Increased adenylate cyclase catalytic activity explains how estrogens “in vivo” promote lipolytic activity in rat white fat cells

Estradiol administration (5 μg per day × 4 days) to ovariectomized rats resulted in a 60–70 % increase in the maximal lipolytic response of their white adipocytes to isoproterenol, epinephrine, IBMX and forskolin. These altered lipolytic responses were accompanied by parallel changes in the intracellular cyclic AMP levels found in response to 1 mM IBMX alone (+ 106 %) or combined with submaximal concentrations of isoproterenol (+ 205 %), epinephrine (+ 190 %) and forskolin (235 %). Studies of the adenylate cyclase activity revealed an overall increase in the stimulatory responsiveness of the enzyme (+ 150 to + 200 %) after the estradiol-treatment, regardless of the stimulatory agents tested (GTP, GppNHp, fluoride, isoproterenol, ACTH, forskolin). Finally, the finding of a 2-fold enhancement of the Mn 2+ (± GDP β S)-stimulated adenylate cyclase activity after the estradiol-treatment strongly suggests that increased activity of the catalytic subunit of this enzyme is the likely mechanism whereby estrogens promote lipolysis in rat fat cells.