Nutritional efficacy of a spermidine supplemented diet

Polyamines (PA) are ubiquitous cell components essential for growth. Dietary PAs are directed preferentially to tissues and organs that have been stimulated to grow by metabolic signals. Nutritional efficacy and growth potential of an oral PA supplement, spermidine (SD), was examined in growing rats. A group of 24-male Sprague-Dawley rats (200-220 g) was adapted to our vivarium conditions for 3 d, then fed ad libitum continuously for 14 d. During feeding they received either a basal diet (n = 8) or a test diet containing the basal diet with 0.05% SD (test diet 1, n = 8) or 0.10% SD (test diet 2, n = 8). This dose of SD corresponds to an intake of 54 and 108 mumol of SD per rat per day. At the end of 14 d of feeding, the animals were sacrificed and plasma, cerebral spinal fluid (CSF) and tissues (muscle, brain, and liver) were harvested for amino acid analysis. Voluntary food intake, body weight gain, and nitrogen excretion and balance were significantly decreased in test diet 2 fed rats compared to test diet 1. The opposing trends in the accumulation/depletion of free amino acids (AA) in muscle and plasma suggests that the exogenous supply of SD blocks the transport of amino acids, as well as PAs from the cells, since AA and PA share the same transport systems. A trend toward decreased weight gain and feeding efficiency was observed when high concentrations of SD were fed. It was concluded that feeding of SD at moderate intake is not toxic and does not retard growth. Oral administration of a smaller dose (<0.05%) of SD may promote further growth. The optimal level of SD dietary supplementation has thus yet to be established.