The effect of thyroid hormones on prolactin secretion by cultured bovine pituitary cells

The effect of thyroid hormones and thyrotropin releasing hormone (TRH) on prolactin (PRL) secretion has been studied using a primary calf anterior pituitary cell culture system. After mechanical and enzymatic dispersion, cultured pituitary cells were preincubated with T 3 or T 4 for 48 hr prior to a 24 hr experimental incubation. T 3 stimulated the release of PRL into the medium in a dose-related fashion, with an ED 50 of 3 nM; at 10 nM T 3, a maximal 52 ± 5% stimulation ( p < 0.001) was observed. T 4 at 100 nM stimulated medium PRL 27 ± 10% ( p < 0.05); the ED 50 for T 4 was 20 nM. Neither T 3 nor T 4 affected intracellular PRL content. The stimulation of medium PRL by T 3 was observed in medium containing 10% euthyroid as well as 10% charcoal-stripped hypothyroid calf serum. The relative stimulation by TRH of PRL release into the medium was significantly diminished by 10 nM T 3 in euthyroid and stripped hypothyroid serum medium, but only as a consequence of the stimulation of basal medium PRL by T 3; there was no change in maximal TRH-stimulated PRL release. In medium supplemented with unstripped hypothyroid serum, however, T 3 did decrease absolute TRH-stimulated PRL release.