Heat loss and energy retention during growth in congenitally obese and lean rats

Abstract

I. Heat losses associated with the utilization of metabolizable energy for synthesis of protein and of fat during growth mere studied in Zuekcr rats selected for normal leanncss or congenital obesity.z. Measurements of energy and nitrogen balance were made on groups of four lean and four fat rats offered food ad lib. and kept at zzo. Balance trials were also conducted on groups of fat or lean rats offered restricted amounts of food at two levels and kept at 22' or 2 8 ' . The medium rations offered to fat and lean rats were the same. The energy and N contents of frlt and lean rats were determined by carcass analysis at 35 d and at about 90 d of age.3. At ad lib. intake, fat rats ate 38 74 more than lean rats. Heat losses and N balance were similar. When fat and lean rats were pair-fed, heat loss and N retention werc lower in fat rats.Absolute values and changes during growth of heat loss (kJ/rat per 24 h) were closely correlated with values obtained for S balance.4. Carcass analysis showed that energy retention in protein was, on average, 75 "/b in lean rats but only 14 % in fat rats. Estimates of energy retention from slaughter experiments and balance trials agreed well, but marked discrepancies existed between the different estimates of N retention.5 . The net efliciencies of utilization of metabolizable energy for growth in lean and fat rats were 0.485 and 0.614 respectively. The energetic efficiencies of net protein synthesis and net fat synthesis were estimated to be 43 and 65 6. The interactions between appetite, growth and activity in the development of obesity in the Zucker rat are discussed.respectively.The efficiency with which a growing animal can synthesize protein and fat dcpends primarily on the amount that it eats. The greatcr the intake of metabolizable energy (ME) in excess of maintenance requirement, the greater the gross efficiency of energy retention. The net efficiency with which fixed increments of a particular food can promote energy retention in an animal may be obtained by measuring the increment of energy retained (kJ) per IOO kJ consumed in excess of maintenance (Blaxter, 1962).Evaluation of different foodstuffs as sources of net energy, e.g. for ruminants, is usually done by measuring their capacity to promote energy retention, principally as fat, in the mature animal (Agricultural Research Council, 1965 ; Nehring, 1969). This is necessary to ensure that the maintenance energy requiremcnt of the animal docs not differ significantly between successive trials and so can be determined with precision (Blaxter, Clapperton & Wainman, 1966). Such experiments cannot however predict the extent to which the efficiency of utilization of energy in the growing animal is affected by the partition of retained energy between protein and fat. The scheme proposed by the Agricultural Research Council (1965) for determining the energy requirements of ruminants for growth avoids the issue by assuming that the efficiency of utilization of ME for production is constant throughout growth, although of course ...

Feeding in response to insulin and 2-deoxy-D-glucose in Zucker rats on dietary self-selection.

“…These results are consistent with the recent report of a dietary self-selection experiment in which Zucker fatty rats were hyperphagic and consumed excessive fat (10). These data suggest that the enhanced appetite for fat may reflect a behavioral mechanism that is related to the lipid storing predisposition of these rats (11)(12)(13). In the preceding paper (2), we observed an inverse relation between fat intake and body energy storage in Sprague-Dawley rats.…”

“…In the preceding paper (2), we observed an inverse relation between fat intake and body energy storage in Sprague-Dawley rats. Although excessive fat accu mulates in fatty rats (11)(12)(13), such a relation was not observed in the present experiment. Furthermore, fatty rats fail to increase their food intake when fed an energy-diluted diet (3), and when large amounts of energy are lost as urinary glucose in diabetes induced by streptozotocin (17).…”

A New Model for Predicting Energy Requirements of Children during Catch-Up Growth Developed Using Doubly Labeled Water

“…Using data from a review of low birth wt infant studies (25), expenditure for formation of fat from dietary triglycerides is 1.8 kcal/g, and that for protein is 7.6 kcal/g. Similarly, evidence from studies of growing pigs and rats (26)(27)(28)35) suggests expenditure for fat deposition from dietary triglycerides and for protein synthesis is 1.4 and 7.2 kcal/g, respectively. Our observed value of 1 kcal/g is consistent with these values.…”

“…FFM was estimated from TBW as described above. Expenditures for fat and protein deposition were estimated as 1.6 kcal/g fat (25,26) and as 7.2 kcal/g protein respectively (27,28) and used to develop the model. Energy stored as fat was assumed to be 9.46 kcal/g and 5.65 kcal/g protein respectively (19).…”

Characterization of embryonic oxygen consumption of two broiler chicken lines differing in body fat content

“…a). Male birds had significanrly higher (P < 0.01) body weight rhan female birds ( (Romanoff 1967 Protein turnover and accretion is an energy demanding process so leaner animals require more energy for maintenance (Pullar and Webster 1974). Protein growth rate during embryonic development is rapid (Muramatsu et al 1987).…”