Five clinically healthy Thoroughbred geldings were injected with Freun
d's adjuvant 3 times to induce a chronic inflammatory response, Blood
was collected at various times before and after adjuvant administratio
n. Clinical responses (rectal temperature and general demeanour) were
also monitored, Adjuvant injection induced increases in rectal tempera
ture and plasma fibrinogen concentration (maximum levels measured were
mean +/- s.d. 39.7 +/- 0.5 degrees C and 8.2 +/- 0.3 g/l, respectivel
y), indicative of an inflammatory response. A mild clinical depression
was also observed in the horses for 24 h after the first injection of
adjuvant only, Plasma cortisol levels decreased significantly from co
ntrol levels of mean +/- s.d. 187.7 +/- 24.3 nmol/l to a minimum of 80
.2 +/- 221 nmol/l (P<0.01) 9 days after the first injection of adjuvan
t. Conversely, plasma insulin levels increased after the first injecti
on of adjuvant to a maximum (96.7 +/- 15.2 iu/ml; P<0.01) 12 days late
r, while plasma glucose concentrations tended to decline. A control gr
oup of horses to rule out contemporary environmental influences on the
physiological and biochemical indices measured was not included in th
is study, The results show that chronic inflammation in the horse depr
essed resting plasma cortisol concentrations.