Effect of cordycepin on CRF stimulation and steroid inhibition of ACTH secretion by rat pituitary cells.

Isolated pituitary cells prepared from adrenalectomized rats secrete ACTH in response to CRF, and this response is inhibited by corticosterone. Both the stimulation of release by CRF and the inhibition of release by corticosterone are antagonized by cordycepin (3'-deoxyadenosine). Inhibition of CRF-stimulated secretion by cordycepin is apparently not related to inhibition of RNA synthesis, since high doses of actinomycin D do not affect ACTH secretion. More likely, cordycepin's inhibition of secretion stems from its inhibition of adenylate cyclase activity. Inhibition of corticosterone action by cordycepin is qualitatively similar to that previously reported actinomycin D. This effect of both drugs is probably due to inhibition of RNA synthesis. Significantly, a low dose of cordycepin has a greater inhibitory effect on corticosterone action than on total cellular RNA synthesis. Cordycepin is reported to preferentially inhibit messenger RNA synthesis, and low dose preferentially inhibits appearance of cytoplasmic RNA in pituitary cells. These data suggest that corticosterone-induced RNA is a cytoplasmic (messenger) RNA.