Investigations of the mechanism of the reduction of plasma glucose by cold-stress in streptozotocin-induced diabetic rats.
Exposure to a cold environment may increase the activity of the sympathetic nervous system inducing an elevation of plasma norepinephrine and may result in hyperglycemia. In the present study, we found that a hypoglycemic effect was produced in streptozotocin-induced diabetic rats after cold-exposure at 4 degrees C for 1 h. In addition to the blockade of this hypoglycemic effect by guanethidine (a ganglion-blocking agent) and prazosin (an alpha1-adrenoceptor antagonist), an increase of plasma norepinephrine was also observed in streptozotocin-induced diabetic rats receiving this cold-stress. Participation of sympathetic hyperactivity can thus be considered. Furthermore, naloxone, in a dose (0.5 mg/kg, i.p.) sufficient to block opioid receptors, reversed this hypoglycemia. Also, an increase of plasma beta-endorphin-like immunoreactivity was observed in streptozotocin-induced diabetic rats receiving this cold-stress. Intravenous injection of beta-endorphin into streptozotocin-induced diabetic rats produced a lowering of plasma glucose. Administration of methoxamine at a dose sufficient to activate the alpha1-adrenoceptors produced hypoglycemia and a similar increase of plasma beta-endorphin-like immunoreactivity in streptozotocin-induced diabetic rats. However, plasma beta-endorphin-like immunoreactivity level was not modified by similar treatment with methoxamine or cold-stress in normoglycemic rats. Therefore, beta-endorphin appears to be responsible for the induction of hypoglycemic effects in streptozotocin-induced diabetic rats after cold exposure which is different to the response in normal rats.
Liu
I M
IM
Department of Pharmacology, College of Medicine, National Cheng Kung University, Tainan City, Taiwan.
Niu
C S
CS
Chi
T C
TC
Kuo
D H
DH
Cheng
J T
JT
D000818:Animals; D001786:Blood Glucose / Q000032:analysis*; D003080:Cold Temperature; D003921:Diabetes Mellitus, Experimental / Q000097:blood*; D008297:Male; D008729:Methoxamine / Q000494:pharmacology; D009638:Norepinephrine / Q000097:blood; D051381:Rats; D017208:Rats, Wistar; D013312:Stress, Physiological / Q000378:metabolism*; D001615:beta-Endorphin / Q000097:blood
D001786:Blood Glucose; D001615:beta-Endorphin; D008729:Methoxamine; D009638:Norepinephrine