RESUMO
UNLABELLED: Hypothalamic hormones represent a peculiar group of hormones present in milk in surprisingly high concentrations. High levels of these neuropeptides raised the question of their origin. The hypothesis suggesting local synthesis of TRH in the mammary gland was, therefore, tested. Acid extracts of human milk contained TRH and TRH-OH immunoreactivity. RIA determinations at various purification steps revealed that only a part of the immunoreactivity may represent authentic peptides. No high molecular weight TRH precursor could be demonstrated upon a sequential enzymatic treatment of human milk and rat mammary gland extracts. Exploration of rat mammary gland tissue for TRH mRNA showed that the TRH gene is not expressed in the mammary gland. Rat mammary gland homogenates were able to deamidate exogenous TRH to TRH-OH. CONCLUSION: TRH is not synthesized in the mammary gland via a high molecular weight precursor. It is likely that the TRH-free acid in milk (demonstrated for the first time in this product) originates from TRH deamidation in mammary gland cells during TRH transport from the blood.
Assuntos
Mama/metabolismo , Leite Humano/química , Hormônio Liberador de Tireotropina/análogos & derivados , Hormônio Liberador de Tireotropina/análise , Mama/química , Desaminação , Feminino , Expressão Gênica , Humanos , Leite Humano/metabolismo , Peso Molecular , Precursores de Proteínas/genética , Precursores de Proteínas/metabolismo , Ácido Pirrolidonocarboxílico/análogos & derivados , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Radioimunoensaio , Hormônio Liberador de Tireotropina/genética , Hormônio Liberador de Tireotropina/metabolismoRESUMO
The decrease of DNA fluorescence caused by an impaired capacity of ethidium bromide to intercalate into the DNA reflected structural changes caused in the DNA molecule by its interaction with platinum complexes. This fall in DNA fluorescence was proportional to the length of exposure of DNA to the platinum complexes, and depended on the environment in which the interaction took place. The therapeutically active cisplatinum (cis-DDP) was more efficient to inhibit fluorescence in a solution of 4 X 10(-3) mol NaCl than its therapeutically inactive trans-isomer (trans-DDP). For comparison, the inhibition of DNA fluorescence was also studied in a solution of 10(-2) mol NaClO4. The inhibitory effect was elicited more rapidly, but no difference was found between the two isomers. We concluded that the larger effect of cis-DDP on DNA was induced by the 4 X 10(-3) mol concentration of NaCl. Since also the intracellular concentration of chloride ions is 4 X 10(-3) mol, it cannot be ruled out that the interaction between DNA and cis-DDP and trans-DDP in vivo might be influenced by the intracellular environment.