title: Is thyrotropin-releasing hormone immunoreactivity in peripheral blood an estimate for hypothalamic thyrotropin-releasing hormone release?
abstract: The significance of TRH for pituitary function is still unresolved mainly due to limitations in determining in vivo hypothalamic TRH release. We therefore examined whether TRH immunoreactivity (TRH-IR) in peripheral blood is an index for hypothalamic TRH release. Peripheral TRH-IR varied between 10 and 55 pmol/l and was similar in euthyroid and hypothyroid rats, but lower in hyperthyroid rats. Destruction of the hypothalamic paraventricular area reduced peripheral TRH-IR, while stimulation of this area increased it. Clearance of TRH during continuous TRH infusion was 1.9 +/- 0.2, 3.5 +/- 0.3 and 5.9 +/- 0.8 ml/min in hypothyroid, euthyroid and hyperthyroid rats, respectively. These and previous data on TRH in hypophysial portal blood indicate that 5-25 pmol TRH/l peripheral blood is of hypothalamic origin. Chromatography revealed that TRH-IR from hypothalamus and portal blood co-eluted with TRH, but in peripheral blood two peaks were found, one of which was authentic TRH. Thus, peripheral TRH-IR alters in experimental conditions and part of it seems to be of hypothalamic origin. However, the presence of TRH-like material in peripheral blood not identical to TRH and the fact that experimental conditions alter TRH clearance indicate that peripheral TRH-IR is not an index for hypothalamic TRH release.
authors.affiliation: Department of Endocrinology and Reproduction, Erasmus University, Rotterdam, The Netherlands.
authors.forename: W J
authors.initials: WJ
authors.lastname: de Greef
authors.forename: J M
authors.initials: JM
authors.lastname: Rondeel
authors.forename: R
authors.initials: R
authors.lastname: Heide
authors.forename: W
authors.initials: W
authors.lastname: Klootwijk
authors.forename: T J
authors.initials: TJ
authors.lastname: Visser
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D007031:Hypothalamus / Q000378:metabolism*; D008297:Male; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013973:Thyrotropin-Releasing Hormone / Q000097:blood* / Q000378:metabolism
chemical_list: D013973:Thyrotropin-Releasing Hormone