SUMMARY1. Glomerular blood flow distribution was studied in seventy-eight new-born mongrel dogs aged 1-40 days by measuring the distribution of radioactive labelled microspheres within the kidney.2. The microsphere technique was found to be a valid indicator of glomerular blood flow distribution for the new-born dog since (a) the spheres were completely extracted by the kidney, (b) more than 95 % of the spheres were trapped in glomerular capillaries, (c) the spheres were evenly distributed within any specific region of the kidney and, (d) the spheres did not interfere with renal haemodynamics.3. Plasma flow per gram tissue to inner cortical glomeruli, relative to that to outer cortical glomeruli, the IC/OC flow ratio, was high at birth, decreased over the first 2 weeks of life and remained relatively constant thereafter. Plasma flow per gram tissue to the outer cortex increased over the whole 40 day period while that to the inner cortex decreased slightly and then increased after 2 weeks.4. The IC/OC flow ratio decreased in a curvilinear fashion as blood pressure rose with maturation. Acute increases or decreases in blood pressure in any animal produced decreases or increases, respectively, in the IC/OC flow ratio.5. There was no correlation between the IC/OC flow ratio and renal extraction of p-amino-hippurate (EPAH)-6. There was histological evidence that glomerular differentiation persists for 2 weeks during the post-natal period in the dog. This continuing post-natal glomerulogenesis takes place only in the outer cortex.7. These results are consistent with the hypothesis that an important factor in renal maturation is a redistribution of blood flow within the kidney. As the animal matures a greater fraction of the total glomerular blood flow goes to outer cortical glomeruli. This is due partly to the 92 LEONARD I. KLEINMAN AND JOHN H. REUTER continuing glomerular differentiation taking place in the outer cortical region and partly to the increasing arterial blood pressure occurring with maturation.
Ventricular performance is higher in premature infants with than in those without patent ductus arteriosus because afterload is lower in the former group. Although ductal ligation increases blood pressure and systemic resistance, wall stress and ventricular performance are maintained. Our results suggest that the premature newborn maintains ventricular performance during stress, at least in part, by manipulating afterload.
SUMMARY1. The renal response to an intravenous saline load was studied in thirty new-born mongrel dogs aged 1-30 days and in seven adult dogs.2. After the infusion of isotonic saline at a rate of 2-0 ml. min-kg-' for 15 min and then at a rate of 0.5 ml. min' kg-' for an additional 105 min, the puppies excreted a significantly smaller fraction of the infused sodium than did the adults (P < 0-01).3. Both puppies and adults increased their glomerular filtration rates after the saline load. However, adults excreted a larger fraction of their filtered sodium than did the puppies (P < 0.01).4. There was no correlation between age and the ability to respond to a saline load during the first month of life.5. Intrarenal blood flow distribution was measured by the radioactive microsphere technique. After saline infusion in the puppy there was an increase in outer cortical blood flow but inner cortical blood flow remained relatively constant. The result was a decrease in the ratio of inner to outer cortical blood flow (IC/OC ratio). In contrast the IC/OC ratio tended to increase in the adult dog after saline expansion.6. There was no correlation between the magnitude of change of sodium excretion and the change ofintrarenal blood flow distribution in the puppy.7. These results confirm that the natriuretic response of the new-born dog kidney is less efficient than that of the adult dog. This is due primarily to the failure of the puppy kidney to decrease fractional sodium reabsorption. Although the new-born dog alters intrarenal blood flow distribution in response to saline loading this alteration does not appear to play a significant role in sodium excretion.
ABSTRACT. Cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMR02) were measured during normocarbia and during both moderate and severe hypocarbia. Eighteen newborn mongrel dogs, 1 to 7 days of age, were given pancuronium and ventilated with 70% N2O and 30% 02. The respirator was adjusted to achieve a PaC02 of 15 torr, all subsequent changes to 25 and 40 torr were made by adjusting the inspired concentration of COz. The sequence of PaC02 levels was randomized. CBF was measured by microsphere technique and CMR02 calculated as arterial-sagittal sinus O2 content difference times hemispheric blood flow. All measurements were made after 30 min at each PaC02. Total CBF was reduced at a PaC02 of 25 torr ( p < 0.001), further reduction in PaC02 to 15 torr resulted in a significant decrease in total CBF ( p < Hypocarbia is a known depressant of CBF in neonatal animals of several species (1-5). Since hyperventilation, for persistent pulmonary hypertension of the newborn, is a common practice in many intensive care nurseries, concern is raised as to whether decreased oxygen delivery to the brain secondary to decreased CBF during hypocarbia could be of such severity as to cause cerebral hypoxia. In separate studies, both Kennealy et al. (6) and Sugioka and Davis (7) have demonstrated significant decreases in cerebral tissue PO2 during hyperventilation in adult dogs. Similarly, hypocarbia has been shown to increase cerebral venous (8) and CSF lactate levels (9) in dogs and to cause electroencephalographic changes in man (10).The CMR02 was reported by Gregoire et al.(1 1) for newborn dogs during mild hypocarbia. Their value for CMR02 was not different from that measured during normocarbia but PaC02 was lowered only to 31 torr. We decided to test the hypothesis that the decrease in CBF during hyperventilation can result in a reduction in the cerebral metabolic rate of oxygen. The current study was therefore designed to measure total and rCBF and total CMR02 in the newborn dog during normocarbia and during both moderate and severe hypocarbia. MATERIALS AND METHODSSurgery. Eighteen newborn mongrel dogs, 1 to 7 days of age, weighing 265 to 475 g, were removed from the litter on the morning of study. The animals were given an intravenous injection of 0.1 mg/kg of pancuronium, immediately intubated (2.5-3.0 Portex endotracheal tube) and ventilated (Harvard Rodent Respirator, Harvard Apparatus So. Natick, MA) with 70% nitrous oxide and 30% oxygen. A rectal temperature probe was inserted and the animal placed on an electric heating pad and servocontrolled to 37.5" C. Halothane ( I to 1.25%) was administered during surgical procedures which included catheterization of the femoral artery and vein with PE-50 tubing. The femoral artery catheter was advanced to the level of the sternum for aortic pressure monitoring (Statham physiologic pressure transducer, Gould pre-amp and recorder) and procurement of reference flow samples. A left ventricular catheter for injection of microspheres was inserted in the following manner. Th...
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