Nitric oxide generated from L-arginine is a messenger for cell- to-cell communication. Abnormalities in nitric oxide release have been implicated in diseases ranging from hypertension and atherosclerosis to septic shock and rheumatoid arthritis. We report here the in vivo and in vitro measurements of nitric oxide in the cardiovascular system using a porphyrinic sensor specific for NO. The sensor has a detection limit 10“9 M, response time of 0.1-10 ms and diameter of 1-20 fi m. Protected by an intravenous catheter or Swan-Ganz catheter, the sensor can be implanted into tissues as well as into the blood stream. Nitric oxide concentrations were measured directly in the heart and also in veins and arteries, ranging in diameter from 100 nm to 5 mm. Nitric oxide production was induced by the action of different physical agents (shear stress, stretching) as well as various chemical substances agonists (bradykinin, acetylcholine, ATP).
Our study concerned the findings that rat and rabbit heart transplants do not survive after six hours. They become dark, hard and fail to contract within 2 min after reperfusion and never regain their function. We tested the supplementation of solutions for heart transplant preservation with tetrahydrobiopterin (H4B) and L-arginine (L-ARG) to maintain the oxidative and reductive domains of the endocardial NO synthase. We decided to study the excised rabbit hearts preserved in Hank’s balanced salt solution (HBSS) at 0 °C supplemented with different concentrations of H4B (0, 1, 5, 10 or 100 /¿M). At desired time intervals, successive pieces stored in the above solutions were warmed to rabbit body temperature in 4 ml of HBSS and maximally agonized by direct application of 20 l of 200 M bradykinin (or other agonist) onto the exposed endocardium. Nitric oxide bursts were monitored with a porphyrinic NO sensor lying on the exposed endocardium. Our goal was to find the lowest H4B concentration which would maximally agonize NO * and prolong the time of heart preservation to more than 6 hours. Ten /iM are a minimum H4B concentration which achieves maximum prolongation of heart preservation time up to 90 hours. This effect was based upon maximal potentiation of NO* release and minimizing of superoxide production.
Nitric oxide concentration in the periendothelial area of the femoral vein in anaesthetized dogs was measured directly with a catheter- protected porphyrinic sensor. A 2- to 4-fold increase occurred in the basal NO concentration of 90±12 nM after acetylcholine injection (1-1.5 ,wg/kg). A linear correlation was found between femoral artery blood flow and NO concentration in the periendothelial area of the femoral vein. Noradrenaline decreased NO levels below the detection limit of the porphyrinic sensor (10 nM).
• NO concentration was measured in the periendothelial area of the femoral artery by Malinski’s porphyrinic • NO sensor in seven anaesthetized dogs. The basal concentration was 154.2 ±5.6 nM and two-minute intraarterial infusions of acetylcholine (3-4 /tg/ml/min) or bradykinin (30 - 40 ng/ml/min) increased this value significantly to 204.3±16.4 and 266.5±16.4 nM (P<0.01), respectively. Inhibition of »NO synthase by L-NAME (50 mg/kg) declined the basal • NO concentration only to 137.2±3.3 nM (PcO.Ol). Subsequent administration of acetylcholine and bradykinin attenuated significantly the increase in • NO concentration. Surprisingly, both agonists still induced a significant increase of *NO concentration by 125.3±8.3 and 156.6±26.9 nM, respectively (PcO.Ol). One of the possible explanations may be that besides arginine-citrulline plus the • NO pathway other sources of • NO could be involved in the high level of • NO after • NO synthase blockade by L-NAME.