Rodionov Im

The role of purinergic and adrenergic transmitters of the sympathetic system in the control of arterial blood pressure variability

Variability of mean arterial pressure (MAP) was examined in chronically instrumented, conscious, freely moving rats with pharmacologically altered efferent sympathetic influences on the cardiovascular system. MAP was recorded for 30 min beat-to-beat, using a computer under both control and experimental conditions: after administration of adrenoceptor antagonists (prazosin or phentolamine) or under P2X receptor inactivation produced either by desensitization with alpha, beta-methylene ATP or by PPADS blockade. Inhibition of adrenergic sympathetic effects on the cardiovascular system produced long-lasting and stable decrease in MAP. Prazosin did not modify MAP variability whereas phentolamine enhanced it. Under P2X receptor desensitization MAP decreased, the hypotensive effect being accompanied by a significant increase in MAP variability. A similar increase in MAP variability was observed after PPADS administration, while MAP level was not changed. Administration of PPADS in combination with phentolamine increased MAP variability more significantly than each of the drugs given separately. Changes in MAP variability under the various experimental conditions were not consistently correlated with changes in heart rate variability. We propose that ATP, being a mediator of sympathetic vasoconstriction, participates in baroreceptor-induced stabilization of MAP level.

Low-Frequency Blood Pressure Oscillations in Mesenteric Vessels in Conscious Rats

Accessible online at: www.karger.com/journals/jvr This work was supported by grants 99–04–49634 and 98–04–49222 from the Russian Foundation for Basic Research. Systemic arterial pressure is determined by a complex interaction between the general control of the circulation and locally acting mechanisms which serve the local demands of the vascular region. The general control can be studied by measuring fluctuations in the systemic mean arterial blood pressure (sysMAP) and cardiac output. Specific mechanisms, characterizing a given vascular region, can be studied by measuring local blood pressure simultaneously with sysMAP. By comparing these two signals the activity of local mechanisms can be elucidated. The present work was aimed at studying the characteristics of tone regulation in the mesenteric vascular bed. Recently, a new technique was developed for recording the mean intravascular pressure at the base of the mesenteric arcade (mesMAP; at the point where the arcade runs closest to the intestinal wall) in conscious, unrestrained rats [1, 2]. This technique showed that, in the rat mesenteric vascular bed, arteries proximal to the mesenteric arcade (with diameter of 1200 Ìm) contribute substantially to the control of peripheral resistance. In the present study we applied this approach for the investigation of short-term blood pressure variability. This allowed us to observe regular oscillations of mesenteric vascular tone, probably resulting from vasomotion-like vessel activity.

Internet Discussion Forum

The study by Steeds et al. [1] was selected for this forum since it investigates not only the association between polymorphisms and diseases but also the possible functional consequences. Specifically, the authors investigate two gene polymorphisms of components of the renin angiotensin system (RAS) which have been previously associated with cardiovascular disorders. The D allele of the angiotensin converting enzyme (ACE) I/D polymorphism as well as the C allele of the A1166-C-polymorphism of the angiotensin II (AT1) receptor gene have been previously associated with myocardial infarction and changes in vascular structure. The authors ask the important question whether these associations between genotype and disease have a functional correlate at the level of the vascular wall. For the study, resistance arteries were obtained after colon surgery and studied in a small vessel wire myograph. Vascular function was characterized using a number of stimuli and the genotypes of the individual samples were determined. Results revealed no significant effect of the ACE I/D polymorphism on vascular function. The AT1 polymorphism was only associated with an increase to prostaglandin F2alpha but not with any other changes. The authors conclude that neither polymorphisms are associated with any significant functional vascular changes in mesenteric resistance arteries in subjects without cardiovascular disease.

The reflex control of the cardiac activity in fishes

SummaryThe author studied the relation between the stimulation strength of the pressorreceptors located in the gill blood vessels of fish and the character of the reflex responses of the heart, peripheral blood vessels, and respiration in them. It was demonstrated that with mildly stretched gill blood vessels the rhythm of the cardiac contractions increases, while with vigorous stretching it decreases. Since in fish there is heart tone along the vagus nerves, and the cardiac sympathetic innervation is absent, the reflex intensification of the heart rhythm evidently is caused by the active impulse action of the vagus nerve.Gill vessel stretching of variable intensity may also cause constriction and dilatation of the intestinal vessels and various changes in respiratory motions.

Effect of Transmural Pressure on Constrictor Reactions of Caudal Artery in Hypotensive and Hypertensive Rats

Clipping of the abdominal aorta distally to the renal arteries produces a persistent decrease in blood pressure in hindquarter vessels by 35-40%. On week 6-7 postoperation, the reactions of the caudal artery perfused in vitro under constant pressure to norepinephrine were studied. At transmural pressure of 150 mm Hg, the vascular responses in hypotensive rats were reduced compared to those in normotensive control. By contrast, the responses of hypertensive vessels were more pronounced at 75 mm Hg even after deendothelization.

Role of ATP as a sympathetic nervous system transmitter in the smoothing of rapid arterial pressure changes

Arterial pressure lability and its variations were examined in unrestrained rats following selective elimination of adrenergic or purinergic sympathetic influences on the circulatory system. Both the α1-andrenoceptor blocker prazosin and the nonselective α-adrenoceptor blocker phentolamine lowered the arterial pressure without affecting its lability. When P2x purine receptors were desensitized with α,β-methyleneATP, the resulting pronounced hypotension was accompanied by a two-fold increase in the lability of mean arterial pressure.

Age changes in vasomotor reflexes and ultrastructure of sympathetic neurons in rats after chemical desympathization

The number of cells in the sympathetic ganglia of rats was reduced by means of guanethidine to 30% (group 1) and to 1% (group 2) of normal. In rats aged 2 months pressor responses to asphyxia and to stimulation of the femoral nerve were absent. In the animals of group 1 (but not of group 2) recovery of the reflexes was observed at the age of 4 months. An increase in the number of neurofibrils was demonstrated in the neurons surviving guanethidine treatment, indicating growth of the axon of these cells. Investigation of responses to the indirect sympathomimetic tyramine revealed an increase in the number of effector sympathetic endings at the periphery at the age of 4 months in the animals of group 1. It is suggested that restoration of reflex responses in the animals of this group at the age of 4 months took place on account of growth and branching of the axons of the surviving nerve cells, as a result of which the density of the effector innervation at the periphery was restored.