The potential reproductive toxicity of caffeine in Sprague-Dawley rats was evaluated using the Reproductive Assessment by Continuous Breeding (RACB) protocol. Based on decreased body weights and feed consumption, increased water consumption, and mortality noted during Task 1, dose levels for the continuous breeding phase for this study were set at 12.5, 25, and 50 mg/kg.
Male and female Sprague-Dawley rats were exposed to caffeine in deionized water by oral gavage at a dose volume of 5 ml/kg. Individual dose volumes were adjusted weekly. During 16 weeks of cohabitation, live pup weight adjusted for litter size was decreased by 7, 7, and 8% in the 12.5, 25, and 50 mg/kg dose groups, respectively. No differences were observed in other reproductive endpoints.
A crossover mating trial (Task 3) revealed no changes on male or female fertility or in pup weight. Reproductive parameters were comparable between dose groups when naive males were mated with control or 50 mg/kg females and when naive females were mated with control or 50 mg/kg males.
The decreased pup weight was observed concomitant with reduced dam weight gain. Throughout the study, the body weights were less than controls in the F0 12.5 (4-7%), 25 (9-15%), and 50 (9-18%) mg/kg males and 12.5 (5-18%), 25 (5-19%), and 50 (8-19%) mg/kg females. Mean feed consumption (g/animal/day) was decreased by approximately 17 and 20% in the 25 and 50 mg/kg animals of both sexes, respectively, during the first week of the study. At necropsy, no differences were noted in F0 male or female absolute organ weight data; however, many relative organ weights (mg/g body weight) were increased in all dosed groups when compared to controls. These differences were attributed to the decrease in terminal body weights. No treatment-related gross or microscopic lesions were observed in the F0 animals.
Evaluation of F0 computer-assisted sperm analysis (CASA) data revealed a treatment-related decrease (3%) in percent motile sperm in the 50 mg/kg F0 males compared to controls. The sperm velocity (mm/sec) was decreased (7-12%) in all treated males. The average radius (m) was also decreased (22-36%) in all treated males. The percent normal sperm was decreased slightly in the 50 mg/kg males when compared to controls. The remaining sperm endpoints were comparable among all groups.
In Task 4 (second generation evaluation), no treatment-related differences were observed in pup weights during lactation (PND 1-21). From the initiation of dosing (PND 22) through the maturation phase up to the termination of Task 4, mean body weights of the F1 low-to-high dose males and females were decreased by approximately 12%, 18%, and 23% when compared to controls. Mean feed consumption values (g/animal/day) were decreased (5-19%) in all treated groups during Task 4. No mortality was observed in any of the F1 animals.
Measures of reproductive performance of second generation breeding pairs revealed a decrease in the number of live F2 pups per litter (21%) and proportion of pups born alive (4%) in the 50 mg/kg dose group. No differences were observed between dose groups in other endpoints.
At necropsy, many decreases were noted in F1 absolute organ weight data and many increases in F1 relative organ weights were observed in all treated groups when compared to controls. These differences may be attributed to the decreased terminal body weights. No treatment-related gross or microscopic lesions were observed in the F1 animals.
As observed in the F0 males, a decrease in percent motile sperm (4%) and sperm velocity (9%) was observed in the 50 mg/kg F1 males compared to controls. The average radius (m) was also decreased (23-26%) in the 25 and 50 mg/kg groups. The remaining sperm parameters were unchanged.
Results of this study show that caffeine is not a selective reproductive toxicant, because the minor effects on sperm motion parameters and pup weight/viability occurred concomitant with, or at doses greater than, those doses that reduced body weight gain. It was demonstrated that exposure to caffeine reduced pup weights in the F0 females at greater than or equal to 12.5 mg/kg and litter size and viability in the F1 generation at 50 mg/kg. The delay to conception observed in humans consuming caffeine (Wilcox, 1988, Williams, 1990, Christianson, 1989) was not observed in this study. The no-observable-adverse-effect level (NOAEL) was not established in this study as the 12.5 mg/kg animals displayed reduced body weight gain.