Transient Intrauterine Hypotension Causes Apoptosis in Fetal Rat Brain and Affects Learning

Abstract

Hypotensive episodes are frequent during pregnancy, and their functional effect on fetal brain has not been studied. We produced systemic hypotension for 30 min during mid-gestation in pregnant rats and examined their offspring on postnatal days 1 and 28. When compared with sham controls, the brain of the hypotensive group contained more TUNEL-positive cells in the hippocampal and periventricular regions on both time points. Spatial learning assessed by water milk maze test was impaired in 28-day-old pups of the hypotensive mothers. According to these results, transient maternal hypotension can induce apoptotic cell death in fetal brain and affect learning. Similar mechanisms may be considered and investigated in the pathogenesis of human learning disorders. Maternal, fetal, or placental factors that diminish uteroplacental and fetal circulation are associated with an increased incidence of fetal CNS malformations (1-3). While marked intrauterine perfusion failure might be related to major malformations, less severe or shorter hypoperfusion may take part in the pathogenesis of minor or functional cerebral disturbances. A frequent cause of hypoperfusion in pregnant women is hypotension: uteroplacental blood flow is known to diminish at blood pressures below 110/65 mm Hg. Hypotension may occur spontaneously, but is most frequently induced by position or drug treatment (4 -6). Orthostatic hypotension in late pregnancy was found to be associated with low birth weight (7,8). Although hypotension is considered potentially harmful for the fetus, its symptoms may be unnoticed or disregarded in pregnancy, and little clinical evidence exists on the effects of moderate and transient hypotension. In our previous experiments simulating hypotensive episodes encountered in pregnant women, we reported that transient maternal hypotension increased apoptotic cell death in the fetal brain (9). In the current study, we investigated the effect of intrauterine hypotensive episodes on cognitive functions in addition to morphologic features. METHODS Gestational hypotension.Ten 3-mo-old pregnant Wistar rats were included in the study: on the 15th day of pregnancy, five were subjected to transient hypotension by femoral artery catheterization (hypotension group) and five underwent all procedures except hypotension (control group) as described before (9). According to preliminary experiments this was associated with an average 46% reduction in uterine blood flow. Briefly, rats were anesthetized following an overnight fasting by intraperitoneal 30 mg/kg ketamine (Ketalar®, Eczacibasi, Istanbul) and 8 mg/kg xylazine (Rompun®, Bayer, Istanbul), the left femoral artery was catheterized, blood pressure (BP) was recorded using a pressure transducer (Transbridge W P I, Sarasota, FL, U.S.A.) and data were sent to computer via MacLab 4/s data acquisition unit (AD instruments, Castle Hill, Australia). Heart rate (HR) and mean BP

Effect of Transient Maternal Hypotension on Apoptotic Cell Death in Foetal Rat Brain

“…To model this physiological phenomenon that occurs during the natural course of pregnancy, maternal hypotension was induced on the 15 th day of pregnancy in rats and we sacrificed animals on the 17 th day and 19 th day (late term) of the pregnancy, representing the last trimester of human pregnancy. In our previous study in which a similar hypotension protocol was used, we demonstrated increased apoptosis in newborn rat brains on postnatal days 1 and 28 (10). Furthermore, increased apoptosis on postnatal day 28 was positively correlated with the impairment of spatial learning, highlighting the clinical significance of hypoxic/ischemic injury in late pregnancy.…”

“…The duration and severity of hypotension may also contribute to the distribution of brain injury, as demonstrated by us and others (3,10,29,30). Clamping of the umbilical cord for 10 minutes caused an injury predominantly in the telencephalon region (29); shorter but repeated episodes (5 minutes, four times) of umbilical cord occlusion damaged the striatum (30).…”

“…Leverkusen, Germany). Pregnant rats underwent surgery on the 15 th day of pregnancy (3,10). Body temperature was monitored with a rectal probe (BIOPAC SS6L, BIOPAC Systems Inc., California, USA) and maintained at 37°C by a heating lamp throughout the experiment.…”

“…The catheterised femoral artery was joined to a pressure transducer (BIOPAC SS13L, BIOPAC Systems Inc., California, USA), which was connected to a data acquisition/analysis system (BIOPAC MP30, BIOPAC Systems Inc., California, USA) to monitor blood pressure. After a 30-minute stabilisation period following catheterisation, systemic hypotension was induced by blood withdrawal (approximately 1 mL per 100 g body weight) within 5 minutes in hypotension groups, as described previously (10,11). As clamping of the uterine vasculature for 30 minutes was previously reported to be sufficient to cause damage in the foetal brain (12), mean arterial blood pressure (MABP) was maintained at 50 mmHg for a period of 30 minutes.…”

Evaluation of apoptotic cell death following transient maternal hypotension in fetal rat brain: temporal pattern within the first 24 h after procedure

“…Low blood pressure and syncopal episodes during pregnancy have been reported to alter fetal perfusion and are associated with increased rates of stillbirth, preterm deliveries, and low birth weight (3)(4)(5)(6). As demonstrated by previous research, perfusion failure during pregnancy causes HI injury to the fetal brain (7)(8)(9), which may subsequently result in fetal brain malformations and increased morbidity and mortality (10)(11)(12).…”