Kinin-forming system in the genesis of hypertension

Basic and clinical aspects of bradykinin receptor antagonists

Bradykinin and related kinins may act on two types of receptors designated as B1 and B2. It seems that the B2 receptors are most commonly found in various vascular and non-vascular smooth muscles, whereas B1 receptors are formed in vitro during trauma, and injury, and are found in bone tissues. These bradykinin (BK) receptors are involved in the regulation of various physiological and pathological processes. The mode of kinin actions are based upon the interactions between the kinin and their specific receptors, which can lead to activation of several second-messenger systems. Recently, numerous BK receptor antagonists have been synthesized with prime aim to treat diseases caused by excessive kinin production. These diseases are rheumatoid arthritis (RA), inflammatory diseases of the bowel, asthma, rhinitis and sore throat, allergic reactions, pain, inflammatory skin disorders, endotoxic and anaphylactic shock and coronary heart diseases. On the other hand, BK receptor antagonists could be contraindicated in hypertension, since these drugs may antagonize the antihypertensive therapy and/ or may trigger the hypertensive crisis. It is worth suggesting that the BK receptor agonists might be useful antihypertensive drugs.

Role of tissue kallikrein-kininogen-kinin pathways in the cardiovascular system

All the components of the kallikrein-kinin system are located in the cardiac muscle, and its deficiency may lead to cardiac dysfunction. In recent years, numerous observations obtained from clinical and experimental models of diabetes, hypertension, cardiac failure, ischemia, myocardial infarction and left ventricular hypertrophy have suggested that the reduced activity of the local kallikrein-kinin system may be instrumental for the induction of cardiovascular-related diseases. The cardioprotective property of the angiotensin converting enzyme inhibitors is primarily mediated via kinin-releasing pathway, which may cause regression of the left ventricular hypertrophy in hypertensive situations. The ability of kallikrein gene delivery to produce a wide spectrum of beneficial effects makes it an excellent candidate in treating hypertension, cardiovascular and renal diseases. In addition, stable kinin agonists may also be available in the future as therapeutic agents for cardiovascular and renal disorders.

Does the kinin system mediate in cardiovascular abnormalities? An overview

All the components of the kallikrein-kinin system are located in the cardiac muscle, and its deficiency may lead to cardiac dysfunction. In recent years, numerous observations obtained from clinical and experimental models of diabetes, hypertension, cardiac failure, ischemia, myocardial infarction, and left ventricular hypertrophy have suggested that the reduced activity of the local kallikrein-kinin system may be instrumental for the induction of cardiovascular-related diseases. The cardioprotective property of the angiotensin-converting enzyme inhibitors is primarily mediated via the kinin-releasing pathway, which may cause regression of left ventricular hypertrophy in hypertensive situations. The ability of kallikrein gene delivery to produce a wide spectrum of beneficial effects makes it an excellent candidate in treating hypertension and cardiovascular and renal diseases. In addition, stable kinin agonists may also be available in the future as therapeutic agents for cardiovascular and renal disorders.

Cardiovascular properties of the kallikrein-kinin system

All the components of the kallikrein-kinin system are located in the vascular smooth muscle as well as in the heart. In recent years, numerous observations obtained from clinical and experimental models of diabetes, hypertension, cardiac failure, ischaemia, myocardial infarction and left ventricular hypertrophy, have suggested that the reduced activity of the local kallikrein-kinin system may be instrumental in the induction of cardiovascular-related diseases. The ability of kallikrein gene delivery to produce a wide spectrum of beneficial effects makes it an excellent candidate in treating hypertension, and cardiovascular and renal diseases. In addition, stable kinin agonists may also be available in the future as therapeutic agents for cardiovascular and renal disorders.

Blood pressure regulation by the kallikrein-kinin system

1. The kallikrein-kinin system has a significant role in regulating arterial blood pressure. 2. Reduced formation of the kinin compontents may cause hypertensive diseases. This is because of the fact that this system is responsible for vasodilatation, reduction in total peripheral resistance, natriuresis, diuresis, increasing renal blood flow and releasing various vasodilator agents. 3. Reduced kinin-kallikrein generation in hypertensive subjects may also be associated with genetic and environmental defects. 4. The kallikrein-kinin system when administered to hypertensive patients can lower their raised blood pressure to normotensive levels. 5. The mode of action of angiotensin-converting enzyme inhibitors principally may be dependent on the kinin system protection.

