Cardiac polyamine metabolism in spontaneously hypertensive rats: effect of antihypertensive treatment.

The importance of changes in polyamine metabolism for myocardial growth was assessed by measuring the activity of ornithine decarboxylase (ODC) and the polyamines spermidine, spermine and putrescine in hearts from spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. The rats were 30-weeks-old and had received 6 weeks treatment with either minoxidil (0.08 mg/ml) or alpha-methyldopa (5 mg/ml in drinking water). Left ventricular ODC activity was greater in the untreated SHR than the WKY rats at 4, 16 and 20 weeks of age. Spermidine content was consistently raised and spermine content reduced in the untreated SHR left ventricles, resulting in the high spermidine/spermine ratios characteristic of rapidly growing systems. Minoxidil treatment increased left ventricular weight and spermidine (83 and 61% in WKY and SHR rats, respectively) and spermine (44 and 28%) content. Methyldopa also caused an increase in left ventricular spermidine content (30 and 57% in WKY and SHR rats, respectively) despite a marked reduction in ventricular mass. Thus the ventricular hypertrophy in SHR rats is accompanied by enhanced synthesis and accumulation of polyamines. The fact that myocardial spermidine content increased during methyldopa treatment, which reduced myocardial mass, suggests that the polyamines are not causally related to the development of ventricular hypertrophy.