The causes of perinatal death induced by prenatal exposure of rats to the pesticide, mirex. part II: Postnatal observations

Abstract

Prenatal exposure to mirex induces a high rate of perinatal death without obvious cause. Part I of this study (Grabowski and Payne, 1982), in which fetuses were exposed to a moderate dose of mirex and observed just prior to parturition, it was found that 14% had died recently and an additional 9% were apparently dying with serious cardiovascular symptoms. In the present study, electrocardiograms of normal (oil‐fed controls) and mirex‐exposed rats (6 mg/kg·d of insecticide on d 8 to 15 of gestation) were obtained at birth and for several days afterwards. An ECG was obtained from most individuals within 5 min of birth. Pups were then weighed and tattooed so that individuals could be followed to postnatal d 5. Data on 70 control newborns were compared with that on 131 mirex‐treated pups. In the treated group, 23% were stillborn. Of those born alive, 8% died within 6 h of birth, and another 13% within 48 h. At birth, 14% had first‐degree heart blocks, and 2% had second‐degree blocks. All of those with second‐degree blocks died shortly after birth. Some of the other deaths were also correlated with cardiovascular problems. Respiratory problems were also common: 4% were born alive but failed to initiate breathing and several others died several hours after birth after a period of dyspnea. Histological examination of lungs from the latter showed alveolar collapse and evidence of fluid problems. Cardiovascular and respiratory problems are responsible for the majority of the numerous perinatal deaths induced by prenatal exposure to a moderate dose of mirex.