Growth hormone releasing factor decreases long form leptin receptor expression in porcine anterior pituitary cells

Pituitary cells from six pigs, 180-200 days of age, were studied in primary culture to determine if growth hormone releasing factor (GRF) affects long form leptin receptor (Ob-Rl) expression. On Day 4 of culture, 10(5) live cells per well were challenged with either 0, 10(-6), 10(-7) or 10(-8)M [Ala15]-hGRF-(1-29)NH(2) (3 wells per treatment per pig). Secretion of growth hormone (GH) into the media and pituitary Ob-Rl mRNA expression were determined at 4 h after treatment. Media were analyzed for GH by radioimmunoassay, and total RNA was isolated from cells for determination of Ob-Rl expression by semi quantitative reverse transcription PCR. Basal GH concentration was 32+/-2 ng per 10(5) cells per well (n=18 wells) for 4 h. Relative to control at 4 h, 10(-6),10(-7) and 10(-8)M GRF increased (P<0.01) GH secretion by 151, 129 and 120%, but decreased (P<0.05) Ob-Rl expression by 32, 50 and 38%, respectively. These results indicate that GRF directly modulates Ob-Rl expression at the level of the pituitary, and thereby playing a role in regulating pituitary sensitivity to leptin.