Nitric oxide biphasically modulates GH secretion in cultured cells of GH-secreting human pituitary adenomas

Nitric oxide (NO) biphasically modulates osteoclast function, sperm motility and testosterone production by exerting a positive effect at low concentrations and a negative effect at high concentrations. In this study the effect due to administration of four NO-donors, each releasing an individual amount of NO, was studied on GH secretion from human adenomatous GH-secreting cells.

Sodium nitroprusside (SNP), diethylenetriamine NO adduct (DETA/NO), diethylamine/NO complex sodium salt (DEA/NO), and S-nitroso-N-acetylpenicillamine (SNAP) were administered at a concentration of 10-4 M to cells isolated after transsphenoidal adenomectomy from five acromegalic patients.

SNP significantly (p < 0.01) increased GH secretion, while the other NO donors inhibited GH secretion in comparision with the amount of GH spontaneously released by unstimulated cells. Each drug showed an individual degree of inhibitory potency: DEA/NO > DETA/NO > SNAP. Nitrite accumulation in the media was measured as a marker of NO released by each individual drug and was found to be different for each drug (DEA/NO > DETA/NO > SNAP > SNP). A negative correlation (R = -0.93; p < 0.05) was found between nitrite release and GH secretion induced by each drug.

These data show that low and quasi-physiological levels of NO, such as those released by SNP, stimulate GH secretion, while high NO levels, such as those released by the other NO-donors, inhibit GH secretion. Thus, NO is shown to be able to modulate GH secretion in a dose-dependent manner in GH adenomatous cells from human pituitary adenomas.