AMNIOTIC-FLUID COMPOSITION AND FETAL AND PLACENTAL GROWTH-RATES IN GENETICALLY HYPERTENSIVE AND NORMOTENSIVE RATS

Reduced birth weight has been observed in offspring of the spontaneous ly hypertensive rat (SHR) and in human hypertension. To determine whic h uterine factors might contribute to this fetal underdevelopment, fet al and placental growth rates and the volume and composition of amniot ic fluid were measured in SHR and normotensive control Wistar Kyoto (W KY) rats during the final trimester of intra-uterine development. SHR and WKY fetuses were collected on Days 15-22 of pregnancy, and fetal a nd placental weight and amniotic fluid volume were recorded. The sodiu m and potassium concentrations of amniotic fluid were also measured. P lacental weight was significantly lower in SHR than in WKY between Day s 15 and 20 of gestation, but significantly higher on Days 21 and 22. Fetal weight was significantly lower in SHR between Days 17 and 22. Th ese differences were reduced or abolished when fetal and placental wei ghts were corrected for differences in maternal weight between strains . Amniotic fluid volume was significantly lower in SHR between Days 15 and 18, but significantly higher at Days 20, 21 and 22. Amniotic flui d sodium concentration was relatively constant over the period of obse rvation and not different between strains. SHR amniotic fluid potassiu m concentration was significantly lower than that of WKY near term. Th us, the altered fetal and placental weight of SHR may be due to the ov erall reduced growth rate of this strain. However, the rate of fluid a nd electrolyte resorption close to term is markedly different between strains. The mechanism for this altered fluid and electrolyte handling by the SHR feto-placental unit remains to be determined.