Glycogen phosphorylase activation by progesterone in liver.

Glycogen phosphorylase activity is increased before protein synthesis activation by progesterone. This effect is not blocked by antibiotics (actinomycin D and cycloheximide) that are known to inhibit mRNA or protein synthesis. At times similar to those of phosphorylase activation, cAMP are not enhanced, as would be expected considering the classical glycogenolytic cascade, but depleted with respect to control values. A little earlier, cGMP levels are significantly increased.