Activation of hypothalamo-hypophysial-interrenal system by urophysectomy in goldfish.

Plasma cortisol, pituitary adrenocorticotropin and arginine vasotocin (AVT) contents, and hypothalamic urotensin I (UI) and AVT contents were determined in urophysectomized goldfish (1 wk) with and without dexamethasone injections. Urophysectomy produced marked increases in plasma cortisol. These marked increases could not be observed in urophysectomized fish that received dexamethasone injections. These findings suggest that the hypothalamo-pituitary-interrenal axis is activated after urophysectomy. This activation may be due to the enhanced secretion of U I from the goldfish hypothalamus, suggesting that U I may be a fish corticotropin-releasing factor.