Influences of water deprivation and fasting on hypothalamic, pituitary and plasma opioid peptides and prolactin in rats.

To study the physiological roles of endogenous opioid peptides in drinking and feeding behaviors, the effects of water deprivation and fasting on plasma immunoreactive (IR) beta-endorphin (beta-end), IR-Antidiuretic hormone (ADH) and IR-Prolactin (Prl), pituitary IR-beta-end and IR-methionine-enkephalin (IR-Met-enk) and IR-ADH, and hypothalamic IR-beta-end and IR-Met-enk were observed in rats. The effects of water deprivation on hypothalamic dopaminergic system was also studied. In water deprived rats, plasma IR-beta-end and Prl were decreased significantly. In the neurointermediate lobe, IR-Met-enk, but not IR-beta-end, was decreased, although these peptides did not change in the anterior lobe and hypothalamus. Intraperitoneal injection of haloperidol reversed the decrease in plasma IR-beta-end in water deprived rats but did not change it in control rats. Subcutaneous injection of CB-154, on the other hand, decreased the plasma IR-beta-end in control rats but not in water deprived rats. The dopamine (DA) turnover rate in hypothalamus, in addition, was increased in water deprived rats as compared with controls. In fasted rats, IR-beta-end in plasma, but not in pituitary lobes and hypothalamus, was increased. The present results suggest that the increase of hypothalamic dopaminergic activity, in part, is related to the suppressed secretions of pituitary IR-beta-end and Prl in water deprivation, and plasma IR-beta-end play some roles in feeding behavior in rats.