Tolbutamide alters glucose transport and metabolism in the embryonic mouse heart.
BACKGROUND
Tolbutamide is a sulfonylurea oral hypoglycemic agent widely used for the treatment of non insulin-dependent diabetes mellitus. Tolbutamide produces dysmorphogenesis in rodent embryos and becomes concentrated in the embryonic heart after maternal oral dosing. Tolbutamide increases glucose metabolism in extra-pancreatic adult tissues, but this has not previously been examined in embryonic heart.


METHODS
CD-1 mouse embryos were exposed on GD 9.5 to tolbutamide (0, 100, 250, or 500 microg/ml) for 6, 12, or 24 hr in whole-embryo culture. Isolated hearts were evaluated for (3)H-2DG uptake and conversion of (14)C-glucose to (14)C-lactate. Glut-1, HKI, and GRP78 protein levels were determined by Western analysis, and Glut-1 mRNA was measured by RT-PCR.


RESULTS
Cardiac (3)H-2DG uptake increased after exposure to 500 microg/ml tolbutamide for 6 hr, and 100, 250, or 500 microg/ml tolbutamide for 24 hr, compared to controls. Glycolysis increased after exposure to 500 microg/ml tolbutamide for 6 or 24 hr compared to controls. Glut-1 protein levels increased in hearts exposed to 500 microg/ml tolbutamide for 12 or 24 hr, and Glut-1 mRNA increased in hearts exposed to 500 microg/ml tolbutamide for 24 hr compared to controls. HKI protein levels increased in hearts exposed to 500 microg/ml tolbutamide for 6 hr, but not 12 or 24 hr. There was no effect on GRP78 protein levels in hearts exposed to tolbutamide for 6, 12, or 24 hr.


CONCLUSIONS
Tolbutamide stimulates glucose uptake and metabolism in the embryonic heart, as occurs in adult extra-pancreatic tissues. Glut-1 and HKI, but not GRP78, are likely involved in tolbutamide-induced cardiac dysmorphogenesis.
Smoak
Ida W
IW
North Carolina State University College of Veterinary Medicine, 4700 Hillsborough Street, Raleigh, North Carolina 27606, USA. ida_smoak@ncsu.edu
D000818:Animals; D046508:Culture Techniques; D003847:Deoxyglucose / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D005260:Female; D015870:Gene Expression; D005947:Glucose / Q000378:metabolism*; D051272:Glucose Transporter Type 1; D006019:Glycolysis / Q000502:physiology; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006321:Heart / Q000187:drug effects* / Q000196:embryology / Q000502:physiology; D006593:Hexokinase / Q000378:metabolism; D007553:Isotope Labeling; D019344:Lactic Acid / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D012333:RNA, Messenger; D013723:Teratogens / Q000633:toxicity*; D014044:Tolbutamide / Q000633:toxicity*
D000091342:Endoplasmic Reticulum Chaperone BiP; D051272:Glucose Transporter Type 1; D018840:HSP70 Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D012333:RNA, Messenger; C495678:Slc2a1 protein, mouse; D013723:Teratogens; C018551:glucose-regulated proteins; D019344:Lactic Acid; D014044:Tolbutamide; D003847:Deoxyglucose; D006593:Hexokinase; D005947:Glucose