Breeding Performance of Rats Exposed Repeatedly to 18,000 Feet Simulated Altitude

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Abstract
Breeding performance was studied . in Sprague Dawley rats exposed to 18,000 feet simulated altitude 4 hrs. daily. A marked increase in hematocrit and oxy-hemoglobin values of exposed rats indicated a pronounced acclimatization response. There was a significant reduction in fertility even though no structural alterations were found in the primary sex organs. The subnormal seminal vesicle/body wt. ratio and abnormal gestation found in exposed rats indicated endocrine imbalance and possibly a constitutional debility. Laparotomy studies showed that a reduced litter size in exposed rats was due principally to fewer successful implantations, and to an increase in fetal resorptions. In controls the mean number of implantation sites per uterus was 9.5, which was reduced to 9.1 after resorption. The mean number of control young per litter observed at birth was 7.6. In exposed rats the number of implantation sites per uterus was 7, which was reduced to 5.3 after resorption. The mean number per litter at birth was 4.1. Cannibalism was of secondary importance in the reduction of litter size in exposed rats. In rats exposed since 14 days of age resorption was not excessive until after 250 days; in rats exposed only as adults faulty gestation occurred at all times throughout the expt. Histologic examination of gestational sacs of re-sorbing fetuses indicated that marginal necrosis and hemorrhage of placenta was a probable cause of fetal death through consequent hypoxia. No structural defects were found in growing fetuses.