Influence of pH, dose volume, human pancreatic juice and bile on 64Cu absorption from the rat closed duojejunal loop.

Paul Tasker, FRCS, Harbans Sharma, MSc, PhD, DSc, Joan Braganza, DSc, FRCP, Maynard Case, BSc, PhD. Manchester Royal Infirmary.

INTRODUCTION: In the rat closed duodenal-jejunal loop, rat pancreatic juice (PJ) inhibited ⁶⁴Cu absorption. Pancreatic insufficiency in man was found not to increase ⁶⁴Cu absorption in man, so the rat closed duodenal-jejunal loop was re-examined testing for pH influences and repeating the ⁶⁴Cu 2h instillation with test solutions.

METHOD: Using Antimony electrodes, the resting pH values in the loop lumen were measured and the influence of both alkaline and acid single-shot buffers examined. The loop management was modified to examine the influence of dose volume. Human pancreatic juice and bile were used as test solutions.

RESULTS: In the rat duodenal-jejunal loop, single-shot test solutions had only transitory effects on pH. The volume of dose influenced the amount ⁶⁴Cu absorbed from the loop. The procedure was therefore modified. Although diluted human bile decreased ⁶⁴Cu absorption by 62% as before, human pancreatic juice injected into the loop did not influence absorption either in the original loop or the modified loop.

A sample of some of the results described:

Test solution           Dose     Liver           Total              Liver                 Total
                             Volume Mean ± S.D. Mean ± S.D. Mean ± S.D. Mean ± S.D.
                                ml        % of dose                         % of gut cpm/ G / cm

original loop using flush-on volume:

0.9% saline(n = 4) 0.5+ ml 3.02 ± 0.22 7.40 ± 0.66 37.1± 11.3 90.0 ± 22.7
Human PJ (n = 8) 0.5+ ml 2.48 ± 0.91 6.18 ± 1.78 38.2 ± 9.2 99.1± 23.5

modified loop with exact volume placement

0.9% saline (n = 3) 0.5 ml 1.16 ± 0.25 3.31 ± 0.71   11.4 ± 0.9     32.5 ± 2.7
Human PJ (n = 3) 0.5 ml 1.18 ± 0.10   3.55 ± 0.46   13.3 ± 2.3     39.6 ± 3.5
0.9% saline (n = 3)1.0  ml 2.37 ± 0.55   6.67 ± 1.60   27.2 ± 7.8     76.7 ± 23.5
Human PJ   (n = 2)1.0 ml 2.48 ± 0.36   7.42 ± 0.33   36.2 ± 4.7    108.1 ± 3.3

Liver Carcass Total

0.9% saline (n = 3) 1.0 ml 2.06 ± 0.49 4.56 ± 0.56 6.62 ± 0.92
Bile solution (n = 3) 1.0 ml 0.66 ± 0.17 1.83 ± 0.25 3.49 ± 0.40

0.9% saline (n = 12) 0.5+, 1.0 2.53 ± 0.58 6.84 ± 0.97
Human PJ (n = 10) 0.5+, 1.0 2.48 ± 0.81 6.46 ± 1.64 (n=9)

CONCLUSION:

The closed loop had a pH in the alkaline pH range, and neither acid nor alkaline buffers had more than a slight or transient effect on the resulting pH. Using a modified loop, ⁶⁴Cu absorption at one ml was twice that at 0.5 ml. Higher dose volumes showed no further increment. The effect was due to increased gut surface contact. The results with 0.5-ml plus the flush-on volume and one ml were very similar.

Human pancreatic juice did not produced the inhibition in ⁶⁴Cu absorption,which was seen with rat pancreatic juice, either in the original or modified protocol. This may relate to reduction in protein content of the juice (e.g. metallothionein). Human gall bladder bile however, even with a one in four dilution, with saline, inhibited ⁶⁴Cu absorption to approximately one third of the control value.

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