| Abstrakt: |
SYNOPSIS. The mammalian hypothalamic releasing factors regulating thyroid, gonadal and adrenal function as well as growth hormone secretion have been isolated, characterized and their nucleotide sequences determined. In general, their hypophysiotropic effects are replicated in lower vertebrates though thyrotropin releasing hormone (TRH) does not appear to stimulate thyroid function in amphibia and fish. The releasing factors, or peptides structurally related to these substances, are found throughout the CNS of all vertebrates where they likely function as neurotransmitters or neuromodulators. High concentrations of TRH and other neural peptides includingsauvagine, which is related to corticotropin releasing factor (CRF) and has CRF-like activity, are found in amphibian skin, a neural crest derived tissue. mRNA extracted from the skin of was cloned and led to the identity of the DNA sequence of pre-pro TRH. Molecular variants of somatostatin have been recognized from studies on the pancreatic islets of the anglerfish and catfish. Within mammalian species there is heterogeneity of growth hormone releasing factor (GRF), the 44 (and 40) amino acid peptides isolated from a human(h) pancreatic tumor. In the teleost brain-pituitary, 2 distinct hGRF-like neuronal systems are present. Additionally, various molecular forms of hGRF exist in the fish brain showing structural changes from the human variety. [ABSTRACT FROM PUBLISHER] |
