Teratogenicity in rats of two dopaminergic agonists

The teratogenic potential of 2 structurally related dopaminergic agonists, BRL 16644 (2-[[3,4-dihydro-2,2-dimethyl-4-[3-(trifluoromethyl)phenyl]-2H- 1-benzopyran-7-yl]oxy]-N,N-dimethyl-Ethanamine: Chemical Abstracts No. 59257-18-0) and BRL 16657 (2-[[3,4-dihydro-2,2-dimethyl-4-[4-(trifluoromethyl)phenyl]-2H- 1-benzopyran-7-yl]oxy]-N,N-dimethyl-Ethanamine: Chemical Abstracts No. 59257-24-8), has been investigated in pregnant Sprague-Dawley rats. These compounds were administered orally from Days 6 to 15 of gestation inclusive at dose levels of 10, 20 and 40 mg/kg/day for BRL 16644 and 10, 20 and 35 mg/kg/day for BRL 16657. At caesarean section on Day 21 of gestation increased post-implantation loss, reduced foetal weights and high incidences of gross abnormalities were found with both compounds at their high dose levels. Maternal toxicity was evident at the intermediate and high dose levels but teratogenic effects extended to the low dose of each compound where treatment was well tolerated by the dams. The maternal effects were thought to be due to the dopamine potentiating properties of BRL 16644 and BRL 16657. When pimozide, a specific dopamine antagonist, was co-administered with BRL 16657 the maternal effects were considerably reduced and, although teratogenicity remained, effects of BRL 16657 on the embryo were extensively modified. This suggests that at least certain of the abnormalities were associated with prolonged dopamine potentiation. Pimozide alone was not teratogenic.