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Data concerning cardiovascular effects of peripherally and centrally located histamine H3 receptor stimulation are contradictory, and despite excessive studies their role in the control of the cardiovascular function have not been cleared yet. Effect of histamine H3 receptors activation have been attributed to modulation of sympathetic system activity but exact role of peripherally and centrally located histamine H3 receptors stimulation in the modulation of vascular tone of the mesentery and intestinal metabolism remains unexplored. Aim of the present study was to evaluate the role of centrally and peripherally located histamine H3 receptors in the modulation of vascular tone of the mesentery and metabolic activity of intestinal tissue. In anesthetized rats total mesenteric blood flow (MBF), mucosal intestinal blood flow (LDBF), intestinal oxygen uptake (VO2) and arterial pressure (AP) were determined. Intestinal arterial conductance (C) was also calculated. Administration of the selective histamine H3 receptor agonist imetit (10 µmol/kg i.a) evoked marked changes in hemodynamic and metabolic parameters; MBF, LDBF, C and VO2 were significantly increased, whereas AP was significantly decreased. Pretreatment with histamine H3 receptor antagonist clobenpropit (4 µmol/kg i.a.) abolished imetit-induced circulatory and oxygen uptake responses. Clobenpropit (4 µmol/kg i.a.) alone failed to affect the MBF, LDBF, AP, C and VO2 values. Central administration of imetit (0.1 µmol i.c.v.) markedly increased AP and decreased MBF, LDBF, C and VO2. Pretreatment with histamine H3 receptor antagonist clobenpropit (0,4 µmol i.c.v.) diminished circulatory and metabolic responses to centrally injected imetit. Central histamine H3 receptors blockade by clobenpropit evoked no significant changes in the mesenteric arterial and mucosal microcirculatory blood flow, intestinal metabolism and mean arterial pressure. We conclude that, peripheral histamine H3 receptors when stimulated decreases vasoconstrictory tone of the mesenteric artery and precapillary structures and evokes increase of intestinal oxygen uptake. This might be in part due to inhibition of sympathetic postganglionic fibers vasopressor activity. Central histamine H3 receptor stimulation activates vasoconstrictory sympathetic adrenergic system with possible involvement of other, presumably non-histaminergic receptors system. At basal conditions neither central nor peripheral histamine H3 receptors are involved in the control of mesenteric macro - and microcirculation and intestinal oxygen consumption.
Background: Smooth muscle cells (SMC) constitute the major contractile cell population of blood vessels and inner organs. SMC contraction depends on energy provided by adenosine triphosphate (ATP) catabolism, which can be generated through oxidative phosphorylation in mitochondria or by anaerobic glycolysis. Mitochondrial activity may also modulate smooth muscle tone by biotransformation of vasoactive mediators. Here, we study the role of mitochondrial DNA gene expression for vascular function in vivo. Methods: Since loss of functional mitochondria in SMC may not be compatible with normal development, we generated mice with inducible SMC-specific abrogation of the mitochondrial transcription factor A (Tfam). Deletion of this gene leads to dysfunctional mitochondria and prevents aerobic ATP production in affected cells. Results: Invasive blood pressure monitoring in live animals demonstrated that SMC specific Tfam deletion results in lower blood pressure and a defective blood-pressure response to stress, changes that were not compensated by increased heart rate. The contractility to agonists was reduced in arterial and gastric fundus strips from Tfam-deficient mice. Endothelium-dependent relaxation of arterial strips in response to ACh was also blunted. Conclusion: Our data show that mitochondrial function is needed for normal gastric contraction, vascular tone, and maintenance of normal blood pressure.
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