Journal of developmental physiology最新文献

There is evidence from fetal sheep near term that cerebral oxygen delivery decreases during a moderate maternal hypoxemia, whereas cerebral oxygen consumption is maintained. However, since in immature fetuses circulatory centralization may be in part ineffective, cerebral concentrations of high-energy phosphates may fall during a moderate maternal hypoxemia due to an insufficient cerebral oxygen supply. On the other hand anaerobic glycolysis may accelerate to prevent the depletion of high-energy phosphates. To determine, whether or not there is an energy failure in the immature fetal brain in this situation, we studied the effects of 60 min moderate maternal hypoxemia on cerebral concentrations of high-energy phosphates and glycolytic intermediates in fetal guinea pigs at 0.75 gestation. Maternal hypoxemia resulted in no change in fetal mixed arterio-venous pH (7.41 +/- 0.05 vs. 7.38 +/- 0.05; n.s.) or PCO2 (39.0 +/- 4.2 vs. 36.4 +/- 5.6 mmHg; n.s.), but in a fall in fetal PO2 (17.3 +/- 2.2 vs. 11.2 +/- 1.9 mmHg; P < 0.01). There was an increase in fetal cerebral concentrations of lactate (1.50 +/- 0.24 vs. 2.82 +/- 0.91 mumol/g; P < 0.01), whereas those of high-energy phosphates remained unchanged. From these results we conclude that during moderate isocapnic hypoxemia cerebral energy metabolism of immature fetal guinea pigs is maintained by an acceleration of the anaerobic glycolytic rate.

Transferrin receptors (TfR's) on the syncytiotrophoblast mediate transferrin (Tf) dependent Fe uptake and transfer to the fetus. We studied TfR number and density at the microvillous membrane isolated from guinea pig placentas at day 40, 50 and 64 (near term), together with the K(a) values for the main serum isotransferrins being biantennary Tf(slow) and triantennary Tf(fast). The effect of desialylation of either the microvillous membranes or of Tf(slow) and Tf(fast) on the binding characteristics was also studied. The number of TfR's per mg placenta- or membrane protein increased significantly from day 40 to term (P < 0.01 resp. P < 0.025). The K(a) values for Tf(slow) and Tf(fast) did not change during pregnancy. K(a)Tf(slow) = 0.3 nM-1, K(a)Tf(fast) = 0.19 nM-1 (P < 0.01). It is suggested that the increase in F(e) transfer during pregnancy is directly related to number and density of the TfR's at the syncytial border, and that adaptive adjustment of K(a) values does not play a role in the maturation of the transfer process. The pregnancy dependent shift to iso-transferrins with a higher degree of glycosylation offers no explanation for the increase of F(e) transfer during pregnancy. Desialylation of the microvillous membranes did not effect the binding parameters of Tf(slow) and Tf(fast), unless desialylation surpassed the 50% level. Then Ka values decreased and TfR number increased (P < 0.05). Desialylation of Tf(slow) and Tf(fast) had no effect on K(a) nor on the number of TfR. The maternal fetal interface therefore lacks an asialo-glycoprotein receptor.

The present study was undertaken to assess GH secretory profiles in 12 light-breed foals and their dams during forty days after delivery, and the possible influence of GRF and TRH on plasma GH concentrations in these newborn foals. GH secretory pattern was pulsatile in one day- as well as in forty days-old foals. The number of secretory spikes (10 per 24 h) did not vary between days 1 and 40. In the same times, GH secretion did not show any circadian rhythm either in foals or in their dams. Mean daily plasma concentrations (measured through blood samples collected every 20 min for 24 h) were lower in mares (3.4 +/- 0.3 ng/ml) than in their foals (7.4 +/- 0.9 ng/ml; P < 0.05). This difference resulted from both a lower number of GH spikes per 24 h (5 +/- 2 vs 10 +/- 1; P < 0.01) and from a lower pulse amplitude average (8 +/- 5 vs 16 +/- 1; P < 0.05). In three days- and in six days-old foals, synthetic human GRF (0.3 microgram/kg body wt, i.v.) significantly increased plasma GH concentrations. TRH (3 micrograms/kg body wt, i.v.) did not significantly modify plasma GH.

