Pertussis Toxin Administered Spinally Induces a Hypoglycemic Effect on Normal and Diabetic Mice

Abstract

Background/Aims: To show whether intrathecal (i.t.) treatment with pertussis toxin (PTX) produces a hypoglycemic effect in ICR, db/db and streptozotocin-treated mice. Methods: The blood glucose level (BGL) was measured after i.t. treatment with PTX, AB₅ toxins and PTX subunits. Insulin or leptin levels were measured after PTX injection. The effect of PTX on the BGL was examined in adrenalectomized (ADX) mice. Glucose transporter (GLUT) levels were determined by Western blotting. Results: PTX attenuated the elevated BGL in the <smlcap>D</smlcap>-glucose-fed model in a long-term manner. Heat-labile toxin (HLT), HLT subunit B or Shiga toxin, which belong to the AB₅ toxins, administered i.t. did not affect the BGL. PTX A protomer (PTX-A) or PTX B oligomers (PTX-B) injected i.t. did not have an effect on the BGL as well. However, combined treatment with PTX-A and PTX-B subunits caused a hypoglycemic effect. The leptin level was gradually reduced by PTX for up to 6 days, without affecting the insulin level. PTX administered i.t. significantly decreased the BGL further in ADX mice. Moreover, GLUT-2 (hypothalamus and pituitary gland), GLUT-4 (muscle) and GLUT-3 (adrenal gland) expression levels were increased, whereas GLUT-1 (brain cortex, liver, muscle and spinal cord), GLUT-2 (liver) and GLUT-3 (brain cortex and pituitary gland) expression levels were decreased. Discussion: Our data suggest that PTX administered spinally produces a hypoglycemic effect in a long-term manner, and PTX-induced hypoglycemia appears to be mediated by the reduction in activity of the glucocorticoid system. Furthermore, PTX may modulate the insulin level during hypoglycemia. Among GLUTs, GLUT-4 in muscle, GLUT-2 in the liver, hypothalamus and pituitary gland as well as GLUT-1 in the adrenal gland may be responsible for PTX-induced hypoglycemia.