Journal of developmental physiology最新文献

Fetal growth is known to be correlated with the size of the placenta and the exchange surface area. Reduction in the growth of the materno-fetal exchange surface areas may be a mechanism by which the effects of maternal undernutrition on fetal growth are mediated. In the compact placenta of the guinea pig the exchange surface is equivalent to the peripheral labyrinth. The effect of a 40% reduction in maternal feed intake on the growth of the peripheral labyrinth was investigated in pregnant guinea pigs between gestational days 25 and 65. Fetal and placental weights were significantly reduced in the last trimester by 32% and 38% respectively (P < 0.01). Placental efficiency in early gestation was significantly impaired in restricted animals but equivalent to ad lib. fed controls by the last trimester. The volume of the peripheral labyrinth increased as a percentage of the total placental volume with gestational age. Restricted placentae tended to be composed of a smaller volume of peripheral labyrinth tissue in early gestation. It is suggested that maternal undernutrition results in an impaired or delayed expansion of the peripheral labyrinth in early gestation causing a reduction in placental efficiency. By the last trimester the weight of the peripheral labyrinth of restricted animals was reduced by 33% (P < 0.05). The weight of the peripheral labyrinth was also significantly correlated with fetal weight is limited by the size of the peripheral labyrinth in the later stages of gestation.

Muscle contraction patterns and mandibular movements of infant rabbits during suckling and chewing were compared. Oral muscle activity was recorded by fine-wire electromyography, while jaw movements and milk bottle pressure were registered. Suckling and mastication have a comparable cycle duration and share a common pattern of oral muscle activity which consists of a succession of a jaw closer burst, during which the jaw closes and undergoes a power stroke (in mastication), a suprahyoid burst with a stationary or slightly opening jaw and a digastric burst with fast jaw opening (the power stroke of suckling). Compared to suckling, mastication shows decreased jaw opener activity, increased jaw closer activity, development of jaw closing activity in the lateral pterygoid, and increased asymmetry in the masseter by development of a new differentiated motor pattern on the working side. The study shows that the suckling motor pattern enables the infant rabbits to change to chewing with just a few modifications.

A technique has been developed for prelabelling and permeabilisation of guinea pig uterine myocytes to enable measurement of arachidonic acid release/phospholipase A2 activity in cells with intact membranes. Intact cells were prelabelled with [3H]inositol or [3H]arachidonic acid for measurement of phospholipase C and A2 respectively. In intact cells 10 nM endothelin-1 or 1 microM bradykinin stimulated both inositol polyphosphate and arachidonic acid release, whilst 1 microM oxytocin, arginine vasopressin or histamine were without effect. In Streptolysin-O permeabilised myometrial cells calcium-stimulation of inositol polyphosphate and arachidonic acid release was detected between 10 microM and 1 mM free calcium. The patterns of inositol polyphosphate and arachidonic acid release were broadly similar. Responses to 1 mM calcium were not detected in intact cells not treated with Streptolysin-O. For arachidonic acid release the K0.5 for calcium activation was about 7 microM, a level above that normally likely to be found in the uterine myocyte. Hence it is concluded that unless there are high local concentrations of calcium close to the plasma membrane, calcium is unlikely alone to be the primary regulator of arachidonic acid release and phospholipase A2.

Phospholipase A2 activity has been measured in membrane and cytosolic fractions from non-pregnant and pregnant guinea pig myometrium has been studied. Enzyme activity was measured with 1-stearoyl-2- [3H]arachidonoyl-phosphatidylcholine exhibiting Michaelis-Menton kinetics with Km of 83.8 +/- 21.6 and 53.2 +/- 14.1 for membrane and cytosolic enzymes respectively. Fractionation of the myometrium from non-pregnant guinea pigs suggested that 35% of the activity was membrane associated compared with 20% (P < 0.01) in tissue from pregnant animals. In the presence of 1 mM calcium total activity rose from 3.03 +/- 0.41 to 1737 +/- 368 nmol/h per uterus between non-pregnant and late pregnancy. Calcium activated the membrane enzyme, but the effect was greater late in pregnancy with almost a 6-fold increase in activity at 1 mM calcium compared with a doubling in membrane from non-pregnant guinea pigs. The K0.5 for calcium activation was about 150 microM. Immunoblotting with anti-human-110 KDa phospholipase A2 showed in guinea pig uterus a 34 KDa form of the enzyme that, consistent with changes in activity, showed a fifteen-fold increase in quantity between non-pregnant and late pregnancy. The data are consistent with dramatic increases in the capacity for arachidonic acid release and prostaglandin production in the guinea pig myometrium late in pregnancy.

