The total energy metabolism of non‐pregnant rats

Abstract

Much information has accumulated over the years on the so-called 'basal' metabolism of many mammalian species. Such information is of great value for some purposes, notably for the comparison of the effects on energy metabolism of various pharmacological and hormonal agents. There are, however, objections to the use of 'basal' determinations as a measure of the normal energy economy of the organism. 'Basal' metabolism, better described as the resting, post-absorptive metabolism, can be determined only over relatively short periods, not more than 1 hr and usually not more than 10 or 15 min; the extrapolation of measurements of such short duration to a period of 24 hr can introduce errors of considerable magnitude. Also, it has been pointed out by and by Forbes, that the apparent effect of specific dynamic action (S.D.A.) in the post-absorptive animal is different to that in the normally feeding animal. The diurnal variations in energy expenditure, pointed out by many workers (e.g. , cannot be taken into account by means of single 'basal' determinations; repeated short-period determinations at intervals throughout the day and night, on the other hand, disturb the normal pattern of behaviour of the animal.In the case of small animals a more serious difficulty in the evaluation of the significance of 'basal' energy arises since the post-absorptive animal is difficult to distinguish from the frankly starving animal; in addition, the true resting state is almost impossible to achieve in small animals for more than a few minutes at a time. Brody, Riggs, Kaufman & Herring (1938) have shown that, in the post-absorptive rat, lactation is severely depressed, and within 8 hr of the last feed completely fails. Such a drastic effect on a normal function at the beginning of what is usually regarded as the post-absorptive period is a strong indication that, in the rat, the post-absorptive state cannot be regarded as physiological.

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).…”

“…Diurnal variation in oxygen con8umption. This was found from the total oxygen consumption over each 4-hr period throughout the day and night as described previously (Morrison, 1955). The mean 4-hr oxygen consumption for each 24 hr of experiment has been expressed (Fig.…”

“…The technique has been described in detail previously (Morrison, 1955). Body weight was measured daily.…”

“…Derived values, such as energy expenditure, were computed as described previously (Morrison, 1955). The total respiratory quotients (R.Q.)…”

The total energy and water metabolism during pregnancy in the rat

“…The total energy and water exchanges were measured by 24 hr indirect calorimetry. The closed-circuit respirometer and the analytical and computational methods used were identical with those described previously by Morrison (1955) for work on the non-pregnant rat.…”