Streptozotocin diabetes protects against arrhythmias in rat isolated hearts: role of hypothyroidism.
We examined the contribution of hypothyroidism to streptozotocin diabetes-induced alterations in the arrhythmia susceptibility of ex vivo hearts to regional zero-flow ischaemia. Diabetic rats received either protamine zinc insulin (10 IU/kg/day, s.c.) or triiodothyronine (10 microg/kg/day, s.c.) for 8 weeks commencing 72 h after injection of streptozotocin (60 mg/kg, i.p.). Arrhythmias were determined in ex vivo Langendorff-perfused hearts, subjected to a 30-min main left coronary artery occlusion, followed by 30-min reperfusion. Serum free thyroxine concentrations, rectal temperature and ex vivo heart rate were significantly decreased in the 8-week diabetic group (P<0.001). These changes were prevented by administration of triiodothyronine or insulin. Ventricular fibrillation during reperfusion was abolished in hearts from diabetic rats. This protection was prevented by treatment with either triiodothyronine or insulin. Hearts from methimazole-hypothyroid rats also showed no ventricular fibrillation during reperfusion. The protection against ischaemia-reperfusion-arrhythmias observed in hearts from streptozotocin-diabetic rats may be due to diabetes-induced hypothyroidism.
Zhang
Liqun
L
Department of Physiology and Pharmacology, Strathclyde Institute of Biomedical Sciences, University of Strathclyde in Glasgow, 27 Taylor Street G4 ONR, Scotland, Glasgow, UK.
Parratt
James R
JR
Beastall
Graham H
GH
Pyne
Nigel J
NJ
Furman
Brian L
BL
D000818:Animals; D001145:Arrhythmias, Cardiac / Q000503:physiopathology / Q000517:prevention & control*; D001786:Blood Glucose; D001831:Body Temperature; D001835:Body Weight; D003921:Diabetes Mellitus, Experimental / Q000097:blood / Q000188:drug therapy / Q000201:enzymology / Q000503:physiopathology*; D004195:Disease Models, Animal; D006321:Heart / Q000502:physiology*; D006339:Heart Rate; D007037:Hypothyroidism / Q000139:chemically induced / Q000209:etiology*; D007328:Insulin / Q000627:therapeutic use; D008133:Long QT Syndrome; D008297:Male; D008713:Methimazole; D017202:Myocardial Ischemia / Q000503:physiopathology; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology; D009929:Organ Size; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013311:Streptozocin; D013963:Thyroid Hormones / Q000097:blood; D014284:Triiodothyronine / Q000627:therapeutic use; D014693:Ventricular Fibrillation / Q000209:etiology
D001786:Blood Glucose; D007328:Insulin; D013963:Thyroid Hormones; D014284:Triiodothyronine; D008713:Methimazole; D013311:Streptozocin; D011493:Protein Kinase C