The insulin-like growth factors (IGF-I and -II) are potential mediators of the effects of maternal undernutrition on fetal growth and muscle development. The effects of a 40% reduction in maternal feed intake on serum levels of the IGFs, the thyroid hormones and cortisol, were investigated for the last two trimesters (day 25 to birth). This level of undernutrition is known to cause a 35% reduction in fetal and placental weights, and a 20-25% reduction in muscle fibre number. Maternal IGF-I level was greater than non-pregnant levels on day 25 gestation, in both control and restricted dams, and declined with gestational age. The increase in IGF-I level in the 40% restricted group was approximately two-thirds that of control animals. Fetal serum IGF-I was also reduced in undernourished fetuses throughout gestation. Maternal IGF-II did not change with gestational age and was unaffected by undernutrition. Fetal IGF-II reached a peak at day 55 of gestation, this peak was greatly diminished by maternal feed restriction. Both IGF-I and IGF-II tended to be related to fetal, placental and muscle weights at day 65 of gestation. Thyroid hormone concentration declined in maternal serum and increased in fetal serum with increasing gestational age. Levels were not significantly affected by undernutrition. Both triiodothyronine (T3) and thyroxine (T4) were correlated with IGF-I in maternal serum (P < 0.05), but not in fetal serum. Cortisol levels were elevated by undernutrition in both maternal and fetal serum, and increased with gestational age. Cortisol was inversely correlated with serum IGF-I in both maternal and fetal serum. Maternal serum IGF-I may mediate the effects of undernutrition on fetal growth by affecting the growth and establishment of the feto-placental unit in mid-gestation. Fetal IGF-I may mediate the effects on muscle growth, whereas IGF-II seems to be related to hepatic glycogen deposition. Cortisol may play a role via its effect on the IGFs, but the thyroid hormones are unlikely to be important until the late gestation/early postnatal period.

Ontogenic changes in the kinetics of exchangeable cellular calcium were studied in embryonic (ECV) and post-hatch (PHCV) chick ventricular tissue by monitoring 45Ca-efflux. The isolated whole ventricle (5 & 7 days ECV) or ventricular strips (12 & 18 days ECV and 1-2 days PHCV) were "loaded" with 45Ca (37 degrees C) and then passed through a series of tubes containing efflux solution (4 degrees C) to determine 45Ca-efflux. Curve 'peeling' of the efflux curve indicated existence of 3 kinetically distinct components of exchangeable cellular Ca2+ compartments: C1, C2 & C3. The size of C1, which was the largest in 5 & 7 days ECV decreased significantly to become minimum in 18 days ECV & PHCV. The rate constant of this compartment, however, reduced with the age of the embryo. In contrast, the size of C3 increased with the embryonic development to become the largest in 18 days ECV & PHCV. An increase in the rate constant of this compartment was also observed during embryogenesis. The size and rate constant of C2 remained unaltered during development. However, the increase in size of C3 during embryonic development indicates differentiation of Ca2+ storage sites, like sarcoplasmic reticulum (SR), during the later stages. Caffeine (10 mM) and ryanodine (10 microM) enhanced fractional escape rate during slow phase (ie 120-180 min) of efflux at all developmental stages. The magnitude of enhancement increased during later stages of development indicating greater prominence of SR with the age of embryo.(ABSTRACT TRUNCATED AT 250 WORDS)

