Retinoic acid stimulates the dynamics of mouse gastric epithelial progenitors.

The gastric epithelial progenitors proliferate and undergo bipolar migration associated with their differentiation into pit, parietal, and zymogenic cell lineages. Retinoids have long been known to modulate proliferation and differentiation of various renewing epithelia, and the expression of their receptors has been demonstrated in the gastric mucosa. The aim of this study was to examine the effects of retinoic acid on progenitor cell proliferation and cell lineage formation in the mouse stomach. By using subcutaneously inserted osmotic pumps, mice were continuously infused with all-trans retinoic acid (5 mg/kg per day) for 3 days. To label S-phase cells and their progeny, bromodeoxyuridine was administered for different time intervals. Analysis of gastric mucosal tissues of retinoic acid-treated mice revealed a significant increase in the number of S-phase progenitor cells and an enhancement in the production of their progeny. The life span of pit cells was reduced, and their apoptosis became apparent at the luminal surface. Immunofluoresence probing of pit, parietal and enteroendocrine cell lineages in control and retinoic acid-treated mice showed no significant change in their labeling pattern. However, there was an increase in the labeled gland area of zymogenic cells. In conclusion, 3-day treatment of retinoic acid enhances the proliferation of gastric epithelial progenitors and the dynamics of their progeny.

Mechanism of ipamorelin-evoked insulin release from the pancreas of normal and diabetic rats.

OBJECTIVE: To examine the effect of ipamorelin (IPA), a novel pentapeptide with a strong growth hormone releasing potency, on insulin secretion from pancreatic tissue fragments of normal and diabetic rats. MATERIALS AND METHODS: Diabetes mellitus was induced by streptozotocin (60 mg kg(-1)). Four weeks after the induction of diabetes, pancreatic tissue fragments of normal and diabetic rats were removed and incubated with different concentrations (10(-12) - 10(-6) M) of IPA. Insulin release from the pancreas was measured by radioimmunoassay. RESULTS: Ipamorelin evoked significant (p<0.04) increases in insulin secretion from the pancreas of normal and diabetic rats. Either diltiazem or yohimbine or propranolol or a combination of atropine, propranolol and yohimbine inhibited IPA-evoked insulin secretion significantly (p<0.03) from the pancreas of normal and diabetic rats. Atropine caused a significant (p<0.007) reduction in the IPA-induced insulin secretion in diabetic but not in normal rats. CONCLUSION: IPA stimulates insulin release through the calcium channel and the adrenergic receptor pathways. This is the first study to examine the effect of ipamorelin on insulin secretion in the pancreas.

Cytokine expression by attenuated intracellular bacteria regulates the immune response to infection: the Salmonella model.

Attenuated Salmonella strains have shown excellent efficacy as mucosal vaccine delivery systems. In the present report, several recombinant strains of Salmonella enterica serovar Typhimurium, engineered to express defined murine cytokines, were used to study their potential immunoregulatory capacity in the mouse model of typhoid fever. Specifically, recombinant strains expressing IL-2 (known as GIDIL2) or TNF-alpha (GIDTNF) were compared with the parental, non-cytokine-secreting, strain (BRD509) for their ability to induce a variety of immune responses in susceptible BALB/c mice. Our findings indicate that bacterially-expressed cytokines are functional in vivo and do induce a unique pattern of responses, quite distinct from that induced by BRD509 organisms. Both the type and magnitude of specific immune parameters were affected. These included the capacity to induce an inflammatory response resulting in a state of profound splenomegaly and hepatomegaly, activation of individual immune cells (particularly macrophages and other myeloid lineage cells), and the induction of nitric oxide (NO) secretion. Furthermore, a structural analysis using light as well as electron microscopy was undertaken to examine the host cellular response to infection with the different bacterial strains. The results indicate that cytokine expression by the invading pathogen can dramatically influence host immunity from a very early stage following infection. These findings may well have important consequences for the potential utilization of bacterial vector-encoded cytokines in immunoregulation in different disease settings.

Distribution of serotonin and its effect on insulin and glucagon secretion in normal and diabetic pancreatic tissues in rat.

OBJECTIVES: The distribution of serotonin (5-HT) and its effect on insulin and glucagon secretion were investigated to examine whether there are changes in the pattern of distribution and effect of 5-HT after the onset of experimental diabetes. METHODS: The pattern of 5-HT and its effect of insulin and glucagon secretion was examined using immunohistochemical and radioimmunoassay techniques, respectively. RESULTS: 5-HT was demonstrated mainly in the neural elements of the pancreas. 5-HT-containing fine varicose nerve fibers were discerned in the wall of blood vessels and pancreatic ducts. 5-HT-containing nerves were also observed in the periacinar and periinsular regions of normal pancreas. The pattern or intensity of the distribution of serotonergic nerves did not change after the onset of diabetes. The perivascular, periductal, periacinar and periinsular regions of diabetic pancreas all contained 5-HT positive nerves. 5-HT elicited marked increases in insulin secretion from normal pancreas but had an inhibitory effect on insulin secretion from diabetic pancreatic tissues. In contrast, 5HT inhibited glucagon secretion from normal pancreatic tissue fragments but stimulated glucagon release from diabetic pancreatic tissue fragments. conclusion: 5-HT is well distributed in normal and diabetic pancreatic tissues and has stimulatory effects on insulin secretion from normal pancreas and glucagon secretion from diabetic pancreas. This result indicates that although 5-HT may help in the maintenance of the blood sugar level in normal pancreas by increasing insulin secretion and decreasing glucagon secretion, it may also aggravate the hyperglycemia observed in diabetes mellitus and hence exacerbate the symptoms of hyperglycemia in poorly controlled diabetes mellitus.