Organic Origin, Development and Change in Anuran Larvae to the Completion of Metamorphosis
The preceding account emphasises that in order to prepare for terrestrial life amphibian larvae, especially of anurans, undergo a complex metamorphosis that embraces elaborate morphological, biochemical, physiological, and behavioral changes. During premetamorphosis there is no real effective level of hormonal secretion in the circulation (Myauchi et al., 1977) and thyroid activity is minimal (Etkin and Gona, 1974). From the end of premetamorphosis (at the hindlimb bud stage) through prometamorphosis and climax (Etkin, 1964, 1970) larval development is under endocrinological control of high complexity (Dodd and Dodd, 1976). Thyroxine and triiodothyronine from the thyroid, growth promotion hormone(s) from the pituitary, and possibly glucosteroids of the interrenals, act directly (or indirectly in some way) on reactive larval tissues. These hormones are influenced in their synthesis and release by thyroid stimulating hormone(s) (TSH) and adrenocorticotropic hormone(s) (ACTH) of the pituitary, and by the hypothalamus, which secretes a thyroid releasing factor (TRF) controlling the activity of TSH and possibly the growth promoting hormone(s) of the pituitary (Etkin and Lehrer, 1960). Indeed extirpation of the hypothalamus wholly inhibits metamorphosis (Voitkevitch, 1962; Dodd and Dodd, 1976).
KeywordsThyroid Hormone Xenopus Laevis Nerve Cord Granular Endoplasmic Reticulum Rana Pipiens
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