Plasma angiotensin-converting enzyme activity and blood pressure during the first year of life in normotensive and spontaneously hypertensive rat.
Plasma angiotensin-converting enzyme (ACE) activity and systolic blood pressure were studied every consecutive month during the first years of life in male spontaneously hypertensive (SHR) and in normotensive rats (NWR). During the first month after birth neither ACE activity nor systolic blood pressure showed significant difference between SHR and NWR. ACE activity in SHR was significantly reduced from 2nd till 12th month of age in comparison with age-matched NWR. In the 2nd month of age the systolic blood pressure was significantly higher in SHR than in NWR, it increased further until the 5th month and was maintained at this high level till the 12th month. No correlation between changes in the systolic blood pressure and the ACE activity was found in SHR after the 2nd month of age. During the investigation period no age-related dynamics of ACE activity was observed in SHR. The observed difference of ACE activity was not due to an increase of plasma his-leu hydrolyzing activity in SHR and was not abolished after a 24-hour dialysis of plasma. This difference could not be caused by the altered effect of chloride ion on the enzyme since similar pattern of Cl-dependent activation of plasma ACE in 4-month-old SHR and NWR was observed. Lineweaver-Burke plot analysis revealed that this difference appears to be due to a decrease of the enzyme maximal velocity in SHR but to a change of the Km value of ACE for the substrate hippuryl-1-his-1-leu. Our data provide evidence for a lower concentration of the available active enzyme molecules in SHR plasma in respect to NWR after the 1st month of life. Whether the reduced ACE activity in SHR is a consequence of the increased blood pressure remains to be elucidated.
Shisheva
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AC
Department of Chemistry and Biochemistry, Institute of Medical Biology, Medical Academy, Sofia, Bulgaria.
Dimitrov
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T
Ikonomov
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OC
D000818:Animals; D000831:Animals, Newborn; D001794:Blood Pressure; D002712:Chlorides / Q000494:pharmacology; D004151:Dipeptides / Q000097:blood; D004789:Enzyme Activation; D006973:Hypertension / Q000201:enzymology* / Q000503:physiopathology; D007700:Kinetics; D008297:Male; D007703:Peptidyl-Dipeptidase A / Q000097:blood*; D051381:Rats; D011918:Rats, Inbred SHR; D011919:Rats, Inbred Strains; D012044:Regression Analysis
D002712:Chlorides; D004151:Dipeptides; C020357:histidylleucine; D007703:Peptidyl-Dipeptidase A