Effect of leptin on thyroid-stimulating hormone secretion and nitric oxide release from pituitary cells of ewe lambs in vitro.

Taking into account that the relationship between leptin and thyroid-stimulating hormone (TSH) secretion in ewe lambs is not clear, the objective of the present study was to estimate the effect of leptin on basal TSH secretion from ovine pituitary cells in vitro. Moreover, the influence of leptin on nitric oxide (NO) release and its role in the leptin-modulated secretion of TSH was studied. Pituitary cells were cultured in the McCoy 5A medium without hormones (the control), with 10⁻¹⁰-10⁻⁵ mol/L of leptin or with 10⁻¹⁰-10⁻⁵ mol/L of leptin and L-NAME (N(ω)-nitro-L-arginine methyl ester, 3 x 10⁻⁴ mol/L, the inhibitor of NO synthesis). The secretion of thyroid-stimulating hormone as well as concentration of nitrite (as an indicator of nitric oxide release) were analysed after 2-72 hours of experiment. The obtained results show that TSH secretion from ovine pituitary cells in vitro is dependent on leptin concentration: 10⁻¹⁰-10⁻⁶ mol/L of leptin causes an increase in TSH secretion, whereas the highest concentration of leptin (10⁻⁵ mol/L) suppresses thyroid-stimulating hormone release compared to the control. TSH secretion reaches the highest values under the influence of 10⁻⁸ mol/L of leptin. Moreover, leptin, depending on its dose and time of cell exposition, stimulates NO release from anterior pituitary cells of ewe lambs in vitro. The inhibition of NO synthesis with L-NAME annihilates the stimulating effect of leptin on thyroid-stimulating hormone secretion.