In VitroSecretion of Thyrotropin (TSH): Stimulation by a Hypothalamic Peptide (TRF)

Abstract

Identical populations of anterior pituitary tissue were obtained by separating rat anterior pituitary in halves or quarters. When incubated in vitro in Krebs-Ringer bicarbonate glucose buffer, such identical fragments of pituitary released identical minute amounts of TSH into the incubation fluid. Addition of hypothalamic TSH-releasing factor (TRF) of sheep origin (prepared by molecular sieving and characterized with an in vivo bio-assay) increased the amount of TSH present in the incubation fluid of the experimental pituitary population when compared to its control. The stimulation of TSH release was a linear function of the log of the dose of added TRF. The ability of TRF to stimulate TSH release in vitro was inhibited by in vivo pretreatment or in vitro preincubation with L-thyroxine. TRF does not act by inhibiting destruction (in vitro) of released TSH nor by potentiating TSH in the bioassay. LRF (LH-releasing factor), CRF (corticotropin- releasing factor), lysine-vasopressin, oxytocin, α-MSH and β-MSH were inactive, within the limits of the doses tested here, to stimulate release of TSH. These results are in agreement with what has been reported earlier regarding in vivo studies with TRF. The hypothalamic peptides TRF, CRF and LRF appear to be different chemical entities.