Inhibition of secretory activity of atrial myocytes in hypertensive rats after losartan treatment.

Male ISIAH rats with inherited stress-induced arterial hypertension (BP 174.0 ± 1.3 mm Hg) received antagonist of angiotensin II receptors losartan in a dose of 10 mg/kg/day for 16 days. Ultrastructural study of the right atrium showed signs of dramatic and pronounced inhibition of synthesis of the natriuretic peptides (changes in the composition of secretory granules and decrease in their population density and size) the atrial myocytes against the background of persistent BP decrease in hypertensive rats to 142.0 ± 4.2 mm Hg. We concluded that myoendocrine cells in rats with stable hypertension retain ability to respond adequately to distention of the atria with blood.

[Changes of right atrial myoendocrine cells during hypertension and after arterial pressure decrease].

It is well known now that atrial cardiomyocytes carry out both contractile and endocrine activities--they synthesize, accumulate in specific secretory granules and release the natriuretic peptides. The main physiological effects of natriuretic peptides are antagonistic to the renin-angiotensin-aldostrol system, but their role in the development of hypertension is still disputable. The aim of this investigation is to estimate using electron microscopy the secretory activities of atrial myoendocrine cells in rats with inherited stress-induced arterial hypertension (ISIAH stain). It has been shown that myoendocrine cells in the ISIAH rats with arterial pressure about 180 mm Hg reveal morphological features of increased synthesis, extra accumulation and release of natriuretic peptides compared with normotensive control rats. In the ISIAH rats treated with losartan (angiotensin II receptor blocker) and therefore having a sustained decrease in arterial pressure to 140 mm Hg, changes in granular pool composition, reduction of the number and diameter of the secretory granules, reduction of Golgi complexes, and increased intracellular degradation of secretory stores were found in the myoendocrine cells. At the same time the marked capillary hyperemia and interstitial edema in the myocardium were observed. Thus, in rats with severe inherited hypertension, the secretory activity of heart myoendocrine cells is sharply increased and directly depends on the arterial blood pressure level. This proves that natriuretic peptides actively participate in the regulation of hemodynamics during with cardiovascular pathology.

[Ultrastructural estimation facilities of atrial cardiomyocyte secretory activity].

The wide experience in the ultrastructural study of myoendocrine cells of different animal species in normal and experimental conditions allows us to choose the optimal methodology that gives the most complete information about the state of intracellular secretory apparatus. It is revealed that the combined set of atrial myoendocrine cell qualitative and quantitative parameters allows defining the natriuretic regulatory system status, as well as it's acute and chronic responses to hemodynamic changes. The information value of such approach is illustrated by examples of the ontogenetic investigation in two rat lines: with normal arterial blood pressure and with inherited stress-induced arterial hypertension. The proposed methodology is quite sensitive and descriptive; so it is of high importance due to insufficiency of other universal, specific, and accurate methods for cardiac natriuretic peptides investigation.

[Cardiac natriuretic peptides and hypertension: experimental study].

The peculiarities of cardiac natriuretic peptide secretion have been investigated during ontogenesis using the hypertonic disease model in ISIAH rat line (with inherited stress induced arterial hypertension). The qualitative and quantitative ultrastructural investigations of right atrium myocardium revealed that the cardiac hormonal synthetic and secretory activities in ISIAH rats are higher as compared with normotensive even-aged rats from control group. Secretory hyperactivity of atrial myocytes in ISIAH rats during early ontogeny precedes the manifestations of hereditary hypertension. Natriuretic peptides present the hypotensive circuit of hemodynamic regulation during the whole ontogeny and the complementary chain in hypertension development.

[Age-related structural and functional characteristics of cardiac myoendocrine cells of rats in a normal state and with hereditary hypertension].

