Vasoconstrictor-mediated thermogenesis present in perfused skeletal muscle but absent from perfused heart

Resting muscle thermogenesis as controlled by vasocontrictors was compared in rat hindlimb and cardiac muscle. An α-adrenergic agonist combination of phenylephrine + atenolol increased oxygen uptake and perfusion pressure in the constant flow hindlimb and neither increase was blocked by 10 μM tetrodotoxin. The same adrenergic combination also increased oxygen uptake and perfusion pressure in the perfused heart but the former along with beating was Completely blocked by tetrodotoxin. Vasoconstriction by phenylephrine occurs in the heart but is not linked to thermogenic increases as in hindlimb, implying that all metabolic energy in heart is conserved for contractile activity. The findings highlight a fundamental difference between skeletal and cardiac muscle. © 2002 Elsevier Science Ltd. All rights reserved.