1. Synephrine and other related monophenolic drugs were tested for potency of luminescence induction in the extirpated lantern of larval fireflies. Synephrine was found to be the most potent drug so far tested, with a threshold concentration of 10-6M.
2. Immersion of glowing lanterns in a solution containing 10-3M synephrine and 10-3M-KCN resulted in rapid extinction of luminescence. Luminescence extinction times in KCN were found to be proportional to synephrine concentration and suggest that only a small ATP pool exists in the lantern. It is hypothesized that synephrine must stimulate ATP production in order to maintain high luminescence intensities.
3. The vertebrate adrenergic blocking agent, dichloroisoproterenol (D.C.I.), was found to slowly induce luminescence which eventually declined to extinction. Synephrine was ineffective in luminescence induction after the declining phase of D.C.I, action began. A close analogue of D.C.I., isoproterenol, acted in a weak but similar manner to synephrine. It is suggested that D.C.I, prevents synephrine action by blocking the photocyte receptor sites.