No description available.

Enteroendocrine cells (EEs) are critical components in our bodies' ability to maintain homeostasis after eating a meal. Hormones released by EEs mediate processes ranging from triglyceride processing to glucose balance to hydration maintenance. Despite their importance, they remain relatively poorly understood in terms of development as well as function. Drosophila melanogaster is a promising model in which to study EEs. I performed a gene expression assay in Drosophila, and found 19 transcription factors likely to be specific to EEs. I am in the process of analyzing their mutant phenotypes in the fly midgut. Additionally, by a limited screen of the homologs to the fly EE-specific transcription factors, I was able to identify two candidates for novel transcriptional regulators involved in EE specification or functionality. I will be analyzing the mutant phenotypes for these two genes, Lmx1a and Lmx1b, in addition to a third mutant Prox1, chosen because of the strong phenotype of its homologous gene's knockdown in the fly. I am hoping I will be able to add to the ever-growing body of knowledge in reference to enteroendocrine development. Additionally, several assays were performed on flies lacking EEs. I found that flies without EEs lay significantly fewer eggs, and have apparent defects in oviposition and defecation. I will outline several experiments to continue the phenotype analysis of flies lacking EEs.

Thesis (M.S.)--Baylor University, 2005. / Includes bibliographical references (p. 61-68).

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Thesis (M.Sc.)--University of Adelaide, 1952. / "November 1951." Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1940. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

