Insects prothoracic hormone

The similarities between ecdysone synthesis in the insect prothoracic gland and the ovary are obvious and in each case synthesis is initiated in response to a hormone originating in the brain. Both bear a striking resemblance to the mammalian system where steroid hormone synthesis in the various endocrine tissues is initiated in response to the release of appropriate hormones from the anterior pituitary. 

Triterpenes Ecdysone, ecdysterone Insects (Prothoracic gland) Molting hormones... 

The main types of insect-specific hormone are a-ecdysone, from the prothoracic glands, which causes moulting the brain hormone that stimulates the prothoracic glands and the juvenile hormone, in the corpora allata, which causes metamorphosis. Further, the corpus cardiacum releases a hormone that increases the amplitude of the muscles of heart and gut (Davey, 1964), and also an adipokinetic hormone which regulates the use of lipids as a source of energy in flight (Stone et al. 1976). 

Ecdysone is a steroid that is formed and secreted by the prothoracic glands of immature insects but also by the ovaries of adult female insects. It was first isolated from the silk worm, Bombix mori. Bedstone is the prohormone of the moulting hormone eedysterone, but the prohormone has also effects on its own at other stages of insect development. 

Hormones have an important role in insect metamorphosis. In many species, two classes of hormones, moltirp hormones (made by the prothoracic glands) and juvenile hormones (made by the corpora allata) act together to control metamorphosis. Each regulates the expression of different genes, so that a charpe in their relative concentrations causes metamorphosis, the development of different body patterns. 

Molting, which is defined as the shedding of an outer covering as part of a periodic process of growth, is central to the development of insects. Release of ecdysteroids, or molting hormones, from the prothoracic glands is controlled by a neuropeptide called the prothoracicotropic hormone (PTTH) produced by neurosecretory cells and released by corpora cardiaca. 

In insects, ecdysone is secreted from the prothoracic glands (PG) at every moulting and pupal stage. Conversion of ecdysone to 20-hydroxyecdysone occurred in fat body, Malpighian tubules, gut and body wall tissues [189]. Although ecdysone may have direct hormonal effects, it is generally held that ecdysone serves as a prehormone that is converted to 20-hydroxyecdysone which functions as the active hormone. This is because in many bioassay systems, 20-hydroxyecdysone appears to be much more active than ecdysone. 

In insects and in crustaceans, the synthesis of both ecdysteroids and JH/MF are subject to control by neuropeptides. Although ecdysteroids are considered to be growth promoting hormones in both insects and crustaceans, these steroid hormones are differently regulated in the two taxa. In insects, the synthesis and release of ecdysteroids from the prothoracic gland is positively regulated by the prothoracicotropic hormone (PTTH) which is synthesized in neurosecretory cells of the brain and released from the CA [37]. PTTH was first completely identified in B. 

Fig. I. Hormonal control of insect development. Three hormones are involved the brain hormone, acting on the prothoracic glands, the juvenile hormone, secreted by the corpora allata and ecdysone, secreted by the prothoracic glands. The bottom row shows the development from the caterpillar through the pupa to the moth. The larval ecdyses are controlled by ecdysone and juvenile hormone, but the pupal and imaginal ecdyses are induced only by ecdysone. (from P. Karlson, Lehrbuch der Biochemie, with kind permission of G. Thicme Verlag, Stuttgart.)...

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