Pulmonary intravascular macrophages in horses and ponies.

The research studied the effect of blood-borne particles on the pulmonary circulation in horses and ponies, finding that certain particles do not cause vascular obstruction and that horses exhibit a high sensitivity to them due to the presence of pulmonary intravascular macrophages.

Research Methodology

• The study involved seven horses, with four of them anesthetized and three awake, and two anesthetized ponies.
• The aim was to evaluate the sensitivity of the their pulmonary circulation to various blood-borne particles and detect the presence of intravascular macrophages in the lungs.
• In some animals, researchers measured pulmonary and systemic pressures and cardiac output before and during the injection of particles.

Experiments and Results

• One anesthetized foal demonstrated a significant increase in pulmonary arterial pressure within a minute of intravenous (IV) administration of small test doses of radioactively labeled liposomes or a suspension of blue pigment.
• Using real-time gamma camera imaging, high retention of the labeled liposomes was observed during their first pass through the foal’s lungs.
• Postmortem analysis showed that a substantial percentage of liposomes and blue pigment were retained in the lungs.
• In anesthetized ponies following administration of blue pigment, there was increased pulmonary artery pressure, decreased cardiac output, and 42% lung retention.
• Three awake horses also exhibited increased pressure after being given latex microspheres.

Conclusions

• None of the injected particles caused vascular obstruction, indicating absence of pulmonary vascular reactivity in species that lack pulmonary intravascular macrophages.
• Post-infusion of blue pigment in three horses, these animals’ lungs were perfusion-fixed to confirm the specific labeling of the pulmonary intravascular macrophages.

In general, this study revealed the role and presence of pulmonary intravascular macrophages in horses and ponies, their reaction to blood-borne particles, and how it affects pulmonary circulation.