Paul Tasker, FRCS, Harbans Sharma, MSc, PhD, DSc, Joan Braganza, DSc, FRCP, Maynard Case, BSc, PhD. Manchester Royal Infirmary.
INTRODUCTION: In the closed duodenal-jejunal loop, single shot doses of standard pH solutions had a very transitory effect on duodenal luminal pH.
METHOD: To produce a more persistent change in luminal pH at different levels, the duodenal-jejunal loop with the common duct still ligated was opened and two methods of fixing pH in the gut perfusion were investigated.
RESULTS: The first method was a pH-stat re-circulation technique using single rats. As an index of 64Cu absorption, 64Cu retention in liver, as a percentage of the input concentration, from unbuffered pH stat perfusion was 36.61 (±5.61)% (n=6) (% body count per g perfusate count) at pH 6 and 22.98 (±3.09)% (n=4) at pH 8 (Mean ±SD). The second method was a triple rat buffered single pass system providing perfusion in a steady state. Four levels of pH were studied, and the same trend was observed. From a MOPS, MES and HEPES (MMH) buffer with glucose liver 64Cu retention was 33.95 (±7.84)% (n=7) at pH5, 28.02 (±5.02)% (n=3) at pH 6, 20.54 (±3.65)% (n=5) at pH7, and 16.43 (±3.60) (n=7) at pH8. Carcass and total body absorption was also measured. Then using MMH buffer without glucose, 64Cu retention in the liver only was assessed: 22.58 (± 4.53)%(n=4) at pH 5, 19.08 (±4.03)%(n=5), at pH 6, 13.84 (±3.89)%(n=4) at pH7, and 10.73 (±2.95)%(n=6) at pH 8.
As gut length varies considerably even after taking a set length (17 cm), the stretched length and mucosal weight of gut was assessed at autopsy. As independent variables their sum was divided into the percentage absorption to give gut-related absorption. For method one total 64Cu absorption was 4.21 (±0.42) (% body count per g perfusate count per g (mucosa) plus cm (length of gut loop) (n=5) at pH6 and 2.75 (±0.32) (n=4) at pH 8 (P2 <0.001). 5.5% of the gut uptake at pH 6 and 4.1% at pH 8 absorbed leaving 95% in the gut mucosa. For method two total 64Cu absorption was 4.58 (±1.72) (n=6) at pH5, 4.15 (±0.16) (n=2) at pH6, 2.33 (±0.45) (n=4) at pH 7 and 2.32 (± 0.43) (n=7) at pH8 (P2<0.001). With total absorption a jump between pH 6 and pH7 was observed which might relate to the properties of the Cu(II). 3% of 64Cu uptake absorbed leaving 97% in the gut mucosa. Net effective absorption (mucosa to body transfer) was thus a rate-limiting process.
In the pH stat recirculation study, the ratio of mucosa over the initial perfusate specific activities (counts/g) was 6.5 at pH 6 and 5.5 at pH 8. In the single pass study, the ratio was 15.8 (±5.4), at pH 5, 11.5 (± 1.1), at pH 6, 6.1 (±2.2), at pH 7 and 8.8 (±8.3), at pH 8. The specific activity ratio was greater than five to 16 times the perfusate concentration depending on pH and gut preparation.
CONCLUSION: The pH effect had its main influence at the brush-border membrane or adjacent protein binding sites. The more acid the pH the more copper was absorbed.
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