The effect of phytohaemagglutinin at different dietary concentrations on the growth, body composition and plasma insulin of the rat

Abstract

Young growing rats weighing approximately 83 g were fed on diets containing kidney bean (Phaseofus vulgaris) lectin (phytohaemagglutinin, PHA) in the range of 0 4 4 5 g / k g body weight for 10d to ascertain whether there was a minimum dose below which the lectin had no significant effect on body and skeletal muscle weights in comparison with pair-fed lectin-free controls. Averaged over all experiments, PHA doses of less than 10 mg/d (012 g/kg body weight) reduced body dry weight by 1.14 (SE 0.25) g when compared with controls. Between 10 and 27 mg/d ( 0 1 2 4 3 2 g/kg body weight) a further reduction of 0-64 (SE 0.21) g occurred, suggesting a slight but steady decline of body dry weight with increasing dose. However, above 27 mg/d the depression of growth and changes in body composition accelerated. The difference between the proportional losses of skeletal muscle and body weight was not significant at doses of PHA below 10 mg/d (0.12 g/kg body weight) but the ratio of these losses rose to 1.5-2.0 at doses above this. The proportional decrease in lipid weight exceeded that of both body and skeletal muscle weights at all lectin doses, suggesting that lipid catabolism was the first target of the PHA effect.Plasma insulin level was depressed at the PHA dose of 0.02 g/kg body weight at which growth depression and muscle atrophy were minimal but, contrary to expectations, plasma glucose levels remained stable over the whole PHA dose range. It appears that despite a PHA-induced lowering of blood insulin, glucose catabolism is elevated by an unknown, possibly hormonal, compensatory mechanism. Thus, because low insulin levels facilitate the mobilization and catabolism of lipids, it may be possible to use low doses of PHA to reduce hyperglycaemia and body fat.

Local (gut) and systemic metabolism of rats is altered by consumption of raw bean (Phaseolus vulgarisL. var.athropurpurea)

“…This was consistent with findings with other cultivars (Pusztai, 1991;Bardocz et al 1996). Body reserves are generally low at this stage if rats have been fed with raw beans and blood glucose levels are maintained primarily from dietary sources.…”

“…As a result, the normal healthy gut accounts for 20-35 % of whole-body protein turnover despite forming only 3 -6 % of body weight (Reeds et al 1999). However, turnover times can be reduced to 16-24 h and cell proliferation rates increased when the intestine is stimulated to grow by lectin (King et al 1986;Pusztai, 1991;Bardocz et al 1995Bardocz et al , 1996. The already high requirements of the gut for nutrients are therefore greatly elevated.…”

“…Total saponin content was evaluated by TLC (Johnson et al 1986). Albumin and globulin protein fractions were prepared as described previously (Carvalho, 1992;Bardocz et al 1996), analysed by SDS-PAGE (Hajos et al 1985), and lectins isolated and determined (Martinez-Aragón et al 1995;Bardocz et al 1996). Trypsin inhibitory activity was measured according to Armour et al (1998).…”

“…These are generally present in high concentrations and can be detrimental if consumed in quantity (Pusztai, 1991;Bardocz et al 1996). However, the lectins may also have significant beneficial effects if they are present at low to moderate levels in the diet (Pusztai, 1991;Bardocz et al 1996;Grant, 1999b). In addition, Phaseolus vulgaris contains a number of other bioactive substances with possible health-promoting properties (Ali & Muzquiz, 1998).…”

“…However, the nutritional quality of raw Phaseolus vulgaris is poor, primarily due to the constituent lectins (haemagglutinins). These are generally present in high concentrations and can be detrimental if consumed in quantity (Pusztai, 1991;Bardocz et al 1996). However, the lectins may also have significant beneficial effects if they are present at low to moderate levels in the diet (Pusztai, 1991;Bardocz et al 1996;Grant, 1999b).…”