Studies on Lead Intoxication in the Rat.

The studies described are directed towards the problem of lead intoxication in children and the literature related to this is reviewed. The rat was used as an experimental model. Newborn rats, of albino Wistar and black-and-white Hooded strain, were exposed to lead from birth, first indirectly through mother's milk, then directly through diets containing 0, 0.5, 1.0 or 2.0% lead acetate. By 5 weeks of age the Wistar rats receiving lead, showed various symptoms of lead intoxication ranging from mild growth retardation to total paralysis of the hind part of the body. No paralysis was observed in any of the lead-intoxicated Hooded suckling rats. The growth of lead-intoxicated Wistar suckling rats was retarded compared with their pair-fed controls, indicating that the growth retardation in young lead-exposed animals was partly due to lead and partly due to decreased food consumption. The lead-intoxicated Hooded suckling rats showed less retardation of growth than did the Wistars. This was thought to be due to the fact that the Hooded dams accepted the diets containing lead acetate more readily than the Wistar dams. The determination of the blood and tissue lead concentrations revealed that at 3 weeks of age the lead-intoxicated Wistar suckling rats had significantly higher concentrations of lead than their mothers after a similar period of exposure, and than the lead-intoxicated Hooded suckling rats of same age. Cross-fostering experiments showed that the strain of the lactating mother had no effect on the blood and tissue lead concentrations in the suckling rats at 3 weeks of age. By 7 weeks of age the blood, kidney and liver lead concentrations in the Wistar rats fell to levels observed in the mothers. The concentrations of lead in the brains of the young rats stayed consistently higher than in the mothers. Exposure to lead during the suckling period did not affect the maturation of various physical features and reflexes in the young rats. However, the rate of development was significantly different in the two strains studied, most of the physical features and reflexes appeared fully matured in the Hooded rats 1-2 days earlier than in the Wistar rats. Male Wistar rats exposed to lead (0.5% lead acetate in the diet) for 3, 6, or 12 months did not show any observable ill effect other than a 10% reduction in the body weight. The blood and tissue lead concentrations were similar at 3 and 6 months, slightly increased at 12 months. Except for a slight increase in the aggressive behaviour towards the end of the experimental period and a small, but consistent increase in exploration, the social behaviour of the male rats was not affected by the long-term lead exposure