CHARACTERIZATION OF DOSE-DEPENDENT METABOLIC RESPONSES TO CLOSE ARTERIAL INFUSION OF CIMATEROL IN THE HINDLIMB OF STEERS

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.