Phenylephrine contracts porcine pulmonary veins via alpha(1B)-, alpha(1D)-, and alpha(2)-adrenoceptors

Long-Term High-Altitude Hypoxia and Alpha Adrenoceptor-Dependent Pulmonary Arterial Contractions in Fetal and Adult Sheep

Autonomic innervation of the pulmonary vasculature triggers vasomotor contractility predominately through activation of alpha-adrenergic receptors (α-ARs) in the fetal circulation. Long-term hypoxia (LTH) modulates pulmonary vasoconstriction potentially through upregulation of α₁-AR in the vasculature. Our study aimed to elucidate the role of α-AR in phenylephrine (PE)-induced pulmonary vascular contractility, comparing the effects of LTH in the fetal and adult periods on α-AR subtypes and PE-mediated Ca²⁺ responses and contractions. To address this, we performed wire myography, Ca²⁺ imaging, and mRNA analysis of pulmonary arteries from ewes and fetuses exposed to LTH or normoxia. Postnatal maturation depressed PE-mediated contractile responses. α₂-AR activation contracted fetal vessels; however, this was suppressed by LTH. α_1A- and α_1B-AR subtypes contributed to arterial contractions in all groups. The α_1D-AR was also important to contractility in fetal normoxic vessels and LTH mitigated its function. Postnatal maturity increased the number of myocytes with PE-triggered Ca²⁺ responses while LTH decreased the percentage of fetal myocytes reacting to PE. The difference between myocyte Ca²⁺ responsiveness and vessel contractility suggests that fetal arteries are sensitized to changes in Ca²⁺. The results illustrate that α-adrenergic signaling and vascular function change during development and that LTH modifies adrenergic signaling. These changes may represent components in the etiology of pulmonary vascular disease and foretell the therapeutic potential of adrenergic receptor antagonists in the treatment of pulmonary hypertension.

Pulmonary Microcirculation in Experimental Model of Pulmonary Thromboembolism under Conditions of α-Adrenoceptor Blockade

Changes in the pulmonary microcirculation in isolated perfused rabbit lungs during modeling of pulmonary thromboembolism were studied in control animals and against the background of α-adrenoceptors blockade with phentolamine. Intravenous injection of emboli to control animals was followed by an increase in pressure in the pulmonary artery, mean capillary hydrostatic pressure, capillary filtration coefficient, pulmonary vascular resistance, as well as precapillary and postcapillary resistances. Against the background of α-adrenoceptor blockade, the increase in most parameters was less pronounced than in control animals, while capillary filtration coefficient increased more drastically. Thus, adrenergic mechanisms are involved in the constrictor reactions of both arterial and venous pulmonary vessels under conditions of pulmonary thromboembolism.

[Adrenergic mechanisms of regulation of pulmonary microvessels tonicity and endothelial permeability]

The review contains the data on adrenergic mechanisms of regulation of pulmonary microvessels tonicity and endothelial permeability. On smooth muscle cells of pulmonary vessels there are postsynaptic α1A-, α1B-, α1D- and α2A-, α2B-, α2C-adrenoreceptors whose activation by norepinephrine induces vasoconstriction. Excitation of β1- and β2-subtypes of adrenoreceptors leads to vasodilatation, Activation of α1-2- and β1-3-adrenoreceptors of the endothelium contributes to enhancement of nitric oxide synthesis. The resulting reaction of pulmonary microvessels in response to administration of catecholamines appears be determined by interaction of adrenergic mechanisms of regulation of tonicity of smooth muscle cells and synthesis of nitric oxide by the endothelium. Constrictor and dilator reactions of pulmonary venous vessels in response to activation of α- and β-adrenoreceptors, respectively, are more pronounced than in pulmonary arteries and make a significant contribution to the shifts of pulmonary vascular resistance. Excitation of α2- and β2-adrenoreceptors of endothelial cells of microvessels of the lungs contributes to a decrease in their permeability. In order to find out the role of adrenergic mechanisms in shifts of the capillary filtration coefficient in simulating various pathology of pulmonary circulation, it is necessary to carry out integral studies that would make it possible to evaluate alterations in macro- and microhaemodynamics of the lungs.

