Modulation of kidney renin messenger RNA levels during experimentally induced hypertension

Several experimental procedures produce dramatic alterations in kidney renin production, leading to increased plasma renin levels with attendant hypertension in animal model systems. The pattern of changes for kidney renin messenger RNA (mRNA) levels relative to changes for tissue and plasma renin activity was studied in Sprague-Dawley rats made hypertensive by either coarctation of the aorta between the two renal arteries or clipping of the left renal artery. In both models, the renin mRNA content of the contralateral hypertrophied kidney transiently decreased to undetectable levels while the ischemic kidney exhibited transient increases in renin mRNA. In aorta-coarctated rats ischemic kidney renin mRNA increased 10-fold to 16-fold during the first 3 days after coarctation but returned to the level observed in sham-operated rats 14 days after operation. However, differences between the time course and magnitude of changes in renin mRNA levels and the pattern of alteration in tissue and plasma renin activities were observed. Thus, although the kidney renin mRNA transiently increased in hypertensive animals, the extent of this increase was insufficient to account for the 30-fold to 50-fold increases in plasma renin activity. Similarly, the transient increase in kidney renin mRNA was inconsistent with only a twofold increase in tissue renin enzyme activity of the ischemic kidney. These data indicate that in addition to alterations in the kidney renin mRNA pool, posttranslational processing and/or release of renin from the kidney are cocontributors in regulating the plasma renin levels in these experimental models.