Why lead may leave kids short.

Several studies have shown that high levels of lead in the blood can hinder a child's growth (SN: 9/21/91, p.189). To explore why, Carol A. Huseman of the University of Nebraska Medical Center in Omaha and her co-workers studied 12 children for up to one year, measuring growth rates and levels of hormones that play pivotal roles in regulating growth.

Six children were studied before and after chelation therapy to reduce their toxic levels of lead (41 to 81 micrograms per deciliter of blood). Lead levels in the other six (5 to 38 [unkeyable]g/dl) did not warrant chelation, Huseman says.

In the August PEDIATRICS, her team now reports diminished levels of two secretions -- growth hormone and insulin-like growth factor-1 (IGF-1) -- among children in the higher-lead group. In contrast to the low-lead group, children requiring chelation also grew far more slowly than normal. Following therapy, however, each lead-chelated child experienced a growth spurt; in one case, the bone-growth rate almost tripled.

The researchers also assayed several growth-hormone characteristics every 20 minutes throughout one 24-hour period prior to chelation therapy in two children with extremely high blood-lead levels. Nearly all of the features studied in this pair -- such as average and peak nighttime growth-hormone concentrations, and the number of hormone pulses released into the blood -- compared unfavorably with values seen in normal short children, and even in children suffering from growth-hormone neurosecretory dysfunction.

Earlier work by the Omaha group showed that high levels of lead inhibit thyroid-stimulating hormone, a pituitary-gland secretion that also helps regulate growth. In the new study, when Huseman's team administered drugs to stimulate the pituitary gland's release of growth hormone, all 12 children produced levels of the hormone that fell within a normal range. Taken together, Huseman says, these findings suggest lead's role in limiting height may occur early in the chemical chain of events regulating bone growth, perhaps in the brain.

Indeed, says Mark Hartman of the University of Virginia in Charlottesville, the new study suggests that the pituitary may be able to respond, but is not doing so because lead keeps the brain from secreting enough of the hormones that trigger the pituitary's growth-hormone release. However, Huseman adds, the new data cannot rule out that lead may also affect height more directly -- by inhibiting IGF-1, which stimulates cell proliferation in the "growth plate" at the ends of bones.