The aim of this study was to document arterial blood pressure wave forms at two sites along the arterial tree of the neonate: in the radial and posterior tibial arteries. Using a high-fidelity catheter tip-transducer system, peripheral arterial blood pressure wave forms in 26 critically newborn infants were studied. In 14 infants the radial artery and in 12 infants the posterior tibial artery was cannulated. Radial artery blood pressure waves resembled those of proximal aortic rather than those of the radial artery in adults. Quantitative analysis of the waves was performed to reassure this finding. Blood pressure waves obtained from posterior tibial artery resembled those of femoral artery rather than those of posterior tibial artery waves in adults. We conclude that radial and posterior tibial artery wave forms in neonates appear to have a central appearance. This phenomenon might be explained by the close proximity of the radial and posterior tibial artery to the central aorta and femoral artery respectively, due to the small and short limbs of the neonate. The finding allows an "easy central pressure look" at both ends of the neonatal aorta.

We hypothesized that exposure of neonatal swine to chronic alveolar hypoxia (CH) would cause increased PVR, blunt acute hypoxic vasoconstriction, and increase VA/Q mismatch. After exposure to either normobaric alveolar hypoxia (FIO2 = 0.10) or room air for 2 weeks, animals were anesthetized and ventilated first with room air and then with hypoxic gas (FIO2 = 0.12). PVR, and pressure-flow (P/Q) relations were measured between 15-100% of baseline cardiac output. VA/Q matching was measured by the multiple inert gas elimination technique. During room air breathing, the mean PVR and P/Q slope in the CH animals was significantly greater than in the control (C) animals. P/Q intercepts were similar and near the origin for both groups. The absolute PVR and P/Q slope were greater for CH compared to C animals during acute alveolar hypoxia. The fractional increase in PVR and P/Q slope in the response to acute hypoxia was similar for both groups. PaO2, intrapulmonary shunt, and SDQp (an index of VA/Q heterogeneity) were similar for both groups. We conclude that CH in neonatal swine causes pulmonary hypertension, but does not attenuate acute hypoxic pulmonary vasoconstriction, nor VA/Q matching.

Behavioral state and cerebral glucose utilization were measured in six fetal sheep subjected to high intrauterine sound pressures created with a vibroacoustic stimulator pressed against the maternal abdomen. The signal consisted of a complex waveform that varied over time with a 50% duty cycle. An implanted hydrophone showed highest spectral levels between 3,000-16,000 Hz. The pulsed sound resulted in a significant loss of fetal rapid eye movement and non-rapid eye movement sleep. The stimulus also resulted in a disruption in the normally close relationship between these sleep states and cerebral glucose utilization rates in the brain as a whole and in its component parts.

5 alpha-reductase activity was measured in the developing rat urogenital tract using [3H] testosterone as substrate. At fetal day 22, the activity in the vagina (67 pmol/h per mg protein) was as high as in the differentiated prostate (41 pmol/h per mg protein). Both tissues are derived from the urogenital sinus. Although the activity of 5 alpha-reductase remained high in the prostate, the enzyme activity in the vagina declined steadily such that by postnatal day 20, the levels were not different from those expressed in urinary bladder which had low, baseline levels (approximately 10 pmol/h per mg protein) throughout the period examined. The uterus, which is derived from the embryonic mullerian duct, also expressed high levels (50-70 pmol/h per mg protein) of 5 alpha-reductase activity initially (before postnatal day 10). In contrast, the "Wolffian-derived" epididymis had levels of activity that were indistinguishable from the relatively low levels seen in the urinary bladder. In the ovary, neither 5 alpha-reductase nor aromatase activities were appreciable at fetal day 22 and at postnatal day 2. By postnatal day 5 both activities increased dramatically in ovaries. After postnatal day 10, aromatase activity declined in ovaries but 5 alpha-reductase remained elevated. These observations suggest (1) that major remodeling of the tissues derived from the urogenital sinus takes place even after differentiation and (2) that 5 alpha-reductase may regulate ovarian estrogen levels at the time of primary folliculogenesis.

