Age-related changes seen in a study of the major arteries of horses

An example of the proximal aorta, mounted in the pressurisation system, but not in the salt water bath in which the pressure test was conducted.
An example of the proximal aorta, mounted in the pressurisation system, but not in the salt water bath in which the pressure test was conducted. The lower image shows the ultrasound images derived at 30mmHg, left, and 300mmHg, right. Vera et al.

Researchers have described changes that occur in the ageing blood vessels of Warmbloods, which go some way toward explaining why arterial rupture is a well-recognised cause of sudden death in horses.

Lisse Vera and her fellow researchers at Ghent University, Belgium, noted that arterial ruptures affected mainly older horses.

The arterial wall is known to stiffen with age, they said, although the underlying age-related microscopic and biomechanical changes remain unclear.

Vera and her colleagues set out to investigate the effect of aging by microscopic analysis of the arterial wall and examination of their biomechanical properties using an inflation-extension test.

Circular sections of the proximal and distal aorta, carotid, external iliac, femoral and median arteries were collected from 14 Warmbloods aged 15 or older, and six younger Warmbloods.

All had been euthanized for clinical reasons, none of which involved cardiovascular issues.

Samples of all arteries were examined under the microscope to assess the thickness of the intima media thickness (the innermost two layers of the artery wall), as well as the area percentage of elastin, smooth muscle actin, and collagen type I and III.

Older horses were found to have a significantly larger intima media thickness. The older horses also had a significantly higher area percentage of smooth muscle actin when compared to young horses. The researchers found no age-related differences in the amount of elastin and collagen.

Samples of the aorta, the caudal common carotid and the external iliac artery were mechanically assessed using a specially developed inflation-extension device, with ultrasound analysis.

Rupture occurred in eight of the 78 artery samples tested at high pressures (between 250–300 mmHg). All but one of the eight ruptures occurred in tissue samples from the older horses.

The study team, whose findings are reported in the journal PLOS ONE, also explored how the pressure affected the arteries, finding significant differences between the two age groups. They found significant differences in the pressure-area curves of the lower aorta, common carotid artery and external iliac artery, the pressure-compliance curves of the proximal aorta and carotid artery, and the pressure-distensibility curve of the proximal aorta between young and old horses.

The results, they said, demonstrate an effect of age on the microscopic and biomechanical properties of the arterial wall, which might explain why arterial rupture occurs more often in older horses.

Discussing their findings, the researchers said their study showed a significant effect of location on the amount of elastin in the arterial wall.

The largest amount of elastin was found in the proximal aorta, while the lowest amount was found in the median artery and the external iliac artery.

The highest area percentage of collagen type III, on the other hand, was found in the distal aorta, external iliac artery and femoral artery.

The present study also revealed age-related arterial wall thickening in horses, a phenomenon that has been described in human patients, although it seemed to be for different reasons.

The Ghent University team comprised Vera, Sofie Muylle, Glenn Van Steenkiste, Patrick Segers, Annelies Decloedt, Koen Chiers and Gunther van Loon.

Vera L, Muylle S, Van Steenkiste G, Segers P, Decloedt A, Chiers K, et al. (2021) Histological and biomechanical properties of systemic arteries in young and old Warmblood horses. PLoS ONE 16(7): e0253730.

The study, published under a Creative Commons License, can be read here

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