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.

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.

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.

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.