Influence of exercise and joint topography on depth-related spatial distribution of proteoglycan and collagen content in immature equine articular cartilage.
BACKGROUND
There is ample evidence on topographical heterogeneity of the principal biochemical components of articular cartilage over the surface of the joint and the influence of loading thereon, but no information on depth-related zonal variation in horses.


OBJECTIVE
To study depth-related zonal variation in proteoglycan (PG) and collagen content in equine articular cartilage.


METHODS
Two techniques (safranin-O densitometry and Fourier transform infrared spectroscopy) were applied to sections of articular cartilage from the proximal phalangeal bone of the metacarpophalangeal joint of 18-month-old Thoroughbreds that had been raised at pasture from age 0-18 months without (PASTEX) and with (CONDEX) additional exercise. Two sites were investigated: site 1 at the joint margin that is unloaded at rest or at slow gaits, but subjected to high-intensity loading during athletic activity; and site 2, a continuously, but less intensively, loaded site in the centre of the joint.


RESULTS
Proteoglycan values increased from the surface to the deep layers of the cartilage, collagen content showed a reverse pattern. PG content was significantly higher at site 2 in both PASTEX and CONDEX animals without an effect of exercise. In the PASTEX animals collagen content was significantly higher at site 1, but in the CONDEX group the situation was reversed, due to a significant exercise effect on site 1, leading to a reduced collagen content.


CONCLUSIONS
Collagen and PG content gradients agree with findings in other species. The observations on PG levels suggest that the exercise level was not strenuous. The collagen results in the PASTEX group confirmed earlier findings, the lower levels at site 1 in the CONDEX group being possibly due to an advancement of the physiological maturation process of collagen remodelling.


CONCLUSIONS
This study confirms earlier observations that even moderate variations in exercise level in early age may have significant effects on the collagen network of articular cartilage.
Section of Veterinary Surgery, School of Agriculture, Food Science & Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland.
P A J
PA
Brama
J
J
Holopainen
P R
PR
van Weeren
E C
EC
Firth
H J
HJ
Helminen
M M
MM
Hyttinen
D000375:Aging; D000818:Animals; D002358:Cartilage, Articular / Q000502:physiology*; D003094:Collagen / Q000378:metabolism*; D003720:Densitometry; D005260:Female; D005552:Forelimb; D006736:Horses / Q000502:physiology*; D007596:Joints / Q000033:anatomy & histology*; D008297:Male; D010805:Physical Conditioning, Animal / Q000502:physiology*; D011509:Proteoglycans / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared
D011509:Proteoglycans; D003094:Collagen