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The aim of this study was to investigate how blocking functional endothelin-converting enzyme activity may offer a new approach to inhibition of changes in pulmonary vessels reactivity due to development of hypoxia-induced pulmonary arterial hypertension in rats. This data shows that treatment with endothelin-converting enzyme blocker PP36 significantly reduced pathological changes due to hypoxia-induced pulmonary hypertension. One of the reasons may be the increased production and role of nitric oxide in pulmonary artery tone.

Experiments on chronically instrumented Wistar rats demonstrated that 15 mm microsphere embolization of coronary arteries led to a significant decrease in the systemic (APsyst) and maximal left ventricular systolic pressures (LVSPmax) to 10.1 and 21.1%, respectively (p0.05). To evaluate the role of endothelin in this pathology, the inhibitor of endothelin-converting enzyme (ECE), PP-36, was used. PP-36 abolished hemodynamic changes caused by embolization after 4 days per os treatment (starting 2 days before surgical procedure). Dobutamine test revealed marked decrease of LVSPmax and +dP/dtmax responses in the embolized versus sham operated animals. PP-36 normalized ischemical heart response to beta-adrenergic stimulation. Maximal APsyst and LVSPmax increases were observed in embolized rats. PP-36 abolished this effect and led to parallel rising reaction to aminoguanidin in embolized (APsyst: +12.4 +/- 1.6 vs. +6.8 +/- 2.3 mmHg, p0.05) as well as in sham operated rats (APsyst: +8.5 +/- 1.1 vs. +5.6 +/- 0.7 mmHg, p0.05). Thus, the present research showed the possibility to correct ischemical heart disturbance by using a new ECE inhibitor, PP-36. One possible mechanism of this drugs action may include systemic or myocardial changes in NO contribution to the maintenance of normal arterial pressure.

The effect of N(alpha)-carboxyalkylated dipeptides on angiotensin-converting and kinin-degrading activity of angiotensin-converting enzyme (ACE, dipeptidyl carboxypeptidase) was studied. These inhibitors selectively affected ACE-induced hydrolysis of angiotensin I-like and bradykinin-like (hippuryl-His-Leu and hippuryl-Phe-Arg, respectively) substrates in microsomal fractions of rat lungs and kidneys and rat blood serum. The inhibition constants of both types of activity were determined for these enzyme preparations and also for ACE from porcine seminal fluid and highly purified ACE from porcine lung. In all cases high inhibition selectivity of angiotensin-generating and kininase activities of ACE was found.

New fluorogenic substrate of carboxypeptidase H, Cum-Phe-Ala-Arg-OH, is hydrolyzed by this enzyme to give Cum-Phe-Ala-OH, which is completely extracted by chloroform from the reaction mixture and whose fluorescence increases remarkably by the presence of triethylamine. When the hydrolysis of the novel substrate is compared with Dns-Phe-Ala-Arg-OH, the former has Km twice as low (30 microM) and kcat four times as high (5.8 s-1). Activation of the enzyme by Co2+ in reactions with the two substrates was also studied. The novel substrate is useful for the enzyme's assay in homogenates of various animal tissues.

Muricidal and non-muricidal Wistar rats were studied regarding the changes of the body weight, the volume of the liquid intake, the sensitivity threshold to electrical shock, horizontal and vertical locomotor activity during 40-days period of 20% ethanol consumption. The transition to the situation of "choice" (water and/or ethanol) was accompanied by a division of the animals into two groups: "water preferring" and "ethanol-preferring" rats. The angiotensin-converting enzyme and enkephalin-forming carboxypeptidase H activity in different brain regions, hypophysis and peripheral tissues, were defined. The results allow one to conclude that neurochemical mechanisms underlying aggressive behavior (muricidity) and alcohol addiction have originally distinct nature.

Activities of enkephalin- and angiotensin II-forming enzymes (carboxypeptidase H and angiotensin-converting enzyme, ACE) were changed in different brain regions and peripheral tissues of rats with various alcohol motivation. The carboxypeptidase H activity was elevated in midbrain, striatum, hypophysis and adrenal glands, while the ACE activity was increased in hypophysis and striatum. The ACE activity was decreased two-fold in thalamo-hypothalamic region of ethanol-preferring rats.

