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The present study was designed to investigate the influence of Se deficiency on serum histamine concentration and the expression of histamine receptor in the jejunum of chickens. Forty neonatal chickens were randomly divided into two groups. Experimental chickens were fed a low-Se diet (0.034 mg/kg), whereas chickens in the control group were fed a diet with a Se level of 0.229 mg/kg. Ten chickens were sacrificed on days 30, 45, 60 and 75. Blood and jejunum samples were collected. Histamine concentration in the jejunum was measured by ELISA, the jejunal mast cell (MC) ultrastructure was studied by transmission electron microscopy, and the expression level of histamine H2 receptor (H2R) mRNA in the jejunum was examined using real-time PCR. Results: The jejunal histamine concentration in chickens fed the low-Se diet was significantly higher than that in the control group (P<0.01). Se deficiency induced degranulation of MC in the jejunum of chickens in the low-Se diet group; their cytoplasm was filled with fused granules and vacuoles. The expression level of jejunal H2R mRNA in chickens fed the low-Se diet was also significantly higher than that in the control group (P<0.01). The results obtained suggest that Se deficiency stimulates MC degranulation and release of histamine, binding H2R promotes both regulation of digestion and cell proliferation while protects the jejunum from injury induced by Se deficiency.
Prostaglandins can protect the in vivo gastric mucosa against necrosis produced by a variety noxious agents. Cimetidine has also been shown to have protective properties in humans and in some models of experimental injury. Whether prostaglandins or cimetidine may protect gastric mucosal cells directly in the absence of systemic factors remains controversial. In the present study, the potential protective actions of prostaglandin and cimetidine against indomethacin injury were assessed in isolated rat gastric glands. Gastric glands were pre-incubated in oxygenated medium with either placebo, 16,16 dimethyl prostaglandin E2 (dm PGE2) or cimetidine and incubated at 37°C in medium containing 0.5 mg/ml of indomethacin for 2, 4 and 6 hrs. Cell injury and protection was assessed by the Fast Green exclusion test (viability test), leakage of lactate dehydrogenase (LDH) into the medium, and by scanning and transmission electron microscopy. In addition, the generation of PGE2 by the gland cells was determined using RIA assay. Indomethacin by itself significantly reduced the viability of gastric glands, increased LDH release into the medium and produced prominent ultrastructural damage. In contrast to cimetidine, co-incubation of gastric glands with dm PGE2 added to indomethacin, significantly reduced indomethacin-induced injury, increased the number of viable cells, reduced LDH leakage and diminished the extent of ultrastructural damage. The dose of indomethacin (5 µg/ml) which significantly inhibited the generation of PGE2 (up to 90% inhibition) had no effect on cell viability nor LDH release. We conclude that 1) exogenous PGE2 exerts a potent protective activity in vitro which is independent on neural, vascular and hormonal factors; 2) inhibition of endogenous PGs may not the primary mechanism in the deleterious action of indomethacin against damage to gastric glandular cells and 3) indomethacin can exert a direct cytotoxic effect on the mucosal cells in gastric glands.
Functional role of endothelial alpha2-adrenoceptor in coronary circulation remains unclear. Clonidine, an agonist of alpha2-adrenoceptors, was reported to induce coronary vasodilatation via stimulation of endothelial alpha2-adrenoceptors or coronary vasoconstriction involving vascular smooth muscle alpha2-adrenoceptors. Moreover, H2 receptor-dependent responses to clonidine were described. Here, we reassess the contribution of endothelial alpha2-adrenoceptor and H2 receptors to coronary flow and contractility responses induced by clonidine in the isolated guinea pig heart. We found that clonidine (10-9 - 10-6 M) produced concentration-dependent coronary vasoconstriction without a significant change in contractility. This response was inhibited by the alpha1/alpha2-adrenoceptor antagonist - phentolamine (10-5 M) and the selective alpha2-adrenoceptor antagonist yohimbine (10-6 M), but it was not changed by the selective alpha1-adrenoceptor antagonist prazosin (10-6 M). In the presence of nitric oxide synthase inhibitor, L-NAME (10-4 M) the clonidine-induced vasoconstriction was potentiated. Clonidine at high concentrations of 10-5 – 3 x 10-5 M produced coronary vasodilatation, and an increase in myocardial contractility. These responses were abolished by a selective H2-receptor antagonist, ranitidine (10-5 M), but not by phentolamine (10-5 M). We conclude that in the isolated guinea pig heart, clonidine-induced vasoconstriction is mediated by activation of smooth muscle alpha2-adrenoceptors whereas clonidine-induced coronary vasodilatation is mediated by activation of vascular H2 histaminergic receptors. Accordingly, endothelial alpha2-adrenoceptors does not seem to play a major role in coronary flow response induced by clonidine.
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