The responses of plasma free fatty acid, glucose, lactate, insulin and growth hormone to intravenous administration of the predominantly β-2 stimulant, salbutamol, were studied in nine normal subjects. Four subjects received the predominantly β-1 blocking agent, practolol, together with salbutamol. Salbutamol produced a marked rise in free fatty acid levels and there was also an appreciable increase in insulin values; lactate levels rose moderately and glucose values increased slightly; growth hormone levels were not affected. Practolol did not alter the free fatty acid response; it diminished but did not appear to abolish the insulin response, and it appeared to suppress the lactate and glucose rises. Tentative proposals are made regarding the nature of the preceptor subtypes responsible for mediating these effects; most definite is the suggestion that lipolysis is subserved by β-2 receptors. Possible clinical implications are briefly discussed.
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