Failure of L-Triiodothyronine to Alter Significantly Glucose Utilization by Human Erythrocytes. §

Abstract

It was demonstrated that parenteral administration of L-Triiodothyronine (L-T3) initially increased and then decreased utilization of glucose by the RBC of rabbits(1). Because of this fact, we became interested in studying the effects of clinically large doses of this compound on utilization of glucose by the human erythrocytes. Certainly, if a peripheral cellular effect could be demonstrated, then there would be a possibility of establishing a clinically useful tool for reflecting total body metabolism and perhaps evaluating thyroid function. The present investigation was therefore designed to study in humans: 1) normal fluctuations in rate of glucose utilization by RBC, and 2) effect of L-T3 on this rate.

Methods and material. Fasting venous blood was obtained from healthy volunteer men and women to insure satisfactory range in age and sex distribution. These individuals were clinically free of any disease and not taking medication. The laboratory procedure followed has been described(1). Blood samples were collected with siliconized equipment, and heparin was used as the anticoagulant. In vitro tests were conducted by centrifuging the samples for 20 minutes at approximately 2700 RPM (1000 g's) in an International Clinical centrifuge. The buffy coats and upper red cell layers were carefully aspirated and discarded and the RBC were then resuspended in the subject's own plasma. The final hematocrit was adjusted to approximately 50%. Preparation of RBC suspensions were conducted at room temperature. White blood counts were done on the original sample of blood and on the final suspension of RBC to estimate efficiency of removal of WBC, because of their relatively high rate of glucose metabolism(2,3,4). Glucose determinations were made in duplicate using the Somogyi-Nelson procedure(5). Within one hour after venipuncture, samples in glass-stoppered centrifuge tubes were incubated at 36–37°C in a water bath and equilibrated in air atmosphere since previous experiments did not reveal a significant difference in glucose metabolism under aerobic and anaerobic conditions.