In mammals, extensive studies have documented the presence of GR immunore-activity in catecholamine^c neurons, and it is well known that glucocorticoids and/or dexamethasone increase the steady-state levels of TH mRNA under various stress conditions in vivo and in vitro. However, the precise sites for GR binding on the TH promoter remain unidentified, raising the possibility that multiple elements on the TH gene act in a cooperative fashion to promote transcriptional regulation by glucocorticoids. Therefore, as TH is the rate-limiting enzyme for catecholamine synthesis, it is possible that cortisol increases the TH transcription and ultimately the dopamine stores in the ventral preoptic area. This could eventually lead in rainbow trout to increased dopaminergic inhibition of GTH-2 secretion, although this remains to be demonstrated. ventolin 100 mcg
The present study also shows that virtually all GTH-1 and GTH-2 cells express rtGR in vitellogenic female rainbow trout, indicating that those cells are potentially subject to direct cortisol regulation. Similar observations have been reported in the rat pituitary gland, in which a large majority of both FSH and Lh cells were shown to exhibit GR im-munoreactivity. Such results may account for some of the known physiological effects of glucocorticoids on GTH synthesis and release.