chelation therapy causes growth spurt

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Why lead may leave kids short - research suggests that chelation therapy

causes growth spurt - Brief Article

Science News, August 29, 1992

E-mail Print Link 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.