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

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Abstract
Prenatal exposure to mirex [insecticide] induced a high rate of perinatal death without obvious cause. When fetuses were exposed to a moderate dose of mirex and observed just prior to parturition, 14% died and 9% were apparently dying with serious cardiovascular symptoms. ECG of normal (oil-fed controls) and mirex-exposed rats (6 mg/kg .cntdot. day of insecticide on days 8-15 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 weighed and tattooed so that individuals could be followed to postnatal day 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 1st degree heart blocks and 2% had 2nd-degree blocks. All those with 2nd-degree blocks died shortly after birth. Some 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 were responsible for the majority of the numerous perinatal deaths induced by prenatal exposure to a moderate dose of mirex.