Raymond D. Gilbert

Nifedipine: Effects on fetal and maternal hemodynamics in pregnant sheep

We investigated the effects of nifedipine, a calcium entry blocker, on the fetal and maternal circulation. Nifedipine was administered intravenously for 30 minutes to chronically instrumented pregnant ewes. Infusion of 5 micrograms.kg-1.min-1 resulted in a 30% to 50% increase in total and regional fetal cerebral blood flow to the brain stem, watershed, and subcortical regions (p less than 0.05), without a significant change in fetal oxygenation or cardiac output. Infusion of 10 micrograms.kg-1.min-1 decreased uterine blood flow by 21% (p less than 0.001) and fetal arterial oxygen content by 15% (p less than 0.01), with no further increase in fetal cerebral blood flow. Maternal arterial pressure decreased and heart rate increased (p less than 0.001) without variation of arterial blood gases. Significant plasma levels of nifedipine were detected in the fetal and maternal circulations. In view of the potential adverse effects on the fetus, further studies are needed before nifedipine is considered for use in human pregnancy.

Effect of fetal hypoxia on heart susceptibility to ischemia and reperfusion injury in the adult rat

Objective: Epidemiologic studies showed an association between adverse intrauterine environment and ischemic heart disease in the adult. We tested the hypothesis that prenatal hypoxia increased the susceptibility of adult heart to ischemia-reperfusion (I-R) injury. Methods: Time-dated pregnant rats were divided between normoxic and hypoxic (10.5% oxygen from day 15 to 21) gbroups. Hearts of 6-month-old male progeny were studied using Langendorff preparation and were subjected to two protocols of I-R: 10 minutes of ischemia and 3 hours of reperfusion (I-R10) or 25 minutes of ischemia and 3 hours of reperfusion (I-R25). Results: Prenatal hypoxia did not change basal left ventricular (LV) function. I-R10 produced myocardial stunning and a transient decrease in LV function in control hearts but caused myocardial infarction and a persistent decrease in postischemic recovery of LV function in hypoxic hearts. I-R25 caused myocardial infarction in both control and hypoxic hearts, which was significantly higher in hypoxic hearts. The postischemic recovery of LV function was significantly reduced in hypoxic hearts. I-R25-induced activation of caspase-3 and apoptosis in the left ventricle were significantly higher in hypoxic than control hearts. there was a significant decrease in LV heat shock protein 70 and endothelial nitric oxice synthase levels in hypoxic hearts. Prenatal hypoxia did not change β1-adrenoreceptor levels but significantly increased β2-adrenoreceptor in the left ventricle. In addition, it increased Gsα but decreased Giα. Conclusion: Prenatal chronic hypoxia increases the susceptibility of adult heart to I-R injury. Several possible mechanisms may be involved, including an increase in β2-adrenoreceptor and theGsα/Giα ratio, and a decrease in heat shock protein 70 and endothelial nitric oxide synthase in the left ventricle.

Placental anatomy and diffusing capacity in guinea pigs following long-term maternal hypoxia

To determine the relation of placental structure to placental diffusing capacity (DPCO), we exposed Hartley guinea pigs to 12 or 14 per cent O2 from day 15 of gestation to near term (64 days). At that time we measured DPCO and fetal body and placental weights. In addition, we used stereological techniques to measure placental parameters important to diffusing capacity. We also used a mathematical model with results from the stereological measurements to predict the diffusing capacity. In the first hypoxic group (E1), measured DPCO decreased 10.1 +/- 3.7 per cent, while that predicted was 2.4 per cent less than control. Total vascular volume decreased 6.6 +/- 3.6 per cent, while tissue volume and mean diffusion distance increased 10.2 +/- 5.6 per cent and 12.9 +/- 7.0 per cent, respectively. In the pair-fed animals, measured DPCO decreased 22.6 +/- 4.6 per cent, while that predicted was 20.0 per cent less than control. There were no significant stereological differences in this group. In the second (E2) hypoxic group, measured DPCO increased 27.2 +/- 7.4 per cent, while that predicted increased 38.2 per cent. For this same group, total vascular volume increased 11.7 +/- 3.0 per cent, and tissue volume and mean diffusion distance decreased 18.2 +/- 4.6 per cent and 17.8 +/- 3.8 per cent, respectively. These results demonstrate the dependence of placental diffusing capacity upon placental structure.

