Protein synthesis during hypoxia in fetal lambs

The goal of this study was to test the hypothesis that the rate of fetal protein synthesis decreases during fetal hypoxia. Catheters were inserted into 13 sheep fetuses under maternal spinal and local fetal anesthesia. Five days after surgery, an infusion of L-[1-14C]tyrosine (0.05-0.25 muCi/min) was begun. Measurements were first made when tyrosine-specific activity reached steady state at 3 h and then again 3 h after fetal oxygen delivery was reduced by lowering the maternal inspired oxygen concentration. Fetal tyrosine uptake across the umbilical circulation was 1.34 +/- 0.20 mumol X kg-1 X min-1 during normoxia and decreased to 0.72 +/- 0.12 mumol X kg-1 X min-1 during hypoxia (P = 0.017). Tyrosine use from the plasma compartment was 1.25 +/- 0.18 mumol X kg-1 X min-1 during normoxia and decreased to 0.64 +/- 0.12 mumol X kg-1 X min-1 (P = 0.0005) during hypoxia. Fetal tyrosine use decreased during reduced oxygen delivery because the rate of tyrosine use for fetal protein synthesis decreased from 0.97 +/- 0.17 to 0.38 +/- 0.09 mumol X kg-1 X min-1 (P = 0.0004). Fetal oxygen consumption decreased by 40 mumol X kg-1 X min-1 during hypoxia. Decreased protein synthesis reduced the energy needed for protein synthesis and explained 28 mumol X kg-1 X min-1 of this reduction.