The role of platelets and the release of serotonin and histamine during anaphylaxis in the rabbit

Serotonin and cardiac morphogenesis in the mouse embryo

The possible involvement of the neurotransmitter serotonin (5-HT) and its binding protein (SBP) in cardiac morphogenesis was studied using mouse whole embryo culture (together with immunocytochemistry or 3H-thymidine autoradiography) and a cell migration assay. Embryos were cultured before and during the period of endocardial cushion formation, embryonic (E) days 9-12, in the presence of 5-HT, the monoamine oxidase (MAO) inhibitor nialamide, or an uptake inhibitor (fluoxetine or sertraline). For the migration assay, cells from the outflow tracts of E12 embryos were dissociated and placed in a chemotaxis chamber together with different concentrations of 5-HT. E9 embryos cultured in the presence of 10 microM 5-HT and nialamide exhibited intense 5-HT immunoreactivity (5-HT IR) throughout the myocardium. This staining was greatly diminished by fluoxetine, sertraline, or the absence of nialamide. As morphogenesis proceeded, myocardial staining in embryos exposed to 5-HT became restricted to developing endocardial cushion forming regions and was more completely blocked by uptake inhibitors. No evidence for 5-HT synthesis by myocardium was found at any age studied using the precursor L-tryptophan. SBP was present in endocardial cushions in cultured and uncultured embryos. 3H-thymidine autoradiography demonstrated that both fluoxetine and sertraline inhibited proliferation of cardiac mesenchyme, endocardium, and myocardium. These effects were most pronounced when exposure began at E9 (prior to cushion formation). Dose-dependent effects of 5-HT on migration of outflow tract cells were also observed. Taken together, these results suggest that 5-HT may play a role in cardiac morphogenesis during endocardial cushion formation.

The role of histamine in the physiologic alterations of IgE anaphylaxis in the rabbit

The respiratory and circulatory alterations induced by intravenous histamine in the pentobarbital anesthetized rabbit were examined and compared to those alterations associated with IgE anaphylaxis following antigen challenge. Histamine induced several graded alterations including an increase in total pulmonary resistance, a decrease in dynamic compliance, an increase in breathing frequency, a decrease in tidal volume, a rise in right ventricular systolic pressure and systemic hypotension. Qualitatively similar alterations occurred during the anaphylactic response, but a quantitative comparison of the two responses revealed that the respiratory alterations in systemic anaphylaxis corresponded to relatively low equivalent histamine doses, whereas the anaphylactic circulatory alterations exceeded the maximum response obtainable with histamine. Pretreatment with H1 antihistamine competitively blocked all of the ventilatory and lung mechanical changes induced by histamine, but it inhibited only the increase in pulmonary resistance induced by antigen. The right ventricular hypertension induced by histamine was also inhibited by H1 antihistamine but the antigen-induced change in this variable was not significantly attenuated. Inhibition of the histamine-induced systemic hypotension required pretreatment with both H1 and H2 histamine antagonists. Such pretreatment, however, did not attenuate the fall in systemic arterial pressure induced by antigen. H1 antihistamine pretreatment prevented histamine- but not antigen-induced lethality. We conclude that histamine is an important mediator of the increase in pulmonary resistance but is not the major mediator of the other physiological alterations of IgE systemic anaphylaxis in the rabbit.

Leukocyte-dependent platelet vasoactive amine release and immune complex deposition in African swine fever

Fifteen pigs were inoculated with African swine fever virus in a study of the pathogenesis of the disease. All pigs surviving the first two weeks developed high circulating antibody titers against African swine fever virus and persistent viremia. Hemolytic complement levels declined to 50 to 70 hemolytic complement 50 (CH50) units/ml from mean preinoculation levels of 120 CH50 units/ml. Immune deposits consisting of African swine fever antigen, host immunoglobulin G, and native C3 were found in the glomeruli of surviving pigs. All pigs surviving two weeks after inoculation developed leukocyte-bound antibody functionally characteristic of immunoglobulin E (IgE). Antigen-specific degranulation of antibody-coated leukocytes produced secondary platelet aggregation and vasoactive amine release. The results suggest that the IgE-basophil-platelet loop acting via amplification by leukocyte-derived platelet-activating factor participates in the immune complex deposition process in African swine fever.

The 5-hydroxytryptamine content of rabbit hearts and its release during in vitro perfusion

Rabbit hearts were perfused in vitro at constant pressure by the Langendorff technique. After 30 min perfusion, hearts from untreated animals contained significantly more 5-HT than those from animals pretreated with heparin. The cardiac 5-HT content of the non-heparinized group decreased during a further 55 min perfusion and the amount lost from the hearts was equal to that recovered from the perfusion fluid. In contrast, the 5-HT content of hearts from heparinized animals did not change significantly during this period, and no 5-HT could be detected in the perfusates. Investigation of the distribution of 5-HT within the hearts from heparinized animals disclosed a significantly greater concentration of 5-HT in the right atrium than in the rest of the heart. It is concluded that the small, perfusion-resistant store of 5-HT within hearts from heparinized rabbits represents the true endogenous 5-HT content in this species, but that much higher values may be obtained unless care is taken to exclude a contribution from blood platelets.

Pharmacological significance of biogenic amines in the lungs: histamine

1. Eight animal species were investigated for the histamine content of the lung and can be divided into two groups: the low-level group, ranging from 2 to 7 mug/g, consisting of the mouse, rat, guinea-pig and rabbit; and the high-level group, ranging from 12 to 35 mug/g, consisting of the cat, dog, goat and human. In two species of the high-level group (cat and dog) the amount of histamine that elicited an increase in pulmonary resistance was one-fifth to one-tenth of the dose that elicited an increase in species of the low-level group (rat and rabbit). There is an inverse relationship between the content of histamine and the dose of histamine that produces a 25% increase in pulmonary resistance.2. Anaphylaxis increases the histamine content of the lung of the rabbit but not of the lung of the guinea-pig. In both species, anaphylaxis is accompanied by an elevation of the concentration of 5-hydroxytryptamine in the lung, indicating the trapping of platelets in the lung.3. The development of severe parasitaemia in the mouse inoculated with Plasmodium berghei is accompanied by an elevation of the histamine content of the lung. This increase appears to be part of the response of the lung to parasitaemia.