A qualitative and quantitative ultrastructural study of right atrial cardiomyocytes in WAG (normotensive control) and ISIAH (inherited stress-induced arterial hypertension) rats of different age (on day 18 of embryogenesis, on days 12 and 21 after birth, and at an age of 6 and 13 months) was performed. It was shown that, in embryos with an as yet incomplete atrial morphogenesis, secretory granules containing natriuretic peptides are actively formed, accumulated, and dissolved. In postnatal ontogeny, the secretory product is accumulated in atrial cells. In all ontogeny stages studied, the numerical density of secretory granules in the myoendocrine cells of hypertensive rats is greater and the qualitative composition of these granules is more diverse than in the control. It was established that, in atrial myocytes of ISIAH rats, the morphological signs of natriuretic peptide hypersecretion precede the development of genetically programmed high blood pressure. In adult hypertensive rats, hypertrophic and degenerative changes in myocytes are accompanied by excessive accumulation of secretory granules, some of which undergo intracellular degradation.

Cardiac natriuretic peptides and development of hereditary hypertension in rats.

Ultrastructure of the right atrial cardiomyocytes of suckling ISIAH rats was studied to clarify the role of cardiac natriuretic peptides in hypertension development during the period when blood pressure is not yet elevated. Cardiomyocytes diameter was significantly greater, Golgi complex was more developed, and granules in the sarcoplasm were more abundant in ISIAH rats as soon as on postnatal day 12 in comparison with age-matched normotensive animals. The smaller diameter of granules and their qualitative composition (ratio of forming, mature, and dissolving forms) attest to active synthesis and release of secretory product. In 21-day-old ISIAH rats, granule size and qualitative composition reflected increased accumulation of hormones in the cells. Thus, morphological features of increased production of natriuretic peptides in the right atrial myocytes were revealed in rats during the first postnatal month before manifestation of hereditary hypertension.

[Where and when natriuretic peptides are secreted in the heart].

This review presents recent data on the structure, synthesis, and secretion of cardiac natriuretic peptides. It is known that these hormones have a broad spectrum of activity, but they remain the least studied and poorly understood link in the regulation of the water-salt homeostasis. Emphasis is placed on the problem of ontogenetic formation of the heart secretory activity during embryogenesis. We discuss the available scarce and scattered information on the paracrine and autocrine effects of the peptides on intercellular interactions, and on the division, growth and differentiation of the heart cells. These issues are hardly addressed in Russian literature.

[Morphogenesis and reaction to hypoxia of atrial myoendocrine cells in chick embryos (Gallus gallus)].

The ultrastructural and stereomorphometrical study of the right atrium of chick embryos at the 14th day of incubation has shown the cardiomyocytes to divide by mitosis and to be at different stages of differentiation. In the cytoplasm of some muscle cells we detected secretory granules that by their sizes and morphology can be classified into the forming, mature, and dissolved forms. By the 18th day of incubation most cardiomyocytes are already differentiated, and the number of secretory granules in them rises. Under conditions of hypoxia, after 3 days, in myoendocrine cells there are noted signs of accelerated release of the peptides synthesized earlier and accumulated in granules, while after one week - of enhancement of their synthesis. It can be concluded that in chick embryos, beginning from at least the 14th incubation day, the system of natriuretic heart peptides takes part in regulation of hemodynamics and of water-salt balance and responds to hypoxia.

Delayed effect of hypotensive drugs on blood pressure and structure of the myocardium in hypertensive ISIAH rats during chronic stress.

Administration of antihypertensive drugs alpha(1)-adrenoceptor antagonist and Ca(2+) channel blocker during early ontogeny had various delayed effects on blood pressure in ISIAH rats with inherited stress-induced arterial hypertension under resting conditions and chronic stress. The drugs did not prevent the development of myocardial hypertrophy. Chronic stress had little effect on myocardial structure in adult animals.

[Myocardium development in chick embryo during restriction of external respiration].

The purpose of the present study was to determine the peculiarities of myocardium development in the chick embryos after closure of the half of the eggshell surface on day 11 of incubation. By the end of experimental day 3 (day 14 of incubation), myocardium demonstrated muscle cell hyperplasia and acceleration of their cytodifferentiation. These structural remodeling together with the oxygen blood capacity augmentation and increased vascularization of the intact part of the chorioallantoic membrane, compensate for the oxygen deprivation and provide for the embryo normal growth. By experimental day 7 (day 18 of incubation) the heart structural adaptive resources seem to be exhausted--the morphological signs of cardiomyocyte dystrophy, cardiac and coronary sclerosis, and marked embryo growth retardation were detected.

