Hypotensive Effects of Arginase Inhibition by L-Norvaline in Genetic Models of Normotensive and Hypertensive Rats.

The main effect of arginase inhibition after administration of L-norvaline is a decrease in BP. At the same time, norvaline causes various side effects in normotensive and hypertensive animals. In our experiments, L-norvaline was administered intraperitoneally (30 mg/kg) for 7 days to normotensive WAG rats (Wistar Albino Glaxo) and hypertensive ISIAH rats (Inherited, Stress-Induced Arterial Hypertension). In ISIAH rats, BP decrease was accompanied by an increase in diuresis, while in WAG rats, diuresis remained unchanged or little changed. At the same time, hypertensive rats demonstrated an increase of catecholamine content in the adrenal glands, while in normotensive animals, it was decreased. The differences in the effects of norvaline can be associated with different mechanisms of BP maintenance in normotensive and hypertensive animals. Normally, BP is maintained by the regulatory influences of the nitric oxide system. In hypertension, this system is weakened, and the hypotensive effects are probably achieved via increased diuresis.

[Myocardial Infarction and Natural Defense Mechanisms: The Role of Norepinephrine Reuptake].

PURPOSE: to study effect of norepinephrine reuptake blockade in reperfusion period on size of infarct caused by local ischemia with and without ischemic pre- and postconditioning. MATERIAL AND METHODS: Wistar rats (n=46) were randomly divided into 6 groups. Group (gr) I (n=7) - 30 min occlusion of left coronary artery followed by 120 reperfusion; gr II (n=2) as in gr I +desipramine (0.8 mg/kg intravenously [i.v.]) at the start of reperfusion; gr III (n=6) - ischemic preconditioning before coronary artery occlusion; gr IV (n=7).

Methylarginines in Mice with Experimental Atherosclerosis.

We studied the dynamics of indexes for the system of endogenous regulation of NO bioavailability. The content of NO synthase inhibitors (monomethylarginine and asymmetric dimethylarginine) in the blood of mice was measured after intraperitoneal injections of a nonionic surfactant poloxamer 407 for 2 and 14 weeks. The concentrations of both methylarginines in animals with atherosclerosis due to 14-week administration of poloxamer were much higher than in control specimens. The amount of arginine and symmetric dimethylarginine practically did not differ from the control. Poloxamer-induced model of atherosclerosis is characterized by increased content of NO synthase inhibitors. These changes contribute to the development of endothelial dysfunction and atherosclerosis.

Endogenous regulators of NO bioavailability in rats with acute renal failure.

We studied the impact of acute glycerol-induced renal failure on blood levels and daily urinary excretion of arginine, monomethylarginine, and asymmetric and symmetric dimethylarginine. Acute renal failure was accompanied by enhanced daily excretion of asymmetric and symmetric dimethylarginine, increased plasma level of symmetric dimethylarginine, and decreased plasma level of arginine. Reabsorption of arginine and its methylated analogues decreased, thus compensating for reduced glomerular filtration rate. These data attest to increased production of dimethylarginines during acute renal failure. These changes can decrease NO bioavailability.

Ischemic postconditioning and size of myocardial infarction during inhibition of norepinephrine reuptake.

We studied the effect of inhibition of norepinephrine reuptake during the reperfusion period on the size of infarction zone after focal myocardial ischemia and under conditions of ischemic postconditioning. In groups 1 and 2, 30-min occlusion of the left coronary artery followed by 120-min reperfusion was performed. In groups 3 and 4, ischemia was followed by ischemic postconditioning (six 10-sec occlusions alternating with 10-sec reperfusions). Ringer solution (1 ml, groups 1 and 3) and desipramine (0.8 mg/kg, groups 2 and 4) were injected intravenously at the beginning of reperfusion. The area of myocardial infarction in group 1 was 32.0±3.1% of the area of the risk zone; in groups 2, 3, and 4 the corresponding value was 46.1±3.4% (p=0.006), 22.2±2.6% (p=0.028), and 50.3±3.1% (p=0.018), respectively. It was shown that inhibition of norepinephrine reuptake in the early reperfusion period after ischemia increased myocardial injury and abolished the protective effect of ischemic postconditioning.

Dimethylarginines and serotonin in the blood of spontaneously hypertensive rats.

