An Experimental Study of Effects of Nitric Oxide Synthase on Rat Anterior Pituitary Gland

ABSTRACT

OBJECTIVE: The nitric oxide synthases(NOS) are a group of isoenzymes that convert L-arginine to L-citrulline and generate nitric oxide(NO). The constitutive form of NOS is present in endothelium, adrenal gland, brain, and platelets, while the inducible form of NOS is present in macrophages, hepatocytes, vascular smooth muscle cell and endothelial cells. To determine whether NO has a role in anterior pituitary cell function, immunohistochemistry and molecular techniques were used to study NOS expression in rat pituitary gland. MATERIALS AND METHODS: We treated the rats with two NOS inhibitors: N-mono-methyl amine(NMMA), which is an inhibitor of NOS activity, and aminoguanidine, which a selective inhibitor of the inducible NOS isoform and two NO donors; sodium nitroprusside(SNP), s-nitro-acetyl-penicillamine(SNAP) as well as L-arginine. Rat growth hormone was measured in the serum using radioimmunoassay and NOS producing cells in the anterior lobe of the pituitary was detected by immunohistochemical stains. Also mRNA was extracted from the pituitary and performed RT-PCR using inducible NOS primer. RESULTS: Serum growth hormone levels were increased significantly by administration of NOS inhibitors, such as NMMA and aminoguanidine. Immunohistochemical stains for neuronal and inducible NOS showed strong positivity in the folliculostellate cells and weak positivity in the anterior pituitary cells in the control and various experimental groups. RT-PCR in inducible NOS showed more brighter band in the 222 base pairs in the aminoguanidine treated group than normal control group. CONCLUSION: These data suggest that pituitary NOS may play a pivotal role in the control of growth hormone secretion.