[How chicken embryo survives after half of shell is sealed?].

The goal of this study was to explore the development of the gas transport systems in chick embryos after half of the shell surface is closed on incubation day 11. By the end of day 3 of the experiment (incubation day 14), the vascular reduction in the chorioallantois under the covered zone is fully compensated by the vessel dilatation and growth in the intact half. In parallel, the oxygen capacity of blood elevates and hematopoiesis increases: the indices of hematocrit, hemoglobin, and erythrocyte count increase by half. The development of the left ventricular myocardium accelerates through the myocyte hyperplasia and their more mature ultrastructure. The obtained data indicate that hypoxia accelerates the embryonic development and leads to earlier and faster differentiation of the gas transport systems. However, the efficiency of antihypoxic responses is limited by the upper bound of capillary density in the chorionic respiratory network. After 1 week of the experiment (incubation day 18), the total vascular volume in the chorioallantois is halved relative to control, while the arterial walls substantially thicken in the open part, which increases the peripheral resistance. Atherosclerosis and dystrophy of cardiomyocytes developed in the left ventricle. These general hemodynamic abnormalities are accompanied by a notable embryonic growth inhibition. Thus, the structural compensation of the gas transport systems in the experiment becomes exhausted and cannot provide for increasing metabolic demands of the growing embryo.

[Effect of corticosterone and plasma lipoproteins on working capacity and ultrastructure of isolated rat heart].

Blood lipoproteins (very low density--VLDL, low density--LDL and high density--HDL) penetrate into the myocardium through capillary endothelial layer via receptor mediated endocytosis (all lipoproteins), nonreceptor uptake, or along interendothelial gaps (LDL). In the myocardium lipoproteins are captured by interstitial macrophages and are subjected to degradation in secondary liposomes. Their action on myocardium results in development of perivascular swelling and constriction of substantial portion of capillaries. However part of capillaries (about 20%) stay in a condition of vasodilation. Destructive changes revealed (myelin figures, mild lysis of myofibrils) are presumably caused by activation of lysosomal proteinases. Corticosterone lowered coronary flow velocity, while parameters of working capacity of the heart remained at control level. Combined use of corticosterone and VLDL suppressed myocardial functional activity, to a great extent because of diminishment of coronary flow velocity. Corticosterone and LDL exerted less pronounced negative effect. Corticosterone and HDL caused improvement of parameters of cardiac working capacity.

[SECRETORY ACTIVITY OF ATRIAL CARDIOMYOCYTES IN NORMOTENSIVE AND HYPERTENSIVE RATS DURING STRESS].

The pioneer overall ultrastructural and immune-enzymatic evaluation of the secretory activity of atrial myoendocrine cells in WAG strain (control) and in ISIAH rats with inherited stress induced arterial hypertension has been carried out. It was revealed that under basal conditions the cardiac hormone synthesis, storage and secretion in myoendocrine cells of hypertensive rats were certainly intensified, and the atrial natriuretic peptide (ANP) blood concentration was reliably higher than in normotensive WAG rats. All rats demonstrated the unidirectional reaction during the subchronic restraint stress: the ANP release was depressed, the peptides accumulated in the cardiomyocyte numerous large secretory granules, and ANP blood concentration 6 times decreased, while interline differences preserved. It is concluded that the cardiac natriuretic peptides as a hypotensive chain of the hemodynamic regulation, compensatory response to the development of inherited arterial hypertension and participate in the realization of stress reactions.

[Development of the mitochondrial apparatus and blood supply of skeletal muscle fibers during ontogenesis of domestic fowl].

