SUMMARY The possibility that malabsorbed fat passing through the human ileum exerts an inhibitory feedback control on jejunal motility has been investigated in 24 normal subjects by perfusing the ileum with a fat containing solution designed to produce ileal luminal fat concentrations similar to those in steatorrhoea (30-40 mg/ml). Mean transit times through a 30 cm saline perfused jejunal segment were measured by a dye dilution technique. Thirty minutes after ileal fat perfusion, mean transit times rose markedly to 18 9±2 5 minutes from a control value of 7*5±0-9 minutes (n=5; p<005). This was associated with an increase in volume of the perfused segment which rose to 17541±229 ml (control 976±103 ml, n=5; p<005). Transit times and segmental volumes had returned towards basal values 90 minutes after completing the fat perfusion. Further studies showed that ileal fat perfusion produced a pronounced inhibition of jejunal pressure wave activity, percentage duration of activity falling from a control level of 40 3±5 0% to 14 9±2 8% in the hour after ileal perfusion (p<001). Ileal fat perfusion was associated with marked rises in plasma enteroglucagon and neurotensin, the peak values (218±37 and 68±13 1 pmol/l) being comparable with those observed postprandially in coeliac disease. These observations show the existence in man of an inhibitory intestinal control mechanism, whereby ileal fat perfusion inhibits jejunal motility and delays caudal transit of jejunal contents.

A double lumen jejunal perfusion technique has been used in man to study the effect of peptide chain length on absorption of amino acid nitrogen from two partial enzymic hydrolysates of lactalbumin. Copper-chelation chromatography showed that one lactalbumin hydrolysate (LH2) contained 98% peptides with a chain length greater than 4, whilst the other (LH1) contained a more even spread of chain lengths with 55% less than 4. Absorption of total nitrogen and of 14 amino acid residues occurred to a significantly greater extent from the low molecular weight LH1 than from the higher molecular weight LH2. The results suggest that the pattern of nitrogen and amino acid absorption from partial enzymic hydrolysates of whole protein is markedly influenced by peptide chain length and that brush border peptide hydrolysis has an important rate limiting effect on absorption rates.

A solgel process is described to produce Ta(2)O(5) films as short wavelength antireflective (AR) coatings for silicon. The AR coatings were optimized for 370 nm by controlling the acid catalyzed hydrolysis of Ta(OC(2)H(5))(5), the spin coating parameters, and the heat treatment process (rapid thermal processing (RTP) and muffle furnace). Film thickness uniformity across the wafer was better than 1%, and all the coatings tested passed the standard scotch tape test before and after heat treatment and exhibited no change in optical properties after submersion in liquid N(2). Several heat treatment protocols for densifying the films were studied. Spin coated films heat treated in a muffle furnace at 275 degrees C yielded Ta(2)O(5) AR coatings that reduced the reflectance losses from silicon at 370 nm by 86%, the reduction being within 1% of the theoretical value. Films subjected to RTP at temperatures ranging from 300 to 1000 degrees C reduced the reflectance loss in some cases by as much as 95%. The results demonstrate that spin coated solgel derived Ta(2)O(5) films subjected to a low temperature (<300 degrees C) heat treatment can form durable films suitable for near UV AR coatings for high index silicon devices, such as charge couple imagers and photovoltaic cells.

The jejunal absorption of glucose from (1-4)-linked glucose oligomers including maltotriose has been compared with that from free glucose and sucrose in normal subjects. A steady-state perfusion technique in vivo was used to study proximal jejunal assimilation of isotonic sugar-saline solutions isocaloric with 140 mmol/l glucose. Endogenous alpha-amylase was excluded from the test segment by proximal balloon occlusion. The glucose oligomer mixture consisted mainly of maltotriose, maltotetraose, maltopentaose and maltoheptaose. Glucose absorption was significantly faster from maltotriose alone and from the glucose oligomer mixture than from 140 mmol/l glucose controls, whereas glucose absorption from 70 mmol/l sucrose was similar to that from 70 mmol/l glucose plus 70 mmol/l fructose. Hydrolysis in vivo of maltotriose, the oligomer mixture and sucrose were similar, indicating that capture of glucose released by brush border sucrose hydrolysis was less efficient than that associated with (1-4)-linked oligomer hydrolysis. This suggests that the stoichiometric relationship of the active hydrolysis sites for sucrose to the glucose transport system is less advantageous than that of active sites for maltose hydrolysis. Hydrolysis of oligomers larger than maltohexaose may be rate limiting for glucose absorption in the absence of luminal amylase activity.

A steady-state perfusion technique has been used in vivo in normal subjects to show that at concentrations occurring during therapeutic use (500 mg/1, 1.1 mmol/l) the antibiotic clindamycin reversibly inhibits bicarbonate-stimulated water and electrolyte absorption from the human jejunum. Lactose-stimulated water and electrolyte absorption was not affected by the addition of clindamycin at the same concentration. Clindamycin-induced malabsorption of water and electrolytes may contribute significantly to the diarrhoea that occurs during clindamycin therapy in the absence of pseudomembranous colitis.