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Leptin has a modulator effect on glucose-stimulated insulin secretion. To define the influences of different glucose (4, 8, 12, and 16 mmol/L) and leptin (5, 10, 15, and 20 nmol/L) concentrations on total insulin release in ex vivo pancreatic preparations, a customized perfusion technique was used. Such a profile of concentration brought about an index for the combined effect of leptin and glucose on the production of insulin. Insulin output was measured by radioimmunoassay. Stimulated by glucose alone in the control group, insulin secretion confirmed a bi-phasic pattern. Addition of leptin in the experimental group suppressed insulin secretion compared with control. A U-shape pattern of suppression was observed when the leptin and stimulatory glucose concentrations were combined. At 12 mmol/L glucose, leptin showed maximal insulin suppression. Leptin’s effect on insulin was glucose dependent and showed a reproducible U-shaped pattern of suppression, which implicated possible direct dose-dependent interaction between leptin and glucose on insulin secretion.

Effects of Tween 80, a nonionic surfactant, on size and number of chylomicrons (CM) secreted during lipid absorption in the rat model are reported. Fasted rats were loaded with either 154 mm NaCl or 25% (w/w) olive oil emulsion in 154 mm NaCl with 0, 0.1, 1 or 10% (w/w) Tween 80. After 3 h, either mesenteric lymph or blood was collected and their triacylglycerol-rich lipoprotein fraction (Sf>20 and Sf>400, respectively) isolated. Triacylglycerol (TAG) and apolipoprotein B48 (apoB48) concentrations in the lipoprotein fractions were assayed and their fluxes (lymph) calculated. TAG:apoB48 ratios, indicative of CM size, were determined. The data support the hypothesis that fat loading is accommodated mainly by increased average size, rather than number, of CM. Co-administration of Tween 80 with olive oil resulted in a significant increase in CM apoB48 secretion into the mesenteric lymph duct and in an increased concentration of apoB48 in the blood (Sf>400). Also, Tween 80-treated groups exhibited smaller mean CM size relative to the olive oil only group in both lymph and blood. The observed effect on CM size and number did not appear to be dose dependent at concentrations of Tween 80 above 0.1% (w/w). Incorporation of Tween 80 in the diet at 1 or 10% (w/w) concentrations reduced the TAG concentration in the stools; however, a significant increase in water content was observed at 10% (w/w) concentration. In conclusion, Tween 80 at 1 or 10% (w/w) doses can improve the efficiency of the digestive system to absorb dietary fat but at high concentrations (10%, w/w) it appeared to have a toxic or irritating effect on the gastrointestinal system. More importantly, the effect of Tween 80 on size and number of CM is a condition that favours a delay in their clearance rate.

This study was undertaken to determine the fate and fluxes of materials from Arctic estuaries to the coastal zone. The paper is the first of a series addressing questions relating to the physics and chemistry of the region. Three seasonal cruises were undertaken in the Chupa Estuary, White Sea, Russia; in summer (July 1994), autumn (September, 1995) and spring (May/June 1997). The Chupa is a fjord type estuary about 37 km long with several deep troughs, connected by shallow sills, situated south of the Arctic circle on the western shore of Kandalaksha Bay. Vertical profiles were carried out on an axial grid of 10 stations, at spring and neap tidal states, during which measurements were made of salinity, temperature, current speed and direction, the concentration of suspended particulate material (SPM), pH, dissolved oxygen, nutrients (phosphate, silicate, nitrate, nitrite and ammonia) and particulate trace metals in sediments and SPM (Millwardet al., 1999, Estuarine, Coastal and Shelf Science,48,13–25). Additionally, sampling for the hydrodynamic determinants was carried out on diurnal anchor stations at key points in the estuary. Vertical stratification was pronounced, particularly in summer, with sharp gradients in temperature and salinity. A three layer vertical structure was observed with surface (0–5 m) and deep (20–65 m) water layers providing net down-estuary transport while the intermediate (5–20 m) water layer drives net up-estuary transport and advection of more saline waters into the estuary. Strong internal waves were observed in the seaward half of the estuary at certain tidal states. The mechanism for renewal of deep waters in the troughs was investigated, this being considerably slower than in the near surface waters. Evidence of under-saturation of dissolved oxygen was evident in the deep waters of the troughs during the three surveys