Unlabelled: Aim of this study was to investigate how gastrointestinal hormones such as exogenous s.c. caerulein (6 micrograms/kg body weight), secretin (100 U/kg body weight), bombesin (20 micrograms/kg body weight, s.c.), CCK-8 (10 micrograms/kg body weight, i.p.), the CCK-A receptor antagonist L 364,718 (100 micrograms/kg body weight, i.p.), camostate (400 mg/kg body weight per os) which releases endogenous CCK and the coadministration of camostate with atropin (250 micrograms/kg body weight, s.c) or L 364,718 (1 mg/kg) influence milk intake from nipples, gastric emptying, and discharge of pancreatic trypsin content in 10-day-old rat pups. Saline-treated pups served as controls. The non-fasting Wistar rat pups of both sexes were used in littermate order. The suckling lasted for 30 and 45 min, respectively. One pup was used only once. After suckling the pups were decapitated, their stomach and pancreas were removed and weighed. The gastric food content was regarded as intake of milk and expressed as difference between the filled minus empty stomach. Pancreatic trypsin and protein content, plasma CCK level were measured. The exogenous agents did not influence gastric content. The investigated peptides decreased, L 364,718, however, increased the pancreatic trypsin/protein ratio. Camostate increased gastric content by 60% and decreased pancreatic trypsin/protein ratio vs saline by 90%. The gastric and pancreatic effects of camostate were not reversed by atropine or L 364,718.

Conclusion: Exogenous and endogenous CCK seem not to influence milk intake while decrease pancreatic trypsin/protein ratio. However, endogenous CCK inhibit gastric emptying. The plasma CCK level was elevated due to the applied CCK-8 and camostate during the observed suckling period.

To test the hypothesis that growth hormone gene messenger RNA abundance in the fetus is subject to the same effects of thyroid hormone previously demonstrated in other situations, we evaluated the effect of thyroidectomy on pituitary GH mRNA content at three gestational ages in the ovine fetus. One of each twin pair of fetal lambs underwent thyroidectomy at 90, 100 or 110 days gestation. Fetal pituitaries were collected 25-30 days later. Plasma GH and IGF-I were measured as well as pituitary GH mRNA content. Serum growth hormone in the thyroidectomy group was less than in the control twins (129.8 vs 187.6 micrograms/l, P = 0.0. GH mRNA was likewise decreased in pituitaries of thyroidectomy fetuses compared to controls (1.01 vs 1.80 units, P = 0.0006). Serum IGF-I and body weight were similar in the thyroidectomy and control twins. We conclude that the ovine fetus in the final trimester of gestation exhibits effects of thyroid hormone on serum GH and mRNA abundance similar to those seen in postnatal animals.

The study estimated the mean volume of the clefts between adjacent villi in the normal term human placenta, and the effect on this of increasing the fetal perfusion pressure, using a new stereological tool called the 'star volume estimator'. This enables the measurement of irregular and complex structures, including both particles and cavities, in a mathematically defined and unbiased manner. To achieve this, a total of ten term placentae delivered by caesarean section were obtained. Four fetal arteries supplying opposite quadrants of the placental disc were perfusion-fixed under standard pressures of 40, 60, 80 and 100 mmHg respectively. Stereological estimates relating to the star volume of the clefts between the villi, and to the volume density of the intervillous space were obtained. There was a significant rise in the star volume of the intervillous clefts from 26.8 x 10(4) m3 at 40 mm Hg to 75.1 x 10(4) m3 at 100 mmHg (F = 75, df = 1.38, P < 0.05). The volume density of the intervillous space remained unchanged, thus obviating the possibility of fluid leakage into the intervillous space accounting for this change. It is concluded that the fetal vasculature provides hydraulic support to the villous tree, and that changes in the umbilical perfusion pressure can therefore alter the disposition of the villi within the intervillous space. As fetal blood pressure rises, for example during acute hypoxic episodes, the villi will move apart. The enlargement of the clefts between adjacent villi will have a secondary effect upon the maternal circulation, promoting more even perfusion of the intervillous space at higher overall flow rates.(ABSTRACT TRUNCATED AT 250 WORDS)