Adiponectin and the regulation of gastric content volume in the newborn rat

Adiponectin affects ileal contractility of mouse preparations

Adiponectin (ADPN) has been reported to induce inhibitory effects on gastric motor activity, which, being a source of peripheral satiety signals, would contribute to the central anorexigenic effects of the hormone in rodents. However, peripheral satiety signals can also originate from the small intestine. Since there are no data on the effects of ADPN in this gut region, the present study aimed to investigate whether ADPN affects murine ileal contractility. Immunofluorescence experiments and Western blot were also performed to reveal the expression of ADPN receptors. Mechanical responses of ileal preparations were recorded in vitro via force-displacement transducers. Preparations showed a tetrodotoxin- and atropine-insensitive spontaneous contractile activity. Electrical field stimulation (EFS) induced tetrodotoxin- and atropine-sensitive contractile responses. ADPN induced a decay of the basal tension and decreased the amplitude of either the spontaneous contractility or the EFS-induced excitatory responses. All ADPN effects were abolished by the nitric oxide (NO) synthesis inhibitor NG-nitro l-arginine. The expression of the ADPN receptor, AdipoR1, but not AdipoR2, was also revealed in enteric glial cells. The present results offer the first evidence that ADPN acts on ileal preparations. The hormone exerts inhibitory effects, likely involving AdipoR1 on enteric glial cells and NO. From a physiological point of view, it could be hypothesized that the depressant action of ADPN on ileal contractility represents an additional peripheral satiety signal which, as also described for the ileal brake, could contribute to the central anorexigenic effects of the hormone.NEW & NOTEWORTHY This study provides the first evidence that adiponectin (ADPN) is able to act on ileal preparations. Functional results demonstrate that the hormone, other than causing a slight decay of the basal tension, depresses the amplitude of both spontaneous contractility and neurally induced excitatory responses of the mouse ileum through the involvement of nitric oxide. The expression of the ADPN receptor AdipoR1 and its localization on glial cells was revealed by Western blot and immunofluorescence analysis.

Neuronal Nitric Oxide Synthase as a Shared Target for the Effects of Adiponectin and Resistin on the Mechanical Responses of the Mouse Gastric Fundus

It has been reported that adiponectin (ADPN) and resistin are co-secreted by white mouse adipocytes and exert similar inhibitory effects in the mouse gastric fundus, in which resistin was observed to increase neuronal nitric oxide synthase (nNOS) expression. On these grounds, the present work aimed to investigate whether the effects of the two adipokines on the neurally-induced relaxant responses potentiate each other and whether there is a possible correlation with changes in nNOS expression in preparations from the mouse gastric fundus. In carbachol (CCh)-precontracted strips, electrical field stimulation elicited nitrergic relaxant responses, whose amplitude was increased by ADPN or resistin, but no additional enhancements were observed in their concomitant presence. Western blot and immunofluorescence analyses revealed that ADPN, like resistin, was able to up-regulate nNOS expression and to increase the percentage of nNOS-positive neurons in the myenteric plexus: co-treatment with the two adipokines did not induce additional changes. The results indicate that the two adipokines modulate nitrergic neurotransmission, and both do so by up-regulating nNOS expression. Therefore, nNOS appears to be a shared target for the two adipokines' effects, which, rather than mutually reinforcing each other, may represent a dual physiological control mechanism to guarantee gastric fundus relaxation.