Cardiovascular and biochemical effects of infusion of beta hydroxybutyrate into the fetal lamb.

Previous studies from our laboratory have shown that beta hydroxybutyrate crosses the ovine placenta in small amounts during maternal hyperketonemia and produces significant reductions in fetal PaO2 and increased fetal lactate levels. The present study evaluates the effects of fetal hyperketonemia on fetal and maternal cardiovascular and biochemical parameters. Pregnant ewes (110 to 120 days' gestation) were instrumented with catheters in the femoral artery, femoral vein, and uterine veins, and electromagnetic flow probes were placed on the middle uterine arteries. The fetal carotid artery and jugular vein were catheterized, and a catheter and balloon were placed in the amniotic fluid. Beta hydroxybutyrate (0.44 mmole/min) and antipyrine (0.03 mmole/min) were simultaneously infused directly into the fetal jugular vein for 90 minutes. The fetal beta hydroxybutyrate level increased from a baseline of 0.12 +/- 0.08 to 6.80 +/- 0.46 mmoles/L and was associated with a significant decrease in fetal PaO2 (23.7 +/- 2.4 to 16.0 +/- 0.4 mm Hg) and a large increase in the fetal lactate (1.85 +/- 0.27 to 5.43 +/- 0.92 mmoles/L) at 90 minutes. The present results suggest that during fetal hyperketonemia fetal oxygenation is significantly reduced and may contribute to the increased perinatal mortality in the pregnant diabetic patient.

Effect of maternal ketoacidemia on the pregnant ewe and the fetus.

Poorly controlled diabetic pregnancies are associated with hyperglycemia and elevated ketones. While glucose is known to cross the placenta, there is limited information regarding the placental transfer of ketones and their associated cardiovascular and metabolic effects in the fetus. Thus, the present study was undertaken to evaluate the transfer of the ketoacid beta hydroxybutyrate across the ovine placenta and to determine the effects of this ketoacid on maternal and fetal physiologic and metabolic parameters. Pregnant ewes (110 to 120 days' gestation) were instrumented with catheters in the lateral branch of both uterine arteries, uterine veins, femoral artery, and femoral vein, and electromagnetic flow probes were placed on both middle uterine arteries. Catheters were placed in the fetal carotid artery and jugular vein, and a catheter and balloon were placed in the amniotic fluid. Beta hydroxybutyrate (0.39 mmole/100 ml of uterine blood flow) and antipyrine (00.27 mmole/100 ml of uterine blood flow) as a second reference marker, were infused simultaneously into the uterine arteries for a period of 2 hours. The beta hydroxybutyrate concentrations in the uterine vein increased to 5.93 +/- 1.32 mmoles/L, and were associated with a significant increase in maternal heart rate and a slight but significant reduction in uterine blood flow. No changes in maternal arterial blood gas values were noted. The concentration of beta hydroxybutyrate in the fetal carotid arteries increased from 0.01 +/- 0.01 mmole/l to 0.15 +/- 0.03 mmole/L, and were associated with a significant reduction in fetal PaO2 (24.2 +/- 0.9 to 17.9 +/- 1.9 mm Hg) and an elevation of fetal lactate levels (1.86 +/- 0.17 to 5.07 +/- 1.56 mmoles/L).

Effect of bisenoic prostaglandins and arachidonic acid on the uterine vasculature of pregnant sheep.

Prostaglandins have been implicated as regulators of uteroplacental blood flow during pregnancy. However, the investigation of the vascular effects of these humoral agents has been extremely limited. The present study has evaluated the effects of intra-arterial infusions of prostaglandin D2, E2, F2 alpha, I2, 6-keto-F1 alpha, thromboxane B2, and bolus injections of the prostaglandin precursor arachidonic acid into the uterine vasculature of late-term pregnant ewes. Prostaglandins E2, F2 alpha, 6-keto-F1 alpha, and thromboxane B2 all reduced uterine blood flow, with prostaglandins E2 and F2 alpha being much more active. Since prostaglandins E2 and F2 alpha increase uterine tone, a portion of their vascular effects appears to be due to myometrial compression. In contrast, prostaglandins D2 and I2 produced dose-related increases in uterine blood flow in pregnant animals and did not alter uterine tone or contractile activity. Arachidonic acid produced dose-related increases in uterine vascular resistance in three out of five animals and had no effect in the other two animals. The differential vascular effects produced by the individual prostaglandins and their precursor suggest that the overall effect of these compounds on the uterine vasculature will depend on the summation of the individual actions.

