Thyroliberin (TRH) and TRH free acid (TRH-OH) present in milk do not originate from local synthesis in mammary gland.
Résumé
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.