Cardiac ornithine decarboxylase of diabetic spontaneously hypertensive rat: effects of insulin and thyroid hormone treatment.

Diabetes mellitus causes a more profound reduction of left ventricular weight (LVW) in the spontaneously hypertensive rat (SHR) than it does in nonhypertensive strains. Diabetes also depresses the activity of cardiac ornithine decarboxylase (ODC), an index of cell growth. We measured ODC activity, of ventricular homogenates obtained from diabetic SHR and nonhypertensive WKY rats, with and without chronic treatment with insulin or triiodothyronine (T3). Left ventricular ODC activities of nondiabetic SHR and WKY rats were not different from each other. Streptozotocin-induced diabetes (8 weeks) reduced left ventricular ODC activity of SHR and WKY rats to the same extent; the effect was characterized by a reduction in apparent Vmax with no change in apparent Km. Both T3 and insulin therapy prevented the decline in ventricular ODC activity in both strains, although only the effect of insulin was correlated with LVW. The results suggest that the effects of diabetes on LVW and ODC activity are independent of attendant reductions in serum thyroid hormone levels. However, the results did not reveal any strain-selective effects of diabetes on ODC activity which might have contributed to the pronounced loss of LVW in the SHR strain.