Toxicity and distribution of lidocaine in nonasphyxiated and asphyxiated baboon fetuses

The dosage and blood concentration of lidocaine required to produce central nervous and cardiovascular system toxicity in both nonasphyxiated and asphyxiated fetuses were determined in ten pregnant baboons with fetuses of average gestation of 158 days (term, 185 days). Lidocaine was infused into the fetal jugular vein until cardiac arrest occurred, following which fetal brain, heart, lungs liver and kidneys were obtained. Mean dosage and blood concentration of lidocaine associated with seizures were 9.4 mg/kg and 15.2 micrograms/ml, respectively, in the nonasphyxiated fetuses, and 3.9 mg/kg and 5.6 micrograms/ml, respectively, in the asphyxiated ones. The dosage and blood concentration of the drug required to produce cardiac arrest were significantly higher in the nonasphyxiated group (35 mg/kg and 269 micrograms/ml, respectively) compared to the sphyxiated group (9 mg/kg and 40 micrograms/ml, respectively). Tissue-plasma ratios of lidocaine were significantly higher (P less than 0.05) in the brain, heart, and liver of the asphyxiated fetuses as compared with the nonasphyxiated ones. The relative proportion of the injected dose found in the organs was also higher (P less than 0.05) in the asphyxiated group. These results indicate that the increased sensitivity of the asphyxiated fetus to lidocaine may be related in part to a greater uptake of local anesthetics by the fetal organs.

Fetal lamb lung phosphatidylcholine: response to asphyxia and recovery

Acute fetal asphyxia resulting from maternal blood loss and hypotension causes a reduction in the incorporation of precursors into disaturated phosphatidylcholine, the principal lipid in the pulmonary surfactant. Treatment of the maternal hypotension is associated with return of fetal lung DSPC synthesis to control levels by 72 hours.

Fetal adrenal medulla

The development of the fetal adrenal medulla can be considered an integral part of the complex process of maturation and preparation of the fetus for extrauterine life. Our understanding of the fetal sympathoadrenal function is facilitated by the relative separation that exists between the maternal and fetal catecholamine secretion and metabolism. There is accumulating evidence that the catecholamines fulfill a vital role at the time of delivery by controlling nonshivering thermogenesis and cardiovascular regulatory mechanisms. They also may play a role in the carbohydrate metabolism by triggering the neonatal glucagon surge, known to be important to the augmentation of hepatic glucose output in the newborn. Though the role of epinephrine in the adaptation of the human neonatal lung to extrauterine life remains to be defined, it may be extrapolated from experimental data that the secretion of surfactant from type II alveolar cells is dependent on epinephrine. Additional studies are needed to broaden our understanding of the process of adrenal medullary maturation and responses in the fetus. Further studies will have to e done to define all the roles the catecholamines play in fetal life. The refinement of methodology in recent years will facilitate this task. It is our belief that in the near future catecholamine determinations will be utilized to quantify and evaluate fetal stress in conjunction with biophysical assessments.

[Posthypoxic changes in the metabolism of the developing brain]

Effect of intranatal hypoxia on content of adenylic nucleotides, glycogen, lactic acid as well as on activity of ATP-ases and concentration of free amino acids was studied in rat brain tissue at various periods of postnatal development (I day-5 months). Acute hypoxia was accompanied by a decrease in content of adenylic nucleotides and glycogen, by an increase in concentration of lactic acid and by a decrease in activity of ATP-ases. During the subsequent periods, in brain tissue of animals, subjected to hypoxia, posthypoxic activation of energy metabolism was found, which depended apparently on the decreased intensity of plastic processes during the phase of active growth and of neurone differentiation. Content of the essential amino acids, actively participating in protein synthesis, was increased but concentration of nonessential amino acids was decreased at this step. The subsequent decrease in content of macroergic compounds, increase in concentration of lactic acid and inorganic phosphate as well as the decrease in activity of ATP-ases were observed in 1.5-2 months old experimental animals. The biochemical and mophological data suggest that intranatal hypoxia is responsible for irreversible impairments in developing brain.

