Postnatal development of catecholamine uptake and storage of the newborn rat heart.

The ability of atria and ventricular slices of heart removed from Sprague-Dawley rats at ages 1–21 days to take up and store catecholamines was studied to correlate this activity with the previously observed physiologic immaturity of the cardiac sympathetic nervous system in the neonatal mammal. Total uptake and subcellular distribution at 1, 4, 7, 14, and 21 days were determined at various time intervals between 5 and 30 min. In the artria there was a small amount of uptake observed during the first postnatal day, which increased only slightly by 4 days of age. The greatest change occurred between 4 and 7 days. Uptakes at 7, 14, and 21 days were similar to adult values. Reserpine inhibited the 30-min uptake 57% during the first day of life, increasing to 69% inhibition by 7 days of age. Uptake of norepinephrine into the ventricular slices, both with and without reserpine, was less at each age point until 14 days of age, at which time it equaled atrial uptake. The uptake and the effect of reserpine in the particulate fraction of homogenate from both atria and ventricular slices paralleled the developmental pattern seen in the slice. Application of Michaelis-Menten kinetics to uptake at 4 and 7 days revealed a common K_m but differing V_max. These studies suggest that the increases in the ability of the developing rat heart to accumulate norepinephrine is due to increases in the number or storage capacity of synaptic vesicles.