Abstract
Summary
Cardiac norepinephrine content was determined in rapidly and slowly growing preweaning rats. Between 10 and 20 days of age, when the heart rate normally increases from approximately 400 to 500 beats/min, norepinephrine concentration and heart rate increased simultaneously and the rises of both were greater in rapidly than in slowly growing animals. Rate of growth was directly related to heart rate and norepinephrine content at 15 days of age but not at other times during ontogeny.
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