The effect of induced maternal hyperthermia (1.5 degrees C rise over 60 min) on the uterine and umbilical circulations was examined in two groups of chronically instrumented pregnant sheep. Hyperventilation occurred in both groups. In the group in which the resultant respiratory alkalosis was untreated (N = 5), uterine blood flow decreased to 53 +/- 3% (mean +/- SE; P less than 0.01) of control at maximal maternal temperature. Umbilical blood flow also decreased 30 +/- 6% (P less than 0.01) below control levels. In the other group, normocapnia was maintained (N = 4). Uterine blood flow decreased in this group to 75% +/- 2% (P less than 0.01) of control levels, but umbilical blood flow did not significantly change. There was no significant change in maternal or fetal mean arterial pressure during hyperthermia in either group. Thus, maternal hyperthermia per se results in a significant decrease in uterine blood flow primarily through an effect on uterine vascular resistance, but without a concomitant change in umbilical blood flow.
Changes in the uterine and umbilical circulations during induced hypercapnia were studied in nine unanesthetized near-term pregnant sheep. Blood flows were measured with electromagnetic flow transducers and arterial pressures with vascular catheters implanted under anesthesia 2-16 days prior to experiments. Hypercapnia was induced in the fetus alone by giving acetazolamide iv to the fetus, 100-200 mg/kg. Mean fetal arterial Pco2 increased from 49.5 to 63.4 mmHg but no significant changes in umbilical blood flow occurred. Stepwise increases in both maternal and fetal arterial Pco2 were induced by increasing maternal inspired CO2 concentration to a maximum of 12%. No dignificant changes occurred in uterine or umbilical circulations until hypercapnia was severe (maternal arterial Pco2 greater than 60 mmHg, fetal arterial Pco2 greater than 70 mmHg). With severe hypercapnia uterine vascular resistance increased significantly and uterine blood flow decreased despite an increase in maternal arterial pressure; fetal arterial pressure and umbilical blood flow increased significantly, but umbilical vascular resistance did not. We conclude that hypercapnia in conscious pregnant sheep is associated with significant changes in uterine and umbilical circulations, but only when hypercapnia is severe. Carbon dioxide is unlikely to be a factor in normal physiological regulation of the uteroplacental circulation in this species.
Blood volume changes in the fetal lung following the onset of ventilation were studied by isotopic measurement of red blood cell and plasma volume in rapidly frozen lungs of ten near term fetal lambs. Total pulmonary blood volumes of fetal lambs ventilated with 3% O2 and 7% CO2 in nitrogen (so that blood gas levels were little changed from fetal values), or with air, were compared with measurements in unventilated lambs. Regional correlations of blood volume and blood flow (measured with isotope-labeled microemboli) within the lungs were also examined. Total pulmonary blood volume averaged 5.6 ml/kg body weight in unventilated fetal lambs and was approximately 43% greated in fetal lambs after 5-20 min of air ventilation, but not significantly different in lambs ventilated with 3% O2 and 7% CO2 in nitrogen. Thus it is ventilation with air, rather than the introduction of gas into the alveoli, which enlarges the fetal pulmonary vascular bed. Regional pulmonary blood volume and blood flow were correlated, though poorly, in air-ventilated lungs, but not in lungs ventilated with 3% O2 and 7% CO2 in nitrogen; this suggests that a common factor may operate to increase both blood flow and blood volume in the fetal lung following the introduction of air.
The effect of the electromagnetic spectrum as well as the efficiency of various wave (4000 to 7000 A) on growth and develop-lengths, require further investigation. More merit of avian gonadal tissue has been re-intensive work is also required on birds reviewed thoroughly by Withrow ( 1 ). H~~-ceiving no ocular illumination. The purpose ever, the wave length-intensity relationships, Of this research was to an inexpensive and relatively simple method for con-*This work was partially supported by Canada trolling wave length and light intensity for photoperiodic experiments with birds.
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