Influence of palm olein on protein utilisation in the growing rat.

In view of our preliminary findings that refined palm oil (RPOL) enhanced protein utilisation, and because of the growing importance of palm oil in human diets, two separate studies were conducted. The first study aimed to investigate the effect of the palm oil source and fraction on protein utilisation, as determined by net protein utilization (NPU) in growing rats. The second study aimed to investigate the influence of the dietary concentration of one particular palm oil fraction, refined palm olein (RPO) on net protein utilisation. The fat source of each of the semi-purified diets was as follows: crude palm oil (CPO), refined palm kernel oil (RKO), refined palm olein (RPO), refined palm stearin (RPS), and refined palm oil (RPOL). A sixth control group was offered an identical diet but with olive oil (OO, control) as the fat source. Both the oil source (P < 0.01) and the oil level (P < 0.05) influenced NPU in rats. NPU values were generally higher for rats given the RPO-containing diets, particularly at the 20% dietary level (P < 0.01) compared to the diets containing ground nut oil (GNO). The results of these two experiments indicate that RPO influences protein metabolism specifically at a concentration of at least 20% in the diet. This may suggest that RPO is superior to GNO as a source of fat for the rehabilitation of malnourished children. Human trials notably during the rehabilitation of malnourished children may therefore be the next step in this line of research.

Influence of palm oil and palm oil fractions on protein utilisation.

The influence of dietary palm-oil fractions on protein utilisation has been investigated in the growing rat. At 30 days of age, 4-6 groups of four animals were offered one of six semi-purified diets that differed only in the palm-oil fraction. Diets contained 200g casein, 550 g carbohydrate, and 200g fat/kg. The different palm-oil fractions were: crude palm oil (CPO), refined palm-kernel oil (PKO), refined palm olein (RPO), refined palm stearin (RPS), refined palm oil (RPOL). The control groups were given Olive oil (OO) as the dietary fat source. The conversion efficiency of dietary protein was assessed as Net Protein Utilisation (NPU), using a 10-day comparative carcass technique. Weight gain and food intake were not altered by the various palm-oil fractions. However, the NPU of rats given RPO was significantly higher (p<0.05) than that of rats given all other palm-oil fractions or the OO control. It is concluded that the RPO has the potential to significantly improve NPU in the rat, compared to four other palm-oil fractions as well as olive oil.

Milk whey proteins in plasma of sows: variation with physiological state.

The whey proteins alpha-lactalbumin and beta-lactoglobulin have been investigated as potential markers of mammary development in sows by measuring their concentrations in plasma. The whey proteins were isolated from porcine milk by gel filtration, ion-exchange and hydrophobic interaction chromatography, characterized by several criteria and used to raise antibodies. Specific radioimmunoassays were set up for porcine alpha-lactalbumin and beta-lactoglobulin and validated for use in porcine blood and milk. Plasma levels of the whey proteins were measured in sows that were pregnant, suckling litters post partum, weaned abruptly at birth or were pregnant but mastectomized. Both whey proteins showed similar patterns in plasma post partum, falling from a maximum 1 d after parturition to values < 0.02% those in milk by day 4-5 post partum in suckling sows and showing a transient peak associated with early involution before declining to very low concentrations in non-suckling sows. alpha-Lactalbumin was first detected in the last week prepartum, rising markedly in the 3 d before parturition, correlated with rising prolactin (r = 0.986) and falling progesterone (r = -0.998). beta-Lactoglobulin rose much earlier from 5 weeks prepartum, at the time when lobulo-alveolar mammary development is occurring, and correlated (r = 0.929) with oestradiol-17 beta. In mastectomized sows, concentrations of whey proteins in plasma were reduced by 90% or more when compared with intact animals, though following a similar pattern. This study shows that whey protein concentrations in plasma vary with physiological state and reflect aspects of the development of the mammary gland. The very different profiles for alpha-lactalbumin and beta-lactoglobulin prepartum indicate that they are differently controlled.

Hormonal induction of alpha-lactalbumin and beta-lactoglobulin in cultured mammary explants from pregnant pigs.

Mammary tissue from pigs on days 60, 80, 90, 100 and 100+ (days 106-111) of pregnancy has been cultured in vitro as explants. The total accumulation in tissue and culture medium of the whey proteins alpha-lactalbumin and beta-lactoglobulin has been measured using specific radioimmunoassays. The control, uncultured tissue showed progressive morphological development from sparse, non-secretory epithelial tissue on day 60 to full lobulo-alveolar development with some accumulated secretion from day 100. In uncultured explants beta-lactoglobulin could be detected consistently from day 90 (13 +/- 12 ng/micrograms DNA, n = 4) and alpha-lactalbumin from day 100 (1.3 +/- 0.5 ng/micrograms DNA, n = 11). At all stages of pregnancy, both whey proteins increased markedly during the period of culture (up to 7 d). Stimulation of alpha-lactalbumin appeared to be primarily under prolactin control. Prolactin increased alpha-lactalbumin accumulation to a similar extent alone, or in the presence of insulin and/or corticosterone. The response to prolactin was dose-dependent over the range 0.4-20 nM (10-500 ng/ml). Porcine prolactin was more potent than ovine prolactin. There was no effect of porcine growth hormone and no synergism detected between prolactin and tri-iodothyronine. By contrast, no specific hormonal requirements were established for accumulation of beta-lactoglobulin, which appeared to increase in vitro if tissue remained viable in various combinations of insulin, corticosterone and prolactin. It was not stimulated by growth hormone. There was some indication of a prolactin-sensitive component in longer term cultures after day 4.

Effects of lactulose and lactitol on protein digestion and metabolism in conventional and germ free animal models: relevance of the results to their use in the treatment of portosystemic encephalopathy.

Protein digestion and metabolism have been studied in laboratory rats and miniature pigs to investigate the mechanisms of action of lactulose and lactitol when used in the treatment of patients with portosystemic encephalopathy. Lactulose (beta-D-galactopyranosyl-(1----4)-beta-D-fructofuranose) and lactitol (beta-D-galactopyranosyl-(1----4)-D-glucitol) increased the excretion of nitrogenous material in the faeces and decreased nitrogen excretion in the urine in a similar degree to that reported for human patients. In studies with germ free rats given lactulose no such effect was observed, suggesting that, for lactulose at least, these effects are mediated by the gut flora. Measurement of the alpha-, epsilon-diaminopimelic acid content of the faeces confirmed that the enhancement of faecal nitrogen was due to an increased contribution from bacteria. The similarity in the results for lactulose and lactitol suggests that, from the perspective of protein metabolism, lactitol acts in a similar way to lactulose in the treatment of portosystemic encephalopathy.