The APS Journal Legacy Content is the corpus of 100 years of historical scientific research from the American Physiological Society research journals. This package goes back to the first issue of each of the APS journals including the American Journal of Physiology, first published in 1898. The full text scanned images of the printed pages are easily searchable. Downloads quickly in PDF format.

IN studying the utilization of various metabolites by the heart in the heart-lung preparation, previous experimenters who have wished to obtain low sugar concentrations in the blood have done so either by the use of insulin or by allowing a sufficient lapse of time for the circulating sugar to disappear from the preparation. It appeared to us that it would be advantageous to adopt a method which avoids the use of insulin and also permits immediate observations when the preparation is functioning most efficiently, instead of waiting until such time as the sugar disappears. In such a preparation one would be able to determine readily the lactic acid consumption of the preparation by analysis of reservoir samples of blood without the necessary corrections for the amount of lactic acid added by red cells and by lungs to the circuit during the period of observation. The utilization of other substances by the heart can also be studied in such a heart-lung preparation perfused with sugar-free blood. Further, the rate at which they are used can be determined more accurately as they would not be competing with glucose or lactic acid, nor apparently, as will be discussed below, with any other normal source of cardiac energy present in any appreciable amount in the perfusing fluid. A preliminary report of investigations of this kind has already been published [Waters & Griffiths, 1936]. METHODS Sugar-free blood. Blood from a big donor dog anaesthetized with ether was prevented from clotting by the addition of a suitable amount of heparin. It was immediately centrifuged, and the plasma pipetted from the cells. The cells were well washed on the centrifuge with Ringer's

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FRuCTOSE, when injected intravenously into fasting rabbits, was found by Davidson et al. [1936] to decrease the concentration of the glucose of the blood and to depress the glucose tolerance curve of rabbits. They interpreted both types of result as indicating that fructose stimulated the secretion of insulin by the pancreas, and that it was this excess insulin, so produced, which was responsible for the lowered blood glucose following the injection of fructose. Although this interpretation is in line with the conventional view that the glucose tolerance curve is determined primarily by the response of the pancreas to the ingested glucose (by the amount of extra insulin secreted), no facts were adduced in its support. It seemed to us very doubtful that fructose should possess this property of being able to promote increased secretion of insulin by the pancreas. Certainly the pancreas does not utilize fructose in perfusion experiments [Steinberg, 1927]. It is appreciated that it does not necessarily follow from this fact that pancreatic cells or more particularly the islet cells would not be stimulated.To elucidate this action of fructose the obvious test object is the depancreatized animal in which the amount of available insulin can be rigidly controlled. We therefore planned to find out if fructose similarly affected the blood glucose first of the normal and then of the depancreatized dog. While we were unable to obtain any depression of the blood glucose of the fasted dog by an intravenous injection of fructose, we did obtain by this means a marked depression of the glucose tolerance curve. We could not detect any effect of fructose on the blood glucose of the depancreatized animal, in the complete absence of insulin. These experiments will be reported in greater detail later. It was then decided to repeat these experiments on the depancreatized dog, when the animal was receiving a steady supply of insulin during the period of the test. It seemed to us that the newly discovered protamine zinc insulin would serve this purpose conveniently. It was found that the subcutaneous injection of a fairly large dose of protamine zinc insulin into the fed depancreatized animal, in the late afternoon, resulted in a marked depression of the blood sugar by the following morning, and the concentration of sugar remained fixed at this low value (within a few mg. per 100 ml.) for at least a further 8 hr. Further, it was found that the feeding of a given amount of glucose during this latter period gave a glucose tolerance curve which could be reproduced with somewhat surprising exactness on subsequent experimental days, provided that the conditions were kept constant. With such conditions established it was an easy matter to determine if an intravenous injection of fructose effected any alteration in this glucose tolerance curve. EXPERMENTALMethods. Glucose was estimated in blood by the method of Shaffer & Somogyi [1933], but for convenience we used the combined tungstic acid reagent for protein precipitation, as described by Va...