The total energy and water metabolism during pregnancy in the rat

Abstract

Many investigations have been made on the metabolic exchanges during pregnancy, both in women and in lower animals. The most important of these have recently been reviewed by Newton (1952). Although all the problems examined remain, to a greater or less extent, incompletely answered, the most notoriously refractory problems of metabolism in pregnancy are those of energy and water exchange. While it is generally accepted that the energy expenditure of the pregnant organism increases during pregnancy, is the increase due to the event of pregnancy or is it simply a reflexion of increasing tissue mass (that is, roughly, body weight) and changes in food intake (that is, roughly, specific dynamic action)? Again, does the pregnant organism normally retain water in excess of that required for the formation of tissue and fluids of the conceptus, and of new maternal tissue in the uterus, mammary glands and elsewhere?The present investigation was designed to contribute something towards the solution of these problems, by measurement, in the rat, of the total energy exchange over prolonged periods, as opposed to short-period basal studies, and by simultaneous measurement of the total water exchange with direct measurement of the water balance.Earlier studies on the energy expenditure of pregnancy have been confined, with one or two exceptions, to short-period measurements of basal metabolism from time to time throughout pregnancy. Only in Dewar's (1953) work on the mouse have data been available to examine the total energy metabolism during pregnancy. Neither, until Dewar's (1953) work, has there been any direct estimation of water balance during pregnancy. The belief that water retention is a general phenomenon of pregnancy has been inferred exclusively from indirect evidence, the main lines of which have been reviewed by Chesley (1944). Dewar (1953) was, however, primarily interested in the part played by the placenta in the control of pregnancy, so all his results, including

The total metabolism of rats during fasting and refeeding

“…The cyclical variation throughout the 24 hr was apparent as before (Morrison, 1955(Morrison, , 1956 Faecal energy 1088 (Fig. 4).…”

“…The problems of obtaining a reliable value for this loss by the methods of indirect calorimetry have been discussed in an earlier paper (Morrison, 1956). The method described there for making adjustment for the addition of water evaporated from other sources (notably faeces) to physiologically evaporated water has been used here.…”

The constancy of the energy expended by rats on spontaneous activity, and the distribution of activity between feeding and non‐feeding

“…increase in a non-feeding activity with restriction of food intake (Ahrens & Wilson, 1966); decrease in a non-feeding activity (Slonaker, 1925 a) with increased food intake and increased total metabolic rate (Morrison, 1956) in pregnancy; a similar but more pronounced effect in lactation (Brody, Riggs, Kauffman & Herring, 1938); the inverse relationship between food intake and non-feeding activity in phases of the oestrous cycle (Brobeck, Wheatland & Strominger, 1947); the decrease of a non-feeding activity in hypothalamic hyperphagia with its partial restoration to normal in the obese phase when food intake returns towards normal levels (Kennedy & Mitra, 1963).…”

Interaction of late pregnancy and lactation in rats

“…Such postpartum pregnancies of lactating rats last longer than pregnancies of non-lactating rats as a result of a delay in implantation of the blastocysts, the duration of which depends on various factors, including the size of the suckling litter (Mantalenakis and Ketchel, 1966). This delay in implantation prevents the overlap of lactation with the last week of pregnancy, during which the growth of the conceptus accelerates and the energetic demands of pregnancy are increasing rapidly (Morrison, 1956).…”