Measurement of fetal tissue protein synthetic rate in the lamb in utero.

The fractional synthesis rate of the mixed proteins in the organs of fetal lambs at 123 to 130 days' gestation were calculated from measurements of the rate of uptake of L14Clysine by the protein in the steady state in utero. The fractional synthesis rates were 82, 121 and 99 per cent per day for the brain, liver and cardiac muscle respectively; the average values of 40 per cent for skeletal muscle was significantly smaller than for the other tissues. The fetal fractional protein synthetic rates measured were similar to those of the newborn lamb, but faster than in the adult sheep by a factor of 10. Similar differences in synthesis rates have been observed between the young and adult rat and the possible reasons for the change in fractional rate during growth are discussed.