Studies on Peptide 23: A GHRH-Regulated Protein of the Pituitary and Gastrointestinal Tract

Abstract

The two hypothalamic hormones, growth hormone-releasing hormone (GHRH) and somatostatin (SRIF), are the principal regulators of pituitary growth hormone (GH) secretion. There are other hypothalamic factors that influence GH secretion both directly and indirectly. As well there is a growing body of evidence indicating that intrapituitary factors influence GH secretion through paracrine or even autocrine effects. The list of putative paracrine regulatory factors is a very long one (Jones et al. 1990 O’Halloran et al. 1991) (Table 1). As new peptides are discovered with increasing frequency many have been found to affect GH secretion. If as well they are found to be synthesized in the pituitary the conclusion frequently drawn is that they may be paracrine regulators of GH secretion. However, as pointed out by O’Halloran et al. (1991), a number of conditions must be met to establish a paracrine role for any of the putative regulatory factors. As well the influence may not only be on secretion of GH but also on GH cell proliferation or differentiation.