On the action of RH 5849, a nonsteroidal ecdysteroid agonist, on a cell line from Chironomus tentans

RH 5849 competes with 3 H‐ponasterone A for ecdysteroid binding sites in Chironomus tentans cells with an about fourfold lower relative affinity as compared to 20‐OH‐ecydsone. It does not interfere with glucocorticoid and estrogen binding sites in vertebrates. It is also not recognized by an ecdysteroid antibody. RH 5849 exerts typical morphological and physiological effects ascribed to the action of 20‐OH‐ecdysone on C. tentans cells, namely an increase in acetylcholinesterase activity and an inhibition of chitin synthesis.