Suckling rats were given urogastrone-epidermal growth factor (EGF: 1,000 micrograms/kg body weight) or vehicle by gavage at one of three stages of development: 8 to 10, 11 to 13 or 14 to 16 days of age. Intubation was carried out at 8-hourly intervals over these periods. Fourteen to 16 h after the last intubation the rats were killed; that is, at 11, 14 and 17 days respectively. Samples of proximal and distal small intestine (SI) were taken for enzyme analysis. Five enzymes were assayed; sucrase, lactase, gamma-glutamyl transferase, alkaline phosphatase and neutral amino-peptidase, and their activities expressed per g protein. Treatment with EGF had no effect on body weight or on the length of the small intestine at any age. The nature of the effects on enzyme activities depended on the specific enzyme concerned, the site within the small intestine and the timing of the treatment. Lactase was increased by EGF at both sites only on day 14, whereas gamma-glutamyl transferase was increased in proximal samples at 11 and 14 days, and in distal samples at 17 days. Nor was the outcome always to increase activity. On day 11 alkaline phosphatase was increased in proximal SI, but decreased in distal SI; and so too was aminopeptidase N decreased in distal SI at 11 days. Sucrase showed no response at all. The pattern is complex. Certainly it does not indicate accelerated functional maturation.

The ontogeny of the L-glutamate (GLU) and gamma-aminobutyric acid (GABA) neuronal systems in the guinea pig hippocampus was investigated with respect to tissue amino acid content, and spontaneous and K(+)-stimulated release of GLU and GABA. Transverse hippocampal slices were prepared from the guinea pig fetus at day 45 (brain growth spurt), 55 and 63 of gestation (term, about 68 days), from the 5-days-old neonate, and from the young adult. GLU and GABA release was determined as efflux from hippocampal slices into Krebs'-bicarbonate medium using a dynamic, submerged, superfusion apparatus. Hippocampal GLU content decreased during development, whereas GABA content was constant for all the ages investigated. The magnitude of spontaneous GLU efflux decreased during development; there was no measurable spontaneous GABA efflux. The K+ concentration-GLU efflux response curve was bell-shaped for the fetus at the three selected gestational ages, and was curvilinear for the neonate and adult. The apparent EC75 of K(+)-stimulated GLU efflux was higher for the neonate and adult compared with the fetus. In contrast, the K+ concentration-GABA efflux response curve was curvilinear, and the apparent EC75 of K+ was similar for all the ages investigated. K(+)-stimulated efflux of GLU and GABA was Ca++ dependent, but this was not the case for spontaneous GLU efflux. These data indicate that, in the guinea pig hippocampus, the GLU neuronal system is developing throughout gestation, whereas the GABA neuronal system appears to mature before the brain growth spurt.

Regional norepinephrine and dopamine content and cerebral alpha 1- and beta-adrenergic receptor mechanisms were studied in the brain of sham operated control and single umbilical artery ligation (SUAL) induced growth retarded newborn sheep. Brain sparing was evidenced by relative preservation of brain weight compared to other organ systems. Norepinephrine and dopamine content of the brain were not affected by SUAL. This is in contrast to decreased norepinephrine levels in the brown fat, a normally densely innervated peripheral tissue. Alpha 1- and beta-adrenergic receptor numbers and affinity states were similar between the two groups. Coupling between beta-receptor and guanine nucleotide stimulatory protein and agonist stimulated adenylyl cyclase activity were unaffected by SUAL. Brain regional DNA content and protein/DNA ratios were not different between the two groups. These data suggest that single umbilical artery ligation induced fetal growth retardation modifies peripheral but not central catecholaminergic pathways in the sheep. Both growth and expression of specific catecholaminergic signal transduction system are protected in the brain.

A descriptive study of eleven healthy preterm infants was conducted in which cardiorespiratory (heart and respiratory rates, oxygen saturation), thermal (abdominal, toe and tympanic temperatures) and state behavior responses to two hours of paternal skin-to-skin contact within the first 17 hours of birth in Colombia, South America were evaluated. Infant physiologic and behavioral state measures were recorded each minute as was paternal skin temperature and behavior. Infant heart and respiratory rates increased during paternal contact as did abdominal and core temperatures. Fathers were able to keep their infants sufficiently warm, and five infants became hyperthermic (tympanic temperature greater than 37.5 degrees C) despite cooling measures while being held in this climate. Infants slept most of the time while being held and fathers seldom gazed at, spoke to, or touched their infants while holding them. When mothers are unavailable, fathers may be an alternate source of warmth and comfort to infants.