Lateral hypothalamic injection of GABA(A) antagonist induces gastric vagus-mediated hypocalcemia in the rat.
The involvement of lateral hypothalamic area (LHA) neurons in the regulation of blood calcium homeostasis was investigated in unanesthetized rats. The microinjection of the gamma-aminobutyric acid A receptor antagonist bicuculline methiodide (BM, 4-40 ng x 0.5 microl(-1) x 5 min(-1)) into the LHA decreased the blood concentration of ionized calcium. Total serum calcium also decreased after the BM injection. This hypocalcemic effect was eliminated by a bilateral vagotomy of the gastric branches. An intravenous injection of atropine methyl bromide (a muscarinic antagonist), nadolol (a beta-adrenergic blocker), or ranitidine (a histamine H2 blocker) suppressed the BM-induced hypocalcemia, whereas phenoxybenzamine (an alpha-adrenergic blocker) proved to be ineffective. Although the intra-LHA injection of BM increased the serum gastrin, which is known to have a hypocalcemic effect, neither secretin nor somatostatin (gastrin-release inhibitors) blocked the hypocalcemic response. These results suggest that the hypocalcemia observed after the excitation of LHA neurons was mediated by muscarinic, beta-adrenergic, and histamine H2 receptors through the gastric vagus.
Shiramine
K
K
Department of Physiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Aou
S
S
Hori
T
T
D000818:Animals; D001640:Bicuculline / Q000008:administration & dosage / Q000031:analogs & derivatives*; D002118:Calcium / Q000097:blood; D002245:Carbon Dioxide / Q000097:blood; D003964:Diaphragm / Q000294:innervation; D004573:Electrolytes / Q000097:blood; D005260:Female; D018756:GABA Antagonists / Q000008:administration & dosage*; D006863:Hydrogen-Ion Concentration; D006996:Hypocalcemia / Q000097:blood / Q000139:chemically induced* / Q000188:drug therapy; D007026:Hypothalamic Area, Lateral / Q000502:physiology*; D007267:Injections; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D051381:Rats; D017208:Rats, Wistar; D013270:Stomach / Q000294:innervation*; D014628:Vagotomy; D014630:Vagus Nerve / Q000502:physiology*
D004573:Electrolytes; D018756:GABA Antagonists; D002245:Carbon Dioxide; C017069:bicuculline methiodide; D010100:Oxygen; D002118:Calcium; D001640:Bicuculline