The interactions of exercise and pregnancy: A review

Increasing numbers of women engage in relatively strenuous exercise during pregnancy. The interaction of the increased metabolic demands of physical activity with those of pregnancy is poorly understood. We review what is known and what is not known of the extent to which pregnancy affects a womans ability to perform strenuous activity and the degree to which exercise affects the pregnant woman, the fetus, and the infant.

Fetal Cardiac and Cerebrovascular Acclimatization Responses to High Altitude, Long-term Hypoxia

In response to high altitude long-term hypoxemia, the heart of fetal sheep shows a decrease in cardiac output that is secondary to a decrease in myocardial cell contractile function. The intracellular mechanisms responsible for these reductions might include reduced myofibrillar Mg(2+)-activated ATPase. There is also a decrease in beta(1)-adrenergic receptor stimulated augmentation of myocardial contraction. An overproduction of cAMP by beta(1)-adrenergic receptor stimulation, resulting in overphosphorylation of troponin I, may reduce calcium binding by troponin C. Fetal coronary arteries have a reduced contractile response to K(+) depolarization and a reduced sensitivity to a thromboxane A(2) receptor agonist-stimulated contraction. Cerebral arteries of adult sheep (but not the fetus) show decreased responses to both K(+)-depolarization and norepinephrine-induced contraction. Nonetheless, cerebral arteries in the long-term hypoxic fetus demonstrated a number of significant changes from control. For the cerebral arteries in general, high altitude hypoxia is associated with augmented or upregulation of presynaptic functions. In contrast, postsynaptic functions tend to be significantly depressed or downregulated. The results emphasize the role of high altitude, long-term hypoxemia in modulating adrenergic- and serotonergic-mediated signal transduction in the cerebral vasculature. They specifically highlight the significant differences in acclimatization responses between the fetus and adult.

Prenatal cocaine exposure increases heart susceptibility to ischaemia–reperfusion injury in adult male but not female rats

The present study tested the hypothesis that prenatal cocaine exposure differentially regulates heart susceptibility to ischaemia–reperfusion (I/R) injury in adult offspring male and female rats. Pregnant rats were administered intraperitoneally either saline or cocaine (15 mg kg−1) twice daily from day 15 to day 21 of gestational age. There were no differences in maternal weight gain and birth weight between the two groups. Hearts were isolated from 2‐month‐old male and female offspring and were subjected to I/R (25 min/60 min) in a Langendorff preparation. Preischaemic values of left ventricular (LV) function were the same between the saline control and cocaine‐treated hearts for both male and female rats. Prenatal cocaine exposure significantly increased I/R‐induced myocardial apoptosis and infarct size, and significantly attenuated the postischaemic recovery of LV function in adult male offspring. In contrast, cocaine did not affect I/R‐induced injury and postischaemic recovery of LV function in the female hearts. There was a significant decrease in PKCɛ and phospho‐PKCɛ levels in LV in the male, but not female, offspring exposed to cocaine before birth. These results suggest that prenatal cocaine exposure causes a sex‐specific increase in heart susceptibility to I/R injury in adult male offspring, and the decreased PKCɛ gene expression in the male heart may play an important role.

Fetal Myocardial Responses to Long-Term Hypoxemia

In fetal sheep subjected to high altitude hypoxemia for 110 days beginning on day 30 of gestation, cardiac output was decreased 24% compared to normoxic control fetuses. This decrease was due to a 33% reduction in right ventricular output, with only a 14% reduction in left ventricular output. There were no changes in preload or heart rate, but approximately 7% of the reduction in cardiac output could be explained by an increase in arterial blood pressure (afterload). In papillary muscle isolated from long-term hypoxemic fetal hearts, maximum developed tension in response to increasing concentrations of calcium was reduced in both the right and left ventricles, but sensitivity to calcium was increased in both. This finding suggests alterations in the calcium pathway for excitation-contraction coupling in the hypoxemic fetal hearts may be responsible for the reduction in contractility. The mechanism for the decrease in contractility could not be explained by changes in sarcolemmal L-type calcium channel number or sarcoplasmic reticulum calcium release channel number. In addition, there were no changes in the calcium-induced calcium release mechanism involving the sarcoplasmic reticulum, which could explain the reduced contractility. We speculate that the decreased calcium response may be due to other factors, such as the amount of calcium stored in the sarcoplasmic reticulum, myofilament calcium sensitivity, or cellular content of myofilaments.

