Long‐Term Physical Exercise and Atrial Natriuretic Peptide in Obese Zucker Rats

Endurance training increases natriuretic peptide synthesis in the hypertrophied myocardium of spontaneously hypertensive rats. We examined the effects of 22-week-long treadmill exercise on plasma and tissue atrial natriuretic peptide in Zucker rats, a model of genetic obesity and moderate hypertension without clear cardiac hypertrophy. The blood pressures of the animals were measured by the tail-cuff method, and plasma and tissue samples for the peptide determinations were taken at the end of the study. The training increased heart weight to body weight ratio, while atrial natriuretic peptide contents in the right and left atrium, ventricular tissue, and plasma did not change. The exercise prevented the elevation of blood pressure, which was observed in non-exercised obese Zucker rats, and also reduced blood pressure in the lean rats. In conclusion, these results suggest that in the absence of preceding myocardial hypertrophy, the long-term exercise-induced workload is not deleterious to the heart in experimental obesity, since no changes in plasma and tissue atrial natriuretic peptide were detected. The prevalence of hypertension is high among overweight persons (Landsberg 1992), and physical activity is recom- mended as a non-pharmacological measure for the treat- ment of hypertension and obesity (World Hypertension League 1991). The Zucker fatty rat is a well-established model of genetic obesity with autosomal recessive homo- zygous inheritance (fa/fa), the heterozygous and missing fa gene (Fa/?) producing the corresponding slender control strain, the lean Zucker rat (Argiles 1989). The fatty muta- tion is characterized by insulin resistance, hyperinsulinaem- ia, glucose intolerance, hyperlipidaemia (Argiles 1989), and often by the development of moderate hypertension (Kurtz