Period Of Postnatal Growth Research Articles

Activities of enzymes concerned with pyruvate and oxaloacetate metabolism in the heart and liver of developing sheep

1. 1. In order to assess whether the potential ability of heart ventricular muscle and liver to metabolise substrates such as alanine, aspartate and lactate varies as the sheep matures and its nutrition changes, the activities of the following enzymes were determined in tissues of lambs obtained at varying intervals between 50 days after conception to 16 weeks after birth and in livers from adult pregnant ewes: lactate dehydrogenase (EC 1.1.1.27), alanine amino-transferase (EC 2.6.1.2), pyruvate kinase (EC 2.7.1.40), pyruvate carboxylase (EC 6.4.1.1), phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32), malate dehydrogenase (EC 1.1.1.37), aspartate aminotransferase (EC 2.6.1.1) and citrate ( si)-synthase (EC 4.1.3.7). 2. 2. In the heart a most marked increase in alanine aminotransferase activity was found throughout development. During this period the activities of citrate ( si)-synthase, lactate dehydrogenase and pyruvate carboxylase also increased. There were no substantial changes in the activities of aspartate aminotransferase, malate dehydrogenase or pyruvate kinase. Pyruvate kinase activities were five times greater in the heart compared with those found in the liver. No significant activity of phosphoenolpyruvate carboxykinase (GTP) was detected in heart muscle. 3. 3. In the liver the activities of both alanine aminotransferase and aspartate aminotransferase increased immediately following birth although the activity of alanine aminotransferase was lower in livers of pregnant ewes than in any of the lambs. As with alanine aminotransferase the highest activities of lactate dehydrogenase were found during the period of postnatal growth. No marked changes were observed in malate dehydrogenase or citrate ( si)-synthase activities during development. A small decline in pyruvate kinase activity occured whilst the activities of pyruvate carboxylase and phosphoenolpyruvate carboxykinase (GTP) tended to rise during development.

The chemistry of the collagen cross-links. Age-related changes in the reducible components of intact bovine collagen fibres.

The change in the amounts of the three major reducible cross-links was followed throughout the bovine-life span. The major reducible cross-link in embryonic skin is 6,7-dehydro-N(epsilon) -(2-hydroxy-5-amino-5-carboxypentyl)hydroxylysine, but this is gradually replaced in the latter stages of gestation or early postnatal growth period by two other Schiff bases, 6,7-dehydro-N(epsilon)-(5-amino-5-carboxypentyl)hydroxylysine and a component not yet identified, designated Fraction C. These latter two Schiff bases increase in amount during the rapid growth period to a maximum, after which they then slowly decrease until at maturity they are virtually absent. The proportion of these Schiff bases closely reflects the rate of growth, i.e. the amount of newly synthesized collagen present at any one time. Similarly, the three Schiff bases present in tendon and the one in cartilage slowly decrease during maturation. No evidence for the possible stabilization of these aldimine bonds during maturation by reduction in vivo was found by three different analytical techniques. Concurrently with the decrease in the proportion of the Schiff bases some new reducible components increased during maturation, but their characterization as N(epsilon)-glycosylamines demonstrated that they were not related to the lysine-derived aldehyde components. The significance of these components in the aging process cannot at present be assessed. As no evidence was obtained for any new reducible cross-links replacing the Schiff bases, it is probable that the latter are intermediate cross-links and that during maturation they are stabilized to some as yet unknown non-reducible cross-link as previously proposed (Bailey, 1968).

Changes in striated muscle fibres during contraction and growth with particular reference to myofibril splitting.

ABSTRACT Ultrastructural measurements were carried out on the mouse biceps brachii and soleus muscles fixed at different states of contraction and stretch. At a sarcomere length of 2·7–2·9 μm the more peripheral actin filaments ran slightly obliquely from the Z-disk to the A-band. This is due to a mismatch between the rhombic actin lattice at the Z-disk and the hexagonal lattice at the M-line. For a perfect transformation of a rhombic lattice into a hexagonal lattice the ratio of the lattice spacings has to be 1:1·51. However, at this sarcomere length the ratio is about 1:2·0 (Z:M). During contraction the angle of the peripheral actin filaments remains approxi-mately the same because the expansion of the M lattice is compensated for, partly by an increase in the Z-lattice spacing and partly by the bowing of the peripheral myosin filaments. When the sarcomeres are stretched beyond 3·0 μm the myosin filaments straighten out and the Z:M ratio decreases. The ratio of 1:1·51 is almost attained when there is no overlap of the actin and myosin filaments. Ultrastructural measurements were also carried out on biceps brachii muscles of different ages. The lattice spacings for a standard sarcomere length did not change during the post-natal growth period. The amount of myofibrillar material and sarcoplasmic reticulum plus transverse tubular system were estimated using linear analysis for muscles at 3 different stages of growth. It was found that the myofibrillar cross-sectional area in an individual muscle fibre may increase 40-fold during growth and that the transverse tubular and sarcoplasmic reticulum systems increase at about the same rate. In both the biceps brachii and the soleus muscles the myosin and actin filaments are not built into a continuous mass but they are divided into numerous discrete myofibrils. Subdivision of the myofibril mass occurs because the myofibrils split once they attain a certain size. The evidence presented in this paper supports the suggestion that the longitudinal splitting of the myofibrils occurs by the ripping of the Z-disks. When tension is rapidly developed by 2 adjacent sarco-meres a stress is produced at the centre of the Z-disk resulting from the oblique pull of the actin filaments. This causes some of the Z-disk filaments to rip and the rip then extends across the disk with the direction of the weave of the lattice. Evidence for the mechanism includes electron-micrographs showing Z-disks that are apparently just commencing to split; in these cases a hole can be seen in the centre of the disk. A model experiment is described which demonstrates the importance of the rate of tension development in causing myofibril splitting. Rapid tension development produces a snatch effect which causes the Z-disk filaments to break more readily. This may explain why the myofibrils in fast muscles tend to be small and discrete whilst those in slow muscles are larger and more irregular in shape.

