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Starch is the major source of food glucose and its digestion requires small intestinal alpha-glucosidic activities provided by the 2 soluble amylases and 4 enzymes bound to the mucosal surface of enterocytes. Two of these mucosal activities are associated with sucrase-isomaltase complex, while another 2 are named maltase-glucoamylase (Mgam) in mice. Because the role of Mgam in alpha-glucogenic digestion of starch is not well understood, the Mgam gene was ablated in mice to determine its role in the digestion of diets with a high content of normal corn starch (CS) and resulting glucose homeostasis. Four days of unrestricted ingestion of CS increased intestinal alpha-glucosidic activities in wild-type (WT) mice but did not affect the activities of Mgam-null mice. The blood glucose responses to CS ingestion did not differ between null and WT mice; however, insulinemic responses elicited in WT mice by CS consumption were undetectable in null mice. Studies of the metabolic route followed by glucose derived from intestinal digestion of (13)C-labeled and amylase-predigested algal starch performed by gastric infusion showed that, in null mice, the capacity for starch digestion and its contribution to blood glucose was reduced by 40% compared with WT mice. The reduced alpha-glucogenesis of null mice was most probably compensated for by increased hepatic gluconeogenesis, maintaining prandial glucose concentration and total flux at levels comparable to those of WT mice. In conclusion, mucosal alpha-glucogenic activity of Mgam plays a crucial role in the regulation of prandial glucose homeostasis. [ABSTRACT FROM AUTHOR]

Increasing public concern has been focused on animal production systems as a major nonpoint source of pollution. These studies were conducted to further our understanding of whole-animal N metabolism, N excretion, and its partition between feces and urine in growing dairy heifers. Isocaloric diets [2.31 Mcal of metabolizable energy (ME)/kg of dry matter (DM)], ranging from 12.4 to 34.2 g of N/kg of DM, were fed to Holstein heifers in 2 experiments at approximately 1.8 times maintenance. Diets were formulated to provide 54 to 143% of the ruminal ammonia requirements as predicted by the Cornell Net Carbohydrate and Protein System. Increasing the N content of the diet increased urinary N excretion and N balance, but did not affect fecal N excretion. Holstein heifers fed low N diets were able to maintain growth rates consistent with current recommendations while at the same time reducing N excretion, in particular nitrogenous compounds that are readily converted to ammonia. However, more research is needed before this type of diet is recommended for growing heifers because of possible changes in body composition that may affect future milk production and performance. [ABSTRACT FROM AUTHOR]

One-compartment, mathematical models for pressure controlled ventilation, incorporating volume dependent compliances, linear and nonlinear resistances, are constructed and compared with data obtained from healthy and (oleic acid) lung-injured pigs. Experimental data are used to find parameters in the mathematical models and were collected in two forms. Firstly, the Pe-V curves for healthy and lung injured pigs were constructed; these data are used to compute compliance functions for each animal. Secondly, dynamic data from pressure controlled ventilation for a variety of applied pressures are used to estimate resistance parameters in the models. The models were then compared against the collected dynamic data. The best mathematical models are ones with compliance functions of the form C (V) = a + bV where a and b are constants obtained from the Pe-V curves and the resistive pressures during inspiration change from a linear relation Pr = RQ to a nonlinear relation Pr = RQ ε where Q is the flow into the one-compartment lung and ε is a positive number. The form of the resistance terms in the mathematical models indicate the possible presence of gas--liquid foams in the experimental data. [ABSTRACT FROM AUTHOR]

BACKGROUND: Female carriers of ornithine transcarbamylase deficiency (OTCD) have nearly normal rates of total urea synthesis, but they derive less urea from systemic glutamine amide nitrogen than do healthy persons. OBJECTIVE: The objective of the study was to investigate whether females with symptomatic OTCD rely on alternative pathways to compensate for the reduced urea synthesis activity observed in this disorder. DESIGN: The 5-d study involved 6 control subjects (3 males, 3 females) and 6 female OTCD carriers who had a fixed energy intake of 133 kJ x kg(-)(1) x d(-)(1) and a protein intake of 0.8 g x kg(-)(1) x d(-)(1). They underwent two 12-h periods of isotopic tracer administration, separated by 2 d. On both occasions, [(18)O] or [(13)C]urea was infused intravenously, and the subjects consumed hourly meals. During the first period, [(15)N]NH(4)Cl was given intravenously; during the second period, the tracer was given as hourly oral doses. RESULTS: OTCD carriers produced less urea (P < 0.05) but had a higher (P < 0.05) mean ammonia appearance rate and plasma ammonia concentration than did control subjects. OTCD carriers incorporated a lower (P < 0.001) mean (+/- SE) proportion of the intravenous [(15)N]NH(4)Cl dose into circulating urea than did control subjects (16 +/- 1% compared with 36 +/- 2%), but there was no genotypic difference in the incorporation of orally administered tracer (81 +/- 4% compared with 72 +/- 4%, respectively). CONCLUSION: A good degree of dietary protein tolerance seemed to be retained in OTCD carriers by the maintenance of higher ammonia appearance rates, expansion of the plasma ammonia pool, and reliance on the ability of the perivenous hepatocytes to clear excess ammonia via glutamine synthesis. Copyright © 2003 American Society for Clinical Nutrition [ABSTRACT FROM AUTHOR]

A general mathematical model for the dynamic behaviour of a single-compartment respiratory system in response to an arbitrary applied inspiratory airway pressure and arbitrary respiratory muscle activity is investigated. The model is used to compute explicit expressions for ventilation and pressure variables of clinical interest for clinician-selected and impedance-determined inputs. The outcome variables include tidal volume, end-expiratory pressure, minute ventilation, mean alveolar pressure, average pleural pressure, as well as the work performed by the ventilator and the respiratory muscles. It is also demonstrated that under suitable conditions, there is a flow reversal that can occur during inspiration. [ABSTRACT FROM PUBLISHER]

Most forms of barotrauma related to mechanical ventilation are known to occur in both adult and pediatric patients. The pressure-driven transfer of gas from the alveolar compartment to the systemic circulation, a devastating complication of ventilatory support in infants, is not generally recognized as a consequence of ventilatory support in adults. Two young adult patients who received ventilatory support with high levels of positive pressure for pneumonia and the adult respiratory distress syndrome developed massive sub-pleural air cysts, interstitial emphysema, and tension pneumothoraces. Despite receiving appropriate treatment for these problems, the patients had recurrent episodes of cerebral infarction, myocardial injury, and a characteristic pattern of livedo reticularis. This distinctive triad of findings, otherwise unexplained and occurring in the setting of cystic barotrauma, is highly suggestive of systemic gas embolism. Although our patients presented with dramatic clinical features, we believe that patients with ventilator-related gas embolism may present more commonly with subtler signs, such as puzzling disturbances in heart rhythm or mental status, seizure activity, hypotension, localized pain, or other embolic manifestations readily ascribed to other causes in critically ill patients. [ABSTRACT FROM AUTHOR]

Correlations between the ratio of erythrocyte to plasma lithium (Le/Lp) and clinical status have been reported by some authors and disputed by others. Examination of the literature on Le/Lp and erythrocyte physiology suggests that Le/Lp is determined by peripheral pharmacokinetic parameters and has no direct relationship to central pathophysiology. Because of this, and because of inconsistencies between studies reporting correlations of the ratio with clinical status, such correlations probably cannot illuminate either the pathophysiology of affective illness or the mode of action of lithium. [ABSTRACT FROM AUTHOR]