The serotoninergic system and nitric oxide system were studied in spontaneously hypertensive rats SHR and Wistar rats (control). The contents of serotonin, 5-hydroxyindoleacetic acid (serotonin metabolite), L-arginine, monomethylarginine, and asymmetric and symmetric dimethylarginines were measured in blood plasma. Serotonin content in hypertensive animals was much higher than in Wistar rats. No interstrain differences were found in the concentration of 5-hydroxyindoleacetic acid. The concentration of asymmetric dimethylarginine in SHR rats was higher than in Wistar rats. However, the concentration of monomethylarginine in SHR rats was lower than in Wistar rats. Our results and published data on the serotoninergic system indicate that SHR rats serve as a convenient model of hypertension.

Determination of myocardial norepinephrine in freely moving rats using in vivo microdialysis sampling and liquid chromatography with dual-electrode amperometric detection.

Myocardial norepinephrine (NE) is considered a meaningful parameter for estimation of cardiac function. Long lasting changes in myocardial NE appear to be not only a consequence of pathologic processes in the myocardium, but may be a factor responsible for some diseases (e.g. increased propensity for arrhythmias or negative effect on left ventricular contractility in congestive heart failure). In this respect monitoring of myocardial NE is of great importance. A microdialysis sampling technique coupled with liquid chromatography with electrochemical detection (LCEC) was developed to measure the in vivo NE concentration in the myocardial interstitium of conscious, freely moving rats. LCEC using a dual-electrode amperometric detection in the series configuration provided detection limits for NE of 10 pg/ml in 20 microl microdialysis samples. Microdialysis probes of the linear design were implanted in the myocardial tissue in the periphery of the left descending coronary artery. The basal steady-state concentration of NE in myocardial dialysate of awake, freely moving rats was found to be 0.17+/-0.026 ng/ml. Delivery through the microdialysis probe of the NE reuptake inhibitor desipramine (DMI) at a concentration of 0.1 mM increased NE release to 153+/-13% of control. If the concentration of DMI in the perfusate was increased to 1.0 mM, NE release increased to only 166+/-21% of control.

Experimental studies on genetically determined predisposition to catatonia in rats as a model of schizophrenia.

To check experimentally the hypothesis of schizophrenia being a manifestation of extremely low threshold of hypnotic (catatonic) type of reaction, changes of some neurophysiologic and neurochemical systems in rats with a genetic predisposition to catalepsy were compared to analogous changes found so far in schizophrenia or chronic amphetamine intoxication considered nowadays as the most adequate pharmacological model of schizophrenia. It is found that in rats predisposed to catalepsy the threshold of audiogenic seizures is elevated; the activity of tryptophan hydroxylase in striatum is higher in rats predisposed to catalepsy genetically and due to a chronic methylphenidate intoxication as compared to control animals; noradrenaline content and noradrenaline/dopamine ratio is lower in the diencephalon of rats predisposed to catalepsy than in controls; cataleptic rats have a higher content of homovanillic acid in N.accumbens , and a higher frequency of inversion of hemispheric asymmetry as estimated by levels of dopamine and dioxyphenylacetic acid in N.accumbens and caudate nucleus, than normal rats; MAO-B/MAO-A ratio is higher in the brain stem of cataleptic than normal rats. The effects of haloperidol and apomorphine on motor activity of cataleptic and normal animals point to a higher sensitivity of postsynaptic dopamine receptors in the former. Conditioned avoidance reaction is formed slower, but preserved longer in rats predisposed to catalepsy. Blood serum of wild rats predisposed to akinetic catatonic reactions, unlike the serum of normal wild rats, inhibits the electric activity of snail neurons. The above indicated changes are analogous to those known to be present in schizophrenia and/or chronic intoxication with amphetamine or its pharmacological analogues, which witnesses in favour of the proposed hypothesis.

Neuroendocrine profiling in inherited stress-induced arterial hypertension rat strain with stress-sensitive arterial hypertension.

