Starvation experiments/studies

Our studies of the ERT cell cycles show that they are regulated by nutrition (Britton Edgar 1998). If the newly hatched larva is starved for dietary amino acids, DNA replication in most ERTs is not initiated. Under starvation conditions these tissues express low levels of cyclin E and E2F, the transcription factor which is probably responsible for cyclin E expression. If either E2F or cyclin E is induced in starved larvae, DNA replication in the ERTs is activated, and thus expression of these genes appears to limit the ERT cell cycle. When nutrient-deprived larvae are fed, expression of E2F and cyclin E mRNAs increases approximately sixfold, and DNA replication is initiated in most ERT cells. If the animal is first fed and then starved, the ERT cell cycle is activated and then inactivated quite rapidly. These experiments all indicate that the ERT cell cycle is nutrition-responsive, rather than controlled by a rigid developmental program. 

Very few scientihc studies have been carried out on humans during prolonged starvation. One of the first concerned a single individual and later studies confirmed that the responses observed in this classical experiment were not atypical. Tragically, the Second World War provided the opportunity to study the effects of starvation on much larger populations, for example in the Western Netherlands, the Warsaw Ghetto and German and Japanese... 

Laboratory experiments showed that the water content of the muscle of small, immature cod subjected to starvation rose (reflecting protein depletion) from 80% to around 86%, beyond which level the fish died. Larger fish, however, which had spawned several times, could be depleted until the water content of the musculature was over 95% - a remarkable adaptation to the more severe depletion imposed under natural conditions (Love, unpublished). While this phenomenon differs from that described above in fatty fish, it again illustrates a change in the metabolism of fish in response to growth. Likewise, Borisov and Shatunovsky (1973) studied the possibility of using the water content to estimate the natural mortality rate of Barents Sea cod. 

This view of the growth and division of individual cells of this organism is based upon a variety of experimental studies which have involved growth rate shift experiments, shifts of growing cells into starvation media, and growth of yeast populations in different media supporting different growth rates (29-34). 

Similarly, for intractable diarrhea in infants, there are no randomized controlled studies comparing TPN to starvation. However, two small experiences have been reported with 100% survival in an illness which historically has a 40% mortality rate (Hyman et al, 1971 Keating and Ternberg, 1971). The results of these and similar studies have made parenteral nutritional support an integral part of the therapy of this condition. 

Data for calculation of nutritional analyses are much the same for all methods of statistical analysis described above. Basic precautionary steps recommended for selection of individuals, pretest conditions, and standardization of both test animals and test diets have been discussed elsewhere (Berenbaum 1986). Nutritional indices are extremely sensitive to small errors in computation (Schmidt Reese 1986 Stamp 1991), thus, efforts to reduce such sources of variation are of utmost importance in such studies. All consumption experiments must provide food ad libitum unless effects of starvation are being tested, and careful planning and some preliminary experiments may be required to determine how much food must be prepared or obtained in advance to complete the entire experiment. This is especially important when insects are to be tested on plant food to avoid introducing variation in food quality due to difference in plant or leaf age into the experimental design. 

J. K. Kim and White [48, 49] were also concerned with the distribution of rubber on rotors of varying design when experiments were carried out under standard conditions at different fill factors. They studied R/L and R/R rotors that both pumped in the same direction and starvation appeared symmetrically on both rotors at one end of the mixing chamber. The R/R rotors pump in opposite directions and voids open at different ends of the two rotors. 

Maintenance energy flux in non-growing/starved cells is not easily studied. There are at least two difficulties (/) the low rate of metabolic flux and (//) the complexity of potential intracellular energy sources. Microcalorimetry may be an appropriate technique for studies of maintenance energy flux, both because it is not restricted to the metabolsm of any particular substrate and it is a relatively sensitive method (see also section 2.2. for a review see [4]). Care must be taken, however, in how these experiments are performed. It is quite common to concentrate and/or transfer the cells to a new (starvation) medium for these types of determinations. At least in yeast such a transfer has been shown to trigger some kind of endogenous metabolism [26], which should not be confused with maintenance metabolism since periods of an increased... 

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