Abstract
Immunoreactive thyrotrophin-releasing hormone (iTRH), growth hormone release-inhibiting hormone (iGH-RIH), and luteinizing hormone-releasing hormone (iLH-RH) were measured in spontaneously developing Xenopus laevis tadpoles at various stages of metamorphosis. All three peptides were detected in animals at all stages of metamorphosis. Brain iTRH concentration increased markedly during prometamorphosis and metamorphic climax; skin iTRH concentration was low during prometamorphosis and increased at metamorphic climax. Brain iGH-RIH concentration increased to a maximum at prometamorphosis, then declined during climax; gastrointestinal tract iGH-RIH concentration increased progressively as metamorphosis proceeded; skin iGH-RIH concentration was low throughout metamorphosis. Brain iLH-RH concentration increased progressively during metamorphosis. The widespread tissue distribution of these hypophysiotrophic peptides suggests they might have endocrine and paracrine functions in amphibians. The rise in brain iTRH concentration during early prometamorphosis suggests that hypothalamic secretion of TRH might be the initiating event in thyroid hormone production and metamorphosis.
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