Age‐related dose response of selected reproductive parameters to acute cadmium chloride exposure in the male long‐Evans rat

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Abstract
Groups of male Long‐Evans rats 30, 50, or 70 d old were injected subcutaneously (sc) with a single dose of 0, 5.5, 11.5, or 24.6 μmol Cd/kg as cadmium chloride. All animals were killed 60 d after treatment. At 2 h prior to sacrifice, the rats were injected sc with 100 IU human chorionic gonadotrophin (hCG) to maximally stimulate serum testosterone concentrations. After sacrifice the testes, epididymides and seminal vesicles were removed and weighed. Cardiac blood was taken, and serum concentrations of testosterone (sT) and follicle‐stimulating hormone (sFSH) were determined. Sperm concentration in luminal fluid collected from the vas deferens was determined. Significant (p < 0.01) dose‐dependent effects for all measured reproductive parameters were noted in the 70‐d‐old animals, while no effects were seen in the 30‐ or 50‐d‐old rats in either seminal vesicles weight or hCG‐stimulated sT concentration. In the absence of significant (p > 0.05) changes in body weight gain, effects were seen in testes and epididymides weight, sperm concentration, and sFSH in the 70‐d‐old rats at Cd doses that were lower than those necessary to bring about similar changes in the 30‐ or 50‐d‐old animals. The sensitive indicators of Cd exposure in all age groups were testicular weight > epididymal weight > vas deferens sperm concentration > sFSH concentration. Seminal vesicle weight and sT concentration were found to be the least sensitive. Regression analyses indicated a significant interaction of age with dose; the 70‐d‐old rats required 30–61% less Cd/kg to cause a 50% change in a measured parameter than did the 30‐d‐old animals, while the 50‐d‐old rats required 15–47% less.