Growth hormone release induced by an amino acid mixture from primary cultured anterior pituitary cells of goats.

The effects of amino acids on growth hormone (GH) release and cytosolic calcium concentration ([Ca2+]i) were investigated in caprine anterior pituitary cells cultured for 3 d in Dulbecco modified Eagle medium. The addition of an amino acid mixture consisting of seven nonessential amino acids (NEAA: L-Asp, Gly, L-Ala, L-Ser, L-Pro, L-Asn, and L-Glu; concentration of each 12.5-200 mumol/l) in the medium significantly raised GH release from the cultured cells in a concentration-dependent manner with the maximum release at 200 mumol/l NEAA. Although an addition of L-Asp (0.1-100 mumol/l) caused a significant rise in GH release in a concentration-dependent manner, neither the individual amino acids contained in NEAA except L-Asp nor others (L-Leu, L-Phe, L-Gln, L-Met, and L-Arg) caused a rise in GH release when added alone to the medium. The rise in GH release induced by NEAA (200 mumol/l) and GH-releasing hormone (GHRH, 10 nmol/l) was significantly reduced by the addition of EGTA (1.8 mmol/l) and nifedipine (1 mumol/l) to the medium, respectively. The addition of NEAA (200 mumol/l) caused a rapid and transient [Ca2+]i increase, followed thereafter by a steady increase. The prior addition of nifedipine (1 mumol/l), which itself significantly reduced the basal [Ca2+]i, completely abolished the response induced by NEAA or GHRH. From these findings, we conclude that: 1) NEAA raises GH release and [Ca2+]i in cultured caprine anterior pituitary cells, and 2) Ca2+ influx from the medium may be responsible for the cellular action of NEAA.