angiotensin-i and amastatin

In homogenates of the endothelium and smooth muscle cum adventitia of the rat aorta, exogenous angiotensin (ANG) I was found to be degraded to des-aspartate-ANG I (des-Asp-ANG I) instead of ANG II. ANG II and ANG III were not detectable in either of the homogenates after 5, 10 and 30 min of incubation with the decapeptide. However, both the homogenates were able to catalyse hippuryl-L-histidyl-L-leucine (HHL) to hippuric acid and the catalysis was completely inhibited by 3 microM captopril. The data show that the angiotensin converting enzyme (ACE) present in the homogenates of rat aorta, prepared by normal laboratory procedures, is not able to hydrolyse ANG I to ANG II. This finding has important consequences in the study of vascular ACE as the assay of the enzyme is often carried out using crude homogenate and HHL or other artificial substrates. In addition, the aminopeptidase that degraded ANG I to des-Asp-ANG I was not inhibited by either amastatin or bestatin, indicating that it was not aminopeptidase A or B. Together with the recent findings of other investigators which show that the de novo production of ANG II in vascular tissues is stimulated and inhibited by beta- and alpha-agonists, respectively, our present data may suggest that production of vascular ANG II occurs only in intact tissues and is probably under adrenergic regulation.

Topics: Amino Acid Sequence; Aminopeptidases; Angiotensin I; Angiotensin II; Angiotensin III; Animals; Anti-Bacterial Agents; Aorta; Endothelium, Vascular; Leucine; Male; Molecular Sequence Data; Muscle, Smooth, Vascular; Oligopeptides; Peptides; Rats; Rats, Sprague-Dawley

We have investigated the effect of chronic administration of enalapril on the carboxypeptidases responsible for the formation of angiotensin II from angiotensin I and other peptidases known to recognize angiotensin I as a substrate in the rat. These studies have shown an increase in activity in rate of formation of des-Leu-angiotensin I in both kidney S2 and P2 centrifugal fractions as well as a decrease in the rate of degradation of angiotensin I substrate. Similar increases in the formation of A(1-8) have been observed in kidney using A(1-9) as substrate. These two enzyme activities have been named carboxypeptidase K1 and K2, respectively to reflect their presence in rat kidney. These changes were accompanied by significant decreases in the activity of an amastatin-sensitive aminopeptidase and endopeptidase 24.11 in the kidney P2 fraction. These data suggest that chronic treatment with ACE inhibitors may differentially affect the activity of other enzymes capable of degrading angiotensin causing a substantial re-direction of angiotensin metabolism.

Topics: Aminopeptidases; Angiotensin I; Angiotensin II; Angiotensin-Converting Enzyme Inhibitors; Animals; Anti-Bacterial Agents; Captopril; Carboxypeptidases; Chromatography, High Pressure Liquid; Enalapril; Kidney; Neprilysin; Oligopeptides; Peptide Fragments; Peptides; Rats; Rats, Inbred WKY; Thiorphan

In superfused anterior pituitary reaggregate cell cultures angiotensin II (AII) stimulated both spontaneous and dopamine-inhibited prolactin (PRL) release from subnanomolar concentrations. Angiotensin I (AI) and angiotensin III (AIII) also stimulated PRL release. The magnitude and rate of response to AI was equal to or only slightly lower than that to AII. However, the angiotensin converting enzyme (ACE) inhibitors captopril and teprotide (1 microM) completely abolished the PRL response to 0.1 nM AI and strongly reduced that to 1 nM AI. The intrinsic activity of AIII was lower than that of AII but could be enhanced by adding 2 microM of the aminopeptidase inhibitor amastatin to the superfusion medium. After withdrawal of AIII, PRL secretion rate rapidly returned to baseline levels, whereas after withdrawal of AI or AII, secretion fell to a level remaining significantly higher than basal release. The present findings indicate that stimulation of PRL release by AI is weak unless it is converted into AII by ACE and that aminopeptidase may be important in determining the magnitude and termination of the PRL response. Furthermore, the active peptides induce a different pattern of response.

Topics: Angiotensin I; Angiotensin II; Angiotensin III; Angiotensins; Animals; Anti-Bacterial Agents; Captopril; Cells, Cultured; Dopamine; Dose-Response Relationship, Drug; Male; Oligopeptides; Peptides; Pituitary Gland, Anterior; Prolactin; Radioimmunoassay; Rats; Rats, Inbred Strains