| Summary: | King and Lui (1975) reported that ascorbic acid (1 mg) was effective in protecting against embryotoxic and teratogenic effects of lead acetate (75 ug/egg) administered to chick embryos on the fourth day of incubation. The purpose of the present study was to confirm the work of King and Lui (1975) and to elucidate the mechanism, by which ascorbic acid may afford such protection. It was hypothesized that if ascorbic acid afforded protection by meeting an increased requirement for it, d-isoascorbic acid with only five percent of the antiscorbutigenic activity of ascorbic acid would be less effective in affording protection than ascorbic acid. Secondly, it was hypothesized that if ascorbic acid was acting as a chelator, that other agents known to chelate lead would afford protection against the same effects as ascorbic acid. Since no stability constants had been published for the lead ascorbate complex, ascorbic acid was compared to
ethylenediaminetetraacetate, which has a high stability constant for lead and is not metabolized in vivo and citric acid, which has a low stability constant for lead and like ascorbic acid is metabolized in vivo. The purpose of these comparisons was to determine if ascorbic acid does indeed act as a chelator if it is a weak chelator such as citric acid with very little potential for prophylactic and therapeutic use or a more stable chelator like ethylenediaminetetraacetate with good potential for such applications. Administration of lead acetate (75 ug/egg) to chick embryos at 96 hours of incubation resulted in 50 % mortality, 74 % hydrocephalocele and significant decrements in body weight, crown rump length and wet and dry brain weights in comparison to controls on the 19th day of incubation. No relationship was observed between the presence of hydrocephalocele and decrements in body weight and crown rump length in lead acetate treated chick embryos. However, wet and dry brain weights were significantly less for lead acetate treated embryos exhibiting hydrocephalocele than those not exhibiting this lesion.
The administration of lead acetate (75 ug/egg) simultaneously with ascorbic acid (15 to 80 times the molar concentration of lead acetate) or isoascorbic acid (15 to 60 times the molar concentration of lead acetate) resulted in a significant decrease in mortality, hydrocephalocele, growth retardation and decrements in brain weight induced by lead acetate. Ethylenediaminetetraacetate (15 times the molar concentration of lead acetate) administered simultaneously with lead acetate (75 ug/egg) provided a similar degree of protection to that of ascorbic acid and isoascorbic acid (60 times the molar concentration of lead acetate) with respect to lead induced mortality, hydrocephalocele, and decrements in brain weight. Citric acid (15 to 60 times the molar concentration of lead acetate) administered simultaneously with lead acetate (75 ug/egg) provided a similar degree of protection against lead acetate induced mortality and decrements in crown rump length, but was only half as effective as ascorbic acid (15 to 40 times the molar concentration of lead acetate) in preventing hydrocephalocele. These findings suggest that ascorbic acid prevents the embryotoxic and teratogenic effects of lead acetate in the chick embryo by acting as a chelator, rather than by meeting an increased requirement for the vitamin. As to chelator effectiveness the results suggest that ascorbic acid is more effective than citric acid and less effective than ethylenediaminetetraacetate in preventing the embryotoxic and teratogenic effects of lead acetate on chick embryos. === Land and Food Systems, Faculty of === Graduate
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