Arterial metabolism as studied in vitro by NMR: preliminary results in normotensive and hypertensive aortas

The effects of anti-hypertensive therapy on the structural, mechanical and metabolic properties of the rat aorta

The vascular system exhibits altered growth, calcium responses and metabolism during hypertension. To relate such changes, we compared histological, tension and metabolic responses in the aorta from 32-week-old spontaneously hypertensive rats (SHRs), normotensive Wistar-Kyoto (WKY) rats, and SHRs treated with Verapamil (V) and ACE-inhibitor, Trandolapril (T) as well as a combination of the two treatments (C). Vascular hypertrophy was apparent in the SHRs. Contractile responses induced by 50 mmol/1 KCl and 2.5 mmol/1 Ca2+ were significantly lower in the SHR (64.4 mN/mm2 vs. 49.2 mN/mm2), but an associated increase in Ca2+ -sensitivity (EC50 of extracellular Ca2+ (mumol/1): SHR, 456 vs. WKY, 616) normalised tension generating ability. All treatments led to significant decreases in blood pressure, although only T and C treated animals became normotensive with concomitant normalisation of vascular hypertrophy. An increase in oxygen consumption was apparent in the SHR aorta, which was associated with significant differences in the activities of key metabolic enzymes. Anti-hypertensive treatment normalised many of the metabolic parameters, with the C therapy being the most efficacious. We conclude that the treatment of hypertension by combined therapy leads to a better normalisation of structural, contractile, and metabolic parameters in the SHR, than either treatment alone and that metabolic changes with the pathology are resolved with appropriate therapy.

Phosphorous compounds studied by 31P nuclear magnetic resonance spectroscopy in the taenia of guinea-pig caecum

1. In the isolated taenia (0.4-0.6 g) of guinea-pig caecum, the intracellular phosphorous compounds and pH were investigated using 31P nuclear magnetic resonance (NMR) under various metabolic conditions. 2. The ratios of the intracellular concentration of phosphocreatine ([ PCr]) and inorganic phosphate [( Pi]) to nucleotide triphosphate ([ NTP]) were 1.71 +/- 0.14 and 0.58 +/- 0.11 (n = 25), respectively, in normal solution (32 degrees C). The intracellular pH estimated from the chemical shift of Pi was 7.05 +/- 0.06 (n = 25), agreeing well with those previously obtained. 3. In the absence of glucose, the [PCr] and [NTP] were decreased to almost a half after 150 min exposure to 40 mM-K+ solution, while [Pi] was increased 3-fold. These changes were much faster than the rate of decline in tension. When glucose was readmitted, the contractile response to K+ fully recovered in 50 min. However, this was accompanied with only a partial recovery of [PCr] and [Pi], but no recovery of [NTP]. The intracellular pH was lowered by about 0.2 of a unit, suggesting an increase in glycolysis. 4. In Ca2+-free solution, respiratory inhibition with hypoxia or CN (1 mM) only decreased [PCr], leaving [NTP] nearly unchanged. On the other hand, respiratory inhibition in excess-K+ solution containing Ca2+ (2.4 mM) severely depleted PCr and decreased [NTP] to 40%. Increasing glucose to 50 mM did not prevent these changes, although it increased tension development. 5. The simultaneous decrease of [NTP] and [PCr] during K+ contracture suggests that the activity of creatine phosphokinase is low. The recovery from respiratory inhibition was much better for [PCr] than for [NTP]. Slow, but perfect, recovery of all NTP peaks was produced by adding 1 mM-adenosine to normal solution. 6. It was suggested that tension development is closely related to the turnover rate of ATP, and not to its concentration, and that deamination of adenosine is a limiting factor in the recovery of ATP after excessive consumption.

Biological 1H NMR spectroscopy

Proton nuclear magnetic resonance spectroscopy (1H NMR) is a powerful analytical method used to identify and quantitate chemical compounds. In recent years, it has been used to study rates of metabolism in microbes, isolated perfused tissues, intact animals, and human beings. This review highlights some of the more recent biological applications of 1H NMR in the study of metabolic pathophysiology in animals and man. 1H NMR can rapidly analyze complex mixtures of metabolites found in body fluid and biopsy specimens. In vivo 1H NMR methods can measure intracellular pH, a wide variety of metabolites, tissue perfusion, and rates of metabolism of endogenous and exogenous compounds. Using 13C labeled compounds or magnetization transfer techniques metabolic fluxes may be measured in vivo during virtually all normal and abnormal physiological conditions.

A phosphorus nuclear magnetic resonance study of metabolites and intracellular pH in rabbit vascular smooth muscle

1. 31P nuclear magnetic resonance (n.m.r.) spectroscopy was used to investigate metabolites, intracellular pH (pHi) and the effects of pHi on tone in rabbit blood vessels. The vessels were bathed in mammalian Ringer solution and maintained at 20 degrees C while inside the spectrometer. 2. Vascular spectra showed relatively low phosphocreatine (PCr) concentrations compared to skeletal muscle. The [PCr]/[ATP] ratio was only 1.32 +/- 0.09 (n = 7). There was also a prominent phosphomonoester (PME) peak. Similar features have been reported for other smooth muscles examined by 31P n.m.r. 3. The [PCr] was higher and the inorganic phosphate (Pi) concentration lower than values deduced from chemical analysis of arterial extracts. However, the [PCr] value fell within the range obtained for other smooth muscles when studied by 31P n.m.r. 4. Measurement of pHi under control conditions (external pH 7.25) gave a mean value of 7.19 +/- 0.03 at 20 degrees C (n = 5). Metabolic inhibition brought about by 0.5 mM-cyanide and 0.2 mM-fluoride did not significantly alter pHi. At higher inhibitor concentrations (3 and 1 mM respectively) there was a significant acidosis. 5. The effects of NH4Cl upon pH were investigated in metabolically inhibited preparations. During 10 min applications of 30 mM-NH4Cl (isosmotically substituted for NaCl) the pHi rose; during subsequent NH4Cl removal it fell below control values. In the least inhibited tissues the total pHi excursion between NH4Cl applications and removals was 0.5 unit. 6. Rabbit ear vessels have been found to increase vascular tone during manoeuvres which were expected to decrease pHi. From the direct measurement of pHi reported in this study, it is concluded that the vascular tone changes brought about by NH4Cl application and withdrawal may be attributed to the alteration of pHi.