Effects of beta3-adrenoceptor activation on the interaction between adrenoceptors and angiotensin II receptors in apolipoprotein E knockout mouse lung

Hyperlipidemia can be harmful to the lung and β3-adrenoceptor agonist can improve lipid metabolism disorders. In this study, we aim to investigate the effects of β3-adrenoceptor activation on the interactions of adrenoceptors and angiotensin II receptors in aged apolipoprotein E gene knockout (ApoE(-/-)) mouse lung. Ten wild type C57BL/6J mice were included as normal control, 40 ApoE(-/-) mice were randomly divided into hyperlipidemia model (saline), low dose and high dose β3-adrenoceptor agonist and β3-adrenoceptor antagonist groups. After 26 weeks of high-fat diet, treatments were given for 12 weeks. Total cholesterol (TC), triglycerides (TG) and low-density lipoprotein cholesterol (LDL-C) were examined by an automatic biochemical analyzer. Quantitative real-time PCR and Western blot were used to analyze the mRNA and protein expression of α1A-, α1B-, α2A-, β1-, β2-, β3-adrenoceptors and angiotensin II type 1 and type 2 receptors in lung. We found that β3-adrenoceptor agonist could decrease TG, TC and LDL-C in aged ApoE(-/-) mice (P<0.01) and down-regulate the expressions of α1A-, α2A-adrenoceptors and angiotensin II type 1 receptor which were significantly increased in model mice (P<0.01, P<0.05). Compared with model mice, α1B-, β1-, β2-, β3-adrenoceptors and angiotensin II type 2 receptor expressions were increased in β3-adrenoceptor agonist-treat mice (P<0.01, P<0.05). These findings suggest that the expressions of adrenoceptors and angiotensin II receptors in lung are regulated towards adverse directions after taking β3-adrenoceptor agonist, which shows there are interactions between β3-adrenoceptor and other adrenoceptor subtypes and angiotensin II receptors. These interactions may play a protective role in lung under condition of hyperlipidemia.

Anthrax edema toxin has cAMP-mediated stimulatory effects and high-dose lethal toxin has depressant effects in an isolated perfused rat heart model

While anthrax edema toxin produces pronounced tachycardia and lethal toxin depresses left ventricular (LV) ejection fraction in in vivo models, whether these changes reflect direct cardiac effects as opposed to indirect ones related to preload or afterload alterations is unclear. In the present study, the effects of edema toxin and lethal toxin were investigated in a constant pressure isolated perfused rat heart model. Compared with control hearts, edema toxin at doses comparable to or less than a dose that produced an 80% lethality rate (LD(80)) in vivo in rats (200, 100, and 50 ng/ml) produced rapid increases in heart rate (HR), coronary flow (CF), LV developed pressure (LVDP), dP/dt(max), and rate-pressure product (RPP) that were most pronounced and persisted with the lowest dose (P ≤ 0.003). Edema toxin (50 ng/ml) increased effluent and myocardial cAMP levels (P ≤ 0.002). Compared with dobutamine, edema toxin produced similar myocardial changes, but these occurred more slowly and persisted longer. Increases in HR, CF, and cAMP with edema toxin were inhibited by a monoclonal antibody blocking toxin uptake and by adefovir, which inhibits the toxin's intracellular adenyl cyclase activity (P ≤ 0.05). Lethal toxin at an LD(80) dose (50 ng/ml) had no significant effect on heart function but a much higher dose (500 ng/ml) reduced all parameters (P ≤ 0.05). In conclusion, edema toxin produced cAMP-mediated myocardial chronotropic, inotropic, and vasodilatory effects. Vasodilation systemically with edema toxin could contribute to shock during anthrax while masking potential inotropic effects. Although lethal toxin produced myocardial depression, this only occurred at high doses, and its relevance to in vivo findings is unclear.