Increased voluntary running and decreased motor coordination in mice after neonatal corticosterone implantation

This is an initial report on the long-term functional effects of intensive corticosterone treatment in infancy. Mice given corticosterone during the period of postnatal brain growth have been shown to undergo a permanent reduction in brain size and DNA, that is particularly marked in the cerebellum. Animals so treated exhibit an increased voluntary running in activity wheels, that outlasts the period of steroid administration, but does not persist indefinitely in all cases. Maze learning by adults was unimpaired, although the treated mice tended to show a poorer initial adjustment to the maze. Despite the reduction in cerebellar size, the mice were able to run, swim, and climb a cord without obvious disability. However, the steroid treated mice showed a marked reduction in their ability to remain standing on a slowly rotating bar, and were less skillful in crossing a space between a cord and a narrow surface. The observations suggest that the mice given corticosterone in infancy had a lasting impairment in fine adjustment mechanisms of motor control, compatible with some interference in cerebellar function, secondary to the 25% reduction in cerebellar DNA. Furthermore, the treated mice were less active in an open field, and showed other behavior suggestive of differences in emotional reactivity.

Reductions in size and total DNA of cerebrum and cerebellum in adult mice after corticosterone treatment in infancy

This study was designed to examine the long-term effects on the brain of intensive corticosterone treatment during the period of rapid postnatal brain growth and maturation. Mice were given a single subcutaneous implantation of a pellet of corticosterone at 2 days of age. This produced a temporary interference with growth that resulted in a 10% reduction in body weight of the adults; a slightly greater reduction in cerebral weights and a 21% reduction in cerebellar weights. Determinations of DNA, RNA and cholesterol were made, as indices of cell number and maturation. the total DNA of the normal mouse cerebrum increased 25% between 2 and 14 days of age, while cerebellar DNA increased 580%. Total cerebral DNA did not change in control mice between 14 and 350 days of age. Corticosterone given between 2 and 14 days reduced total cerebral DNA 18% at 14 days and 10% at 8 months; and reduced cerebellar DNA 25%. In the cerebrum there was a small but significant decrease in cholesterol at all ages studied. There was a transient decrease in the RNA DNA ratio. The findings indicate that corticosterone given in infancy interfered with the synthesis of DNA, RNA, and protein in the brain, and produced an irreversible reduction in brain size and cell numbers, which was particularly marked in the cerebellum, because of the high rate of postnatal mitosis characteristic of certain cerebellar neurons.

INTRAUTERINE GROWTH AS ESTIMATED FROM LIVEBORN BIRTH-WEIGHT DATA AT 24 TO 42 WEEKS OF GESTATION

Percentile curves representing intrauterine growth of Caucasian infants in Colorado are constructed from the birthweights of liveborn infants at gestational ages ranging from 24 to 42 weeks. The median weights of Colorado babies were found to be lower at 40 weeks of gestation than the national median, and mean weights at 40 and 42 weeks were lower than those given by other authors. The use of the intrauterine growth chart in studying the nutrition of babies at birth and during their postnatal growth period has been described.

INTERPOLATIN FORMAULAE FOR THE GROWTH OF THE HUMAN BRAIN AND ITS MAJOR PARTS IN THE FIRST YEAR OF POSNATAL LIFE

Descriptive curves of brain growth from birth to maturity may be represented by a number of expressions, some quite elaborate and some fairly simple. However the brain as a whole and its several major parts increase so rapidly in the first year that straight line expressions for the relationship between masses of these structures and time seem justifiable for practical use in this period. Such straight lines are, in effect, secants of the very abrupt early segments of brain-growth curves that cover the entire postnatal growth period.