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Biomedical subjects

D M Small

Publications and source records attributed to D M Small.

At least 199 records · Page 11Linked to original sources
PubMed1971

Biliary lipid secretion and bile composition after acute and chronic interruption of the enterohepatic circulation in the Rhesus monkey. IV. Primate biliary physiology.

Bile salts and phospholipids are both required to solubilize biliary cholesterol. Since interruption of the enterohepatic circulation (EHC) depletes bile of bile salts, we have examined in the rhesus monkey the effects of controlled interruption of the EHC on biliary secretion of bile salt, phospholipid, and cholesterol and on the relative proportions of these components in bile. Immediately after complete interruption of the EHC, bile secretion and bile composition remained normal for 2-3 hr. During the next 3 hr, however, secretion of all components decreased. Bile salt decreased to a greater extent than phospholipid and cholesterol, and the bile was now supersaturated with cholesterol. 12-24 hr after interruption of the EHC, a new steady state was reached in which there was a relative deficiency of bile salt and a relative increase in phospholipid and cholesterol. The resulting bile, although somewhat more saturated with cholesterol, was not supersaturated with cholesterol but was stable with respect to cholesterol solubility. Thus, bile instability conducive to gallstone formation occurs transiently within hours after interruption of the EHC. Prolonged large interruptions in the steady state animal also produce a relative bile salt deficiency, but in this situation cholesterol remains soluble in the bile of these animals because there occurs a concomitant relative increase in phospholipid. When the EHC was only partially interrupted, secretion rates and the relative concentration of bile salt, phospholipid, and cholesterol did not change significantly from control values until more than 20% of the bile was diverted. Modest changes in the relative composition of bile occurred when 33 and 66% of the bile was diverted, and these changes were very similar to those produced by resection of the distal small bowel.

Animals↗
PubMed1971

Micellar properties of sodium fusidate, a steroid antibiotic structurally resembling the bile salts.

The properties of sodium fusidate micelles were determined by a spectral shift technique, surface tension measurements, and ultracentrifugal analysis. The critical micellar concentrations, mean molecular areas, and apparent aggregation numbers were estimated as a function of the concentration of counterion (0.001-1.0 m Na(+)) at 20 degrees C. The critical micellar concentrations were studied over a temperature range of 10 degrees C to 40 degrees C at one counterion concentration (0.001 m Na(+)), and from these data the standard thermo-dynamic functions of micellization were calculated. The ability of sodium fusidate solutions to solubilize the insoluble swelling amphiphiles, lecithin and monoolein, was investigated, and the results were compared with the solubilizing properties of sodium taurocholate. The critical micellar concentrations of sodium fusidate approximated those of sodium taurocholate. The values fell in the range of 1.44-4.56 mm, varying with the technique used, counterion concentration, and temperature. The percentage of counterions bound to fusidate micelles in water, calculated from the log critical micellar concentration-log Na(+) curve, was estimated to be negligible, which compares with sodium taurocholate micelles. The critical micellar concentration of sodium fusidate exhibited a minimum at 20 degrees C, a phenomenon observed with other ionic detergents and with bile salts. Micelle formation in sodium fusidate solutions was shown to be primarily entropy-driven at 10 degrees and 20 degrees C, whereas at 30 degrees and 40 degrees C the enthalpy factor predominated. From the surface tension measurements the molecular areas of sodium fusidate and sodium taurocholate were calculated. The mean molecular area of fusidate was 101 A(2), whereas sodium taurocholate possessed a molecular area of 88 A(2). It was demonstrated that the sodium fusidate molecule, like a bile salt molecule, lies with its longitudinal axis horizontal at an air-water interface. The apparent aggregation number of sodium fusidate micelles increased from 5 to 16 as the concentration of counterion increased from 0.01 to 0.60 m Na(+). These values are slightly larger than the corresponding aggregation numbers of sodium taurocholate micelles.

Bile↗
PubMed1970

Effects of controlled interruption of the enterohepatic circulation of bile salts by biliary diversion and by ileal resection on bile salt secretion, synthesis, and pool size in the rhesus monkey.

The effects of controlled interruption of the enterohepatic circulation (EHC) of bile salts by biliary diversion on bile volume, bile salt secretion and synthesis rates, bile salt pool size, and the relationship to fecal fat excretion were studied in 16 rhesus monkeys. Bile from a chronic bile fistula was returned to the intestine through an electronic stream-splitter which, by diverting different percentages of bile to a collecting system, provided graded and controlled interruption of the EHC. The increase in hepatic bile salt synthesis in response to interruption of the EHC was limited and reached a maximum rate at 20% interruption of the EHC. Up to this level of biliary diversion, the increased hepatic synthesis compensated for bile salt loss so that bile salt secretion and pool size were maintained at normal levels. With diversion of 33% or more, there was no further increase in hepatic bile salt synthesis to compensate for external loss, and as a result there was diminished bile salt secretion, a reduction in bile salt pool size, and steatorrhea was observed. The effects of interruption of the EHC by the streamsplitter were compared with those produced by resection of the distal one-third or two-thirds of small bowel. While ileal resection appreciably reduced bile salt secretion, the EHC was by no means abolished. Bile salt reabsorption from the residual intestine was greater after one-third than after two-thirds small bowel resection. These observations suggest that jejunal reabsorption of bile salts occurs and may well contribute to the normal EHC.

Animals↗
PubMed1968

Gallstones.

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Bile↗