Corticotropin-releasing factor accelerates metamorphosis in Bufo arenarum:Effect on pituitary ACTH and TSH cells

The actions of several neuropeptides as hypothalamic mediators in the regul ation of Bufo arenarum metamorphosis were investigated. Prometamorphic larv ae were injected with 1.5 mu g thyrotropin-releasing hormone (TRH), 2 mu g ovine corticotropin-releasing factor (oCRF), 2 mu g mammalian gonadotropin- releasing hormone (mGnRH), 2 mu g human growth hormone-releasing hormone (h GHRH), or Holtfreter solution (control group). Larvae received two injectio ns with the same dose: one at the beginning of the experiment and the other 7 days later. Several morphologic parameters (total length, tail length, w et weight, hind limb length, and metamorphic stages) were measured as indic ators of growth and metamorphic development. These measurements were taken in 20 larvae per treatment or control group at the beginning of the experim ent, at day 7 and at day 14 when the experiment ended. We observed that onl y the administration of exogenous CRF stimulated resorption of the tail and accelerated the rate of metamorphosis. In the pituitary of CRF-treated lar vae we observed that thyrotropin (TSH) and adrenocorticotropic hormone (ACT H) producing cells' showed a weaker immunoreactivity, a decrease in cell nu mber and a reduction of volume density when compared with normal larvae. In conclusion, the results obtained indicate a possible role for CRF in Bufo arenarum metamorphosis. CRF may regulate interrenal and thyroid activity by acting directly upon TSH and ACTH cells. On the other hand, TRH, GnRH and GHRH were inactive in stimulating growth or metamorphosis of Bufo arenarum. (C) 2000,Wiley-liss, Inc.