European Journal of Clinical Pharmacology

Europ. J. clin. Pharmacol. 11,485-486 (1977)

© by Springer-Verlag 1977

CORRESPONDENCE

Letter to the Editor With much interest we read the article by Dr. Andersson and his colleagues on aspects of the intestinal absorption of zinc in man [1]. We wish to make three comments. The test proposed by the authors is very simple and may be of diagnostic value not only for detecting variation in the rate of absorption from the G. I.tract but possibly of other conditions as well. However, it seems dangerous to us to interpret the shape of the concentration-time curves in other than qualitative terms. For instance, the authors conclude from the lower area under this curve in the case of jejuno-ileostomy that the remaining section of the small intestine probably absorbs 1/3 of the zinc taken up by the bowel of healthy subjects. Since each of these curves is the sum of two curves, viz. one describing the absorption of zinc from the G. L-tract into the circulation, and another describing the uptake of zinc from the blood into the tissues, the flat curves after jejuno-ileostomy could be explained either by a lower rate of absorption or a higher rate of uptake into the tissues, particularly in the liver [2]. In contrast to Dr. Andersson and his colleagues, who believe that the abnormal shape of the curve is caused only by reduced absorption, we believe that a higher rate of uptake of Zn into the tissues must be considered as an important factor, even if not the main reason for the abnormal shape. There are two arguments to support this point: a. the initial slope of the curve, e.g. during the first hour, is similar in patients and controls, suggesting that the rate of absorption cannot be very different, and b. the initial and final plasma zinc concentrations are lower in obese patients, suggesting a state of relative zinc deficiency which will lead to a faster uptake of the zinc in the tissues. We have found a similar situation for copper in copper- deficient rats (unpubl. results).

The equality of zinc concentration in portal and peripheral blood during the test is interpreted by the authors as suggesting slow passage of zinc across the intestinal wall. The shape of the concentration-time curves for portal and peripheral blood looks quite similar to that found by us [3] and others for 64Cu in venous blood, suggesting a similarity in this respect between zinc and copper. It seems to us that comparison of the two zinc concentrations shows rather that only a small part of the absorbed zinc is cleared from the circulation in one passage through the tissues, in other words that the uptake in tissues is slow compared to the rate of absorption from the G.I.tract. Finally, the authors mention the drawbacks of 65Zn for human use. We should like to point out that another zinc isotope, namely 69mZn, is much more suitable: its physical halflife is only 13.8 h and the characteristics of its radiation are more favourable for human use. It is less readily available at the moment than 6SZn but hopefully a growing demand will change this situation. September 20, 1976 C. J. A. van den Hamer and H.W. Prins, Interuniversity Reactor Institute, Dept. of Nuclear Biotechnique, Delft, The Netherlands

1. Andersson, K.-E., Bratt, L., Dencker, H., Lanner, E.: Some aspects of the intestinal absorption of zinc in man. Europ. J. clin. Pharmacol. 9, 423-428 (1976) 2. Stortenbeek, A.J., van den Hamer, C.J.A.: Binders of intravenously administered 65Zinc in rat liver cytoplasm. Bioinorg. Chem., 6, 313-327 (1976) 3. Van den Hamer, C.J.A., Willemse, J., de Haas, G.: Coppermetabolism, particularly in relation to Wilson's and Menkes' diseases. In: Nuclear Medicine (eds. K.H. Ephraim and O.H. Yoe), pp. 204-216. Utrecht: State University, 1975

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We are grateful for the comments made by Dr. van den Hamer and Dr. Prins about our article "Some Aspects of the Intestinal Absorption of Zinc in Man". We agree that the concentration-time curves should not be interpreted in other than qualitative terms. We calculated and compared the amounts of zinc absorbed by patients with a jejuno-ileostomy and by normal controls, primarily to illustrate the possible significance of the difference in intestinal length between the two groups. We are well aware that there are other factors of equal or greater importance for the shape of the concentration-time curve, and we regret not discussing the possibility of an increased rate of uptake by the tissues as an explanation for the flat curves after jejuno-ileostomy. We do not agree, however, that the almost equal concentrations in portal and peripheral blood during the test only show that uptake in tissues is slow compared to the rate of absorption from the G.I.-tract. Differences in plasma concentration between simultaneous samples of portal and peripheral blood provide direct information about the appearance rate of

drugs in the blood. As stated in our article, the mechanisms involved in the G.I. absorption of zinc are not known. Compared with, for example digoxin [1], which probably is absorbed by a passive transport process independent of metabolic energy [2], the rate of appearance of zinc in portal blood is slow. 1. Andersson, K.-E., Nyberg, L., Dencker, H., G6thlin, J.: Absorption of digoxin in man after oral and intrasigmoid administration studied by portal vein catheterization. Europ. J. clin. Pharmacol. 9, 39--47 (1976) 2. Caldwell, J.H., Martin, J.F., Dutta, S., Greenberger, N.J.: Intestinal absorption of digoxin-3H in the rat. Amer. J. Physiol. 217, 1747-1751 (1969) December 6, 1976

K.E. Andersson Dept. of Clinical Pharmacology University Hospital S-58185 Link6ping Sweden

Intestinal absorption of zinc.

European Journal of Clinical Pharmacology Europ. J. clin. Pharmacol. 11,485-486 (1977) © by Springer-Verlag 1977 CORRESPONDENCE Letter to the Edit...
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