In vivo interaction of pulmonary intravascular macrophages with activated platelets in microvessels of equine lung after multiple exposures to halothane, isoflurane, and thiamylal: a comparative ultrastructural and cytochemical study.

This study explores how multiple exposures to different anesthetics – halothane, isoflurane, and thiamylal – affect the pulmonary intravascular macrophages (PIMs) in the lungs of horses. Findings indicate that halothane specifically causes changes in PIMs and their interactions with platelets in the lungs, while isoflurane and thiamylal do not provoke similar responses.

Methodology and Considerations

• The research observed the effects of the anesthetics halothane, isoflurane, and thiamylal on the pulmonary intravascular macrophages (PIMs) in equine lungs. PIMs are unique cells with a specialized surface layer predominantly composed of lipoproteins. Anesthetics, particularly halothane, caused changes in these cells.
• Researchers administered these anesthetics via inhalation and intravenous methods to ponies at increased intervals of 1, 2, and 6 weeks to observe and compare the effects of each.
• Particular focus was placed on how halothane, known to cause acute and chronic liver toxicity due to its transformation into trifluoroacetylated polypeptides, affected the PIMs and evoked a response.

Findings

• The study found that exposure to halothane resulted in a visible impact on the PIMs in equine lungs. The surface layer of the PIMs was redistributed into their internal system, causing an enlargement and enrichment of the Golgi apparatus – a part of the cell heavily involved in processing and packaging proteins – with acid phosphatase.
• This redistribution of the surface layer in PIMs caused by halothane also resulted in extensions of the cell membrane, which facilitated interactions with platelets within the narrow confines of the lung capillaries. This interaction developed into large aggregates of platelets.

Comparisons and Conclusions

• The anesthetics isoflurane and thiamylal sodium did not elicit the same responses. Despite causing redistribution of the surface layer in PIMs, they did not affect circulating platelets or invoke the enlargement and enrichment of the Golgi apparatus by acid phosphatase.
• Notably, despite being a lipid-soluble inhalant anesthetic like halothane, isoflurane showed very little biotransformation after use, implying that it has a lesser chance of producing harmful or altered by-products. No immune response was observed in the model used for the study, illustrating a key difference between these two anesthetics.
• The study’s findings provide important insights into the differing effects of various anesthetics on the lung cellular responses and interactions, which could have implications for their use in veterinary and human medicine.