Regional anatomy of the term human placenta

We have studied regional anatomical variability in four term placentae, comparing both whole placental regions and intralobar zones and plates. In addition, we have emphasized the need for careful selection of the area to be sampled, rather than strictly randomized sampling of the whole placenta. A unique contribution is our quantitative data for a number of structures of the several intralobar zones and plates. The data confirm the hypothesis that the area best suited to physiological exchange is the central region parabasal plate. The relative homogeneity of the intralobar zones in this area make it a representative area for sampling for various placental studies.

Effects of long-term, high-altitude hypoxia on the capillarity of the ovine fetal heart

To determine the effect of chronic hypoxia on myocardial capillarity, we exposed pregnant ewes to an altitude of 3,820 m from day 30 to day 139 of gestation and compared the fetus to low-altitude (∼300 m) controls. We hypothesized that capillarity would increase in the hypoxic myocardium to optimize oxygen and metabolite flux to hypoxic tissues. Fetal hearts were fixed by retrograde aortic perfusion and processed for microscopy and stereological evaluation. Fiber cross-sectional area and capillary density were measured and standardized to sarcomere length. Capillary volume density and capillary diameter were measured, capillary-to-fiber ratio and capillary length density were calculated, and the capillary anisotropy coefficient was obtained from a table of known values. Capillary-to-fiber ratio, capillary volume density, and the capillary anisotropy coefficient were not different between hypoxia and control groups. Capillary diameter was significantly larger in the right compared with the left ventricle of hypoxic but not control hearts; fiber cross-sectional area tended to be larger in the right ventricle of both groups, but this was not significant. As a result of larger fiber size, capillary density and capillary length density were significantly smaller in the right ventricle of hypoxic but not control fetal hearts. Contrary to our hypothesis, the ovine fetus does not show morphological adaptation in the myocardium after ∼109 days of high-altitude hypoxic stress.To determine the effect of chronic hypoxia on myocardial capillarity, we exposed pregnant ewes to an altitude of 3,820 m from day 30 to day 139 of gestation and compared the fetus to low-altitude (approximately 300 m) controls. We hypothesized that capillarity would increase in the hypoxic myocardium to optimize oxygen and metabolite flux to hypoxic tissues. Fetal hearts were fixed by retrograde aortic perfusion and processed for microscopy and stereological evaluation. Fiber cross-sectional area and capillary density were measured and standardized to sarcomere length. Capillary volume density and capillary diameter were measured, capillary-to-fiber ratio and capillary length density were calculated, and the capillary anisotropy coefficient was obtained from a table of known values. Capillary-to-fiber ratio, capillary volume density, and the capillary anisotropy coefficient were not different between hypoxia and control groups. Capillary diameter was significantly larger in the right compared with the left ventricle of hypoxic but not control hearts; fiber cross-sectional area tended to be larger in the right ventricle of both groups, but this was not significant. As a result of larger fiber size, capillary density and capillary length density were significantly smaller in the right ventricle of hypoxic but not control fetal hearts. Contrary to our hypothesis, the ovine fetus does not show morphological adaptation in the myocardium after approximately 109 days of high-altitude hypoxic stress.

Effects of Long-Term Hypoxia and Development on Cardiac Contractile Proteins in Fetal and Adult Sheep

Objective: We studied the effect of long-term, high-altitude hypoxia on cardiac myosin, actin, and troponin T (TnT) isoforms and Ca2+ and Mg2+-activated myofibrillar adenosine triphosphatase (ATPase) activities in fetal and adult sheep. Methods: We exposed pregnant (beginning at day 30 of gestation) and nonpregnant sheep to high altitude (3820 m) for 110 days. Myosin, actin, and TnT isoforms were analyzed by Western analysis. In purified myofibrillar preparations, Ca2+ and Mg2+-ATPase activities were measured by the appearance of inorganic phosphate after the addition of NaATP and various concentrations of either calcium or magnesium to the reaction mixture. Results: We found no change in myosin, actin, or TnT isoform composition after exposure to long-term hypoxia in either fetal or adult sheep. However, Mg2+-activated myofibrillar ATPase activity decreased significantly in the right ventricle of both fetus and adult after hypoxic exposure. There was also a significant maturational increase in both Ca2+ and Mg2+-ATPase activity in control animals. Conclusion: The decrease in Mg2+-activated myofibrillar ATPase activity might affect the decrease in cardiac contractility previously noted in the right ventricle of fetal sheep after exposure to long-term hypoxia. Likewise, the increase in Ca2+ and Mg2+-activated ATPase activities from the fetus to adult could partially explain the previously found maturational increase in cardiac contractility.