Renal Transport of Urea and Some Carbohydrates in Lophius piscatorius'

The renal handling of urea has been studied by many investigators on a host of animals. It has been found that urea is actively secreted by certain species (Munro, '53; Forster, '54), reabsorbed by others (Smith, '31a, b), and in some the renal handling seems to be entirely passive (Shannen, '36). The aglomerular goose fish (Lophius piscatorius) is reportedly able to secrete urea actively from peritibular blood into the tubular urine (SchmidtNielson, '51; Smith, '51). This conclusion is based upon the observation by Graffiin (Grafflin, '36) that after exogeneous urea was injected intramuscularly into goose fish, the U/P ratios for urea were appreciably above one. However, Grifffin pointed out that when endogenous urea was considered, the U/P ratios were equal to or less than one. Grafflin recognized that without any information on water reabsorption it was impossible to determine if U/P ratios above 1.0 resulted from secretion or from passive concentration due to water removal. Interpretation of these experiments is further complicated by technical considerations. Because Grafflin injected urea intramuscularly into the tail of the goose fish, blood perfusing the kidneys would have had a high concentration of urea relative to that in mixed venous or arterial blood, since the goose fish kidney is supplied almost entirely by venous blood which has been derived from the caudal portions of the animal. It is apparent that the systemic blood urea concentration of Lophius under these conditions would be lower than that existing in blood perfusing the renal tubules, and would continue to be lower until all injected urea is absorbed from the muscles in the tail. Since Grafflin obtained blood samples from either the heart or from the mixed venous pool, the analyzed blood urea concentration values were lower than those actually existing in blood perfusing the kidneys. Consequently, he would have calculated erroneously high U/P ratios, leading to the conclusion of an apparent urea secretion. The present study was undertaken to determine whether in fact the goose fish secrete urea, or whether the findings of apparent urea secretion result from the experimental technique used by GrafAin. In addition we have studied the rate of entry of arabinose and fructose into goose fish urine.