Biochemical and functional alterations in renal and cardiac development resulting from neonatal methylmercury treatment.

Administration of methylmercury (1 or 2.5 mg/kg daily) to neonatal rats caused alterations in both cardiac and renal growth patterns. Heart weights were elevated in the preweaning period in association with hyperplasia (supranormal DNA content); after weaning, the cardiac overgrowth regressed and there was an eventual hypoplasia as evidenced by low DNA content in young adulthood. Renal overgrowth was more pronounced and persistent, but reflected a pure hypertrophy, with no changes in DNA. Renal function was affected by neonatal methylmercury exposure, as assessed through basal clearance techniques. In the immediate period after beginning treatment, there was an impairment of renal function (elevated serum urea, creatinine and osmolality; increased fractional excretions of water, sodium and osmotic particles), with a return to normal by 10 days postnatally. Thereafter, there was a secondary phase of tubular impairment which peaked at the time of maximum hypertrophy. Thus, biochemical and functional indices of organ development can be adversely affected at doses of methylmercury which are usually associated primarily with nervous system-specific damage; effects of methylmercury on neuronal and/or hormonal factors may contribute to the perturbations.