Is a positive association between lead exposure and blood pressure supported by animal experiments?

The possible association between low-level lead exposure and blood pressure and the causal nature of any such relationship continue to be debated. A recent meta-analysis of the human model data showed that on average a doubling of blood lead was associated with a rise in blood pressure averaging 1 mm Hg systolic and 0.6 mm Hg diastolic. The older animal studies, however, failed to show a significant pressure increase with massive lead exposure. This review therefore attempts to determine whether the more recent animal studies are supportive of a positive association between lead exposure and blood pressure elevation. Of the 21 animal studies published since 1977, one was carried out in dogs, one in pigeons, and the remainder in various rat strains. In the articles in which all the lead doses had been higher than 1 ppm, the association between blood pressure and exposure was found to be positive in seven, inconsistent in three, absent in four, and negative in one. Of the six animal experiments that employed lead doses not exceeding 1 ppm, five reported a small pressor effect. One of these five positive low-dose studies, however, failed to show a dose-effect relationship when exposure was increased from 0.1 to 1 ppm. In conclusion, most, but not all animal studies published since 1977 found a positive association between blood pressure and lead exposure. However, publication bias may have inflated the number of positive studies appearing in the literature.(ABSTRACT TRUNCATED AT 250 WORDS)