Effects of vasoactive polypeptides on the uterine vasculature.

Estrogen-induced increases in uterine blood flow appear to require de novo protein or polypeptide synthesis. In the present experiments a chronically catheterized nonpregnant sheep preparation was used to determine the uterine vascular effects of vasoactive intestinal polypeptide (VIP), neurotensin, and substance P. These effects were compared to those of bradykinin and the most potent vasodilator prostaglandin, prostacyclin. An intra-arterial catheter was placed in a branch of the main uterine artery to allow administration of the compounds directly into the uterine vasculature. Uterine blood flow was continuously monitored via an electromagnetic flow transducer on the maine uterine arteries. VIP, bradykinin, and prostacyclin were equally potent as vasodilators of the uterine vasculature, while neurotensin and substance P were totally devoid of vasoactivity. Unlike estradiol, bradykinin and VIP produced significant changes in systemic arterial pressure and heart rate, suggesting that these compounds may not have responsible for mediating the uterine vascular response observed after estrogen. However, VIP was a potent uterine vasodilator and was able to totally ablate uterine contractile activity, suggesting that this endogenously occurring polypeptide may be important in regulating uterine hemodynamics and contractile activity.

Current concepts of amniotic fluid dynamics.

Amniotic fluid at term in the human is the product of numerous exchanges with the fetal and indirectly, the maternal compartments. Our current information on the formation, circulation, and removal of this fluid is limited but provides an interesting concept of the steady-state regulation of this space. Further confirmation of this model comes from data describing drug exchange between mother, fetus, and amniotic fluid.

Comparison of human and sheep chorion laeve permeability to glucose, beta-hydroxybutyrate, and glycerol.

Significant permeability of in vitro human chorion laeve to glucose, glycerol, and beta-hydroxybutyrate (betaOH butyrate) and in vitro sheep chorion leave to glycerol and betaOH butyrate was measured. Diffusion across these tissues of glycerol and betaOH butyrate corresponded to the relative molecular size, charge, and lipid solubility of these compounds. The simple diffusion of glucose across human chorion leave was somewhat reduced by metabolic conversion of this compound during the transfer process. Demonstration of in vitro human placental tissue permeability to ketoacids and glycerol suggests that these compounds cross to the fetus when elevated in the maternal diabetic state.

Changes in amniotic fluid glucose, beta-hydroxy-butyrate, glycerol, and lactate concentration in diabetic pregnancy.

Amniotic fluid glucose, beta OH butyrate, glycerol, and lactate concentrations were measured in 75 samples collected in the third trimester of pregnancy from 50 diabetic patients, all but four of whom required insulin. Increases in maternal fasting plasma sugar were accompanied by corresponding increases in amniotic fluid glucose and on occasion increases in amniotic fluid beta OH butyrate. These data correspond to previous reports of placental glucose transfer and in addition, provide statistically significant evidence of placental betaOH butyrate transfer since the hyperglycemic, hyperinsulinemic fetus of a diabetic mother would be a poor primary source for ketogenesis. Relatively poor correlation of elevated fluid levels of these solutes to fetal outcome probably reflects a low incidence of maternal hyperglycemia, ketogenesis. Relatively poor correlation of elevated fluid levels of these solutes to fetal outcome probably reflects a low incidence of maternal hyperglycemia, ketoacidosis, and over-all reduced neonatal morbidity-mortality rates in this group of metabolically well-controlled, predominantly insulin-requiring diabetic patients managed in a regional high-risk perinatal center.

The effects of changes of maternal PaO2 and PaCO2 on the fetal PaO2 and PaCO2--in vivo study.

