What are ecdysteroids? Insect hormones, essential mammalian D-vitamins or polar sterols used for growth in plants?

      The polyhydroxylated derivatives of 6-keto,7-dehydro-cholesterol (Ecdysteroids; Ec) are distributed  in 251 species of taxonomically unrelated plants. They were accidentally discovered in the  search for an insect moulting hormone in the late 1960ies. It was believed at that time that the insect moulting hormone had been released from special prothoracic glands (PG) for the stimulation of ecdysis. Accordingly, the first Ec isolated from pupae of the silkworm, Bombyx  mori, was named ecdysone. After the identification of ecdysone, a number of similar Ec were found in varous plants, occasionally in amounts surpassing by a million-fold the content of Ec in insects.  After 1970, the ability to produce Ec was encountered in insect tissue and organs other than PG, such as in oenocytes, disintegrating larval muscles or pupal intestine. However,  the production of Ec by various peripheral organs  is in serious conflict with the definition of an animal hormone. The administration of Ec into vertebrate animals resulted in the stimulation of muscle and bone growth in Japanese quails, anabolic growth effects in mice, rat, swine, cattle and other domestic animals.These vitamin-like effects of Ec, were corroborated by pronounced pharmacological effects  (anabolic, tonic, immunogenic, antiallergenic, neurogenic, metabolism stimulating) in human patients in the clinique. Within the polar milieu of the plant system, Ec were reported to be used as a source of polar, easily mobilised sterol required for the growth of plant tissue, although Ec had no property of growth hormone in plants. These facts strongly imply that Ec constitute a  biologically and pharmacologically very important class of the amphoteric, water and lipid soluble D-vitamins, whose pharmacological qualities have been neglected for a long time due to a persistent belief in the PG hormone of insects.