Possible Factor Produced During Muscular Contraction which Influences the Passage of Glucose. ∗

Abstract

Muscular work increases glucose utilization by muscle possibly by a mechanism which regulates the permeability to glucose. Sacks and Smith(1) have shown that there is a specific steric requirement for the Eon-metabolized sugar to penetrate the cell membrane during muscular contraction. The effects of insulin and muscular work are additive. Goldstein and co-workers (2,3) have suggested that this increased permeability for glucose could be due to a humoral effect.

Our experiments have been performed to determine if a buffer solution which has been surrounding a contracting uterine muscle, affects the passage of glucose to diaphragm, adipose tissue of the epididymis, kidney and brain.

Materials and methods. Buffer solutions surrounding uteri in periodic contraction and permanent relaxation were obtained as previously described(4). The effect of buffer (C-B) used for contracting tissue on glucose up-take was measured by diluting it in Warburg flasks with Krebs-Henseleit buffer. When diaphragm was used, 1 ml of C-B was mixed with 1 ml of Krebs-Henseleit, when kidney, epididymal fat or brain were employed, 0.1 ml of C-B was mixed with 1.9 ml of Krebs-Henseleit. Pyruvate was also added to the latter when brain tissue was incubated. Equal volumes of “relaxation buffer” (R-B) were used for the controls. Incubation conditions were as follows: the final volume was 2 ml, glucose concentration was 3 mg/ml, the wet weights of brain slices were 50-75 ma, those of kidney, diaphragm and epididymal fat 150-200 mg. Incubation lasted 1½ hours for muscle and kidney, 1 hour for brain and 4 hours for epididymal fat and was carried out at 37°C with 70-80 cycles of 2 cm amplitude/min in air, except for brain tissues. In the latter case a 9576 O₂-5% CO₂ mixture was used.