Pd. Guirnalda et al., Effects of age and recombinant equine somatotropin (eST) administration onimmune function in female horses, J ANIM SCI, 79(10), 2001, pp. 2651-2658
Aging has been associated with declines in somatotropin and IGF-I levels as
well as declines in immune function. To determine the effects of age and w
hether ST administration could reverse immunosenescence in horses, eight yo
ung and eight aged female standardbred horses were given 10 mg/d recombinan
t equine somatotropin (eST) or vehicle buffer for 49 d. Plasma IGF-I concen
trations in both age groups were higher in eST-treated animals (P < 0.001),
and higher in young eST-treated mares than in aged eST-treated mares durin
g wk 4 to 7 (P < 0.001). There was a trend toward lower monocyte and granul
ocyte numbers (P = 0.07) in mares treated with eST. Aged mares treated with
eST had lower lymphocyte numbers (P < 0.005). The percentage of CD4(+) lym
phocytes was higher in aged mares (P < 0.001), and the percentage of CD8(+)
lymphocytes was higher in young mares (P < 0.01). Lymphocyte proliferation
in response to concanavalin A, phytohemagglutinin, and pokeweed mitogen wa
s not lower in aged mares (P = 0.17, 0.17, and 0.13 respectively). Aged mar
es treated with eST showed a lower peak primary antibody response to keyhol
e limpet hemocyanin (P < 0.05). Young mares treated with eST showed a highe
r peak primary antibody response to keyhole limpet hemocyanin (P < 0.05). L
ike other species, horses exhibit similar signs of age-related declines in
various immune parameters, but those of aging were not reversed with eST tr
eatment.