METAIODOBENZYLGUANIDINE UPTAKE IN THE HYPERTENSIVE DIABETIC RAT-HEART- A MARKER FOR MYOCARDIAL DYSFUNCTION

The purpose of this study was to investigate the cardiac adrenergic ne uronal changes induced by diabetes and hypertension by using an analog ue of norepinephrine, meta-iodobenzylguanidine (MIBG), and to compare these changes with the contractile state of ventricular papillary musc le. The tissue concentration of norepinephrine in the cardiac apex was also measured for direct comparison with [I-123]MIBG uptake. One week following the induction of diabetes by streptozotocin injection (55 m g/kg, i.v.), male Sprague-Dawley rats were given subcutaneous injectio ns of a hypertension-inducing agent, deoxycorticosterone acetate (DOCA , 25 mg/kg), or DOCA vehicle twice weekly for 3, 6, 9, or 12 weeks. At the end of each time point, the animals were injected intravenously ( 15 mCi/mg; 1 Ci = 37 GBq) with [I-123]MIBG. The results showed a progr essive decrease in MIBG uptake into the hearts of diabetic, hypertensi ve, and diabetic-hypertensive rats during the 12-week observation peri od, compared with the control group. However, length-tension papillary muscle studies at 12 weeks indicated that only the diabetic group had a diminished performance compared with control. Furthermore, an inver se relationship was observed between MIBG uptake and norepinephrine le vels in the cardiac apex of the diabetic and diabetic-hypertensive gro ups. Therefore, we concluded that either MIBG does not provide an accu rate indication of adrenergic integrity or that there is no relationsh ip between sympathetic activity and myocardial function at the time po ints measured. MIBG did not prove to be a useful marker for myocardial dysfunction in diabetic rats.