Modulation of growth hormone (GH) secretion and GH mRNA level in cultured bovine adenohypophyseal cells : effects of neurohormones, steroids and insulin-like growth factor-I

Abstract

A series of experiments was conducted to investigate the regulation of GH synthesis/secretion in cultured bovine adenohypophyseal cells. The effects of: 1) bovine growth hormone-releasing factor (bGRF; 100 nM); 2) somatostatin-14 (SS; 100 nM); 3) forskolin (FSK; 10 μM); 4) dibutyryl cAMP [(Bu)2cAMP; 1 mM]; 5)phorbol-12-myristate-13 acetate (PMA; 1 μM); 6) dihydrotestosterone (DHT), progesterone (P) and zeranol (Z), each 1 μM; 7) insulin-like growth factor-I (IFG-I; 1, 10, 20, or 100 ng/ml); or 8) medium alone (control) were studied in cow (F) or steer (M) cells. Medium content of GH was determined by radioimmunoassay and cellular content of GH m RNA was determined by Norther analysis. Bovine GRF increased (P<.05) GH secretion 2.8- (F) or 5-fold (M) compared to control cultures (3.3 [plus or minus] .5 and 7.2 [plus or minus] 1.2 ng/ml, respectively). Secretion of GH by FSK-treated culture was increased (P<.05) 1.9- (F) or 2.5-fold (M) relative to control cultures (2.9 [plus or minus] .4 and 4.2 [plus or minus] .6 ng/ml, respectively). Secretion of GH by (Bu)2cAMP-treted cultures (F) was 1.7-fold greater (P<.05) than control cultures (2.9 [plus or minus] .4 ng/ml). Cultures treated with PMA secreted 11-(F) or 6.6-fold (M) more (P<.05) GH than control cultures (3.5 [plus or minus] .4 and 10.5 [plus or minus] 2.2 ng/ml, respectively). Somatostatin inhibited (P<.05) basal and bGRF-stimulated GH secretion 50 and 48% (M) or 40 and 49% (F), respectively, compared to control (8.5 [plus or minus] 1.7 and 4.5 [plus or minus] 2.3 ng/ml, respectively) and bGRF-treated (39.5 [plus or minus 9.3 and 17.3 [plus or minus] 5.3 ng/ml, respectively) cultures. Treatment of cultures with SS inhibited (P<.05) FSK-stimulated GH secretion 62 (M) and 47% (F) compared to control cultures (11.2 [plus or minus] 4.3 and 6.0 [plus or minus] 1.0 ng/ml, respectively). Similarly, SS inhibited (P<.05) Bu2cAMP-stimulated (3.62 [plus or minus] .8 ng/ml) GH secretion 67% (F only). Secretion of GH by PMA-treated cultures was not affected (P>.05) by cotreatment with SS...