Stimulatory effects of nitric oxide donors on histamine release in isolated rat gastric mucosal cells

Luminal amino acid sensing in the rat gastric mucosa

Recent advancements in molecular biology in the field of taste perception in the oral cavity have raised the possibility for ingested nutrients to be "tasted" in the upper gastrointestinal tract. The purpose of this study was to identify the existence of a nutrient-sensing system by the vagus in the rat stomach. Afferent fibers of the gastric branch increased their firing rate solely with the intragastric application of the amino acid glutamate. Other amino acids failed to have the same effect. This response to glutamate was blocked by the depletion of serotonin (5-HT) and inhibition of serotonin receptor(3) (5-HT(3)) or nitric oxide (NO) synthase enzyme. Luminal perfusion with the local anesthesia lidocaine abolished the glutamate-evoked afferent activation. The afferent response was also mimicked by luminal perfusion with a NO donor, sodium nitroprusside. In addition, the NO donor-induced afferent activation was abolished by 5-HT(3) blockade as well. Altogether, these results strongly suggest the existence of a sensing system for glutamate in the rat gastric mucosa. Thus luminal glutamate would enhance the electrophysiological firing rate of afferent fibers from the vagus nerve of the stomach through the production of mucosal bioactive substances such as NO and 5-HT. Assuming there is a universal coexistence of free glutamate with dietary protein, a glutamate-sensing system in the stomach could contribute to the gastric phase of protein digestion.

Nitric oxide regulates receptor activator of nuclear factor-kappaB ligand and osteoprotegerin expression in bone marrow stromal cells

Bone remodeling reflects an equilibrium between bone resorption and formation. The local expression of receptor activator of nuclear factor-kappaB ligand (RANKL) and osteoprotegerin (OPG) in bone determines the entry of monoblastic precursors into the osteoclast lineage and subsequent bone resorption. Nitric oxide (NO) inhibits osteoclastic bone resorption in vitro and regulates bone remodeling in vivo. An interaction of NO with RANKL and OPG has not been studied. Here, we show that treatment of ST-2 murine stromal cells with the NO donor sodium nitroprusside (100 microm) for 24 h inhibited 1,25 dihydroxyvitamin D(3)-induced RANKL mRNA to less than 33 +/- 7% of control level, whereas OPG mRNA increased to 204 +/- 19% of control. NOR-4 replicated these NO effects. The effects of NO were dose dependent and associated with changes in protein levels: RANKL protein decreased and OPG protein increased after treatment with NO. PTH-induced RANKL expression in primary stromal cells was inhibited by sodium nitroprusside, indicating that the NO effect did not require vitamin D. NO donor did not change the stability of RANKL or OPG mRNAs, suggesting that NO affected transcription. Finally, cGMP, which can function as a second messenger for NO, did not reproduce the NO effect, nor did inhibition of endogenous guanylate cyclase prevent the NO effect on these osteoactive genes. The effect of NO to decrease the RANKL/OPG equilibrium should lead to decreased recruitment of osteoclasts and positive bone formation. Thus, drugs and conditions that cause local increase in NO formation in bone may have positive effects on bone remodeling.