ABSTRACT

We have previously demonstrated that retinoic acid (RA) as well as thyroid hormone stimulates GH gene expression. To clarify the relationship between the action of RA and thyroid hormone, pituitary-specific gene expression was investigated further in rat pituitary cells.

Rat clonal pituitary cells, GH₃, were treated with RA with or without tri-iodothyronine (T₃) for up to 3 days. After treatment with 10–1000 nmol RA/1 with or without 0·1–10 nmol T₃/1, medium was collected for radioimmunoassay and cells were subjected to RNA extraction, and GH and prolactin gene expression was analysed using ³²P-labelled rat GH and rat prolactin cDNA probes respectively. The data demonstrated the dose–responsive manner of the stimulatory effects of RA and T₃ on GH secretion with T₃-depleted media. The action of RA was additive to that of T₃ for GH secretion when maximum effective doses of RA or T₃ were used. Using dot blot and Northern gel analysis, it was shown that RA increased GH mRNA levels in T₃-depleted media, and that this action of RA was additive to that of T₃ on the induction of GH mRNA levels. In contrast, neither RA nor T₃ stimulated the secretion of prolactin and prolactin mRNA levels in these cells.

Our results indicate that RA stimulates GH mRNA increment and GH secretion in T₃-depleted media, and that the stimulatory effect of RA is additive to the maximum effective dose of T₃.

Journal of Endocrinology (1990) 125, 251–256

Neuropeptide W (NPW) is a 30-amino-acid peptide initially isolated from the porcine hypothalamus as an endogenous ligand for the G protein-coupled receptors GPR7 and GPR8. An intracerebroventricular administration of NPW increased serum prolactin and corticosterone concentrations, decreased dark-phase feeding, raised energy expenditure, and lowered body weight. Peripherally, GPR7 receptors are abundantly expressed throughout the gastrointestinal tract; the presence of NPW in the gastrointestinal endocrine system, however, remains unstudied. Using monoclonal and polyclonal antibodies raised against rat NPW, we studied the localization of NPW in the rat, mouse, and human stomach by light and electron microscopy. NPW-immunoreactive cells were identified within the gastric antral glands in all three species. Double immunohistochemistry and electron-microscopic immunohistochemistry studies in rats demonstrated that NPW is present in antral gastrin (G) cells. NPW immunoreactivity localized to round, intermediate-to-high-density granules in G cells. NPW-immunoreactive cells accounted for 90% chromagranin A- and 85% gastrin-immunoreactive endocrine cells in the rat gastric antral glands. Using reversed-phase HPLC coupled with enzyme immunoassays specific for NPW, we detected NPW30 and its C-terminally truncated form, NPW23, in the gastric mucosa. Plasma NPW concentration of the gastric antrum was significantly higher than that of the systemic vein, suggesting that circulating NPW is derived from the stomach. Plasma NPW concentration of the gastric antrum decreased significantly after 15-h fast and increased after refeeding. This is the first report to clarify the presence of NPW peptide in the stomachs of rats, mice, and humans. In conclusion, NPW is produced in gastric antral G cells; our findings will provide clues to additional mechanisms of the regulation of gastric function by this novel brain/gut peptide.