Dehydration reduces kappa-opiate receptor binding in the neurohypophysis of the rat.
Quantitative autoradiography was used to examine the effects of dehydration on kappa-opiate receptor binding in the neural lobe of the pituitary in rats. Dehydration was produced by 5 days of water deprivation or ingestion of 2% saline. Brattleboro rats homozygous for diabetes insipidus were used as a model of chronically disturbed water balance. Slide-mounted pituitary sections were incubated with [3H]bremazocine using kappa-receptor-selective assay conditions. Binding in the neural lobe was quantified by densitometry of film autoradiographs. Specific [3H]bremazocine binding in neural lobe sections of control rats was 45.4 fmol/mg wet weight. In contrast, binding in neural lobe sections of water-deprived, saline-treated, and water-sated homozygous Brattleboro rats was lower by 50%, 35% and 37%, respectively. We suggest that chronic dehydration elevates levels of endogenous neurohypophyseal dynorphin and produces a down-regulation of kappa-opiate receptors in the neurohypophysis, a change in affinity of the receptors for kappa-agonists, or both.
Brady
L S
LS
Unit on Functional Neuroanatomy, National Institute of Mental Health, Bethesda, MD 20892.
Herkenham
M
M
D000818:Animals; D001575:Benzomorphans / Q000378:metabolism; D001835:Body Weight; D003681:Dehydration / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D003720:Densitometry; D004326:Drinking; D008297:Male; D010904:Pituitary Gland, Posterior / Q000378:metabolism*; D051381:Rats; D011910:Rats, Brattleboro; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000378:metabolism*
D001575:Benzomorphans; D011957:Receptors, Opioid; C027248:bremazocine