Rapid-sequence phosphorus-31 magnetic resonance spectroscopy of the human heart using a 1.5-T clinical system.

PURPOSE: To compare a 'standard' slow phosphorus-31 magnetic resonance spectroscopy (31P-MRS) sequence with two faster sequences in phantoms and healthy volunteers using a 1.5-T clinical system. MATERIAL AND METHODS: Complete 3D localization was performed using a 2D phosphorus chemical-shift imaging sequence in combination with 30-mm axial slice-selective excitation. Two 31P-MRS rapid sequences (RS8-4: 8 x 8 phase-encoding, with an average of 4 acquisitions, and RS16-1: 16 x 16 phase-encoding, 1 acquisition) were compared with the standard sequence (StdP: 16 x 16 phase-encoding, with an average of 8 acquisitions) in phantom and healthy volunteers. RESULTS: Acquisition time for the 31P-MRS procedure with StdP, RS8-4, and RS16-1 in the healthy volunteer studies ranged from 30 to 45, 3 to 5, and 3 to 5 minutes, respectively. Metabolite measurements of healthy volunteers obtained from 31P-MRS using RS8-4 correlated with values obtained using StdP (PCr r2=0.63, P<0.001; ATP r=0.41, P<0.01 and PCr/ATP ratio r2=0.25, P<0.05). There was no correlation between StdP and RS16-1 for either ATP or the PCr/ATP ratio (r2=0.03, P=0.60, and r2=0.11, p=0.26, respectively). Reproducibility (intensity of phosphorus signal) with RS16-1 was worse than that of RS8-4 or StdP. CONCLUSION: 31P-MRS using RS8-4 may be a valid diagnostic tool for patients with cardiac diseases.

Measurement of angiotensin converting enzyme induction and inhibition using quantitative in vitro autoradiography: tissue selective induction after chronic lisinopril treatment.

Angiotensin converting enzyme (ACE) inhibitors lead to induction of ACE in animals and humans. This complicates the use of ACE enzymatic activity as an index of inhibition in plasma or tissues after chronic administration of ACE inhibitors. We have, therefore, developed a method for ACE measurement by in vitro autoradiography using an 125I-labelled inhibitor to quantitate total ACE and the concentration of free (not inhibited) ACE in tissues after prolonged administration of ACE inhibitors to rats. Measurements made on unprocessed tissue sections reflect residual free ACE activity in the presence of the unlabelled inhibitor. In a parallel series of adjacent sections, the ACE inhibitor is dissociated from the enzyme by reversibly denaturing the enzyme by zinc chelation. This is followed by reconstitution of the active enzyme by zinc ion replacement and measuring total enzyme concentration. This technique permits measurement of the extent of ACE inhibition and induction. This method was evaluated in tissues of rats following chronic oral administration of lisinopril (10 mg/kg per day) for 2 weeks. The pattern of ACE inhibition was similar to that seen in our previous acute studies. However, induction of ACE was found to be organ specific; plasma total ACE increased 1.75-fold and total ACE in the lung increased by 30% compared with untreated animals, but there was no demonstrable change in total ACE concentration in the kidney, adrenal or aorta. Despite this, during chronic treatment with lisinopril, ACE activity in all of these organs was inhibited with low levels of free ACE.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypotensive and natriuretic effects of nifedipine in essential hypertension. Role of renal kallikrein-kinin-prostaglandin and renin-angiotensin-aldosterone systems.

To assess the role of renal kallikrein-kinin-prostaglandin and renin-angiotensin-aldosterone systems in the diuretic and natriuretic actions of nifedipine, a calcium-channel blocker, 20 mg of nifedipine was administered orally to 15 patients with essential hypertension. Nifedipine promptly induced a hypotensive effect and an increase in pulse rate. Urine volume, urinary sodium excretion, and creatinine clearance were significantly increased after the administration of nifedipine by 63.5%, 48.5% and 12.4%, respectively. Urinary excretion of kallikrein and prostaglandin E were also significantly increased after the administration of nifedipine by 29.4% and 50.0%, respectively. The change in urinary kallikrein excretion was significantly correlated with that in urine volume (r = 0.70, p less than 0.01) or that in urinary sodium excretion (r = 0.86, p less than 0.01). In addition, the change in urinary prostaglandin E excretion was also significantly correlated with that in urine volume (r = 0.72, p less than 0.01) or that in urinary sodium excretion (r = 0.53, p less than 0.05). Plasma aldosterone concentration did not change despite of the marked increase in plasma renin activity, and plasma aldosterone concentration/plasma renin activity ratio decreased after the administration of nifedipine. These results suggest that the augmented renal kallikrein-kinin-prostaglandin system and the suppressed secretion of aldosterone may be associated with the diuretic and natiuretic action of nifedipine and may contribute to the reduction in blood pressure that is caused mainly by its vasodilatory action.