Regional distribution of collagen and haemosiderin in the lungs of horses with exercise-induced pulmonary haemorrhage.
BACKGROUND
Regional veno-occlusive remodelling of pulmonary veins in EIPH-affected horses, suggests that pulmonary veins may be central to pathogenesis. The current study quantified site-specific changes in vein walls, collagen and haemosiderin accumulation, and pleural vascular profiles in the lungs of horses suffering EIPH.


OBJECTIVE
In the caudodorsal lung regions of EIPH-affected horses, there is veno-occlusive remodelling with haemosiderosis, angiogenesis and fibrosis of the interstitium, interlobular septa and pleura.


METHODS
Morphometric methods were used to analyse the distribution and accumulation of pulmonary collagen and haemosiderin, and to count pleural vascular profiles in the lungs of 5 EIPH-affected and 2 control horses.


RESULTS
Vein wall thickness was greatest in the dorsocaudal lung and significantly correlated with haemosiderin accumulation. Increased venous, interstitial, pleural and septal collagen; lung haemosiderin; and pleural vascular profiles occurred together and changes were most pronounced in the dorsocaudal lung. Further, haemosiderin accumulation colocalised with decreased pulmonary vein lumen size. Vein wall thickening, haemosiderin accumulation and histological score were highly correlated and these changes occurred only in the caudodorsal part of the lung.


CONCLUSIONS
The colocalisation of these changes suggests that regional (caudodorsal) venous remodelling plays an important role in the pathogenesis of EIPH.


CONCLUSIONS
The results support the hypothesis that repeated bouts of venous hypertension during strenuous exercise cause regional vein wall remodelling and collagen accumulation, venous occlusion and pulmonary capillary hypertension. Subjected to these high pressures, there is capillary stress failure, bleeding, haemosiderin accumulation and, subsequently, lung fibrosis.
Derksen
F J
FJ
Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan 48824, USA.
Williams
K J
KJ
Pannirselvam
R R
RR
de Feijter-Rupp
H
H
Steel
C M
CM
Robinson
N E
NE
D000818:Animals; D003094:Collagen / Q000378:metabolism*; D006470:Hemorrhage / Q000209:etiology / Q000473:pathology / Q000662:veterinary*; D006485:Hemosiderin / Q000378:metabolism*; D006734:Horse Diseases / Q000209:etiology / Q000473:pathology*; D006736:Horses; D008168:Lung / Q000098:blood supply / Q000378:metabolism; D008171:Lung Diseases / Q000209:etiology / Q000473:pathology / Q000662:veterinary*; D010805:Physical Conditioning, Animal / Q000009:adverse effects*; D011667:Pulmonary Veins / Q000473:pathology
D003094:Collagen; D006485:Hemosiderin