The dissociation between the plasma levels of aminopeptidases A and B in spontaneously hypertensive rats.

We performed a longitudinal study for 20 weeks on spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKR) to determine the relationship between peptide metabolism and the age-dependent increase in blood pressure. In both SHR and WKR, the plasma level of aminopeptidase A (AP-A) clearly showed an age-dependent decrease. The plasma level of aminopeptidase B paralleled that of AP-A in WKR, but such an age-dependency was not observed in SHR, thus showing a dissociation between the two aminopeptidases. With age in both strains, the level of angiotensin-converting enzyme tended to decrease, while that of kallikrein activity tended to increase. In addition to these findings, a multivariate study testing the relationship of blood pressure to these enzyme activities, as well as to plasma levels of angiotensin I and renin activity, suggested abnormalities in the networks of proteolytic enzymes and in the peptide metabolism surrounding the renin-angiotensin system in SHR. These abnormalities may play some important roles in pathophysiological mechanisms of hypertension in SHR.