The results show that during long-term immunization of rats against conjugates of angiotensin II with bovine serum albumin definite age dynamics of immune response have been observed. It was shown that the changes of physiological readings were correlated with growing of antibodies titer against angiotensin II, accordingly, as the immune response was lower, these readings return to the initial level.

The effective doses of substance P, bradykinin and prostaglandin E1 that induced depressor responses in rats and rabbits were compared. On molar conversion substance P showed the most pronounced activity. There was an essential difference in doses that evoked standard responses in rabbits (the preparations were administered into the right or left heart ventricle). For bradykinin the dose difference was fivefold and prostaglandin E1 twenty-twofold. Substance P did not undergo inactivation in the lungs.

Kinin-damaging activity (KDA) has been studied in 8 brain areas of normotensive rats and rats with spontaneous hypertension, aged 3 to 12 months. A significant depression in KDA was revealed in midbrain, striatum, thalamus, and pituitary body of normotensive rats 6 months of age, as compared to 3-month-old animals. A tendency towards KDA increase was noted in the hypothalamus. In 12-month-old normotensive rats KDA level returned to baseline (3 months of age). Comparison of KDA in rats with spontaneous hypertension aged 3 to 12 months has revealed no age-dependent differences and it is, therefore, believed that rats with spontaneous hypertension lack certain mechanisms inducing a considerable decrease of KDA in 6-month-old normotensive rats.

In vitro experiments showed that caoline-induced contact activation of the kallikreine-kinine system and streptokinase-induced activation of plasmin could possibly occur in rabbit blood plasma. Preliminary short-term treatment of plasma with chloroform removed the factor, inhibiting the two mentioned activation processes. The results obtained provided an indirect evidence for the existence of a functional relationship between the kallikreine and plasmin systems of the blood at the level of the initial step of their activation, i.e. the Hageman factor.

The examination of enzymes involved in the neuropeptides metabolism shows that the same substance can be hydrolysed by different peptidases. At the same time each of these enzymes can take part in destruction of different in their structure and functional significance peptides. The analysis of the conditions ensuring selective, regulating action of the definite neuropeptidases in the process of peptides formation and destruction is necessary for the understanding of the regulatory peptides physiological role. Substrate specificity of the enzyme, its localisation in some tissues and organs in brain and periphery, the organisation of enzyme or enzymatic complexes in a cell, the specific inhibitors influence are considered as such conditions. These conditions are examined for a number of peptidases involved in enkephalin metabolism, angiotensin I and II, bradykinin, substance P and others. The significance of such enzymologic approach in the investigation of regulatory peptides function is illustrated by concrete examples.

The microthrombogenesis parameters were studied after local laser injury to the rat mesenterial venule in the presence of infusion of bradykinin (20 micrograms/kg/min) and thrombin (10 Units/kg/min). Bradykinin diminished and thrombin, on the contrary, increased the hemostasis parameters, this effect being observed only during the first minutes after the drug infusion. Activation of the blood kallikrein-kinin system preceded the action of thrombin. It is suggested that apart from prostaglandins, the component of the Hageman factor system may play an important role in the control of microhemostasis in the injured vascular wall.

A study was made of the influence of ciproheptadin, serotonin and histamine inhibitor, on the effects of exo- and endogenous bradykinin. Ciproheptadin inhibited the effect of bradykinin on a section of a guinea pig intestine in vitro, eliminated the hypotensive effect of bradykinin in rats in vivo, and also blocked the constriction of the vessels of the ear in rabbit and a fall of the blood kininogen level caused by the administration of pyrogenal.

Experiments on rats have shown that during immobilization stress, there takes place an intense activation of the kallikrein-kinin system (KKS). The control animals do not show arteriovenous difference in the KKS values. Study of the time course of immobilization stress has demonstrated changes in the KKS values attesting to the system activation seen only in venous blood in the early stages of immobilization. With time activation of the kinin system is also seen in arterial blood, and by 24 hours of immobilization the arteriovenous difference disappears. Thus the arteriovenous difference in the KKS values, which occurs during immobilization stress indicates the compensatory role of the lungs in the early stages of immobilization.