Does kinin mediate the hypotensive action of angiotensin converting enzyme (ACE) inhibitors?

The lack of kinin formation in systemic circulation and in the renal system may lead to the pathogenesis of high blood pressure (hypertension). Angiotensin converting enzyme inhibitors are able to protect the kinin inactivation by kininase II, therefore, causing an accumulation of kinin. Although the concentrations of kinin in plasma after oral administration of ACE inhibitors are conflicting this is mainly due to methodological difficulties. Kinin receptor antagonists are becoming most reliable pharmacological probes for defining the molecular actions of kinin in several physiopathological states, and in the mechanism of actions of drugs which are dependent on the kinin system. The blood pressure lowering effect of ACE inhibitors can be antagonized by the pretreatment with kinin receptor antagonists. I have therefore proposed that the hypotensive action of ACE inhibitors may reflect the activation of kinin receptor. It is suggested that the development of compounds having protective properties on the kallikrein-kinin system might be therapeutically applicable as anti-hypertensive drugs.

The role of chemical mediators in the pathogenesis of inflammation with emphasis on the kinin system

In recent years, numerous agents have been recognized as inflammatory mediators. In this review, however, we discuss only those having direct relevance to human inflammatory diseases These mediators are clinically important due to their proinflammatory properties such as vasodilatation, increased vascular permeability, pain and chemotaxis. They may lead to the fifth cardinal sign, loss of function in inflammatory diseases. Agonists and non-specific antagonists are used as pharmacological tools to investigate the inflammatory role of PGs, LTs, PAF, IL-1, histamine, complement, SP, PMN-leukocytes, and kallikrein-kininogen-kinin systems. Unfortunately, no compound is known which concurrently abolishes all actions and interactions of inflammatory mediators. Therefore it would be highly useful to promote efforts in developing selective and competitive antagonists against proinflammatory actions of these chemical mediators. This may help to a better understanding of the pathogenesis of inflammatory reactions, and it may also be useful for the therapy of inflammatory diseases.

Interrelationship between the kallikrein-kinin system and hypertension: a review

The evidence presented here suggests strongly that the kallikreins-kininogens-kinins-kininase II system has most significant role in regulation of systemic BP. This system is involved in mediation and modulation of renin-angiotensin-aldosterone, PGS and vasopressin in the regulation of sodium water balance, renal hemodynamic and BP. Therefore, reduction in the kinin-formation due to high production of kininase II, and lower formation of tissue kallikrein might result in an increased release of vasoconstrictor angiotensin II on one side, and on the other side much reduced production of PGE, vasodilator. These changes might lead to deranged vascular smooth muscle structures and cell membrane functions, retention of sodium and water, increased plasma volume, and renovascular constriction. These physiological defects might result in the development of essential hypertension (Fig. 4). Although, it is possible now to treat hypertensive conditions with tissue kallikrein and kininase II inhibitors. These discoveries have opened up new vistas to research on the pharmacological applications of kallikreins-kininogens-kinins-kininases in human diseases.

Effects of a prostacyclin analog iloprost on kidney function, renin-angiotensin and kallikrein-kinin systems, prostanoids and catecholamines in man

Iloprost (ZK 36 374), a stable analog of carbaprostacyclin, was infused for 72 h to nine patients with advanced obliterative arterial disease. Iloprost caused a marked vasodilation and a compensatory increase in cardiac output. The glomerular filtration rate increased by 45% and tubular reabsorption of sodium and water were reduced by 80% and 107%, respectively. The urine excretion rate increased by 122%. Tubular handling of potassium and calcium were not influenced by iloprost but magnesium reabsorption was stimulated. The renin-angiotensin system was not activated while serum angiotensin converting enzyme activity was decreased. Kallikrein excretion in urine was increased 4.4-fold but plasma kininogen, a substrate for kallikrein in producing vasoactive kinins, was unaffected by the drug. Plasma levels of 6-keto-PGF1 alpha and TxB2 were decreased and their excretion in urine increased. Plasma catecholamines were not changed by iloprost. Several of the changes persisted for at least the first postinfusion day. The results indicate that iloprost increases urine excretion rate by increasing glomerular blood flow and by inhibiting sodium and water reabsorptions. The kinin-forming system, but not the renin-angiotensin system or plasma catecholamines, may be activated. The decrease in plasma level of prostanoids can be, at least partly, due to their increased excretions in urine.