Serotonin in the lung. Demonstration of a close correlation to blood platelet

Misunderstandings Between Platelets and Neutrophils Build in Chronic Inflammation

Regulated hemostasis, inflammation and innate immunity entail extensive interactions between platelets and neutrophils. Under physiological conditions, vascular inflammation offers a template for the establishment of effective intravascular immunity, with platelets providing neutrophils with an array of signals that increase their activation threshold, thus limiting collateral damage to tissues and promoting termination of the inflammatory response. By contrast, persistent systemic inflammation as observed in immune-mediated diseases, such as systemic vasculitides, systemic sclerosis, systemic lupus erythematosus or rheumatoid arthritis is characterized by platelet and neutrophil reciprocal activation, which ultimately culminates in the generation of thrombo-inflammatory lesions, fostering vascular injury and organ damage. Here, we discuss recent evidence regarding the multifaceted aspects of platelet-neutrophil interactions from bone marrow precursors to shed microparticles. Moreover, we analyse shared and disease-specific events due to an aberrant deployment of these interactions in human diseases. To restore communications between the pillars of the immune-hemostatic continuum constitutes a fascinating challenge for the near future.

In vivo platelet response to lipopolysaccharide in mice: proposed method for evaluating new antiplatelet drugs

We previously found evidence (based on the use of 5HT as a marker) that i.v. injection of a lipopolysaccharide (LPS) into mice induces a rapid accumulation of platelets in liver and lung. Our previous studies lacked measurement of the platelet count itself, but we have now compared the LPS-induced changes in 5HT levels with the change in platelet count. We also examined the effects on the platelet response of some drugs that act on platelets. In mice, sublethal doses of LPS induced parallel decreases in platelets and 5HT in the blood. The 5HT lost from the blood accounted well for the 5HT accumulated in liver and lung. Soon after this accumulation, the levels of platelets and 5HT in the blood recovered in parallel, and these recoveries corresponded well with the decreases in 5HT occurring in liver and lung. Aspirin and dexamethasone were effective at both reducing pulmonary platelet-accumulation and promoting their return to the circulation. By contrast, oestrogen tended to reduce the return of platelets from lung to circulation. Heparin did not inhibit pulmonary platelet-accumulation but it did decrease their return to the circulation. These results suggest that (i) in response to sublethal doses of LPS, platelets translocate into the liver and lung, then return to the circulation; (ii) this platelet response involves mechanisms that can be modified by drugs; and (iii) the use of this platelet response as a tool for drug evaluation might help identify new drugs with therapeutic potential.

Accumulation of platelets in the lung and liver and their degranulation following antigen-challenge in sensitized mice

1. Mast cells and basophils are believed to trigger allergic reactions and anaphylaxis. They rapidly release histamine (H), a typical mediator of inflammation, in response to antigens. In the mouse, platelets contain much 5-hydroxytryptamine (5HT), an additional inflammatory mediator, while human platelets contain both H and 5HT. Here, we examined the response of platelets in sensitized mice to antigen challenge. 2. Platelets accumulated in the lung and liver almost immediately after intravenous injection of ovalbumin (OVA), in mice sensitized to it, and platelet degranulation occurred during these reactions. 3. These responses of platelets preceded H release from mast cells and/or basophils, occurred at doses of OVA lower than those inducing H release, and contributed to the signs of shock. 4. We reported previously that intravenous injection into mice of LPS (a membrane constituent of gram-negative bacteria) induces a similar platelet response (accumulation of platelets in the lung and liver) and shock. 5. Blood that has passed through the body (other than the digestive tract) passes first to the lungs before being recirculated by the heart, and blood that has passed through the digestive tract passes next to the liver. Thus, our findings suggest that in addition to their role in haemostasis, platelets, tiny anuclear cytoplasts, may be important in both innate and acquired immunity, and that the lung and liver may be the fronts at which platelets wage war on pathogens.

[Hormone expression and opioid receptors in fetal and adult lung]

OBJECTIVES

To describe the cellular distribution and level of expression of certain hormones and opioid receptors during fetal development and in the lung of the healthy adult.

METHOD

We sampled lung tissue from fetuses at three stages of development (pseudoglandular, canalicular and saccular) (3 samples per stage), from newborn infants (3), from 10-month-old infants (2) and from adults (3) who had died without lung disease. After specific immunohistochemical staining for hormones (calcitonin, parathormone, serotonin and adrenocorticotropic hormone - ACTH) and opioid receptors, we assessed the percentage of positive cells for each cell type in each sample.

RESULTS

Serotonin is the first to appear (pseudoglandular stage in isolated neuroendocrine cells) and it disappears later. Calcitonin appears in the canalicular stage in neuroendocrine and lung cells. Expression is at its peak at birth and is less in the adult lung. We found no ACTH or parathormone production. Opioid receptors appear in the canalicular stage and peak at birth. In adult lung, bronchiolar muscle and mesothelial cells, only delta-type opioid receptors are present.

CONCLUSIONS

Pulmonary hormone secretion is significant during fetal development and peaks at birth. Calcitonin is the main hormone produced in the fetal lung. Opioid receptors are present during fetal development in various types of cells and peak at birth. An understanding of the expression of active substances could have therapeutic relevance in certain conditions, such as bronchial asthma or respiratory distress syndrome in the child.

Cervical dislocation of mice induces rapid accumulation of platelet serotonin in the lung

As much as 3-8 micrograms/g wet weight of serotonin (5-hydroxytryptamine, 5HT) has been detected in mouse lung 10 sec after the animal was sacrificed by cervical dislocation. Perfusion of the lung was carried out to determine where the majority of 5HT was located. Of the total 5HT, 84.3% was measured in the perfusate in which 90-98% was recovered in the platelet-rich fraction. When lungs were dissected from mice without cervical dislocation, either after instantaneous killing by irradiation with high power microwaves or under anesthesia, 5HT in the lung was 0.40-1.60 microgram/g tissue. These results show that cervical dislocation induces the entrapment of platelets in the pulmonary capillaries within 10 sec. The pulmonary accumulation of 5HT induced by cervical dislocation was approximately 50% inhibited by both prazosin and yohimbine, suggesting that the alpha-adrenergic receptor plays some part in the process. Norepinephrine but not isoproterenol augmented by 180% the response of pulmonary 5HT to cervical dislocation.