PROTEIN METABOLISM OF THE RAT UTERUS DURING THE OESTROUS CYCLE, PREGNANCY AND PSEUDO- PREGNANCY, AND AS AFFECTED BY AN ANTI- IMPLANTATION COMPOUND, ICI 46,474

Summary. The uptake of [3H]leucine into total uterine protein of the 5-day cycling rat has been examined during the oestrous cycle, early pregnancy and pseudopregnancy and in animals receiving an anti-implantation compound, ICI 46,474. It has been shown that uptake in the oestrous cycle is maximal at dioestrus and minimal at oestrus, an event which is out of phase with the known times of maximal oestrogen release. In the pseudopregnant rat, maximal protein synthesis occurred on Days 3 and 4, the uptake on Days 5 to 8 being the same lowered values as on Day 1. Consideration of this result in relation to changes in the oestrous cycle leads to the con-clusion that the stimulated uptake is not due to oestrogen acting alone. In the pregnant rat, protein synthesis is markedly stimulated by the morning of Day 5 (10.00 hours). Comparing this with results in the pseudo-pregnant rat, it is concluded that the increased protein synthesis is indicative of the commencement of early decidualization which, by this measure, is well advanced at the time of experimentation. It has further been shown that an implantation-inhibiting dose of ICI 46,474 results in a pattern of protein synthesis similar to that found in pseudopregnancy. Examination of this, together with previous data, suggests that ICI 46,474 may suppress the protein synthesis which normally occurs on Day 5 of pregnancy