Tm. Byrem et al., CHARACTERIZATION OF DOSE-DEPENDENT METABOLIC RESPONSES TO CLOSE ARTERIAL INFUSION OF CIMATEROL IN THE HINDLIMB OF STEERS, Journal of animal science, 74(12), 1996, pp. 2907-2916
Dose-dependent effects of cimaterol (CIM) on hindlimb metabolism were
determined in six steers (247 +/- 22 kg BW) using a close arterial inf
usion. The external iliac vessels of both hindlimbs were catheterized
to accommodate measurement of blood flow, circulating concentrations,
and net flux of NEFA, lactate, and alpha-amino nitrogen (AAN) during i
nfusion of CIM at 0,.05,.1,.3,.7, 1, and 3 mu g/min. Close arterial in
fusion of CIM in the hindlimb of steers can be used to achieve a local
concentration elevation that is required to differentiate local and s
ystemic effects in vivo. Calculated plasma threshold CIM concentration
required to initiate cardiovascular responses was 21 pg/mL, which res
ulted from an infusion rate of .3 mu g/min. Threshold concentrations o
f CIM for stimulation of NEFA and lactate net flux in the hindlimb wer
e 38 and 34 pg/mL, respectively, and would be achieved with an infusio
n rate of .7 mu g/min. All measured responses except AAN net flux exhi
bited significant linear and quadratic dose effects, and responses in
the treated hindlimb were always severalfold greater than in the contr
alateral control hindlimb. Maximal differences between treated and con
trol hindlimb blood flow occurred with a CIM infusion rate of .7 mu g/
min, but the highest infusion rate (3 mu g/min) was required to maximi
ze differences in NEFA and lactate flux. Therefore, to minimize cardio
vascular and other systemic responses and optimize direct hindlimb res
ponses, an infusion rate of .5 mu g of CIM/min should cause significan
t stimulation of beta-adrenergic receptors only in the CIM-infused hin
dlimb of young, growing steers.