Hypo-osmolarity stimulates and high sodium concentration inhibits thyrotropin-releasing hormone secretion from rat hypothalamus.
The hypothalamic paraventricular nucleus, representing cell bodies in which thyrotropin-releasing hormone is synthesized, and the median eminence, representing nerve terminals, were incubated in vitro. Various hypo- and hyperosmotic solutions were tested to determine osmotic sensitivity of thyrotropin-releasing hormone secretion. High KCl (56 mM) causing membrane depolarization was used as a non-specific control stimulus to induce thyrotropin-releasing hormone secretion. A 30% decrease of medium osmolarity (from 288 to 202 mOsmol/l) increased thyrotropin-releasing hormone secretion from both the paraventricular nucleus and median eminence. A 30% decrease of medium NaCl content by its replacement with choline chloride did not affect basal thyrotropin-releasing hormone secretion. Increasing medium osmolarity with biologically inactive L-glucose did not affect basal or KCl-induced thyrotropin-releasing hormone secretion from either structure. Medium made hyperosmotic (350-450 mOsmol/l) by increasing the NaCl concentration resulted in a dose-dependent decrease of basal thyrotropin-releasing hormone secretion and abolished KCl-induced thyrotropin-releasing hormone secretion. If an osmotically equivalent amount of choline chloride was substituted for NaCl, there was no effect on thyrotropin-releasing hormone secretion, indicating a specific action of Na+. This study indicates a specific sensitivity to high concentrations of Na+ ions of both thyrotropin-releasing hormone-producing parvocellular paraventricular neurons and thyrotropin-releasing hormone-containing nerve terminals in the median eminence.
Nikodémová
M
M
Institute of Experimental Endocrinology, Slovak Academy of Sciences, Bratislava, Slovak Republic.
Greer
M A
MA
Strbák
V
V
D000818:Animals; D002794:Choline / Q000008:administration & dosage / Q000494:pharmacology; D003470:Culture Media / Q000737:chemistry / Q000494:pharmacology; D005947:Glucose / Q000008:administration & dosage / Q000494:pharmacology; D007031:Hypothalamus / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000008:administration & dosage / Q000494:pharmacology; D013973:Thyrotropin-Releasing Hormone / Q000037:antagonists & inhibitors* / Q000378:metabolism*
D003470:Culture Media; D012965:Sodium Chloride; D013973:Thyrotropin-Releasing Hormone; D012964:Sodium; D005947:Glucose; D002794:Choline