Post-prandial changes in PH and electrolyte concentration, in the upper jejunum after truncal vagotomy and drainage in man

Hyperosmolar Duodenal Saline Infusion Lowers Circulating Ghrelin and Stimulates Intestinal Hormone Release in Young Men

CONTEXT

The mechanisms regulating the postprandial suppression of ghrelin secretion remain unclear, but recent observations in rats indicate that an increase in duodenal osmolarity is associated with a reduction in ghrelin levels. Several hormones have been implicated in the regulation of ghrelin.

OBJECTIVE

We hypothesized that intraduodenal infusion of a hyperosmolar solution would lower plasma ghrelin concentrations.

DESIGN, SETTING, PARTICIPANTS, AND INTERVENTIONS

Eighteen healthy young men were studied after an overnight fast on two occasions in a randomized double-blinded fashion. A nasoduodenal catheter was positioned and isoosmolar (300 mOsm/L) or hyperosmolar (1500 mOsm/L) saline was infused intraduodenally (4 mL/min, t = 0 to 45 minutes). Venous blood was sampled at t = -45, -30, -15, 0, 15, 30, 45, 60, 75, 90, 120, and 180 minutes.

MAIN OUTCOME MEASURES

Plasma concentrations of ghrelin, glucagonlike peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), cholecystokinin (CCK), glucagon, pancreatic polypeptide (PP), neurotensin (NT), peptide YY (PYY), motilin, and glucose.

RESULTS

Ghrelin concentrations were suppressed with hyperosmolar when compared with isoosmolar saline, and remained lower until t = 180 minutes. CCK, NT, GLP-1, PYY, and glucagon all increased during hyperosmolar, but not isoosmolar, saline infusion (P < 0.01 for all), whereas GIP, PP, and motilin levels were not affected by either infusion.

CONCLUSIONS

Plasma ghrelin concentrations are lowered, whereas CCK, GLP-1, PYY, NT, and glucagon concentrations are augmented, by hyperosmolar duodenal content in healthy individuals. These observations have implications for the evaluation of studies comparing the effects of different types and loads of nutrients and chemicals on gut hormone secretion.

In vitro study of triglyceride lipolysis and phase distribution of the reaction products and cholesterol: effects of calcium and bicarbonate

We describe a relatively simple in vitro model for triglyceride (TG) lipolysis which mimics closely the conditions in the human stomach and small intestine. The main model advantages are: (1) as in vivo, sodium bicarbonate is used for buffering; (2) the pH-profile in the small intestine is closely matched; (3) the experimental procedure does not include complex equipment. To test its performance, the proposed in vitro model is applied to quantify the effects of Ca(2+), pH, and bicarbonate on the degree of TG lipolysis and on the solubilization of the lipolysis products and cholesterol in the aqueous phase. We found that TG lipolysis passes through a shallow minimum at 3.5 mM Ca(2+) when varying the calcium concentration between 1 and 11 mM, while the presence of bicarbonate and the increase of pH led to a higher degree of lipolysis. Centrifugation and filtration were used to separate the aqueous phase and to study the solubilisation of the lipophilic components in the aqueous phase. We found that the solubilized cholesterol increases linearly with the concentration of free fatty acids (FFA) which is evidence for co-solubilization of these two components in the bile micelles. At high Ca(2+) concentrations, aggregates larger than 300 nm were observed by cryo-microscopy and light scattering, which solubilize well cholesterol and saturated FFA. In contrast, the monoglycerides were always predominantly solubilized in the small bile micelles with diameters around 4 nm.

Physiochemical and physiological mechanisms for the effects of food on drug absorption: the role of lipids and pH

Drugs are absorbed after oral administration as a consequence of a complex array of interactions between the drug, its formulation, and the gastrointestinal (GI) tract. The presence of food within the GI tract impacts significantly on transit profiles, pH, and its solubilization capacity. Consequently, food would be expected to affect the absorption of co-administered drugs when their physicochemical properties are sensitive to these changes. The physicochemical basis by which ingested food/lipids induce changes in the GI tract and influence drug absorption are reviewed. The process of lipid digestion is briefly reviewed and considered in the context of the absorption of poorly water-soluble drugs. The effect of food on GI pH is reviewed in terms of location (stomach, upper and lower small intestine) and the temporal relationship between pH and drug absorption. Case studies are presented in which postprandial changes in bioavailability are rationalized in terms of the sensitivity of the physicochemical properties of the administered drug to the altered GI environment.