Involvement of formaldehyde in depressed iron absorption in mink and rats fed Pacific hake (Merluccius productus) Public Deposited


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  • Inclusion of substantial levels of raw-frozen Pacific hake (Merluccius productus) in diets of ranch-raised mink (Mustela vison) causes a large percentage of animals to develop an abnormal condition termed "cotton fur" (CF), characterized by depressed body weight, microcytic-hypochromic anemia and a failure of under-fur pigmentation. Observations by several groups of researchers over the past decade indicate that this syndrome is the manifestation of an iron deficiency in the mink and among several causes may be induced by a heat-labile factor present in certain species of marine fish. Further observations suggest that the CF-causative factor in hake and other fish species is related to an antibacterial property of these fish. A series of feeding trials and tracer-iron absorption experiments with more than 650 experimental animals, including both rats and mink, were conducted to determine possible causes of this induced iron deficiency. Feeding black, Long-Evans, laboratory rats diets based on raw-frozen Pacific hake resulted in decreased body weights, hematocrit levels and degree of hair pigmentation. Absorption of ⁵⁹ferric chloride in mink was significantly lowered when administered in the presence of raw-frozen as compared to either cooked-frozen or raw-unfrozen eggs of Pacific hake. These results parallel earlier observations that the factor in Pacific hake responsible for its antibacterial activity was present in raw-frozen but not raw-unfrozen Pacific hake and support observations that the CF-causative and antibacterial properties of Pacific hake are related. Significant depressions in the absorption by rats of ⁵⁹ferric, ⁵⁹ferrous and hemoglobiniron-59 were demonstrated when it was administered in preparations of raw-frozen, vs. either cooked-frozen or raw-unfrozen, whole Pacific hake. Similarly, mink absorbed significantly less ⁵⁹ferric and ⁵⁹ferrous iron in raw-frozen than in cooked-frozen Pacific hake extracts. These data show that Pacific hake in the raw-frozen state depresses absorption of iron-59 in both rats and mink independently of iron form and provide substantial evidence that the anemia in Pacific hake-fed rats is a result of a failure of normal iron absorption. Norwegian researchers reported trimethylamine oxide, a normal, physiologically important constituent of a wide variety of marine fish, was anemiogenic when fed to mink. This observation, coupled with findings by Japanese workers that trimethylamine oxide is converted in the fish tissues to dimethylamine and formaldehyde by the actions of an enzyme present in the cod pyloric caeca, led to the hypothesis at this station that either trimethylamine oxide or one of its breakdown products was responsible for depressed iron absorption in animals fed Pacific hake. Trials with rats showed that added trimethylamine oxide or formaldehyde significantly depressed absorption of ⁵⁹ferric, ⁵⁹ferrous and hemoglobiniron-59 in preparations of either cooked-frozen or raw-frozen Pacific hake while trimethylamine and dimethylamine had no effect. Similar results were obtained when trimethylamine oxide and formaldehyde were added to either raw or cooked, chicken eggs. Additions of sodium bisulfite to either raw-frozen hake extracts, cooked-frozen hake extracts containing added formaldehyde or mink diets including raw-frozen Pacific hake significantly increased absorption of ⁵⁹ferric and ⁵⁹ferrous iron in rats. Sodium bisulfite is known to react with the free aldehyde group of formaldehyde; consequently, it is assumed that this group is involved in the observed depression of iron absorption. These findings together with the fact that trimethylamine oxide is widely distributed in marine organisms suggests that formaldehyde and not trimethylamine oxide is responsible for the effects of Pacific hake on iron absorption. In vitro experiments indicate that trimethylamine oxide reacts directly with both ferric and ferrous solutions forming insoluble iron hydroxide precipitates; whereas, formaldehyde has no detectable, chemical effect. Experiments also indicate that formaldehyde administered either in water or in extracts of raw rockfish had no effect on iron absorption in rats; however, supplemental trimethylamine oxide lowered iron absorption independently of substrate used. Addition of acetaldehyde to cooked-frozen Pacific hake had no significant effect upon iron absorption in rats suggesting that not only the aldehyde group but also the specific organic compound is of importance. It is hypothesized that formaldehyde depresses iron absorption by interfering with normal absorption mechanisms, possibly by reacting with protein components of the gastro-intestinal tract. It is further theorized that some other unidentified compound(s) is necessary for formaldehyde to affect iron absorption since formaldehyde was without effect when administered in water solutions. Additionally, it is conceivable that raw rockfish carcass contains factors, possibly bisulfites, which are able to overcome the effects of formaldehyde on lowering iron absorption. Collectively, these experiments suggest that formaldehyde naturally occurring in raw-frozen but not cooked-frozen or raw-unfrozen Pacific hake significantly depresses absorption of ⁵⁹ferric, ⁵⁹ferrous and hemoglobiniron-59 in rats and mink and consequently is responsible for the CF-causative properies of this fish species.
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