Total parenteral nutrition (TPN) provides an experimental situation where adequate nutrition is provided intravenously, bypassing the gastrointestinal tract. Under these conditions the importance of orally ingested nutrients in the control of gastric and pancreatic endocrine secretion can be assessed. The objectives of this thesis were two-fold. First, to examine the effects of TPN on the enteroinsular axis component of insulin secretion. Second, to study the importance of orally ingested nutrients in the regulation of gastric hormone secretion using the TPN rat model. In order to carry out these objectives, techniques for TPN and enteral feeding (TEN) of the rat were first developed. A dietary regimen for use in TPN and TEN rats was formulated from commercially-available, human TPN components. Under most circumstances, the TPN/TEN regimen met or exceeded the nutritional requirements for growing rats, as determined by the National Research Council (1978). Hematological analysis revealed few side effects of — intravenous or intragastric feeding. Parenterally and enterally-fed animals demonstrated comparable weight gain to that of a control group (ORAL) fed a rat chow (#5012, Ralston Purina) diet ad libitum. In addition, both TPN and TEN animals appeared healthy after the 7-day infusion period. These studies indicated that the infusion formulation was suitable for chronic intravenous and intragastric feeding. In the first series of experiments, the effects of TPN and TEN on the hormonal component of the enteroinsular axis were studied. TPN animals exhibited hyperinsulinemia and mild hyperglycemia. Conversely, TEN animals exhibited normal plasma glucose and immunoreactive insulin (IRI) concentrations. These data suggested that enterally delivered nutrients were assimilated with greater efficiency than intravenously administered nutrients. It was hypothesized that gut factors normally released by oral food intake facilitated the disposal of nutrients by hepatic and/or peripheral tissues. During the infusion period, TPN animals exhibited chronically depressed circulating IR-gastric inhibitory polypeptide (GIP) levels, in contrast to TEN animals where IR-GIP was elevated. Seven days of TPN or TEN resulted in no change in fasting plasma IRI or IR-GIP levels. However, an exaggerated insulin response to an oral glucose challenge (OGC) occurred after TPN, while the glucose response was reduced. The insulin response from the perfused pancreata of TPN animals to a GIP gradient was 20% and 40% greater than from ORAL and TEN pancreata respectively. Shorter periods of TPN (3 and 5-day periods) indicated that the hypersensitivity of the pancreas to GIP was a progressive condition, increasing with longer periods of infusion. Immunocytochemical and morphometric analysis revealed no differences in the jejunal GLP-cell population after chronic (7-day) intravenous or intragastric feeding. In addition, these routes of feeding had no effect on pancreatic islet area or endocrine cell composition of the islets. Based on these results, it was hypothesized that the increased B-cell sensitivity to GIP may have been causally related to the exposure of the pancreas to chronically low plasma GIP levels during the infusion period. To further test this hypothesis, chronically depressed plasma GIP levels, observed during TPN, were elevated by exogenous GIP infusion to levels seen in TEN rats. Chronic GIP —treatment in TPN animals (TPN-GIP) resulted in normalization of the insulin response to an OGC and in the in vitro insulin response of the isolated pancreas to GIP. These data were taken as further evidence that B-cell sensitivity to GIP was affected by ambient plasma GIP levels, and it was hypothesized that changes in sensitivity may be mediated by alteration at the receptor or post-receptor level. The effect of TPN on nutrient and neuronally mediated insulin release was also investigated. During TPN, metabolites and neuronal elements provided the main stimulus for insulin release, since hormonal components of the enteroinsular axis remained inactive. The present experiments indicated that the B-cell was hypersensitive to glucose, vagal stimulation and the cholinergic agonist methacholine, but normally sensitive to vasoactive intestinal polypeptide (VIP) and the insulinotropic amino acid arginine. These results indicated that TPN was associated with an increased B-cell sensitivity to specific hormonal, nutritive and neuronal stimuli. It was hypothesized that an increased B-cell sensitivity to these specific stimuli contributed to hyperinsulinemia observed in TPN animals during the infusion period, and to the exaggerated insulin response observed after an oral glucose challenge. Total parenteral nutrition also provided an experimental situation in which to study the importance of gastric nutrients in the regulation of Gl-hormone secretion. TPN resulted in a rapid and progressive depletion of circulating gastrin levels. G-cell secretory activity in vivo under basal and stimulatory conditions was also reduced by TPN. This condition persisted in vitro in the isolated stomach. The antral G-cell population was shown to decrease progressively with longer TPN periods, but G-cell hypoplasia and reductions in antral gastrin content were less dramatic than reductions in G-cell secretory activity. It was hypothesized that reductions in G-cell secretory activity were in part causally related to antral G-cell hypoplasia. The present data further suggested, however, that mechanisms which control synthesis and/or secretion within G-cells may have also been impaired, since various stimulants of gastrin release could not reverse gastrin hyposecretion observed during basal periods. Gastrin hyposecretion also could not be reversed by chronic bombesin administration, but was reversed by a 6-day period of oral — refeeding, indicating that the presence of nutrients in the gastric lumen was the primary regulator of tissue gastrin levels and G-cell secretory activity. The gastric D-cell was much less affected by the absence of nutrients in the gastric lumen than was the G-cell, and antral somatostatin hypersecretion may have contributed to G-cell hyposecretion. The experiments presented in this thesis indicated that total parenteral nutrition had marked effects on both B- and G-cell secretory activity. These studies clearly demonstrated the importance of enteral feeding in the maintenance of normal pancreatic and gastrointestinal endocrine secretion. / Medicine, Faculty of / Cellular and Physiological Sciences, Department of / Graduate

