Despite many previous studies of the osmotic properties of erythrocytes, unequivocal answers have not been given to two important questions: 1) Is the erythrocyte in osmotic equilibrium with its normal surrounding fluid? 2) When the osmotic properties of the surrounding fluid are varied, does the erythrocyte gain or lose water to the extent necessary to remain in osmotic equilibrium with the new surroundings-that is, does the erythrocyte behave as a perfect osmometer over a wide range?Previous work related to these questions has been of two general types: measurements of changes of volume of the erythrocytes as the osmotic concentration of the extracellular phase was altered; and measurements of one or more of the colligative properties of the solutions involved. The present study is of the latter type. The osmotic behavior of the normal human erythrocyte has been investigated over a wide range of concentrations by a cryoscopic method and a method for measuring the melting point of microscopic samples. The results give affirmative answers to both of the above questions and illustrate some of the difficulties which may be expected in studies of osmotic properties of any tissues.
There is little available information regarding the quantitative relationship between the rate of secretion of antidiuretic hormone (ADH) and the rate of reabsorption of water by the renal tubules. From the work of Shannon (1) and Lauson (2) it has been suggested that in both dogs and adult humans the rate of secretion of ADH is equivalent to the intravenous administration of vasopressin at rates varying from less than 0.1 to more than 0.7 milliunit per hour per kilogram of body weight. Utilizing the endogenous creatinine U/P ratios as an index of the renal response, these authors both demonstrated a curvilinear relationship between the rate of infusion of vasopressin and the response of the kidney. The lowest rates of infusion of vasopressin studied were sufficient to produce a marked reduction in the rate of urine flow and increase in the endogenous creatinine U/P ratios, and there do not appear to be any data which define the quantitative relationship between ADH and the renal reabsorption of water in the range in which the concentration of the urine is generally less than that of the plasma. The current studies were designed to establish this relationship with the additional hope that its characteristics might provide some insight with respect to the mode of action of ADH. The subjects were all apparently healthy young adult men of ages twenty to thirty-five. No food or water was allowed for 10 to 12 hours prior to all but three of the experiments. In three studies (R
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