Extrahypothalamic distributions and functions of hypothalamic peptide hormones

The isolation and chemical identification of the hypothalamic hormones somatostatin, luteinizing hormone-releasing factor (LRF), and thyrotropin-releasing factor (TRF) within the last decade have allowed the chemical synthesis of these compounds and the development of radioimmunoassay and immunohistochemical methods for them. As a result, these "hypothalamic" hormones have been detected in many extrahypothalamic locations, including brain and gastroenteropancreatic tissues. The hypothalamoneurohypophysial hormones vasopressin and oxytocin have also been localized in extrahypothalamic neuronal pathways. It has become clear that these neuropeptides subserve multiple endocrine and neurotransmitter functions outside the hypothalamus. The information now available about the extrahypothalamic distributions and possible physiological roles of somatostatin, TRF, LRF, vasopressin, and oxytocin is reviewed.