Modulation of anterior pituitary cell luteinizing hormone secretory activity by neuropeptide Y in early pregnant pigs.

Numerous reports indicate that neuropeptide Y (NPY) is implicated in the regulation of anterior pituitary (AP) gonadotropin secretion in prepuberal and cyclic females. This study was performed to explain whether NPY directly affects basal and gonadotropin-releasing hormone- (GnRH-) induced luteinizing hormone (LH) secretion and intracellular accumulation by AP cells and whether NPY and its receptor (Y1 and Y2) mRNAs are expressed in the AP gland in pregnant pigs (days 14 - 16). Additionally, the expression of genes encoding β subunit of luteinizing hormone (β-LH) and GnRH receptor (GnRH-R) was determined in porcine AP gland. Anterior pituitaries were dispersed with trypsin and the obtained pituitary cells (2 x 105 cells/ml) were pre-incubated (72 h) and then experimentally treated for 3.5 h with GnRH (100 ng/ml), NPY (10-8, 10-7 and 10-6 M) alone, or in chosen combinations with GnRH. The LH contents in culture media and cellular homogenates were measured by radioimmunoassay. The expression of NPY, Y1 and Y2 NPY receptors, GnRH-R and β-LH mRNAs in the AP gland was determined by the real-time PCR method. NPY (10-8, 10-7 and 10-6 M) had no effect on basal LH secretion or basal and GnRH-induced LH accumulation in AP cells. The lowest dose of NPY (10-8 M) decreased, while higher doses of NPY only showed a tendency to inhibit GnRH-induced release of LH from AP cells. The presence of mRNAs for NPY and its receptor Y2, as well as β-LH and GnRHR was confirmed in the porcine AP gland. These results indicate that NPY and one of its receptors (Y2) are expressed in the porcine anterior pituitary and this neuropeptide might be involved in the modulation of LH secretion by AP cells in pregnant pigs.