Dansyl-Phe-Ala-Arg and (D-Ala2, Leu5) enkephalin-Arg6 (dalargine) were studied as possible substrates for enkephalin-forming carboxypeptidase (EFC) and carboxypeptidase B (CPB) in crude tissue homogenates. Activities of these enzymes in rat cerebellum, pituitary and adrenal glands were determined using the dansyl substrate. Kinetic characteristics of CPB and EFC were evaluated for dansyl substrate and dalargine. Affinity of EFC to dalargine was 10-fold higher as compared with CPB. Dalargine may be used as a specific substrate for study of EFC in tissue preparations.

The importance of the platelet count and intactness for contact Hageman's factor-dependent activation of blood plasma kallikrein has been demonstrated. The degree of kallikrein activation was in agreement with the count of platelets contained by the sample. Kallikrein activation was also found to be potentiated by the membrane fraction of washed platelets and of those destroyed by freezing and thawing. The cellular contents did not produce any significant effect on the activation in question.

Aggressive behaviour (muricidal) induced in rats by local electrolyte lesions of septal brain area was accompanied by changes in angiotensin-converting enzyme (ACE) and total kinin-destroying activity (KDA) in different brain regions. In 2-month-old rats (30 days after septal operation) a decrease in ACE activity was observed in hypothalamus and striatum, while in the cerebellum the activity was increased. KDA in this group of aggressive rats was markedly increased in the pituitary body, hypothalamus and striatum. Half a year after septal lesion in spite of aggressive behaviour retention, ACE activity and KDA did not differ from their activity in nonmuricidal rats of the same age. These data show a distinct role of the peptides studied in the formation and maintenance of muricidal behaviour in rats of different age.

Angiotensin-converting enzyme (ACE) activity in serum and some brain areas, level of angiotensin I in the blood and drinking behaviour during immunization of rats against conjugate of angiotensin II with bovine serum albumin (BSA) were studied. The results show that an increase in antibodies against angiotensin II was correlated with elevated ACE activity in serum. There was a distinct tendency towards elevated level of angiotensin I in the blood. After a 6 month's immunization ACE-activity was reduced twofold to threefold in midbrain and hypothalamus-thalamus. During immunization water-uptake was increased by 40-45%.

Angiotensin-converting enzyme (ACE) activity in blood serum and lung tissue was studied in spontaneously hypertensive rats. ACE activity in blood serum and lung tissue in normotensive and spontaneously hypertensive rats (SHR) was significantly different. In normotensive rats (NTR), ACE activity in serum was much higher than in SHR. In the lung tissue, the differences were less marked. During ontogenetic development, NTR demonstrated a decrease in ACE activity in serum and an increase in lung tissue, while SHR showed the total decrease in the enzyme activity.

Spontaneously muricidal rats (SMR) were selected from a group of white male rats. In the remaining animals muricide was induced by the local electrolyte damage of the brain septal area. Both muricidal models had different physiological indexes of aggressive reactions. In SMR a significant decrease in angiotensin-converting enzyme activity was detected in the midbrain and thalamus-hypothalamus areas. In the group of operated muricidal ("septal") rats alterations in angiotensin-converting enzyme activity have been revealed in none of the brain areas examined. The increase in total kinin-destroying activity in the pituitary, cerebellum, striatum and thalamus-hypothalamus areas was detected. The results indicate neurochemical specificity of brain angiotensin II and kinins in the regulation of different muricidal models.

Relation between kallikrein-kinin and renin-angiotensin polypeptide blood systems, main regulators of arterial pressure, is considered. Activities of kallikrein, renin and angiotensin-converting enzyme were studied in healthy persons and in patients with various forms of renin-dependent arterial hypertension under conditions of immobility and after physical loading. In dynamics of hereditary-determined hypertension of rats there were studied the effects of bradykinin and angiotensin II on alterations in reactivity of the vascular bed as well as on alterations in lung metabolic functions. A scheme of functionally important relations between the factors of neurohumoral regulation of arterial blood pressure is developed involving direct and reverse interactions between the blood pressure and depressive components of the polypeptide systems.

