Pregnancy-associated changes in renal toxicity of cadmium-metallothionein: possible role of intracellular metallothionein.

Nulliparous female, 10-day and 20-day pregnant rats were injected intraperitoneally with saline or labelled cadmium-metallothionein (109Cd-MTh) at a single dose of 25 or 250 micrograms Cd as cadmium-metallothionein (Cd-MTh)/kg and sacrificed at 24 h. The renal toxicity was manifested by increased 24-h urinary excretion of beta 2-microglobulin (beta 2-m) and the increased number of damaged convoluted proximal tubules at 24 h. The renal excretion of 109Cd and 109Cd content in the maternal liver and kidney and in the foeto-placental unit were determined. The binding of 109Cd to kidney proteins and the level of intracellular metallothionein (MTh) in livers and kidneys were also determined. It was found that the nephrotoxicity of injected Cd-MTh did not differ in nulliparous and 10-day pregnant rats. This result was consistent with the absence of difference in the renal uptake of 109Cd, its binding to kidney proteins and in the content of endogenous MTh in the kidneys between nulliparous and 10-day pregnant rats. In contrast, 20-day pregnant rats exhibited much more nephrotoxicity than nulliparous rats. The most prominent finding in relation to the extreme sensitivity of 20-day pregnant rats was a lower basal level of intracellular MTh in the kidneys and the accumulation of 109Cd in the high molecular weight proteins in the soluble fraction. It is suggested that the decrease of intracellular MTh in the kidneys of 20-day pregnant rats is the reason for the low protection against the renal toxicity of injected Cd-MTh.