Journal of developmental physiology最新文献

G-protein content (G(i) alpha, Gs alpha, Gq/11 alpha G(o) alpha and beta subunits) has been measured in membranes prepared from guinea pig uterus at different stages of pregnancy using SDS-PAGE and immunoblotting. Quantification using HRP- or 125I-labelled IgG as second antibody showed a good correlation between added membrane protein and measured G-protein content. Gs alpha appears as two bands of 45 kDa and 52 kDa respectively, the content of both were comparatively high in the non-pregnant uterus and fell about 4-fold close to term (60-67 days). G(i) alpha showed the converse with low level in membranes from the non-pregnant uterus with level approximately 6-fold higher by term. G(o) alpha exhibited changes similar to G(i) alpha. The changes in the content of Gq/11 alpha where biphasic, with comparatively high levels in membranes from the non-pregnant uterus, a sharp fall early in pregnancy followed by a 3-fold rise by near term. The uterine membrane content of the common beta subunit exhibited changes comparable to that of G(i) alpha and G(o) alpha with a 6-fold rise in content between non- and late-pregnant. Measurement of the effect of GTP gamma S action on phosphatidylinositol phospholipase C activity in uterine membranes with exogenous substrate showed pregnancy-dependent effects. In membranes from the non-pregnant uterus 0.1 microM GTP gamma S caused a modest stimulation of activity of 16 +/- 1.9%, whilst at 100 microM it inhibited the enzyme by 25 +/- 6.48%. In membranes from the late-pregnant guinea pig uterus GTP gamma S at both concentrations caused stimulation of enzyme activity.(ABSTRACT TRUNCATED AT 250 WORDS)

To see if arginine vasopressin (AVP) influenced fetal sodium balance, we infused AVP i.v. (45 mU h-1 kg-1) into two groups of chronically catheterized fetal sheep. One group had urinary osmolalities of 147 +/- 23 mosm kg-1 (SEM, n = 6) and the other group had higher urinary osmolalities (339 +/- 3 mosm kg-1, n = 4, P < 0.001). The group with high urinary osmolalities had higher systolic pressures (P < 0.05), higher glomerular filtration rates (GFR; P < 0.05), and higher urinary electrolyte excretion rates (P < 0.05), but lower membrane blood flows (P < 0.05) and lower fractional reabsorption of sodium by the proximal tubule (P < 0.01). In the group with low urinary osmolalities, AVP caused a rise in arterial blood pressure (P < 0.001), a fall in heart rate (P < 0.001), a fall in membrane blood flow (P < 0.02), but no change in placental or renal blood flow. Renal sodium excretion increased (P < 0.001) because GFR rose (P < 0.001) and proximal fractional sodium reabsorption fell (P < 0.001). Distal fractional sodium reabsorption increased (P < 0.001), but not enough to compensate for the fall in proximal fractional reabsorption. Lung liquid flow decreased (P = 0.006), as did lung liquid sodium excretion (P = 0.002). There were no changes in fetal plasma sodium, blood volume or haematocrit. The effects of AVP infusion were similar in the group with high urinary osmolalities. This study shows that high levels of AVP, such as occur in fetal "stress", have widespread effects on fetal cardiovascular, renal and lung functions. The characteristic profile of the fetuses with high urinary osmolalities prior to AVP infusion could be entirely explained by high endogenous AVP levels and AVP could possibly be a sole mediator of these widespread effects of fetal "stress". Furthermore, although during infusion of AVP sodium excretion increased, blood volumes did not change. Therefore, the fetuses must have accessed additional sodium from either their extracellular fluids, the amniotic and/or allantoic cavities or across the placenta.

Myoglobin, a hemoprotein found in abundance in the muscle of postnatal animals, increases in concentration in response to hypoxia, thereby protecting tissue from damage. Fetuses exposed to intrauterine hypoxemia are also susceptible to organ damage, but the response of fetal muscle myoglobin to hypoxemia is unknown. To study whether fetal muscle myoglobin concentrations are elevated following intrauterine hypoxemia, we exposed eight chronically catheterized late gestation sheep to a wide range of fetal oxygen levels over 15 to 30 days and correlated the level of fetal oxygenation with heart and skeletal muscle myoglobin concentrations measured at sacrifice. A lower level of fetal oxygenation, expressed as the integrated area under the arterial saturation (SaO2)-time curve, was associated with greater myocardial myoglobin concentration (r = 0.90; P < 0.01). This relationship was not observed for skeletal muscle (r = 0.43; P = ns). A lower level of fetal oxygenation was associated with lower myoglobin:iron (w/w) ratio in skeletal muscle (r = 0.71; P < 0.03), implying less incorporation of iron into myoglobin. A similar relationship was not apparent for cardiac tissue. The higher myocardial myoglobin concentrations found in the more hypoxic fetuses were consistent with previous observations in postnatal animals. This likely represents an intracellular compensatory mechanism for sustaining short-term mitochondrial oxygen delivery in a critical organ with a high rate of oxygen consumption. The lack of myoglobin responsiveness to hypoxia in fetal skeletal muscle may be due to its much lower oxygen consumption rate and activity level.

