Central actions of parathyroid hormone on blood calcium and hypothalamic neuronal activity in the rat.
The central actions of parathyroid hormone (PTH) on the blood ionized calcium level in anesthetized rats and the neuronal activity of the ventromedial nucleus of the hypothalamus (VMH) in vitro were investigated. An intracerebroventricular injection of PTH (0.01, 0.1, and 1 microgram) prevented urethan-induced hypocalcemia in a dose-dependent manner, whereas either an intravenous or an intracisternal injection of PTH (1 microgram) was ineffective. Eighty-three of 177 VMH neurons responded to a bath application of PTH (10(-7) or 3 x 10(-7) M): a majority (72, 83%) of the responsive cells decreased, whereas 11 increased their activity. This inhibitory effect of PTH on neuronal activity still persisted after synaptic blocking in a Ca(2+)-free/high-Mg2+ medium. A PTH receptor antagonist, [Tyr34]bPTH-(7-34)-NH2, suppressed the effect of PTH on the neuronal activity. These findings thus suggest that brain PTH has a calciotropic function and that one of the possible target sites is the VMH, where PTH inhibits its neuronal activity through a postsynaptic mechanism mediated by PTH receptors.
Department of Physiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
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Matsui
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Aou
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Ma
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Hori
D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000097:blood*; D002552:Cerebral Ventricles / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D007276:Injections, Intraventricular; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010281:Parathyroid Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D010446:Peptide Fragments / Q000008:administration & dosage / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D019379:Teriparatide; D013997:Time Factors; D014697:Ventromedial Hypothalamic Nucleus / Q000187:drug effects / Q000502:physiology*
D010281:Parathyroid Hormone; D010446:Peptide Fragments; D019379:Teriparatide; D002118:Calcium