Pregnancy in the Spontaneously Hypertensive Rat

Reports regarding the outcome of pregnancy in the spontaneously hypertensive rat (SHR) as compared to its strain control Wistar-Kyoto rat (WKY) have been contradictory. To determine a profile of pregnancy in these animals 44 female SHR and 40 female WKY were bred, and day 0 of gestation was confirmed by sperm positive vaginal smears. Animals were sacrificed by ether overdose at 15, 18 or 20 days of gestation. The number of corpora lutea, implantation sites, resorptions, dead fetuses, and viable fetuses were counted and the data analyzed by Duncan's multiple range test and ANOVA. P ≤ 0.05 was considered to be significant. To assess histologic differences in placental morphology and deposition of fibrinoid material, placentas were fixed in buffered formalin, paraffin embedded and stained with H&E, PAS, diastase + PAS or colloidal iron. There were no significant strain differences in the number of corpora lutea, total fetal loss (resorptions + dead fetuses) or survival rate (viable fetuses/implants). However, the ratio of implants/corpora lutea for SHR (75.38 ± 2.38) was significantly lower than for WKY (86.35 ± 2.38). This suggests that the lower number of viable fetuses in SHR litters reported previously is due to a smaller number of successful implants. There were no distinct histological differences between SHR and WKY placentas stained with PAS or colloidal iron. However, while areas of hemorrhage in the decidual basalis were frequently observed in both 15 day SHR and WKY placentas, they appeared to be more extensive in the SHR. At 20 days, placentas from 2 SHR were encased by a thick layer of leukocytes. These observations suggest that, in fact, there are differences in the pregnancy of the SHR and WKY; however, whether these differences are directly related to hypertension or other factors, such as hormonal environment, remains to be determined. (Supported by Miami Valley Chapter of American Heart Association.)