The diameter, length, and numerical density of capillaries, diameter of muscle fibers, size and numerical density of their profiles, and relative volume of mitochondria in them were determined in the chicken red oxidative gastrocnemius and white glycolytic pectoral muscle during development from day 10 of embryogenesis to six month of postnatal life. The bulk blood flow was measured in these muscles by hydrogen clearance during postembryonic development. During embryogenesis, the fibers of gastrocnemius muscle develop and grow at a higher rate, while during postembryonic development, those of the pectoral muscle develop faster. The density of mitochondrial profiles increases during embryogenesis and decreases after hatching, while their mean size increases, especially in the oxidative fibers, but it somewhat decreases in 6-month old chicks. Redistribution of mitochondria by the fiber section during development takes place in both muscles: they are localized predominantly in the center in 18-day embryos and in the periphery, especially in the gastrocnemius fibers, in 6-month old fowl. At hatching, the lengths of capillaries are similar in both muscles, but as chicks grow, the proportion of longer (more than 600 microm) capillaries in the pectoral muscle sharply increases, while their density and bulk blood flow decrease. Ratios were determined between structural parameters of the capillary bed and mitochondria, on the one hand, and oxygen consumption (ml/min per 1 mm fiber and 100 g muscle mass), on the other.

[Stereomorphometric study of target organs in rats with hereditary stress-induced arterial hypertension at different periods of postnatal ontogenesis under changed conditions of nursing].

In rats with inherited stress-induced arterial hypertension (ISIAH strain), myocardium, adrenal gland, and renal glomerular apparatus were studied at different periods of postnatal ontogenesis (3 weeks and 6 months) to assess the influence of the changed conditions of nursing on the development of a hypertensive status and structural-functional characteristics of target organs. It was demonstrated that nursing of rats by foster normotensive Wistar females exerted a modulating influence upon the realization of stress-determined program of arterial hypertension development, seemingly delaying it and alleviating the negative consequences in respect to the target organs, through increased effectiveness of recruitment of adaptive-compensatory organism reserves, however, on the whole, it did not interrupt this program.

[C-TYPE NATRIURETIC PEP- TIDE: WHAT, WHERE AND WHAT FOR IS THIS?].

The up-to-day world-wide data about the structure, distribution, and physiological effects of the most poorly known among the natriuretic peptides--the C-type (CNP)--are summarized in the review. Despite its name, this peptide does not stimulate sodium excretion but shares the prominent vasodilating and antyproliferating effects in different organs and tissues. The special emphasis is attended to CNP functions in central nervous system. The information about the peptide molecular biology, including intracellular processing, blood peptide concentration, specific receptors structure, and signaling pathways in target cells is presented.

[Activation of nucleolar DNA and ribosome biosynthesis in hepatocytes under the effect of glucocorticoids and high density lipoproteins]. / Aktivatsiia iadryshkovoi DNK i biosinteza ribosom v gepatotsitakh pod vliianiem glukokortikoidov i lipoproteinov vysokoi plotnosti.

The structural bases of cooperative effect of glucocorticoids and HDL brings about the activation of protein biosynthesis in hepatocytes. Using surviving rat liver it was shown that these two compounds together activate the gene expression which was indicated by increased 3H-uridine incorporation into the total RNA pool. The enhanced incorporation of 14C-leucine into proteins in these experiments confirms protein biosynthesis acceleration. With the use of liver perfusion technique it was morphologically demonstrated that the earliest changes in hepatocyte genome take place in nucleoli. The increase of nucleolar dimensions and granular component reflects the activation of ribosomal precursors synthesis. Considerable number of ribosomes in the hepatocyte perinuclear space indicates their active transport across the numerous nuclear membrane pores into the cytoplasm. In the first place and more prominently in hepatocytes the protein synthesis "for export" is stimulated, which was proved by the dynamics of ribosome accumulation on the membranes of endoplasmic reticulum according the perfusion duration. The kupffer cells play a significant role in HDL transcytosis and in the realization of their cooperative effect with glucocorticoids.

[Effect of combined glucocorticoids and low density lipoproteins on structural and functional changes in hepatocytes and Kupffer cells ]. / Strukturno-funktsional'nye izmeneniia v gepatotsitakh i kletkakh Kupfera pri sovmestnom deistvii gliukokortikoidov i lipoproteinov nizkoi plotnosti.