In the course of studying developmental changes of induction and maintenance of ventricular fibrillation in canine pups, we have documented that at about the third week of age, hearts reach a critical point where ventricular fibrillation may become both inducible and sustainable, thus forming the basis for cardiac arrhythmic death. Since age-related variations of cardiac mass may account for these findings, this study was conducted to systematically investigate the role of changing heart mass on the induction and maintenance of ventricular fibrillation in the canine heart, during the early postnatal development. Repetitive determinations of ventricular fibrillation threshold and individual incidence of spontaneous defibrillation were obtained in 87 puppies 1-6 weeks old, from litters of varied body size breeds, studied at weekly intervals. Overall, ventricular fibrillation threshold correlated positively with ventricular weight (VFTmA = 3.30 + 1.27 Vwtg, r = 0.71). However the slopes were steeper and correlations were stronger for the first, second and sixth week and nonsignificant in the fourth and fifth weeks. The ventricular fibrillation to ventricular weight ratio also varied with age (P < 0.01). Spontaneous defibrillation occurred at least once in 68 of the puppies (78%). In general, spontaneous defibrillation was more likely to occur in hearts weighing less than 9 grams (P < 0.01), but the overall correlation of the decreasing defibrillation incidence to increasing weight was weak (SDF % = 48.6-0.90 Vwtg, r = 0.106). Spontaneous defibrillation was not observed at any age or weight in two litters, totaling 9 puppies.(ABSTRACT TRUNCATED AT 250 WORDS)

The peripheral arterial chemoreceptor response to hypoxemia in the fetus is predominantly cardiovascular, invoking a fall in heart rate and a variable change in blood pressure. No quantifiable measure of chemoreceptor activity has yet been described in the intact fetus. We described the course, quantified the overall response, and defined the reproducibility of the heart rate response to acute hypoxemia in 22 late-term unanesthetized fetal sheep. Fetuses were chronically instrumented and studied between 1-6 days postoperatively. Acute hypoxemia was induced by occluding a balloon cuff around the common hypogastric artery. We performed 151 occlusions, starting at an initial saturation of 66 +/- 11%, decreasing saturation by 8-50%. Soon after balloon inflation, arterial oxygen saturation fell, followed by a decrease in heart rate. We calculated delta HR/delta sat, the fall in heart rate divided by the fall in saturation. Multiple linear regression analysis showed a sensitive chemoreflex, delta HR/delta sat averaging 2.5 +/- 1.2 bpm.%saturation-1. Initial saturation did not alter the first phase of the response (from the onset of the decrease in oxygen saturation to the onset of the decrease in oxygen saturation to the onset of the decrease in heart rate), but it did increase the overall response (delta HR/delta sat) when saturation was less than 65%. After adjusting in the lower range of initial saturations to that predicted at 65%, delta HR/delta sat was very reproducible within animals, with intra-animal variance being only 7% of inter-animal variance.(ABSTRACT TRUNCATED AT 250 WORDS)

Pregnant rats were fed to appetite on diets containing 6, 9, 12 or 18% protein and the fetuses were delivered at 20 days. Compared with the 18% protein diet (7.4 MJ), there was a significant increase in food and energy intake in the rats on the 9% (8.7 MJ) and 12% (8.4 MJ) diets, but not on the 6% (7.4 MJ) diet. The efficiency with which the dietary energy was used for weight gain was reduced on the 6, 9 and 12% diets compared with the 18% diet. The trend towards a decrease in the number of viable fetuses and an increase in the number of resorptions on the 9% and 6% diets did not reach statistical significance. The placental weight was not different to the 18% group (520 mg) on the 12% diet (540 mg), but was significantly increased on the 9% diet (590 mg) and significantly decreased on the 6% diet (510 mg). Fetal weight was greatest on the 12% diet (1.81 g) and significantly decreased on the 9% diet (1.71 g). The fetal:placental ratio, around 3.3 for the 18 and 6% diets, was significantly increased on the 12% diet (3.7) and significantly decreased to 2.9 on the 9% diet. After adjusting for the effect of the fetal position in the uterine horn, the number of pups per litter and an estimate of the number of failed implantations the effect of diet on placental weight was no longer statistically significant, but the effect of dietary protein on fetal weight was more significant statistically, with little change overall on the fetal:placental ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral oxidative metabolism and associated circulatory responses were determined in 14 unanesthetized fetal sheep near term, during a normoxic control period and subsequently, during four days of prolonged and graded hypoxemia induced by progressively lowering maternal inspired oxygen concentration with 1-2% CO2 added; first day 18%, second day 16%, third day 12-14%, fourth day 10-12%. Preductal arterial and sagittal vein blood samples were analyzed for oxygen content, blood gas tensions and pH. Regional blood flow was measured with a microsphere technique. Cerebral blood flow increased in a stepwise manner with the graded reduction in fetal arterial O2 saturation and continued to be well predicted by blood gas and metabolic alterations, with no adaptive change evident. Cerebral oxidative metabolism remained little changed with chronically induced hypoxemia until arterial O2 saturation was less than 30% and with fetal acidemia evident when decreased to 70% of normoxic control values. Whether the decrease in oxidative metabolism by the brain at this time represents an adaptive response whereby growth and functional alterations lead to a decrease in nonessential energy utilization or rather a pathological change, remains to be determined.

