Neuropeptide Y modulates growth hormone but not luteinizing hormone secretion from prepuberal gilt anterior pituitary cells in culture

Pituitary cells, from seven 160- to 170-day-old pigs, were studied in primary culture to determine the affects NPY on LH and GH secretion at the level of the pituitary. On day 4 of culture, medium was discarded, plates were rinsed twice with serum-free medium and cells were cultured in 1 ml fresh medium without serum and challenged individually with 10−10, 10−8 or 10−6 M [Ala15]-h growth hormone-releasing factor-(1-29)NH2 (GRF); 10−9, 10−8 or 10−7 M GnRH or 10−9, 10−8, 10−7 or 10−6 M NPY individually or in combinations with 10−9 or 10−8 M GnRH or 10−8 or 10−6 M GRF. Cells were exposed to treatment for 4 h at which time medium was harvested and quantified for LH and GH. Basal LH secretion (control; n = 7 pituitaries) was 12 ± 6 ng/well. Relative to control at 4 h, 10−9, 10−8 and 10−7 M GnRH increased (P < 0.01) LH secretion by 169, 176 and 197%, respectively. Neuropeptide-Y did not alter (P > 0.4) basal LH secretion nor 10−8 M GnRH-induced increase in LH secretion but 10−9 M GnRH-stimulated LH secretion was reduced by NPY and was not different from control or GnRH alone. Basal GH secretion (control; n = 7 pituitaries) was 56 ± 12 ng/well. Relative to control at 4 h, 10−10, 10−8 and 10−6 M GRF increased GH secretion by 111%, 125% (P < 0.01) and 150% (P < 0.01), respectively. Only 10−6 M (134%) and 10−7 M (125%) NPY increased (P < 0.04) basal GH secretion. Addition of 10−9, 10−8 and 10−7 M NPY in combination with 10−8 M GRF suppressed (P < 0.04) GRF-stimulated GH secretion. However, 10−9 M NPY enhanced (P < 0.06) the GH response to 10−6 M GRF. These results demonstrate that NPY may directly modulate GH secretion at the level of the pituitary gland.