Whole-body fuel selection: 'reproduction'

摘要

Fuelselection during mammalian reproduction is characterized by features that are quite different from those employed postnatally. From a cluster of undifferentiated dividing cells within the zona pellucida, the recently fertilized mammalian ovum develops, in a matter of a few days, into a blastocyst differentiated into trophectoderm and inner cell mass. In so doing, it exhibits degrees of control over gene expression and cellular differentiation that dwarf those required by adult tissues for functional competence (Rieger, 1992). Development beyond this point is equally complex. Recent studies on the preferences of the embryo during organogenesis and of the rapidly expanding trophoblast during implantation for specific metabolic substrates illustrate this point (Wales & Du, 1993; Wales & Waugh, 1993a). Even when organogenesis is complete the requirement for metabolic fuels per unit dry weight of fetus is much higher than later on hi pregnancy (Bell, 1992), These examples illustrate the diverse nature of the developmental processes involved in mammalian reproduction and provide a convenient framework for reviewing knowledge on fuel selection from fertilized ovum to newborn.