Effects of growth hormone on renal renin gene expression in normal rats and rats with myocardial infarction

Background. Published data regarding effects of growth hormone (GH) on the renin system are controversial. The aim of this study therefore was to eval uate the effects of GH on the renin system in normal rats and rats with myo cardial infarction (MI). Methods. Normal rats received 2, 5, or 10 IU GH/kg/day or vehicle subcutane ously for 4 weeks. Furthermore rats with MI were randomized to receive 2 IU GH/kg/day or vehicle for 4 weeks. Subdivision into MI groups (mild, modera te, and large) was by histological determination of infarct size. Renal ren in gene expression was assessed by RNAase protection assay and plasma renin activity by radioimmunoassay. In addition, isolated mouse juxtaglomerular cells were exposed to GH for 20 h, and renin secretion rates were assessed. Results. GH treatment in normal rats for 4 weeks increased body weight, and kidney weight to body weight ratio, but did not affect renin secretion and renal renin gene expression. In rats with large MI, renal renin gene expre ssion increased about fourfold, but was unchanged in rats with small and mo derate MI as compared to normal rats. In rats with MI, body weight decrease d and this decrease was partially reversed by GH treatment. GH treatment di d not change renal renin gene expression, and renin secretion in rats with MI. Renin secretion of isolated juxtaglomerular cells was unaffected by GH. Conclusions. Our study demonstrates that GH treatment has no significant ef fect on renin secretion and on renal renin gene expression in normal rats a nd in rats with stimulated renin system due to MI in vivo. In isolated juxt aglomerular cells in vitro, renin secretion was also unaffected by GH.