Lactic acid release by intraarterial adrenaline infusions before and after dibenyline, and its relationship to blood-flow changes in the human forearm

Relationship between the metabolic and vasodilator effects of epinephrine in human forearm muscle

The effect of intra-arterial and intravenous epinephrine on skeletal muscle blood flow and metabolism were studied in the human forearm following complete suppression of the circulation to forearm skin by epinephrine inotophoresis. Epinephrine by either route of administration increased blood flow, O 2 consumption and CO 2 production, and decreased arteriovenous differences of O 2 and CO 2 across the forearm. The increments in blood flow did not correlate with the increments in O 2 consumption or CO 2 production. In the intact forearm intravenous epinephrine increased deep forearm venous Po 2 but not venous PCo 2 . Hypocapnia, induced by voluntary hyperventilation, did not alter the response of forearm blood flow to intravenous epinephrine. These results show that the vasodilator response of skeletal muscle vessels to epinephrine is not dependent on decrease in Po 2 or increase in PCO 2 in the environment of the high resistance vessels. They also suggest that the calorigenic effect of the hormone is not a dominant factor in its vasodilator effect in skeletal muscle.

Active transport of sodium and potassium in mammalian skeletal muscle and its modification by nerve and by cholinergic and adrenergic agents

1. Active transport of Na(+) and K(+) by Na-rich extensor digitorum and soleus muscles of rat was found to be increased considerably when muscles were innervated during enrichment with Na(+) in K-free modified Krebs solution containing 160 mM-Na at 2 degrees C and recovery in a similar fluid with 10 mM-K and 137 mM-Na at 37 degrees C, bubbled with oxygen.2. Addition of acetylcholine (2.0 mug/ml.) to recovery fluid containing denervated extensors increased active transport, whereas addition of eserine (50 mug/ml.), decamethonium (0.1 mug/ml.) and to a lesser extent tubocurarine (0.26 mug/ml.) inhibited active transport. Blocking of nerve conduction in innervated extensor inhibited K(+) uptake more than Na(+) excretion.3. The membrane potential of Na-rich extensor muscles measured soon after re-immersion in recovery fluid was higher in denervated than in innervated muscles. In the latter it was close to the K-equilibrium potential (E(K)). It is suggested that denervation here makes the Na-pump electrogenic by decreasing K(+) uptake either by decreased permeability or by inactivating a K-pump. Evidence is presented that the latter is more likely.4. Addition of isoprenaline to Na-rich soleus muscles in recovery fluid increased active transport and reduced the membrane potential measured soon after re-immersion in recovery fluid. The Na-pump still remained electrogenic in the presence of isoprenaline. It was suggested that isoprenaline might also stimulate the Na-pump, perhaps through activation of lactic dehydrogenase.