Direct effect of histamine on arterial and venous resistance in isolated dog hindlimb

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and Comorbidities: Linked by Vascular Pathomechanisms and Vasoactive Mediators?

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is often associated with various other syndromes or conditions including mast cell activation (MCA), dysmenorrhea and endometriosis, postural tachycardia (POTS) and small fiber neuropathy (SFN). The causes of these syndromes and the reason for their frequent association are not yet fully understood. We previously published a comprehensive hypothesis of the ME/CFS pathophysiology that explains the majority of symptoms, findings and chronicity of the disease. We wondered whether some of the identified key pathomechanisms in ME/CFS are also operative in MCA, endometriosis and dysmenorrhea, POTS, decreased cerebral blood flow and SFN, and possibly may provide clues on their causes and frequent co-occurrence. Our analysis indeed provides strong arguments in favor of this assumption, and we conclude that the main pathomechanisms responsible for this association are excessive generation and spillover into the systemic circulation of inflammatory and vasoactive tissue mediators, dysfunctional β2AdR, and the mutual triggering of symptomatology and disease initiation. Overall, vascular dysfunction appears to be a strong common denominator in these linkages.

Histamine and H1 -histamine receptors faster venous circulation

The study has analysed the action of histamine in the rabbit venous system and evaluated its potential role in contraction during increased venous pressure. We have found that a great variety exists in histamine sensitivity and H(1) -histamine receptor expression in various types of rabbit veins. Veins of the extremities (saphenous vein, femoral vein, axillary vein) and abdomen (common iliac vein, inferior vena cava) responded to histamine by a prominent, concentration-dependent force generation, whereas great thoracic veins (subclavian vein, superior vena cavas, intrathoracic part of inferior vena cava) and a pelvic vein (external iliac vein) exhibited slight sensitivity to exogenous histamine. The lack of reactivity to histamine was not due to increased activity of nitric oxide synthase (NOS) or heme oxygenase-1. H(1) -histamine receptor expression of veins correlated well with the histamine-induced contractions. Voltage-dependent calcium channels mediated mainly the histamine-induced force generation of saphenous vein, whereas it did not act in the inferior vena cava. In contrast, the receptor-operated channels were not involved in this response in either vein. Tyrosine phosphorylation occurred markedly in response to histamine in the saphenous vein, but not in the inferior vena cava. Histamine induced a prominent ρ kinase activation in both vessels. Protein kinase C and mitogen-activated protein kinase (MAPK) were not implicated in the histamine-induced intracellular calcium sensitization. Importantly, transient clamping of the femoral vein in animals caused a short-term constriction, which was inhibited by H(1) -histamine receptor antagonist in vivo. Furthermore, a significantly greater histamine immunopositivity was detected in veins after stretching compared to the resting state. We conclude that histamine receptor density adapts to the actual requirements of the circulation, and histamine liberated by the venous wall during increased venous pressure contributes to the contraction of vessels, providing a force for the venous return.

Histamine H1- and H2-receptors are differentially and spatially distributed in cerebral vessels

Receptor sites for neurotransmitters may be spatially oriented within cerebral vascular walls. The direction from which neurohumoral stimuli arise (e.g., perivascular or intravascular) and the location and type of receptor activated may therefore determine the nature of vascular response. I review a series of studies that examined cerebrovascular responses to histamine and suggest that histamine receptors are differentially and spatially organized in two profiles within the cerebral circulation. A transmural distribution is suggested from the following results: increases in permeability of the blood-brain barrier (endothelial cells) to intra-arterial infusion of histamine were mediated by H2-receptors; increases in blood flow to intra-arterial infusion of histamine occurred only after the blood-brain barrier was disrupted and were the result of stimulation of both H1- and H2-receptors. These responses probably occur within inner layers of arterial smooth muscle; dilatation of pial arterioles to local microapplication of histamine and its receptor agonists indicates that H2-receptors are the predominant type in outer layers of arterial smooth muscle. A segmental profile of histamine receptors within the cerebrovascular bed is suggested as follows: since both H1- and H2-receptors could mediate dilatation of arterioles and arteries, it may be concluded that both types of receptor are present in resistance vessels; in the capillary bed, H2-receptors are the predominant type; capacitance vessels (pial veins) did not respond to perivascular application of histamine or its agonists. These studies suggest that receptors for histamine may be sparsely populated or absent in cerebral venous smooth muscle.

The effects of histamine on skeletal muscle vasculature in cats

1. Experiments have been made to determine the vascular effects of histamine and the mechanism of histamine-induced oedema formation in cat skeletal muscle. 2. Histamine caused dose-dependent dilatation of resistance vessels and increased intravascular volume over the dose range 1 X 10(-10)-1 X 10(-8) mol/kg min. The dilatation of resistance vessels resulted in dose-dependent increases in capillary hydrostatic pressure. 3. Histamine increased vascular permeability, as measured by accumulation of [131I]human serum albumin in the tissue, during infusions at 1 X 10(-8) mol/kg min but no albumin accumulation could be detected at lower infusion rates. 4. Oedema formation during histamine infusion of 1 X 10(-10) and 1 X 10(-9) mol/kg min seemed to be due to increases in capillary hydrostatic pressure and independent of increased vascular permeability. During infusions of histamine 1 X 10(-8) mol/kg min oedema was due predominantly to increased vascular permeability and to a lesser extent, the increase in capillary hydrostatic pressure.