[Change in the free amino acid concentration of the developing brain under the influence of antenatal hypoxia]

Concentration of free amino acids was studied in various parts of brain (hemisphere, brain stem) of 14- and 30-days old rats with antenatal hypoxia. In hemispheres of 14-days old rats concentrations of 5 amino acids were altered, in the brain stem content of 3 amino acids was altered. In the pool of free amino acids of the 30-days old gats content of 7 amino acids was altered in hemispheres and content of 9 amino acids - in the brain stem. More rapid accumulation of cystathionine in hemispheres and of glycine in the brain stem was observed in animals with antenatal hypoxia. In these conditions accumulation of glutamic acid in hemispheres and of taurine - in the brain stem was retarded as compared with control animals.

Vasopressin in fetal sheep: a review

Advance in fetal sheep surgery has allowed investigation of vasopressin physiology at the end of gestation (100 to 140 days). In the fetus of that age, vasopressin is present in the pituitary and in the blood. The hormonal secretion is stimulated by hypotensive and hyperosmolar stimulus. Hypoxemia is also reported as being a potent stimulus of vasopressin secretion and may have an important effect on blood pressure control.

Lung alterations in newborn rabbits after maternal thrombin-shock. II. Lung phospholipids

Alterations of the lung- and lung lavage fluid-phospholipids (PL's) after a maternal thrombin-shock have been studied in 1 and 5 h old newborn rabbits delivered at days 28 and 30 of gestation. In lung wash the amount of PL increases during the period of gestation and during the first hours of life. In asphyxiated mature animals the PL-content is statistically significantly decreased. The very low PL-content of the lung wash in premature born animals is not affected by asphyxia. The amount of phosphatidyl choline (PC) as a percentage of total PL is unchanged in all animals studied. The PL and PC content in the lung tissue follows the same developmental pattern but the differences are not statistically significant. Changes in the lung weight/body weight (LW/BW)--ratio after asphyxia show a disturbed development of the newborn lung, too.

[Effect of etimizol and sodium hydroxybutyrate on the compensatory-adaptive capabilities of newborns with chronic hypoxia]

Daily injections of 5 mg/kg of aethimizol to female rabbits during the last week of pregnancy results in normalization of the central nervous and cardiovascular systems reactions in response to a graded mechanical stimulation, in an increased ATP content in the erythrocytes, lesser acidotonic shifts in the blood and marked diminution in the number of stillbirths. Under similar conditions of the exeriment sodium oxybutyrate in a dose of 200 mg/kg did not contribute to normalization of the central nervous and cardiovascular systems response reactions, nor did it lower the acidosis in the blood and had no marked effect on the reduction in the number of stillbirths.

Asphyxia-induced disaggregation of cerebral polyribosomes in rhesus monkey fetuses

The effects of 3 hours of controlled intrauterine asphyxia (acidotic hypoxia) on the sedimentation patterns of cerebral polyribosomes and on polyribosome supported in vitro protein synthesis were examined in 16 term monkey fetuses. Three outcomes resulted. Four fetuses showed no changes in polyribosome sedimentation profile or in sedimented polyribosome supported in vitro protein synthesis. Four showed changes in sedimentation profiles indicating partial breakdown of polyribosomes and significant decreases in polyribosome supported in vitro protein synthesis. Finally, 8 fetuses showed almost complete disaggregation of cerebral polyribosomes into 80-S monosomal units. This was associated with marked reduction in sedimented ribosomal mediated in vitro portein synthesis. Both the disaggregation of polyribosomes and the associated loss of in virto protein synthesis were related to the severity of the acidosis produced by asphyxia.

