Adenylate Cyclase Activity in Rat Adipocyte Plasma Membranes after Adrenalectomy and Administration of Cortisone Acetate

Abstract

Adenlyate cyclase activity in rat adipocyte membranes was studied with special reference to the effects of adrenalectomy and administration of cortisone acetate in vivo. The lipolytic hormones ACTH, PTH and noradrenaline were used as stimulators.

Adrenalectomy was accompanied by an increased formation rate of cyclic AMP during basal conditions, which was maintained even seven days after operation. The response to hormonal stimulation, measured as the ratio between stimulated and basal values, was unchanged one day after adrenalectomy but hampered one week postoperatively.

Subcutaneous injection of high doses of cortisone acetate was not accompanied by any changes in cyclic AMP formation rate under basal conditions or in the responsiveness to hormonal activation.

Membranes from adrenal deficient or cortisone injected rats exhibited the same sensitivity to calcium inhibition as the controls. EGTA increased adenylate cyclase activity similarly in membranes from cortisone treated and sham-operated rats. Membranes from adrenalectomized animals were only slightly stimulated by calcium deprivation.

It was concluded that glucocorticoid hormones per se do not affect cyclic AMP formation rates basally or during hormonal activation. However, adipocyte membranes from steroid deficient rats have a diminished capacity to bind calcium, which secondarily will affect basal as well as hormonally activated adenylate cyclase activity.

Key words

Adenylate Cyclase - Cyclic AMP - Adrenalectomy - Cortisone - Calcium