The effects of catecholamines on protein metabolism in pigs and sheep
Using a constant infusion of 1-('14)C leucine and 4,5-('3)H (alpha)-ketoisocaproate (KIC), the rates of whole-body leucine and KIC metabolism were estimated in pigs during acute infusions of epinephrine (EPI) and norepinephrine (NOR), and in sheep during acute infusins of EPI, NOR and a specific (beta)(,2)-adrenergic agonist, cimaterol (CIM). The pigs and sheep responded similarly to EPI, with decreased rates of leucine entry (proteolysis in the pigs, and proteolysis and absorption of amino acids in the sheep) and protein synthesis. EPI infusion in the sheep also resulted in increases in leucine and KIC interconversion. NOR infusion produced decreases in the rates of proteolysis, protein synthesis, leucine and KIC interconversion, and KIC oxidation in the pigs, but had no significant effect on protein metabolism in the sheep. Acute infusions of CIM in the sheep resulted in decreases in the rates of leucine entry, protein synthesis and reamination of KIC to leucine. Glucose concentrations rose during all infusions, while free fatty acid (FFA) levels were elevated during NOR infusion in both species and during EPI infusion in the sheep. Insulin concentrations increased during the infusion of all adrenergic agents in sheep, but did not change in the pigs. Plasma glucagon concentrations increased during the EPI infusion in the sheep and the NOR infusion in the pigs, but decreased during the CIM infusion. Cortisol concentrations rose during NOR infusion in both species, but were unaffected by the other treatments. Despite a general increase in insulin to glucagon ratios with catechol infusion, whole-body protein anabolism was not evident in these acute studies. Differences may exist, however, in individual tissues which may change the distribution of body proteins. The changes in metabolite concentrations in the plasma indicate that acute infusions of these compounds increase the supply of readily available energy in the plasma. The supply of energy would be further supplemented as a result of the reduction in protein turnover seen in these experiments.