On the role of intra-adrenal unesterified cholesterol in the steroidegenic effect of corticotropin

Addition of 10 μM of the α-adrenergic agonist phenylephrine to polymorphonuclear leukocytes suspended in glucose-free Krebs-Ringer bicarbonate buffer (pH 6.7) activated phosphorylase, inactivated glycogen synthase R maximally within 30 s, and resulted in glycogen breakdown. Phenylephrine increased ⁴⁵Ca efflux relative to control of ⁴⁵Ca prelabelled cells, but did not affect cyclic adenosine 3′,5′-monophosphate (cAMP) concentration. The effects of phenylephrine were blocked by 20 μM phentolamine and were absent in cells incubated at pH 7.4.The same unexplained dependency of extracellular pH was observed with 2.5 nM–2.5 μM glucagon, which activated phosphorylase and inactivated synthase-R, but in addition caused a 30-s burst in cAMP formation. 25 nM glucagon also increased ⁴⁵Ca efflux. The activation of phosphorylase by phenylephrine and possibly also by glucagon are thought mediated by an increased concentration of cytosolic Ca²⁺ activating phosphorylase kinase.The effects of 5 μM isoproterenol or 5 μM epinephrine were independent of extracellular pH 6.7 and 7.4 and resulted in a sustained increase in cAMP, an activation of phosphorylase and inactivation of synthase-R within 15 s, and in glycogenolysis. The effects of both compounds were blocked by 10 μM propranolol, whereas 10 μM phentolamine had no effect on the epinephrine action. The efflux of ⁴⁵Ca was not affected by either isoproterenol or epinephrine. The β-adrenergic activation of phosphorylase is consistent with the assumption of a covalent modification of phosphorylase kinase by the cAMP dependent protein kinase.Phosphorylation of synthase-R to synthase-D can thus occur independently of increase in cAMP, but the evidence is inconclusive with respect to the cAMP-dependent protein kinase also being active in this phosphorylation.