Effects of platelet-activating factor on rat airways

Analysis of decreases in systemic arterial pressure and heart rate in response to the hydrogen sulfide donor sodium sulfide

The actions of hydrogen sulfide (H2S) on the heart and vasculature have been extensively reported. However, the mechanisms underlying the effects of H2S are unclear in the anesthetized rat. The objective of the present study was to investigate the effect of H2S on the electrocardiogram and examine the relationship between H2S-induced changes in heart rate (HR), mean arterial pressure (MAP), and respiratory function. Intravenous administration of the H2S donor Na2S in the anesthetized Sprague-Dawley rat decreased MAP and HR and produced changes in respiratory function. The administration of Na2S significantly increased the RR interval at some doses but had no effect on PR or corrected QT(n)-B intervals. In experiments where respiration was maintained with a mechanical ventilator, we observed that Na2S-induced decreases in MAP and HR were independent of respiration. In experiments where respiration was maintained by mechanical ventilation and HR was maintained by cardiac pacing, Na2S-induced changes in MAP were not significantly altered, whereas changes in HR were abolished. Coadministration of glybenclamide significantly increased MAP and HR responses at some doses, but methylene blue, diltiazem, and ivabradine had no significant effect compared with control. The decreases in MAP and HR in response to Na2S could be dissociated and were independent of changes in respiratory function, ATP-sensitive K+ channels, methylene blue-sensitive mechanism involving L-type voltage-sensitive Ca2+ channels, or hyperpolarization-activated cyclic nucleotide-gated channels. Cardiovascular responses observed in spontaneously hypertensive rats were more robust than those in Sprague-Dawley rats.NEW & NOTEWORTHY H2S is a gasotransmitter capable of producing a decrease in mean arterial pressure and heart rate. The hypotensive and bradycardic effects of H2S can be dissociated, as shown with cardiac pacing experiments. Responses were not blocked by diltiazem, ivabradine, methylene blue, or glybenclamide.

The Responses of Pulmonary and Systemic Circulation and Airway to Allergic Mediators in Anesthetized Rats

Lung allergic diseases sometimes accompany pulmonary vaso- and broncho-constriction. Rats are currently used for the experimental study of lung allergies. However, their hemodynamic mechanisms are not fully understood. Therefore the effects of allergic mediators were determined systematically in vivo in rats in terms of pulmonary vascular resistance (PVR), airway pressure (AWP) and total peripheral resistance (TPR). We directly measured pulmonary arterial pressure, left atrial pressure, systemic arterial pressure, central venous pressure and aortic blood flow to determine PVR and TPR, as well as AWP, following injections of platelet-activating factor (PAF), histamine, serotonin, leukotriene (LT) C4, and prostaglandin (PG) D2 in anesthetized open-chest artificially ventilated Sprague-Dawley (SD) rats. PVR was dose-dependently increased by consecutive administration of PAF, LTC4, and PGD2, with the maximal responsiveness being PAF>LTC4>PGD2. However, neither histamine nor serotonin changed PVR. TPR was decreased by all agents except LTC4 which actually increased it. PAF and serotonin, but not the other agents, increased AWP. In conclusion, allergic mediators exert non-uniform actions on pulmonary and systemic circulation and airways in anesthetized SD rats: PAF, LTC4 and PGD2, but not histamine or serotonin, caused substantial pulmonary vasoconstriction; LTC4 yielded systemic vasoconstriction, while the others caused systemic vasodilatation; only two mediators, PAF and serotonin, induce airway constriction.

Overview of animal models of asthma

Asthma is an inflammatory disease characterized by airways obstruction, airways hyperresponsiveness, excessive mucous secretion and cough. Guinea pig airways display many anatomical, physiological and pharmacological attributes of human airways, making this species ideal for modeling the asthmatic condition. This unit provides an overview of animal models of asthma, including definitions, descriptions of available animal models, and discussion of numerous critical issues to consider before designing a model to study this complex disease.

Airway and pulmonary tissue responses to platelet-activating factor in rats

We studied airway and pulmonary tissue responses to platelet-activating factor (PAF) in rats by measuring alveolar pressure with the alveolar capsule technique. We calculated airway resistance (Raw), dynamic elastance (Edyn), and pulmonary tissue resistance (Rtis). PAF was administered intravenously in doses of 0.1, 1, 10, and 30 micrograms (1 dose per animal, 5 rats for each dose). Infusion of PAF resulted in a significant increase in Rtis and Edyn (p < .05). Maximal values of Edyn were observed with the infusion of 10 micrograms of PAF (p < .02). Rtis presented a significant increase after infusion of 1 microgram of PAF (p < .05). The observed increase in Raw was transient and did not reach statistical significance. After infusion of PAF lungs were fixed by a quick-freezing method. Morphometric analysis showed that PAF infusion resulted in significant increases in intraluminal secretion (p = .001) and peribronchiolar edema (p < .001) but did not result in significant airway contraction. We conclude that intravenous infusion of PAF results in significant effects on lung tissue mechanics. The effects of PAF on the mechanical properties of lung parenchyma reflect the inflammatory alterations induced by this agonist in distal airspaces.

Platelet-activating factor (PAF)-induced rhinitis and involvement of PAF in allergic rhinitis in guinea pigs

The effects of inhaled PAF on the guinea pig nasal mucosa were investigated. Intranasal pressure (INP) was recorded as an index of intranasal resistance. To access the capillary premeability of nasal mucosa, exudation of Evans blue into the nasal lavage fluid was determined. Inhalations of histamine and PAF markedly and significantly increased INP and dye exudation into the nasal cavities. The two responses to PAF were about 20-fold and 70-fold stronger than those of histamine, respectively. A PAF antagonist, CV-3988, significantly antagonized both the PAF-induced increases in INP and dye exudation. Indomethacin and OKY-046 had no effect on the PAF-induced responses. FPL-55712 inhibited the PAF-induced increases in INP and dye exudation by 52% and 40%, respectively. Ovalbumin (OA) antigen challenge by inhalation to sensitized guinea pigs resulted in significant increases in both INP and dye exudation. These two responses to 30 mg/ml OA were inhibited by CV-3988 (10 mg/kg, i.v.) by 55% and 40%, respectively. From the above results, it is indicated that: 1) inhalation of PAF evokes rhinitis-like symptoms through activation of PAF receptors, 2) the PAF-induced rhinitis is, in a part, mediated by leukotrienes, and 3) PAF might be involved in allergic rhinitis.

The effect of platelet-activating factor on histamine release from rat peritoneal mast cells

The effect of platelet-activating factor (PAF) on histamine release from peritoneal mast cells of adult and young male rats was investigated. PAF alone tended to release histamine from the mast cells of adult and young rats, although very slightly. On the other hand, PAF significantly inhibited the histamine release induced by the Ca2+ ionophore A23187 in mast cells obtained from rats of either age group, but not that by compound 48/80. Such inhibition was not seen with lyso-PAF. CV-3988, a PAF antagonist, antagonized the inhibitory effect of PAF on the A23187-induced histamine release in mast cells from adult and young rats. These results suggest that PAF does not have a strong histamine-liberating action on mast cells, and that PAF inhibits the calcium influx into mast cells through the activation of PAF receptors.