CONTINUOUS OR PULSE-AND-WITHDRAW SUPPLY OF ASCORBIC-ACID IN THE DIET - A NEW APPROACH TO ALTERING THE BIOAVAILABILITY OF ASCORBIC-ACID, USING TELEOST FISH AS A SCURVY-PRONE MODEL

In scurvy-prone animals ascorbic acid uptake is regulated by the numbe r of intestinal ''brush-border'' carriers available for transport. The number of carriers is negatively affected by an increasing dietary as corbic acid intake, thus limiting the maximum attainable uptake. We re sted a new approach towards manipulating the information of asorbic ac id in rainbow trout by repeatedly feeding a 10 day ascorbic acid allow ance in a 1 to 3 day ''pulse'' followed by withdrawal, rather than spr ead out over the entire 10 day period. Pulse dosing led to initially i ncreased mortalities compared to continuous dosing, but this was rever sed after continuous dosing, but this was reversed after 55 days. Alth ough individual weight and cumulative mortality were not significantly different after 88 days, total liver ascorbic acid levels were signif icantly higher in the 1-day pulse group (16.3+/-3.9 mu g/g) than in th e 3-day pulse (9.8 +/- 0.9 mu g/g) or continuous (9.3 +/- 0.9 mu g/g) groups. This led us to conclude that after an initial adaptation phase a feeding profile with intermittent ascorbic acid withdrawal results in a compensatory increase in uptake of asorbic acid from the diet and /or a better conservation of the body pool of ascorbic acid opening in teresting new avenues for ascorbic acid dosing and therapy.