The myocardial catecholamine content was measured in euthyroid, thyrotoxic, and hypothyroid rabbits. Male rabbits were made thyrotoxic by injection of l-thyroxine, or were rendered hypothyroid by injection of I131. Body weight, basal metabolic rate, serum protein-bound iodine, and appearance were used as criteria of thyroid state. Myocardial norepinephrine and epinephrine concentrations were measured, after alumina column chromatography, by a modification of the trihydroxyindole method. Fluorescence spectra and paper chromatographic analyses confirmed the identity of the trihydroxyindole-fluorescing material, and revealed no extraneous fluorescing substances. In the heart of the euthyroid rabbit, epinephrine concentration averaged 0.3 ± .2 (sd) µg/g in the atrium, and 0.06 ± .03 µg/g in the ventricle. Norepinephrine concentration averaged 2.9 ± .4 µg/g in the atrium, and 2.2 ± .3 µg/g in the ventricle. In thyrotoxicosis, atrial epinephrine and norepinephrine concentrations were decreased, ventricular epinephrine was unchanged, and ventricular norepinephrine was decreased. In hypothyroidism, atrial epinephrine and norepinephrine were decreased and ventricular epinephrine was unchanged, but in the hypothyroid ventricle, norepinephrine content was markedly increased.
Quantifying intracellular single vesicular catecholamine concentration with open carbon nanopipettes to unveil the effect of L‐DOPA on vesicular structure