The functions of the hypothalamic adrenal cortical and sympathetic adrenal medullary systems were studied in rats with inherited stress-induced arterial hypertension (ISIAH strain). A characteristic feature of the ISIAH strain is an increase in arterial blood pressure measured both under basal conditions and after restraint stress in particular. In the control ISIAH rats, the basal plasma ACTH concentration was slightly lower than that in the normotensive Wistar albino Glaxo (WAG) rats, and no differences were found in plasma corticosterone. However, the 0.5-h restraint stress produced higher activation of the adrenal cortex in the ISIAH rats. Gluco- and mineralocorticoid responses to the blood volume reduction stresses and ACTH and corticosterone responses to social stress were stronger in the ISIAH than in the control WAG rats. An increase in epinephrine content in adrenals in the basal state and enhanced response of the sympathetic adrenal medullary system to handling stress were observed in the ISIAH rats. Restraint stress produced significantly higher expression of genes encoding corticotropin-releasing hormone-mRNA in hypothalamus and proopiomelanocortin-mRNA in pituitary in the ISIAH than in the WAG rats. Restraint stress produced a decrease in glucocorticoid receptor (GR) gene expression (GR-mRNA) in hippocampus in the ISIAH, but not in the WAG rats. A persistent increase in tyrosine hydroxylase-mRNA in adrenals of the ISIAH rats was found. It is concluded that the ISIAH rat strain is an appropriate model of stress-sensitive hypertension with the predominant involvement of the hypothalamic adrenal cortical and sympathetic adrenal medullary systems in its pathogenesis.

Effects of slow and rapid cooling on catecholamine concentration in arterial plasma and the skin.

Norepinephrine (NE) and epinephrine (Epi) concentrations in arterial plasma and in skin tissue were measured chromatographically before and after external cooling. Urethan-anesthetized rats were cooled either slowly (0.004-0.006 degrees C/s) or rapidly (0.03- 0.05 degrees C/s). Blood samples were drawn three times from each animal: 1) before cooling and at a rectal temperature decreased 2) by 0.5 degrees C and 3) by 3-4 degrees C. Skin samples were taken from controls and from rapidly or slowly cooled rats at a rectal temperature lowered by 0.5 degrees C. The resting mean values were 36.7 +/- 0.3 degrees C for rectal temperature, 0.62 +/- 0.079 and 1. 09 +/- 0.203 ng/ml for plasma NE and Epi, and 85.6 +/- 4.1 and 137.6 +/- 34.3 ng/g for skin NE and Epi. A decrease in rectal temperature by 0.5 degrees C at rapid cooling produced a 2.6-fold increase of NE and a 2.8-fold increase of Epi in plasma. Concomitantly, there was a significant decrease in skin NE concentration by 28% and Epi by 86%. At a rectal temperature decreased by 0.5 degrees C after slow cooling, plasma catecholamines did not change; at unaltered skin NE concentration, there was a reduction in skin Epi concentration (60%). When rectal temperature was lowered by 3-4 degrees C, the increase in plasma NE was virtually the same at both cooling rates and only plasma Epi increased more after deep rapid cooling than slow cooling. Thus the sympathoadrenal system may be differently activated depending on cooling rate. Rapid cooling, when the dynamic activity of the skin cold receptors is involved in the cold response, may provide conditions for an earlier activation of the sympathoadrenal system. This may evidence the functional significance of the dynamic activity of the skin cold receptors in the formation of the cold defense responses.

Regional serotonin metabolism in the brain of transgenic mice lacking monoamine oxidase A.

The effect of a lack of the gene encoding monoamine oxidase A (MAO A) in transgenic Tg8 mice on the activity of tryptophan hydroxylase (TPH), the rate-limiting enzyme in serotonin (5-HT) biosynthesis, and on the levels of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the midbrain, hypothalamus, hippocampus, striatum, amygdala, and frontal cortex was studied. It was shown that mice with a genetic MAO A knockout differed from mice of the initial C3H/HeJ strain in having a higher level of 5-HT and a lower level of its metabolite, 5-HIAA, in all brain regions but the frontal cortex, where the changes were insignificant. Although the 5-HIAA/5-HT ratio in various brain regions differed considerably, the decrease of the 5-HT oxidative deamination index in Tg8 mice was similar in different brain regions (to 41-45% of control values), with the exception of the frontal cortex, where the decrease of the 5-HIAA/5-HT was somewhat smaller (to 54%). The presence of the remaining 45% +/- 1.9% of the control ratio value indicates rather effective oxidative deamination of 5-HT in MAO A knockout mice and explains the lack of severe behavioral and pathological consequences in MAO A genetic deficiency. An increase of TPH activity in mice lacking MAO A was found in the frontal cortex, hippocampus, and amygdala. No significant changes were found in the striatum, hypothalamus, and midbrain. The data show an effect of the MAO A gene mutation on TPH and indicate a uniform decrease of 5-HT catabolism in different brain regions except for the frontal cortex, which is somewhat more resistant to the lack of MAO A than other brain structures.