title: The inhibitory effect of picrotoxin on basal and cold-induced thyrotropin secretion involves somatostatin mediation.
abstract: This work was undertaken to investigate whether the inhibitory tone exerted by GABA on somatostatin (SRIH) release operates in the control of thyrotropin (TSH) secretion in both basal and cold-stimulated conditions. In a first group of animals (G1) undergoing both carotid and third ventricle push-pull cannulation, i.vt. injection of picrotoxin (10(-5) M) induces a significant decrease in plasma TSH level under basal conditions (0.09 +/- 0.02 versus 0.27 +/- 0.4 ng/100 microliters; P < 0.03, n = 5). In a median eminence (ME) push-pull cannulated group of rats (G2), picrotoxin, peripherally administered, blocks cold-induced inhibition of SRIH release (35.0 +/- 1.8 versus 7.4 +/- 3.3 pg/15 min; P < 0.005; n = 5). In a third group of intact rats (G3), peripheral administration of picrotoxin (2 mg/kg i.p.) blunts the cold-induced TSH release (0.17 +/- 0.03 versus 0.46 +/- 0.04 ng/100 microliters; P < 0.001; n = 5). Our results strongly suggest that a decrease in SRIH release is involved in the GABAergic control of basal and cold-induced TSH secretion.
authors.affiliation: Laboratory of Endocrinological Neurobiology, URA 1197 of CNRS, University of Montpellier, France.
authors.forename: S
authors.initials: S
authors.lastname: Arancibia
authors.forename: D
authors.initials: D
authors.lastname: Lyonnet
authors.forename: J P
authors.initials: JP
authors.lastname: Roussel
authors.forename: G
authors.initials: G
authors.lastname: Ixart
authors.forename: H
authors.initials: H
authors.lastname: Astier
mesh_terms: D000818:Animals; D003080:Cold Temperature; D008297:Male; D010852:Picrotoxin / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A; D013004:Somatostatin / Q000378:metabolism*; D013312:Stress, Physiological; D013972:Thyrotropin / Q000378:metabolism*
chemical_list: D010852:Picrotoxin; D011963:Receptors, GABA-A; D013004:Somatostatin; D013972:Thyrotropin