Reversibility of lead-induced depression of growth.

The overall objective of this investigation was to determine whether the growth-depressive effects of lead (Pb) are reversible. The animal model used was the female weanling rat. In Study 1, one group of animals was exposed to Pb for 10 days, a second group was exposed for an additional 21 days, and a third group of animals served as controls. Animals whose Pb was terminated after 10 days caught up completely with controls in terms of linear growth but only partially in terms of ponderal growth. There was no growth catch-up vis-à-vis controls among animals whose Pb exposure was continued for an additional 21 days, to the end of the study. In Study 2, Pb was terminated after only 3 days of exposure. Depression of body weight gain was completely reversed within 1 day after termination of exposure. In Study 3, the role of undernutrition alone (food restriction) was investigated. Depression of body weight gain was immediately apparent and, as with Pb, decrease in linear growth (tail length) was not apparent until later. Catch-up to controls in terms of weight was achieved within 1 day of free access to food when food restriction was for 3 days. Catch-up was also complete after 10 days of food restriction, but was slower (7 days). Evidence for catch-up in terms of linear growth was equivocal. It is concluded that the reversibility of the effects of Pb on growth is dependent on the duration of Pb-induced reduction of food consumption and that linear growth depression is more readily reversible than ponderal growth depression. A final study (Study 4) was undertaken to assess the role of reduced water consumption in limiting food intake and growth. Comparison groups were (1) control, (2) Pb via drinking water, and (3) Pb via sc osmotic pumps. Water consumption was significantly decreased only with Pb by drinking water. Thus, the reduced water consumption with Pb delivered orally seems not to be causally related to the associated depression of food consumption and growth.