Norepinephrine synthesis from tyrosine-C-14 in isolated perfused guinea pig heart.

The isolated, perfused guinea pig heart contains all the catalysts required to form norepinephrine from the dietary precursor, tyrosine. The conversion of tyrosine-C(14) to norepinephrine in the perfused heart occurred at a rate comparable to that estimated for this conversion in vivo. To account for the maintenance of norepinephrine stores in the normal heart, it is not necessary to postulate that the hormone is extracted from the blood.