Effect of acute exposure to boric acid on the male reproductive system of the rat.

Adult male rats were dosed orally on d 0 with 0 or 2000 mg/kg of boric acid and killed on posttreatment d 2, 14, 28, and 57, or dosed with 0, 250, 500, 1000, or 2000 mg/kg of boric acid and killed on posttreatment d 14. At d 14, atypical structures that appeared to be enlarged irregular cytoplasmic lobes of Step 19 spermatids were observed in Stage VIII seminiferous tubules of rats dosed with 1000 and 2000 mg/kg. Abnormal retention of Step 19 spermatids and residual bodies was also observed in Stage IX-XIII tubules of these rats. The retained spermatids and residual bodies were seen in both the luminal and basal regions of the epithelium. A substantial increase in the testicular sperm head count occurred in animals dosed with 2000 mg/kg. Abnormal caput epididymal sperm morphology and reduced caput epididymal sperm reserves were observed at 1000 mg/kg and higher. Serum LH, FSH, TSH, and prolactin values were not affected at any dosage. At d 28, rats dosed with 2000 mg/kg exhibited continued retention of Step 19 spermatids into Stage X, abnormal caput and cauda sperm morphology, and decreased percentages of motile cauda spermatozoa with reduced straight-line swimming velocities. By d 57 substantial recovery was apparent; some retention of Step 19 spermatids into Stage X tubules was still present in two out of six rats but the sperm parameters were comparable to controls. The study indicated that acute oral exposure to boric acid adversely affected spermiation and sperm quality in the adult male rat. At the dosages used the effects appeared reversible. The no-effect level was 500 mg/kg.