Catecholamine turnover in normotensive and hypertensive man: effects of antiadrenergic drugs

Intravenous administration of tritium-labeled 3,4-dihydroxyphenylalanine (dopa) to human subjects resulted in the labeling of endogenous catecholamines and vanillylmandelic acid (VMA). Determination of the changes in specific activity of these compounds with time in fractional collections of urine and in cardiac biopsies from patients undergoing corrective cardiac surgery permitted estimation of apparent turnover rates. The average half-time of the exponential decline in specific activity of labeled urinary norepinephrine was about 8 hr and that of VMA was 11-16 hr in five normal subjects. No significant differences from normal were observed in eight patients with essential hypertension. The average half-life of norepinephrine was only 5 hr in cardiac patients undergoing surgery, and the levels and rate of decline of cardiac norepinephrine specific activity correlated well with the exponential phase of the urinary disappearance curve. There were significant effects of treatment with alpha-methyltyrosine, reserpine, and pargyline hydrochloride on the labeling and apparent turnover rates of norepinephrine and VMA; the effects noted were consistent with known actions of these three drugs. It is suggested that the technique used is a suitable means of assessing "over-all" catecholamine metabolism in man, particulary if combined with quantitative assay of urinary catecholamine metabolites.

Diminished glucose tolerance and immunoreactive insulin response in patients with nonischemic cardiac disease

Intravenous infusion of glucose in patients with compensated nonischemic cardiovascular disease has demonstrated that the glucose disappearance slope, G K , is significantly lower than in normal subjects. Immunoassay of plasma insulin in 13 of these cardiac patients showed a reduced insulin response to hyperglycemia in the majority. All had a delayed decline of plasma insulin values.

Plasma free fatty acids (FFA) were significantly elevated in the fasting state but were not significantly correlated with the reduced G K . During the acute hyperglycemia, plasma free fatty acid, potassium, and inorganic phosphate concentrations declined as in the normal subjects. Although cardiac index was reduced in most patients, a linear correlation with G K was not obtained.

To examine the possible role of enhanced sympathetic stimulation seen in cardiac patients, norepinephrine was infused into normal subjects during a glucose-tolerance test (GTT). A decline in glucose tolerance and plasma insulin was observed to levels approximating those seen in the cardiac patients, suggesting a neurohumoral mechanism for the glucose intolerance in cardiac patients. It would therefore appear that the glucose intolerance in compensated cardiac subjects with a reduced cardiac output is frequently an acquired rather than a genetically determined metabolic disorder.

Biochemical studies of energy production in the failing human heart

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