Physiological Anatomical Rodent Experiment (PARE) .04 Feasibility Test 1

The objective of this feasibility study was to investigate the environmental/treatment stresses in the proposed PARE.04 experiments in a ground based study to determine if these stresses were of sufficient magnitude to compromise the planned shuttle experiments. Eighty pregnant Sprague-Dawley rats were received on day 2 (day l equals day of vaginal plug) of gestation (G2) and on G7 60 were laparotomized to determine the condition of pregnancy and allow assignment to test groups. The five test groups (N equals 10 each group) were as follows: Group 1, nominal flight; Group 2, laparotomy control; Group 3, hysterectomy control; Group 4, vivarium control; Group 5, caesarean delivery. On G17, groups 1, 2, and 5 were subjected to unilateral hysterectomy to obtain fetuses for evaluation. There was no difference in fetal crown-rump length, fetal weight, or placental weight in any of the test groups subjected to unilateral hysterectomy at G17. Animals were allowed to go to term and animals in each group delivered between the morning of G22 and the afternoon of G23. Rats assigned to Group 5 began delivering vaginally prior to the designated time for caesarean section, thus only 2 animals in this group were delivered by caesarean section. After delivery, a blood sample was taken from the dam, and they were euthanized and the thymus and adrenal glands weighed. Pups from experimental dams were tattooed for identification, the anogenital distance of male pups was photographed for later measurement, and all pups placed with foster dams and litter sizes were standardized to 10. On day 7, all pups were euthanized, and pup adrenal glands and thymus weighed. Laparotomy at G7 with or without unilateral hysterectomy at G17, had no effect on pregnancy maintenance or vaginal delivery. There was no difference in maternal adrenal or thymus weights or plasma levels of catecholamines, estradiol, progesterone, or corticosterone. Likewise, there was no difference in the anogenital distance (index of fetal stress) of neonatal male pups, between any of the experimental groups. From days 0-7, weight gain from dams in all experimental groups was similar. Lastly, there was no difference in weights of thymus and adrenal glands in pups euthanized at day 7. Collectively, these data indicate that treatment stresses inherent in the proposed PARE.04 experimental design should not compromise the planned shuttle experiments.