Studies of the digestion of bradykinin, Lys-bradykinin, and des-Arg9-bradykinin by angiotensin converting enzyme

Localization and regulation of the renal kallikrein kinin system: possible relations to renal transport functions

The complete renal kallikrein kinin system has recently been localized in defined nephron segments. Kallikrein was found to be formed and secreted by connecting tubule cells in the late distal convoluted tubule, whereas kininogen and a novel kininase were located in collecting tubules. Kinins were shown to act on collecting tubule as well as medullary interstitial cells and the renal vasculature. The literature on interactions of this system with renal sodium transport is conflicting. Renal and urinary kallikrein was found to be increased under sodium restricted conditions, whereas kinin has a diuretic and natriuretic effect in the collecting tubule, when added from the basolateral surface. On the other hand renal kallikrein activity and connecting tubule cell morphology change in parallel with dietary potassium load indicating a coupling to potassium secretion. The possible role of the renal kallikrein kinin system in regulating collecting tubule function by tubular and vascular effects is outlined in spite of many open questions which remain to be answered.

Feeding and drinking behaviour following angiotensin converting enzyme blockade: role of injectant pH

Angiotensin converting enzyme (ACE) is a circulating dipeptidase which has a broad specificity and is known to metabolise a range of circulating peptides. While a number of circulating peptides are believed to modulate food intake, it is not known if ACE plays a role in the control of feeding behaviour and therefore in this study we have examined the effect of the potent, specific ACE antagonists captopril (SQ 14225) and enalapril (MK421) on food and water intake following food deprivation and 2-deoxyglucose treatment in the rat. One hour captopril (50 mg/kg, IP) pretreatment significantly reduced the food intake of 24 hr food deprived rats. Because captopril solutions have a low pH (2.0), the effect of buffered captopril on food intake following 24 hr food deprivation was also examined. Buffered captopril also significantly reduced the food intake of 24 hr food deprived rats, but not to the same extent as unbuffered captopril. Naloxone pretreatment (1 mg/kg, IP) did not antagonize the effect of captopril on food intake indicating that the anorexic action of captopril was not due to alterations in opiate peptide levels. Buffered captopril did not reduce the food intake of food-replete rats receiving 2-deoxyglucose (300 mg/kg, IP) or alter blood gases or pH. However, an equimolar buffered dose of the structurally different ACE inhibitor enalapril failed to significantly alter food deprivation-induced food intake, suggesting that this action of captopril in reducing food intake was unrelated to ACE blockade.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptors mediating the increase in vascular permeability to kinins: comparative studies in rat, guinea-pig and rabbit

The effect of bradykinin (BK) and a variety of kinin analogues and modified kinin fragments were assessed in several models representing the vascular permeability aspect of the inflammatory response. The rank order of potency of various kinin analogues to increase paw volume and skin vascular permeability in rats was sigma-cyclo-(Lys1-Gly6)-BK = sigma-cyclo-kallidin much greater than BK greater than kallidin = methionyl-lysyl-BK much greater than des-Arg9-BK. The same order was seen for skin responses in day 21, rheumatoid-arthritic rats. Mepyramine, 10 mg X kg-1 almost completely inhibited rat skin vascular responses to histamine, had no effect on BK and produced a small but significant inhibition of the responses to both cyclic-kinins. A different rank order of potency for the kinins was produced in both the guinea-pig and rabbit skin; this being kallidin greater than methionyl-lysyl-BK greater than BK much much greater than sigma-cyclo-(Lys1-Gly6)-BK = sigma-cyclo-kallidin greater than des-Arg9-BK. Neither of the cyclic kinins antagonised BK-induced increases in skin vascular permeability in guinea-pig or rabbit. Two modified kinin fragments, D-Pro-Phe-Arg-paranitroaniline and D-Pro-Phe-Arg-heptylamide, which have previously been demonstrated to be putative B2 receptor antagonists on in vitro tissues, enhanced the effect of BK in rat skin and when injected alone produced dose-related increases in skin vascular permeability in normal and rheumatoid-arthritic rats both having approximately half the potency of BK.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of kininases in rheumatic diseases and the effect of therapeutic agents

Bradykinin is degraded in human plasma by a carboxypeptidase to yield desArg9-bradykinin (DBK) which is then digested by angiotensin-converting enzyme (ACE) to the pentapeptide Arg-Pro-Pro-Gly-Phe and the tripeptide Ser-Pro-Phe. We have studied the rate of kinin degradation by each of these enzymes in patients with rheumatoid arthritis (RA) and with systemic lupus erythematosus (SLE), compared with the degradation rate in degenerative joint disease and normal subjects. Carboxypeptidase activity was the same in all individuals, but ACE activity was increased in the RA and SLE patients. We examined the effects of aspirin, sodium salicylate, auranofin, penicillamine, and corticosteroids on kinin metabolism, and all of these were marked inhibitors of ACE; however, only penicillamine had any demonstrable inhibition of carboxypeptidase. These observations suggest rapid degradation of DBK in patients with untreated RA and SLE, whereas drugs utilized in therapy have the opposite effects. Studies to examine the role of DBK in disease manifestations are in progress.

Studies of the digestion of bradykinin, lysyl bradykinin, and kinin-degradation products by carboxypeptidases A, B, and N

We have compared the digestion of bradykinin, lysyl bradykinin, and kinin degradation products by carboxypeptidases N, B and A (CPN, CPB and CPA). Carboxypeptidase N removed the C-terminal arginine from bradykinin or lysyl bradykinin to leave the des-Arg derivative of each, and no further degradation occurred regardless of enzyme concentration or time of incubation. However, both CPB and CPA degraded the des-Arg derivatives to remove the C-terminal phenylalanine. The inhibitory effect of phosphate ions upon this activity of CPB (but not CPA) suggests that CPA may be responsible for the formation of free phenylalanine seen upon degradation of kinins in plasma or serum. However, angiotensin converting enzyme degraded des-Arg9-bradykinin in plasma or serum prior to such Phe removal to yield the pentapeptide Arg-Pro-Pro-Gly-Phe and the tripeptide Ser-Pro-Phe. We demonstrated that CPB degraded Arg-Pro-Pro-Gly-Phe but not Ser-Pro-Phe; this reaction was also inhibited by phosphate ions. Carboxypeptidase A, on the other hand, liberated Phe from both peptides in phosphate-buffered saline and accounted, at least in part, for the free phenylalanine detected. Carboxypeptidase N did not digest the aforementioned pentapeptide or tripeptide. It is clear that carboxypeptidase B and carboxypeptidase A had overlapping activities, depending upon the substrate tested, and were distinguished by the effects of different ionic environments. We further suggest a role for carboxypeptidases other than CPN in the degradation of kinins in human plasma or serum.