Glucocorticoids have been shown to accelerate the development of blood coagulation in the fetal lamb (Kisker, Robillard & Bohlken, 1983). The current studies examine the influence of high levels of triiodothyronine (T3) on the development of blood coagulation in the fetal lamb. Eight twin fetal lambs were studied during the last trimester of pregnancy (109-138 days gestation) using chronically placed arterial and venous catheters for infusion of T3 and withdrawal of blood samples. One fetus of each twin was infused intravenously with T3 at a constant rate of 0.6 micrograms T3/0.4 ml/h for 48 h. The other twin was infused with 5% dextrose at 0.4 ml/h for 48 h. Blood samples for measuring PT, PTT, TT, fibrinogen, factors II, V, VII, VIII, IX, X, XI and XII were obtained prior to and at the completion of the infusions. The results were analyzed for differences between the samples from paired control and T3 treated animals. Factor V significantly decreased in the T3 infused animals from 51.2% +/- 12.5% to 44.8% +/- 13.8% (P = 0.038). Factor VII also decreased in the treated animals 57.8% +/- 20% to 43.6% +/- 10.8%, but the changes were not statistically significant (P = 0.06). Factor XII significantly increased in the treated animals from 37% +/- 10.5% to 45% +/- 13.7% (P = 0.004). High levels of T3 in third trimester fetal lambs are accompanied by a moderate decrease in factor V and an increase in factor XII activity.

The release of arachidonic acid and inositol polyphosphates from permeabilised myocytes derived from guinea pig uterus has been studied. Both are enhanced by free calcium at 100 nM and 10 microM and particularly by 50 microM GTP gamma S. To distinguish between the contributions of phospholipase C and A2 to the release of arachidonic acid the phospholipase C inhibitor neomycin was used. At 1 and 10 mM, but not at 0.1 mM, neomycin caused effective inhibition of inositol polyphosphate release of over 95%. Neomycin (1 mM) also reversed GTP gamma S-stimulated, but not calcium-stimulated release of arachidonic acid. This action was reflected in changes in [3H]arachidonic acid labelling of the membrane phosphatidylinositol and phosphatidylcholine pools, which were depressed by over 20% on the addition of 50 microM GTP gamma S, an effect completely reversed by 1 mM neomycin. The effects of neomycin were much more pronounced on inositol phosphate than on arachidonic acid release. The ability of 1 mM neomycin to inhibit arachidonic acid release was reversed by addition of 1 microM phorbol 12-myristate 13-acetate, implying a role for protein kinase C activation in stimulation of arachidonic acid release. Measurement of phospholipase A2 activity with 1-stearoyl 2-arachidonoyl phosphatidylcholine as exogenous substrate demonstrated the ability of 1 and 10 mM neomycin to inhibit the enzyme particularly when it was maximally activated with 1 mM free calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

To investigate the ontogeny of a circadian rhythm in body temperature, we performed 24-h temperature measurements at six postnatal ages in ten newborn lambs reared independently of their ewes. At 18 to 48 h of age, a significant time-of-day variation in body temperature was found, the variation achieving a peak between 5.00 pm and 6.00 pm. Over the next two weeks, this time-of-day variation disappeared, reappearing at 18 days of age, although the phase had shifted such that the peak temperature was achieved between 8.00 am and 9.00 am. At 26 days of age, the time-of-day variation in body temperature was still present, maintaining the same phase relationship as at 18 days of age. It is possible that the significant time-of-day variation observed in the two oldest groups is due to the emergence of a discernable circadian rhythm in body temperature entrained to the light-dark cycle during the second or third week of life, whereas the time-of-day variation observed in the 18 to 48-h old is due to residual effects of entrainment to maternal zeitgebers. We speculate that the lack of any observable time-of-day variation in the 4, 6 and 11 days-old lambs may denote the presence of no rhythm or possibly a free-running rhythm in body temperature in subjects not yet able to entrain to photic zeitgebers.