Thyrotrophin Releasein Vitro:The Role of Metabolism in the Secretory Response to Vasopressin, Oxytocin and Epinephrine

Abstract

The effects of vasopressin, oxytocin and epinephrine on thyrotrophin (TSH) release and 14C-glucose oxidation by bovine anterior pituitary tissue in vitro were examined in attempts to assess the role of cell metabolism in the secretory process. The dose-response curves for TSH release by all 3 hormones were bell shaped, vasopressin and oxytocin maximally enhancing TSH release at 10-10 or 10-9 M, and epinephrine at 10-7or 10-6 m. Phenoxybenzamine, 10-8 -1, blocked the stimulatory effect of epinephrine, but not of vasopressin, on TSH release. 14C-1 or 14C -6 glucose oxidation to 14CO2 was unaffected by concentrations of all 3 hormones which were maximally effective in enhancing TSH release. Incubations carried out aerobically at 0 C resulted in only a slight depression of the stimulated release of TSH by vasopressin, but glucose oxidation was consistently reduced to approximately 10-15% of the level at 37 C. Under anaerobic conditions and at 37 C, neither oxytocin nor vasopressin had a significant effect on TSH release, and glucose oxidation was only 20% of that occurring aerobically. Spontaneous release of TSH was generally greater in anaerobic than in aerobic atmosphere at 37 C. It was concluded that there is no direct coupling between glucose oxidation and the spontaneous or stimulated release of TSH from cytoplasmic stores.