Evidence of enhanced non-enzymatic generation of nitric oxide on the skin surface of acupuncture points: An innovative approach in humans.

The present study quantified total nitrate and nitrite (NOx-) collected from the skin surface along acupuncture points (acupoints) and determined whether non-enzymatic reduction of nitrate by bacteria is involved in chemical generation of nitric oxide (NO) on acupoints. A small plastic tube (0.5 x 7 cm) cut in half lengthwise was taped to the forearm or leg in 50 healthy volunteers. NO-collecting solutions with NO-scavenging compounds, hemoglobin or 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide, was placed inside the tubing attached to the skin surface for 20 min. The concentrations of NOx- in the collected samples were quantified by using chemiluminescence. NOx- concentration was significantly enhanced in four acupoints on the pericardium meridian and in two acupoints on the bladder meridian compared with those collected on non-meridian control areas. The time intervals of NOx- levels were significantly higher at the first 20 min of acupoint collection, but the concentrations were similar among the study groups collected at 20-40, 40-60, and 60-80 min. NOx- concentrations and numbers of bacteria colonies detected on the skin surface were markedly reduced by pretreatment of skin with sodium hypochlorite compared to water treatment. This is the first evidence showing that NO has been successfully quantified on skin acupoints by a non-invasive device in humans. We conclude that NO is physiologically released from the skin surface with a higher level at acupoints, and that the non-enzymatic reduction of nitrate by bacteria is involved in chemical generation of NO on skin acupoints in addition to l-arginine-derived NO synthesis.

Enhanced nitric oxide release/synthesis in the posterior hypothalamus during nitroglycerin tolerance in rats.

We have recently observed that increasing central noradrenergic transmission and sympathomimetic activity is involved with the complex hemodynamic effects during tolerance to nitroglycerin. The present study was to examine the release of nitric oxide (NO) in the posterior hypothalamus during tolerance to depressor responses to nitroglycerin and determine if, during the tolerance, endogenous NO synthesis is induced in the posterior hypothalamus. A microdialysis probe was implanted in the posterior hypothalamus and perfusion fluid was pumped through the probe at 2 microl/min in conscious rats. Tolerance to nitroglycerin was produced by three intravenous (i.v.) injections of 1.3 mg nitroglycerin each within 40 min compared to the same administrations of low dose of the drug, sodium nitroprusside and papaverine. Dialysate samples were collected 1 h before and 1 h each after injections for 8 h. Concentrations of nitrite (NO(2)(-)), nitrate (NO(3)(-)), and total nitrite plus nitrate (NO(x)(-)) were quantified in the samples by using chemiluminescence. The dose-response curve for arterial depressor induced by intravenous injection of the challenge doses of nitroglycerin was markedly shifted to the right at the first hour after nitroglycerin tolerance, lasted 3 to 5 h and reversed at 7 h. The dialysate NO(3)(-) and NO(x)(-) concentrations in the posterior hypothalamus were significantly increased at the first hour following nitroglycerin tolerance but were not altered by low dose of the drug, sodium nitroprusside, and papaverine. Nitroglycerin tolerance predominantly caused an increase in NO(3)(-) release in the posterior hypothalamus with no or small amount of changes in dialysate NO(2)(-) and the response was partially inhibited by pretreatment with N(G)-Propyl-L-arginine (NPLA) (1.0 mg/kg, i.p.), an inhibitor of neuronal NO synthesis. The increase of NO release in the posterior hypothalamus occurred at the first hour, lasted 2 to 3 h and reversed at 5 to 6 h during nitroglycerin tolerance. The results show that systemically administered high dose of nitroglycerin increases NO release in the posterior hypothalamus which matches the time interval of tolerance to arterial depressor response to the drug. Data suggest that there is an enhanced endogenous NO synthesis in the posterior hypothalamus which may affect central sympathetic functions during nitroglycerin tolerance.