Insect prothoracic glands: a role for cyclic AMP in the stimulation of alpha-ecdysone secretion.

The prothoracic glands of the tobacco hornworm, Manduca sexta, were studied to determine if cyclic AMP is involved in the regulation of alpha-ecdysone secretion. Culturing glands in the presence of the phosphodiesterase inhibitors, aminophylline and 1-methyl-3-isobutylxanthine, caused a greater than 2-fold stimulation of ecdysone secretion while cyclic AMP alone was ineffective. Based on a dose-response analysis, 1-methyl-3-isobutylxanthine was 200 times more potent than aminophylline. Measurements of endogenous prothoracic gland cyclic AMP during the fifth larval instar demonstrated that dramatically increased levels preceded the increase in in vitro ecdysone-secretory ability. The data suggest that cyclic AMP may act as a second messenger in the stimulation of prothoracic gland alpha-ecdysone secretion by the prothoracicotropic brain hormone.