THE PHYSIOLOGICAL EFFECTS OF l-TYROSINE AND l-PHENYL-ALANINE ON THE RATE AND QUALITY OF PULSATION IN THE SEVENTY-TWO HOUR EXTIRPATED EMBRYONIC CHICK HEART.

1. 72 hour isolated chick hearts show an increase in pulsation rate when placed in M/1000, M/10,000, and M/50,000 l-tyrosine solutions. The optimal effect is seen in M/10,000 and M/50,000 l-tyrosine. 2. All hearts show disturbance of rhythm either in the form of irregular rhythm or heart block. 3. 62 hour isolated chick hearts are not susceptible to l-tyrosine while 96 hour hearts are markedly sensitive. 4. 72 hour isolated chick hearts placed in 1 part in 10,000 and 1 part in 50,000 l-epinephrine show approximately the same effects as were seen with l-tyrosine. 5. 72 hour isolated chick hearts placed in M/1000 and M/10,000 l-phenylalanine show an initial depression followed by an l-tyrosine effect.