Glut-1 expression and its response to hypoglycemia in the embryonic mouse heart

The embryonic heart depends on glucose during early organogenesis. Glut-1 f unctions in constitutive glucose uptake in adult tissues and is the predomi nant glucose transporter in embryonic and fetal tissues. This study focuses on Glut-1 expression in the heart during normal organogenesis using irrunu nohistochemistry for Glut-1 distribution, Western analysis for Glut-1 prote in levels, and reverse transcriptase polymerase chain reaction for Glut-1 m RNA levels. The role of Glut in glucose uptake response to hypoglycemia in the embryonic heart is evaluated using the Glut inhibitor cytochalasin B. C ardiac Glut-1 expression is also evaluated after in vitro hypoglycemic expo sure. Glut-1 levels art: highest on gestational days 9-10, intermediate on gestational day 10.5, and lowest on gestational days 11.5-13.5 in the norma l embryonic heart. Cardiac Glut-1 mRNA levels similarly decline between ges tational clays 9.5 and gd 13.5. Cytochalasin B produce:; a dose-dependent d ecrease in glucose uptake in hearts exposed to hypoglycemia for 30 min or 6 h, implicating Glut in this response. Glut-1 protein expression is unchang ed after 2 or 6 h but increased after 12 and 24 h of hypoglycemia in the ge stational day 9.5 heart. Thus, Glut-1 expression is prominent in the embryo nic heart and is correlated with changes in cardiac glucose requirements du ring normal organogenesis. Glut activity increases in response to acute hyp oglycemia and the expression of Glut-1 increases in response to prolonged h ypoglycemia. These results support the importance of Glut-1 during normal c ardiogenesis and in response to hypoglycemia in the embryonic heart.