It is important to emphasize that the biochemical systems participating in humoral hemodynamic regulation may function at any level of the circulatory homeostasis: in the blood as a biological fluid constantly circulating along the vessels, at the microcirculatory bed where the exchange with tissues is realized, on the tonic activity of the resistive and capacitance vessels, defining the systemic blood pressure rate and organ redistribution, or, finally, on the main motive force of the blood, the heart. The interrelations of some molecular factors form the biochemical basis for the interaction of the main humoral systems. These factors are kallikrein for kinins and converting enzyme for the renin-angiotensin system, 9-ketoreductase and phospholipase for kinin and prostaglandin systems, and Hageman factors for coagulation, fibrinolysis, and kininogenesis systems. This main scheme includes "functional" connections, which are defined by a physiological interaction, and those between the central and peripheral nervous systems. We may, evidently, postulate an important biological regularity of a multi-functional participation of the same physiologically active factors in maintaining circulatory homeostasis. On the other hand, we have to emphasize the functional unity and joint correlating actions of different biochemical blood systems.

It has been shown that the development in animals of disseminated intravascular coagulation (DIC) caused by long-term intravenous infusion of thrombin was accompanied by appreciable activation of the kallikrein-kinin system, being characteristic of acute pathological processes. In the initial stages of the process development, prekallikrein and kallikrein inhibitor were observed to be secreted from the lungs to arterial blood. Further development of DIC led to the depletion of the reserves of the kinin system. Pretreatment with a single low dose of acetylsalicylic acid considerably reduced the total animals' lethality and postponed blood kinin system activation determined by the development of DIC.

In rat experiments the depressor and pressor responses to kinins and angiotensins recorded in the carotid artery were compared as to the different methods of their administration. With intravenous injection, the responses to bradykinin and kallidin were lower, and to angiotensin I--higher, than with their intra-aortic administration. The responses to angiotensin II remain identical under these conditions. The administration of all the preparations against the background of 2,3-dimercaptopropanol (unithiol) resulted in levelling of the responses irrespective of the mode of administration. In experimental myocardial infarction induced in rats by ligation of the coronary artery a reduction of the kinin-destructing and an increase of the angiotensin-converting activity was noted in the early postinfarction period. The response of the peripheral vessels to angiotensin, bradykinin and noradrenaline is decreased, while that to isoproterenol remain unchanged. The obtained results support the concept of the existence of the kininase and angiotensin-converting activity connected with a common biochemical factor of pulmonary circulation. Changes in the proportion of these functions under normal conditions and in cases of pathological states are interpreted as a particular regulation mechanism of the vascular tone and arterial pressure.

It was shown, that local influence of galvanic current upon the lung angiotensin converting enzyme (ACE) in spontaneously hypertensive rats led to a decrease of systemic blood pressure in consequence of reduced peripheral vascular resistance. The development of the hemodynamic alteration was accompanied by variations of physiological and biochemical indices of the lung ACE-activity. These results indicate that the ACE-dependent processes in the lung play on important role in the mechanisms of vasoconstriction, increase in vascular resistance and development of arterial hypertension.

Angiotensin-converting enzyme (ACE) activity in the pituitary zone and 7 other brain areas has been studied in rats with developing spontaneous hereditary hypertension. ACE activity was significantly different in normotensive and spontaneously hypertensive rats, with the differences most prominent in pituitary body, cerebellum, striatum and medulla oblongata. Age-dependent variability in ACE activity was demonstrated.

The internal surface of the rat mesentery venule was exposed to laser. Microthrombogenesis was studied from the time of maximal thrombus formation, time of the first embolism occurrence, thrombus area, and rate of embolism formation. Intravenous infusion of PGE1 and prostacyclin led to the reduction of microhemostasis as shown by all the characteristics. PGF2 alpha, on the contrary, exhibited prothrombogenous activity; PGE2 was little effective. Comparison of the active concentrations of the substances administered has demonstrated prostacyclin to have the most powerful action.