The combined action of cortisol and low density lipoproteins (LDL) on the hepatic cell functional activity associated with protein biosynthesis was investigated by biochemical, radioisotope, and ultrastructural methods. The preferential uptake from blood serum of high and low density lipoproteins and glucocorticoids in vivo is enhanced, when residential macrophages are stimulated by prodigiozanum belonging to lipopolysaccharides (LPS). Liver macrophages actively take up colloidal gold (labeled LDL) by receptor-mediated endocytosis. The labels are followed in endosomes and lysosomes of Kupffer cells, and in Disse's space, though there are only single granules in hepatocytes. It is suspected that products of glucocorticoid chemical modification (tetrahydrosubstances) and LDL of limited proteolysis, while entering hepatocytes, may co-operatively activate their nucleolar DNA, that manifests in the increase in nucleolar dimensions and relative volume of granular component in them. In the cytoplasm, the density of ribosomes on the rough ER membranes significantly grows, the relative volume of the smooth ER and the number of primary lysosomes increase. In the co-culture of hepatocytes and Kupffer cells under the combined influence of cortisol, LDL and LPS, the protein biosynthesis considerably accelerates. One may suppose that LDL, on transporting steroid hormones and lipophilic xenobiotics into hepatic cells, may take part in the induction of lysosomal and monooxygenase oxidative system enzymes attributed to smooth ER.

[Penetration of lipoproteins through a capillary wall and their effects on the cardiomyocyte ultrastructure during in vitro heart perfusion]. / Proniknovenie lipoproteinov cherez stenku kapilliarov i ikh vliianie na ul'trastrukturu kardiomiotsitov pri perfuzii serdtsa in vitro.

The colloidal gold-labeled lipoprotein (LP) distribution in the myocardium after the 30 min perfusion of isolated working rat heart was studied by electron microscopy. LP of physiological concentrations are shown to be able to interact with the capillary wall and they can be incorporated by endotheliocytes. The velocity and transportation mechanisms of different classes of LP differ. Very low density LP are the most intensively taken up, low density LP enter into interstitium more rapidly than others, high density LP do not leave the capillary wall at all. The passages of labeled LP through endotheliocytes by the receptor-mediated as well as the non-receptor manners are revealed. The transportation through the widened intercellular junctions may be supposed for low density LP. For the fist time LP addendum into the perfusion medium was shown to provoke the activation of interstitial macrophages. During the perfusion duration they take inside and accumulate labeled very low density LP and low density LP in their lysosomes. The internalization may be performed by the specific endocytosis or by the simple phagocytosis. The qualitative and morphometrical analyses show that LP preserve the capillary and cardiomyocyte ultrastructure from perfusion injuries. One may suppose that there are interrelations between the capillary endothelium, the interstitial macrophages and the parenchymal cells in myocardium for realization of plasma LP effects.

[Penetration of lipoproteins and apolipoproteins of very low density into the myocardium and changes of its structure in rat heart perfusion]. / Proniknovenie lipoproteinov i apolipoproteinov ochen' nizkoi plotnosti v miokard i izmeneniia ego struktury pri perfuzii serdtsa krys in vitro.

The method of electron microscopy, involving extra-low density lipoproteins (ELDLP) marked by colloid gold as well as their protein components (i.e. apolipoproteins--apoELDLP), was made use of to show that they are captured by capillary endotheliocytes of the isolated perfusing rat heart. Receptor-mediated endocytosis is the main mechanism of penetration. Within 30 minutes, ELDLP interact with the capillary wall, pass through the endothelial barrier and, from the intersticium, they are captured by tissue microphages, which induces their activity. They have, on the whole, a positive effect on the intactness of muscle cells of the beating heart. During the same time span, apoELDLP remain in endotheliocytes, however, they exert a pronounced negative impact on the myocardium. The capillary endothelium, in whose cells the lysosomal apparatus activates itself and clasmatosis sets on, is affected morphologically most of all. The impairment of the capillary endothelium, development of the perivascular edema and a reduced coronary flow trigger a sequence of events leading to enhanced cytolytic processes in the myocardium due to an activated lysosomal apparatus of cells.