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Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: The uropygial gland of most birds produces a variety of hydrocarbons, lipids, waxes, fatty acids, alcohols and other organic compounds. These compounds have two widely recognized functions, viz. they are considered essential for the maintenance of a good plumage condition, and may be used for fungicidal, bactericidal or other hygienic purposes. Scimitar-billed woodhoopoes, Rhinopomastus cyanomelas, are groupterritorial birds that live in groups comprising between two and twelve individuals. Individuals enter the roost cavities shortly after sunset and exit the following morning soon after sunrise. During the period that the birds are inside the roost, they are vulnerable to a range of vertebrate predators, including snakes, genets and rats. When disturbed while roosting, woodhoopoes immediately face away from the threat hence presenting their uropygial glands in the direction of the threat. Typically, a drop of brown, highly pungent secretion is then formed at the tip of the papilla to the uropygial gland, and kept in place by a few tuft-like feathers. This response pattern has led some observers to believe that the secretion serves an anti-predatory role. It has been found that the synthetic volatile constituents of the uropygial secretion of the green woodhoopoe, P. purpureus, individually or as a mixture, have potent defensive properties against feline and reptilian predators. In addition, the compounds also showed activity against a range of bacteria. The aim of the present study was to determine the chemical composition of the uropygial secretion of the scimitar-billed woodhoopoe, Rhinopomastus cyanomelas, as a first step towards the evaluation of, inter alia, the semiochemical function of the secretion. Using gas chromatography-mass spectrometry, 179 constituents of the uropygial secretion of the scimitar-billed woodhoopoe have been identified. The majority of the constituents of the secretion are branched and unbranched aldehydes (aliphatic and aromatic), acids (aliphatic and aromatic), sulfides and ketones. This group of volatile compounds is responsible for the obnoxious odour of the secretion and possibly also for its defensive action against predators. The secretion also contains a large number of branched and unbranched alkanes and wax esters. The chemical composition of the secretion was compared with the secretion of P. purpureus as well as with that of the hoopoe, Upupa africana. The uropygial gland secretion of the scimitar-billed woodhoopoe is quite similar to that of the green woodhoopoe, although it is much more complex than that of the green woodhoopoe. In contrast to the uropygial secretions of the green and the scimitar-billed woodhoopoes, the secretion of Upupa africana does not have a strongly obnoxious odour and it also does not contain large quantities of alkanes and wax esters. / AFRIKAANSE OPSOMMING: Die uropigiale klier van die meeste voëls produseer 'n verskeidenheid van koolwaterstowwe, lipiede, was-esters, vetsure, alkohole en ander organiese verbindings. Hierdie verbindings het twee algemeen erkende funksies, naamlik die instandhouding van die goeie kondisie van die vere, en 'n swam- en kiemdodende werking. Swartbekkakelaars (Engels: scimitar-billed woodhoopoes ), Rhinopomastus cyanomelas, is groep-territoriale voëls wat in groepe van tussen twee en twaalf saam woon. Individue gaan hul neste net na sononder binne en verlaat dit weer die volgende oggend net na sonsopkoms. Terwyl die voëls binne die neste is, is hulle kwesbaar ten opsigte van aanval deur verskeie gewerwelde roofdiere, insluitende slange, muskeljaatkatte en rotte. Wanneer hulle in hul neste gesteur word, sal kakelaars onmiddellik wegdraai van die bedreiging sodat die uropigiale klier in die rigting van die bedreiging gekeer is. 'n Druppel bruin, uiters onwelriekende afskeiding vorm dan by die punt van die papil na die uropigiale klier, en word in posisie gehou deur 'n verekwassie. Hierdie gedragspatroon het aanleiding gegee tot die gedagte by sommige waarnemers dat die afskeiding as afweerstof teen roofdiere dien. Daar is gevind dat die sintetiese vlugtige komponente van die uropigiale afskeiding van die groenkakelaar, P. purpureus, individueel of as 'n mengsel, sterk afweer-eienskappe teen katte en reptiele toon. Daarbenewens het die verbindings ook aktiwiteit getoon teen 'n reeks van bakterieë. Die doel van die huidige studie was om die chemiese samestelling van die uropigiale afskeiding van die swartbekkakelaar, Rhinopomastus cyanomelas, te bepaal as 'n eerste stap met die oog op die evaluering van, onder andere, die semiochemiese funksie van die afskeiding. Deur van gaschromatografie-massaspektrometrie gebruik te maak, is 179 komponente van die uropigiale afskeiding van die swartbekkakelaar geïdentifiseer. Die meeste van die komponente is vertakte en onvertakte aldehiede (alifaties en aromaties), sure (alifaties en aromaties), sulfiede en ketone. Hierdie groep vlugtige verbindings is verantwoordelik vir die afstootlike reuk van die afskeiding en waarskynlik ook vir sy afweer-aksie teen roofdiere. Die afskeiding bevat ook 'n groot aantal vertakte en onvertakte alkane en wasesters. Die chemiese samestelling van die afskeiding is vergelyk met die van P. purpureus sowel as dié van die hoepoe, Upupa africana. Die uropigiale klierafskeiding van die swartbekkakelaar stem tot 'n groot mate ooreen met dié van die groenkakelaar, alhoewel dit veel meer kompleks is as dié van die groenkakelaar. In teenstelling met die uropigiale afskeidings van die groen- en die swartbekkakelaars, het die afskeiding van Upupa africana nie 'n afstootlike reuk nie en bevat dit ook nie groot hoeveelhede alkane en was-esters nie.