Bombesin Stimulates Growth Hormone Secretion from Cultured Bovine Pituitary Cells

Abstract

Bombesin-like peptides are present in the mammalian hypothalamus. It was previously reported that synthetic bombesin elevates plasma growth hormone (GH) and prolactin (PRL) concentrations in rats. To investigate whether bombesin has a direct action on the pituitary gland, GH and PRL secretion were measured from 5 day cultures of bovine anterior pituitary cells. The effects of bombesin were compared with those of a previously described synthetic pentapeptide which releases rat GH in vitro (GHRP) and with the effects of acetylcholine which stimulates bovine GH secretion. Bombesin stimulate GH but not PRL secretion from pituitary cultures during 90 min incubations. Maximal stimulation to 157 .+-. 16% of the control value was seen with 1.2 .times. 10-7 M bombesin. Half-maximal stimulation occurred with 5 .times. 10-9 M bombesin. The pentapeptide GHRP also stimulated GH but not PRL secretion. Maximal stimulatio to 207 .+-. 14% of the control value was seen with 1.3 .times. 10-5 M GHRP. Half-maximal stimulation occurred with 10-7 M GHRP. Acetylcholine stimulated secretion of both GH and PRL, both responses being abolished by the muscarinic antagonist atropine. Maximal stimulation with 10-4 M acetylcholine was to 381 .+-. 33% of the control value for GH and to 134 .+-. 5% of the control value for PRL. The effects of bombesin and GHRP on GH secretion were not additive, while the effects of both peptides were additive with those of acetylcholine. The synthetic GHRP peptide possibly interacts with native bombesin receptors on pituitary somatotrophs and bombesin or a related peptide may act in vivo as a GH releasing factor.