Search

The factors associated with increased renal excretion of vasopressin (VP) were examined in the hypoxic fetus and newborn. Studies were conducted on six chronically instrumented fetal (117-136 days gestation) and seven newborn lambs (2-6-day-old). Hypoxia was produced by administration of 10% oxygen to the ewe or neonate for 30 min. This procedure caused a 50% reduction in PaO2, no significant change in pHa in either fetus or neonate and a slight fall in PaCO2. Hypoxia caused an increase in VP concentrations in plasma from 1.3 +/- 0.53 to 46.4 +/- 4.71 pg/ml in the fetus and from 5.9 +/- 2.80 to 50.2 +/- 26.68 pg/ml in the neonate. After hypoxia there was a fall in urine output from 0.27 +/- 0.045 to 0.17 +/- 0.046 ml/(min X kg) in the fetus and from 0.15 +/- 0.033 to 0.09 +/- 0.022 ml/(min X kg) in the newborn. The corresponding values for urine osmolality were the following: 168 +/- 30.8 to 325 +/- 30.6 mOsm/kg in the fetus and 388 +/- 65.4 to 523 +/- 51.8 mOsm/kg in the newborn. VP concentration in urine increased from 13 +/- 9.4 to a maximum of 176 +/- 32.4 pg/ml after 30 min of recovery in the fetus and 39 +/- 4.6 to 278 +/- 132.5 pg/ml after 1 h of recovery in the newborn. These levels remained high for at least 1 h after the end of hypoxia. There was a good linear correlation between plasma VP levels and the corresponding urine levels and excretion rates in both the fetus and newborn.(ABSTRACT TRUNCATED AT 250 WORDS)

Using a specific and sensitive epidermal growth factor (EGF) radioimmunoassay, we have shown measurable quantities of EGF in mouse urine during the neonatal period. Sephadex G-50 column chromatography demonstrated the presence of a single immunoreactive component at the position defined by standard EGF (mol wt 6045). Comparison of urine urea nitrogen and urine EGF levels in neonatal and adult mice showed adult values to be 3- and 16-fold higher, respectively. Kidney weights relative to body weight were similar in newborn and adult animals while kidney EGF concentration per mg protein was 2.5-fold higher in the adult. The relative submandibular gland (SMG) weight was slightly higher in adult female mice than in the newborn, whereas SMG-EGF concentration was 15,000-fold higher in the adult than in the newborn. Thyroxine administration to neonatal mice from day 0 to day 6 increased urine EGF concentration 7-fold compared to control pups. Though the hormone treatment elicited a significant increase in relative SMG weight, its EGF concentration like that of the kidneys remained unchanged. The results suggest that urine EGF is subject to thyroid hormone modulation in newborn animals and that the changes in urine EGF concentration are independent of changes in SMG and renal EGF levels.

Recent studies have shown that immature rats display a diminished sensitivity to the phosphaturic effects of parathyroid hormone (PTH), and that the responsiveness to PTH increases with age. The attenuated phosphaturia may reflect an inability of the neonate to respond to the hormone because of functional immaturity of the developing kidney. Alternatively, PTH may actually inhibit tubular phosphate reabsorption in the neonate but, due to other phosphate conservation mechanisms, no phosphaturia occurs. Our objective was to determine whether a phosphaturic response to PTH would be elicited in immature rats during infusion of moderate amounts of phosphate (Pi). Clearance experiments were performed on 26 acutely thyroparathyroidectomized immature Wistar rats (3-5 wk of age) fed a normal Pi diet (0.63%). In response to infusion of either Pi (1 mumol/min.100 g) (group I) or PTH (8.3 ng/min.100 g) (group II) alone, the fractional excretion of phosphate rose minimally (from 0.01 +/- 0.01% to 4.9 +/- 1.9% and from 0.12 +/- 0.12% to 2.9 +/- 1.4% for groups I and II, respectively). However, when Pi and PTH were combined either Pi first followed by PTH (group III) or PTH first followed by Pi (group IV), the fractional excretion of Pi rose dramatically (from 0.01 +/- 0.01 to 21.8 +/- 3.5% and from 0.04 +/- 0.04 to 27.7 +/- 3.3% for groups III and IV, respectively). A significant increase in urinary cAMP excretion occurred during infusion of PTH even when Pi excretion was minimal, but there was no further increase in urinary cAMP during the combined infusion of Pi and PTH.(ABSTRACT TRUNCATED AT 250 WORDS)