Metabolism of chick embryonic heart explants during transition from in vivo to in vitro conditions

• 1.1. 15-day chick embryonic heart explants were grown for up to six days in vitro. Metabolic measurements were made immediately after explantation and at intervals thereafter.
• 2.2. Initially more lactate was produced than could be accounted for by carbohydrate available in the medium and tissue. 24 hours later the lactate produced accounted for only about 70 per cent of the glucose utilised. Later still, when the medium was partially depleted of glucose, lactate and pyruvate were utilised by the tissue.
• 3.3. A very low oxygen consumption was found initially. This increased by a considerable factor over the next 48 hours. On renewal of the medium respiration decreased significantly but never fell to the original low level.
• 4.4. The specific activity of acid-soluble phosphorus and lipid phosphorus decreased during 24 hours after explantation when the medium was not renewed. On renewal of the medium at 48 hours both activities rose to levels considerably in excess of those found in newly explanted tissue. Little change was noted in the specific activity of the ribonucleic acid fraction. The specific activity of the deoxyribonucleic acid fraction increased after explantation and increased further after renewing the medium. Later, when the medium was not renewed, it declined.