Postnatal ontogeny of metallothionein in various organs of the rat.

Newborn rats have high levels of hepatic metallothionein (MT) which decreased to adult levels by 1 month of age. However, little is known about MT in other organs during this period. Therefore, this study was designed to estimate the MT concentration of major organs during postnatal development. Various tissues were assayed for MT on Days 1, 7, 14, 21, 28, and 35 postpartum and compared to levels in adult rats. The highest concentration of MT was found in liver of 1-day-old rats followed by testes, kidney, spleen, pancreas, intestine, stomach, lung, and brain. Levels in all organs except brain were 2- to 90-fold higher in 1-day-old than adult rats. Hepatic MT remained high for the first week and then decreased steadily to adult levels by Day 28. Concentrations in spleen, pancreas, and heart fell steadily to adult values by 3 to 4 weeks while lung MT levels declined much more rapidly. Renal MT was highest on Day 14 and then decreased to adult values by Day 28. Levels in intestine and stomach remained constant until decreasing to adult values on Day 28. Neonatal brain had lower MT concentrations than adult brain, increasing to adult levels by Day 21. Testicular MT concentrations were 50% higher than adult concentrations on Day 1, decreased to 40% of adult levels by 1 week, and stabilized at adult levels by 2 weeks of age. Cd treatment (3 mg Cd/kg, iv) of 1-week-old rats elevated MT concentrations in all organs except liver, testes, and brain. Zn treatment (20 mg Zn/kg, iv) increased MT concentrations only in liver, kidney, intestine, pancreas, and spleen. The increase in MT concentration in the pancreas following Zn treatment was the most marked of any organ; levels here increased to approximately 2000% of control. Results indicate that MT levels in most neonatal tissues were higher than in adults and that the postnatal ontogeny of MT is organ specific.