In addition to providing information with regard to the status of carbohydrate metabolism, the time course of the disappearance of injected glucose from the blood stream offers information concerning the overall effectiveness of a variety of physiological mechanisms involved in maintaining homeostasis. In a number of investigations, reduction in glucose tolerance, i.e., a slower rate of return to fasting levels of blood sugar following the oral (1-17) or intravenous (18)(19)(20) administration of glucose, has been reported in older people. The diminished glucose tolerance in the older individual might be due to: (a) inadequate release of insulin from the pancreas, or greater inactivation of endogenously released insulin, (b) the loss of functioning protoplasm with increasing age so that less metabolizing tissue is removing glucose from the blood, (c) a diminution in the effectiveness of the metabolic processes involved in the removal of sugar from the blood stream, (d) alterations in the rate of release of glucose from the liver, or (e) a reduction in the volume in which the glucose is originally distributed in the aged. By comparing the glucose and glucose-insulin tolerance tests in the same individual, an estimate of the effect of insulin may be obtained (21)(22)(23)(24)(25)(26)(27). In the experiments to be reported, standard amounts of insulin were administered along with glucose to both old and young subjects with the aim of investigating age differences in the response to the insulin. Table I. Experimental procedure. The intravenous glucose tolerance test (GTT) and the glucose-insulin tolerance test (GITT) were performed in each subject under basal conditions and separated by an interval of not less than one week. In 8 of the subjects, each of the tests (GTT and GITT) was carried out twice in order to evaluate reliability.Twenty minutes before either test was begun, a modified Lindeman needle was placed in an antecubital vein and left in place for the duration of the test. The needle was kept patent by heparinization of the stylus and was used subsequently only for withdrawing blood specimens without a tourniquet (29). A vein in the opposite arm was used for the injection of 50 ml. of 50 per cent glucose in water over a period of two minutes. For the GITT, 5 units of hyperglycemic factor-free insulin8 (Lilly), per square meter of body surface area, were rapidly injected, followed immediately by the standard amount of glucose. The fasting blood specimen was obtained through the Lindeman needle a few minutes before zero time, which was recorded as the beginning of the injection of glucose.Blood samples were collected at 5-minute intervals for the first hour and at 20-minute intervals during the second hour, and were placed immediately in tubes containing a dried heparin and sodium fluoride mixture. All analyses were completed the day of the test, using the Nelson-Somogyi method (30). Determinations were in duplicate and were read on a Model DU Beckman Spectrophotometer.Data analysis. For each tolerance test...

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Tilting and standardized exercise caused extensive shifts of heart rate and auscultatory blood )Iressures in 140 ambulatory male subjects from 20 to 92 years of age. Following similar exercise, the older subjects showed a greater increase of heart rate and pulse pressure than did the younger subjects who compensated the changes caused by tilting more completely and rapidly than did the older subjects. These slower compensatory responses of older subjects should be considered in the interpretation of metabolic recovery rates after exercise.T ILTING and step-test exercise have been used often as cardiovascular stress situations and included in tests of the ability of the human subject to make proper hemodynamic adjustments.C ertain questions have arisen in connection with the interpretation of (1) In order to understand better the effects of

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