SUBCHRONIC REPEATED VAPOR EXPOSURE TOXICITY OF 5-VINYL-2-NORBORNENE

5-Vinyl-2-norbornene (VNB: CAS Number 3048-64-4) is an industrial chemical with a potential for exposure to the vapor. To determine any hazards from repeated exposure to the vapor a subchronic exposure study was conducted in which male and female Sprague Dawley rats were exposed to VNB vapor for 6 hours per day, 5 days per week for 14 weeks at mean concentrations of 0, 5, 25.5, and 152 ppm. Subgroups at 0 and 152 ppm were kept for a 4-week post-exposure recovery period. This study was preceeded by a 9-day repeated vapor study in which male and female rats were exposed to mean concentrations of 50, 147, and 352 ppm. In both the 9-day and subchronic studies there were no significant exposure-related effects with respect to signs, mortality, body weights, serum chemistry, or urinalysis. The only hematological effect was an increase in the mean corpuscular volume and mean corpuscular hemoglobin in male rats of the 147 and 352 ppm groups. There were exposure-related increases in liver weights with the 9-day study, but no evidence for liver pathology based on serum chemistry and histology. Liver weights were also increased for males of the 152 ppm group in the subchronic study. Kidney weights were increased in an exposure concentration-related manner for the males of the 9-day study, and for 152 ppm males of the subchronic study. The only histopathological finding was proximal renal tubular hyaline droplet nephropathy in male rats. In the 9-day study, this was present in an exposure concentration-related manner.At 150 and 350 ppm this resulted in scattered areas of proximal tubular necrosis, but there was no serum chemistry or urinalysis evidence for renal dysfunction. At the end of the subchronic exposure period, minimal to mild hyaline droplet nephropathy was seen at 25.5 and 152 ppm, but not at 5 ppm, in the male rats. At the end of the 4-week recovery period, no hyaline droplet nephropathy was seen at any exposure concentration. An association of the nephropathy with f 2u -globulin was demonstrated for male rats of the 9-day study.