RENAL-FUNCTION AND HYPERFILTRATION CAPACITY IN LEAD SMELTER WORKERS WITH HIGH BONE LEAD

Objective-The study was undertaken to assess whether the changes in ur inary excretion of eicosanoids (a decrease of 6-keto-PGF1alpha and PGF 2 and an increase of thromboxane) previously found in lead (Pb) expose d workers may decrease the renal haemodynamic response to an acute ora l protein load. Methods-The renal haemodynamic response was estimated by determining the capacity of the kidney to increase the glomerular f iltration rate (in terms of creatinine clearance) after an acute consu mption of cooked red meat (400 g). A cross sectional study was carried out in 76 male Pb workers (age range 30 to 60 years) and 68 controls matched for age, sex, socioeconomic state, general environment (reside nce), and workshift characteristics. Results-The Pb workers had been e xposed to lead on average for 18 (range 6-36) years and showed a three fold higher body burden of Pb than the controls as estimated by in viv o measurements of tibial Pb concentration (Pb-T) (geometric mean 66 v 21 mug Pb/g bone mineral). The geometric mean concentrations of Pb in blood (Pb-B) and Pb in urine (Pb-U) were also significantly higher in the Pb group (Pb-B: 430 v 141 mug Pb/l; Pb-U: 40 v 7.5 mug Pb/g creati nine). These conditions of chronic exposure to Pb did not entail any s ignificant changes in the concentration of blood borne and urinary mar kers of nephrotoxicity, such as urinary low and high molecular weight plasma derived proteins (beta2-microglobulin, retinol binding protein, albumin, transferrin), urinary activities of N-acetyl-beta-D-glucosam inidase and kallikrein, and serum concentrations of creatinine, beta2- microglobulin, urea, and uric acid. All participants also had normal b aseline creatinine clearances (>80 ml/min/1.73 m2) amounting on averag e to 115.5 in the controls v 121.3 ml/min/1.73 m2 in the Pb group. Bot h control and Pb exposed workers showed a significant increment in cre atinine clearance (on average 15%) after oral protein load suggesting that the previously found changes in secretion of urinary eicosanoids apparently has no deleterious effect on renal haemodynamics in the exa mined Pb workers. Conclusion-The finding that both base line and stimu lated creatinine clearance rates were not only significantly higher in the Pb workers but also positively correlated with Pb-T, suggests tha t moderate exposure to Pb may be associated with a slight hyperfiltrat ion state, which has been found to attenuate the age related decline i n baseline creatinine clearance by a factor of two. Although the relev ance of this effect for the worker's health is unknown, it can be conc luded that adverse renal changes are unlikely to occur in most adult m ale Pb workers when their blood Pb concentration is regularly kept bel ow 700 mug Pb/l. One should, however, be cautious in extrapolating thi s conclusion to the general population because of pre-employment scree ning of the Pb workers for the absence of renal risk factors.