Effects of prenatal X-irradiation on the 14th-18th days of gestation on postnatal growth and development in the rat.

Thirty-nine pregnant adult Wistar strain rats were randomly assigned to one of three exposure groups: 0, 0.75, or 1.50 Gy X-radiation total exposure. Animals were exposed from the 14th to the 18th days of gestation at 0, 0.15, or 0.30 Gy per day. At term, 15 rats were killed and morphologic analyses were completed. Twenty-four rats were allowed to deliver their offspring. On the first day of postnatal life, litters were reduced to a maximum of eight pups per litter, with equal numbers of male and female offspring wherever possible. A total of 187 pups were observed for the age of acquisition of five reflexes (air righting, surface righting, visual placing, negative geotaxis, auditory startle) and the appearance of four physiologic markers (pinna detachment, eye opening, vaginal opening, testes descent). There was significant dose-related weight reduction in term fetuses and offspring throughout the 86-day postnatal period. Postnatal growth rate (g gained/day) was unaffected. Adult offspring brain and gonadal weight and organ weight:body weight ratios were reduced. Using the PAC50 methodology, dose-related alterations occurred in the acquisition of several reflexes. All physiologic markers exhibited a dose-related delay in appearance. These results indicate that fractionated exposure to X-radiation during the fetal period in the rat results in dose-dependent alterations in postnatal growth and physiologic development. These studies are important for our understanding of the long-range effects of prenatal exposure to ionizing radiation late in gestation.