Cerebral oxidative metabolism during intrauterine growth retardation

Cerebral oxidative metabolism during intrauterine growth retardation was investigated utilizing a pregnant-rat model. Dams were subjected to unilateral uterine artery ligation on the 17th day of gestation. At term, they were sacrificed by decapitation and the fetuses delivered by cesarean section. Body and brain weights of fetuses from ligated uterine segments were smaller than those of offspring from nonligated horns of the experimental rats or those from sham-operated dams. Blood glucose at birth was reduced by 25% in growth-retarded fetuses. Cerebral oxidative metabolites, including glycogen, glucose, lactate, ATP, and phosphocreatine, were not different from control levels. These findings suggest that neither tissue hypoxia nor deficient glucose delivery to brain can account for the stunted cerebral growth observed in fetuses following uterine artery ligation.

Perinatal changes in glycolytic function in response to hypoxia in the incubated or perfused rat heart

Glycolysis was assessed in the rat heart during the perinatal period: in the fetus of 16.5 days postcoitum (dpc) and 21.5 dpc (term = 22 dpc) and in the newborn of 1 day postpartum (dpp) and 7 dpp. Glucose uptake, lactate production and glucose incorporation into glycogen were much higher in the fetal than in the newborn heart. Measurements were made of tissue contents of high energy phosphate compounds, lactate and hexose phosphates. Unchanged contents of glucose-6-phosphate and fructose-6-phosphate during hypoxia in spite of an increased flux through the enzyme phosphofructokinase (PFK) suggest that PFK has a regulatory role in the glycolysis as early as 16.5 dpc. The isolated fetal heart was more resistant to hypoxia than the newborn heart: glucose uptake and lactate production were much higher and high energy phosphate compounds and glycogen were better maintained in the fetal heart.

[Influence of intrauterine hypoxia on protein synthesis in different regions of the brain and on functioning of the histo-hematic barrier during late ontogenesis in rats]

Experiments were conducted on sexually mature rats subjected to acute hypoxia at a definite antenatal period. The penetration of six labeled amino acids into the tissue of different regions of the brain and their incorporation into proteins was studied. Inhibition of protein synthesis especially in the hypothalamus and the cerebral cortex was characteristic of the experimental animals; these findings correlated with disturbances of the conditioned reflex activity. Dysfunction of the blood-brain barrier for labeled amino acids and radioactive phosphorus was found in the experimental animals; as to the permeability of other histohematic barriers -- it was unchanged.

The development of some metabolic responses to hypoxia in the foetal sheep

1. Foetal and maternal plasma metabolite and catecholamine concentrations have been measured in chronically catheterized sheep, 95-145 days pregnant. 2. With increasing gestational age there was rise in foetal plasma lactate, free fatty acid and ketone body concentration and in maternal plasma in free fatty acid and ketone body concentration. With the exception of alpha-amino nitrogen none of the plasma metabolites showed any correlation with foetal blood gas or pH values; alpha-amino N was inversely related to foetal blood pH. 3. Hypoxia in the foetuses was induced by causing the ewe to breathe 9% O2 with 3% CO2 in N2. This had a small effect on plasma metabolites in the ewe, mainly producing an increase in free fatty acid and ketone body concentration. 4. In the foetus hypoxia was associated with a large rise in plasma lactate and a small rise in alpha-amino N, the magnitudes of which did not change over the gestational range studied. Consistent and large increases in foetal plasma glucose, free fatty acid and ketone body concentration in response to hypoxia were seen only between 130 and 145 days. 5. In foetuses of 130-145 days the magnitude of the hypoxia-induced rise in plasma glucose and free fatty acid concentration was proportional to the plasma catecholamine concentration. 6. The concentration of acetate in foetal plasma was lower than and proportional to that in the maternal plasma. Neither concentration changed significantly during hypoxia. 7. The results are discussed in relation to the ability of the foetal sheep independently to control the concentration of its plasma metabolites and to mobilize its carbon stores at times of need. They indicate that in the sheep plasma catecholamines are important regulators of plasma glucose and free fatty acid concentrations late in foetal life.