Umbilical PaO2 and PaCO2 were continuously monitored in vivo in acute fetal lamb preparations with a semipermeable membrane connected to a mass spectrometer. The response time of this system (0 to 90% of final value) was 36 sec. In seven pregnant sheep (128--135 days gestation) the maternal inspired mixture was abruptly changed and the following changes in fetal PaO2 and PaCO2 were observed: (1) 100% O2 to room air: PaO2 decreased from 21.5 +/- 0.8 (mean +/- SEM) to 14 +/- 1.1 mm Hg at a rate of 1.63 +/- 0.33 mm Hg/min. Following return to 100% O2 the PaO2 returned to 21 +/- 1.1 mm Hg at a rate of 2.44 +/- 0.4 mm Hg/min. (2) 100% O2 to 12% O2/10% CO2: after 6 min the PaO2 fell from 19.3 +/- 1.3 to 6.3 +/- 0.3 mm Hg at a rate of 4.65 mm Hg/min and the PaCO2 rose from 37 +/- 8 to 70 +/-5 mm Hg. At 100% O2 the PaO2 returned to 19 +/- 1.0 mm Hg at a rate of 11.76 +/- 0.086 mm Hg, the PaCO2 to 39 +/- 7 mm Hg. (3) 100% O2 to 90% O2/10% CO2. The PaO2 and PaCO2 increased by 4.7 and 22 mm Hg, respectively. The changes of fetal PaO2 and PaCO2 occurred after 1 minute of changing in maternal inspired mixture except in the transition from 12% O2/10% CO2 to 100% O2 (34 +/- 12 sec). Following the reinstitution of 100% the fetal PaO2 and PaCO2 returned to their previous values within 4 and 16 min, respectively.

Factors determining human chorion laeve permeability in vitro.

An increased mean diffusion permeability across human chorion laeve in vitro was measured for meperidine (D = 5.26 x 10(-6) cm.2 sec.-1) and diazepam (D = 4.51 X 10(-6) cm.2 sec.-1). These values corresponded to large chloroform-buffer partition coefficients (49 and 29) measured for these two compounds. Diffusion permeability values of 3.98 and 2.18 x 10-6 cm.2 sec.-1 measured for urea and glucose corresponded to their relative insolubility in lipid, as indicated by chloroform-buffer partition coefficients of 0.05 and 0.0004, respectively. An increase in placental permeability in vitro to the weak organic acid 5,5-dimethyl, 2,4-oxazalidinedione at lower pH's corresponded to an increase in the fat-soluble nonionized fraction of this compound. These data support the concept that this tissue is most permeable to compounds of relatively small molecular size and/or with a high level of lipid solubility. The large diffusion permeability values measured for meperidine and diazepam suggest that these compounds will diffuse rapidly between mother and fetus at a maximal rate limited only by uterine blood flow.

Epidemiology of group-B streptococcal carriage in pregnant women and newborn infants.

In a population of pregnant women, the prevalence of group-B streptococcal carriage was relatively low. During the 3rd trimester of pregnancy 5-6% of women haboured group-B streptococci and 8-3% were positive at the onset of labour. Some 42% of women who gave positive cultures in labour had given negative cultures during the 3rd trimester and 19% of women who were positive during late pregnancy were culture-negative in labour. The conversion of culture status observed in these women suggests that carriage may be intermittent or that new acquisition of genital-tract streptococci may occur in late pregnancy. The unpredictability of conversion diminishes the reliability of a single culture taken during the 3rd trimester of pregnancy.

Permeability of chorion laeve to succinylcholine in vitro.

The simultaneous diffusion of 14C-succinylcholine and p-amino hippurate across human placental tissue in vitro was measured. Column chromatographic purification of the radioactivity followed by paper chromatographic analysis showed little alteration of the succinylcholine during the course of these experiments. Similar chloroform-buffer partition coefficients for the two solutes were measured. Thus in these experiments, the nearly identical transfer rates of these two similar sized, lipid-insoluble compounds indicated that succinylcholine crosses human placental tissue in quantitites compatible with its molecular size and lipophobic nature, and that the diffusion rate is not significantly influenced by its increased molecular charge.

Permeability of human chorion laeve to diazepam and meperidine.

In vitro placental permeability to diazepam (Valium) and meperidine (Demerol) in excess of that measured for antipyrine, suggest that these compounds will diffuse across placental tissue in vivo at a maximal or perfusion-limited rate. Such findings correspond to the high fetal blood levels reported for these substances following maternal administration and indicate that these lipid-soluble analgesics cross this tissue by transcellular as well as extracellular pathways.

Non-ionic diffusion of pentobarbital across human chorion laeve.

Diffusion of the weak organic acid, pentobarbital, across human chorion laeve in vitro shows an inverse correlation with pH, when corrected for extracellular space permeation by the concurrent measurement of membrane permeability to the lipid insoluble molecule, p-aminohippurate. The temperature dependence of pentobarbital diffusion at different pHs supports the concept that the additional net flux of solute at lower pH occurs by transcellular permeation by the non-ionized moiety, the observed increase corresponding roughly to the dissociation curve for pentobarbital.