the absence or in the presence of electrical field stimulation. Obestatin (125 nmol kg(-1)) did not inhibit fasting-induced hyperphagia. Our results suggest that peripheral obestatin is not a satiety signal that plays a role in the regulation of gastric emptying and do not support the concept that obestatin is a physiological opponent of ghrelin.     

Activation of the cannabinoid 2 (CB2) receptor inhibits murine mesenteric afferent nerve activity

Abstract Cannabinoid 2 (CB2) receptors have both antinociceptive and antihypersensitivity effects, although the precise mechanisms of action are still unclear. In this study, the modulatory role of CB2 receptors on the mesenteric afferent response to the endogenous immunogenic agent bradykinin (BK) was investigated. Mesenteric afferent recordings were obtained from anaesthetized wild-type and CB2(-/-) mice using conventional extracellular recording techniques. Control responses to BK were obtained in all experiments prior to administration of either CB2 receptor agonist AM1241, or AM1241 plus the CB2 receptor antagonist AM630. Bradykinin consistently evoked activation of mesenteric afferents (n = 32). AM1241 inhibited the BK response in a dose dependent manner. In the presence of AM630 (10 mg kg(-1)), however, AM1241 (10 mg kg(-)1) had no significant effect on the BK response. Moreover, AM1241 had also no significant effect on the BK response in CB2(-/-) mice. Activation of the CB2 receptor inhibits the BK response in mesenteric afferents, demonstrating that the CB2 receptor is an important regulator of neuroimmune function. This may be a mechanism of action for the antinociceptive and antihypersensitive effects of CB2 receptor agonists.