The Relation Between the Developmental Timing of Birth and Developmental Increases in Urea Cycle Enzymes

Summary

Experimental studies of rat development have shown that the first appearance and possibly part of the preweaning increase of many liver-specific enzymes is due to developmental maturation of the liver itself, but that the major increases in enzyme activity in the perinatal and preweaning periods are due to changing hormone levels. To establish the general nature of this type of developmental regulation we have studied enzyme activity changes during development of the spiny mouse, a closely related murine rodent which has apart from a different developmental timing of the moment of birth, a similar developmental timescale as the rat. Comparison of these altricial (rat) and precocial (spiny mouse) modes of development shows that the first appearance of enzyme activity in the liver (but also in the pancreas and small intestine) is developmental stage-specific, but that the first major increase in enzyme activities awaits the (differently timed) perinatal period. The preweaning increase in enzyme activity appears to be at least partly a developmental stage-specific event. These comparative studies therefore confirm the regulatory model of enzyme accumulation which was derived from experimental studies in the rat. Developmental profiles of human liver enzymes resemble those of the spiny mouse more than they do those of the rat.