Investigations on erythropoiesis in newborn rats. Dependence of erythropoiesis in newborn rats on the intensity of the haemopoietic processes in the lactating mothers.

The intensity of haemopoietic processes was investigated in 7, 9, 11, 14 and 19-day-old suckling rats in relation to the intensity of these processes in their mothers. The rate of the haemopoietic processes in newborn rats was determined on the basis of 59Fe incorporation into the blood and haemopoietic organs. The activity of the erythropoietic system in lactating rat females was stimulated by haemorrhage and inhibited by erythrocyte transfusion. Anaemization of lactating rats by haemorrhage did not stimulate erythropoiesis in the suckling rats. Posttransfusion polycythaemia in the lactating mothers inhibited erythropoiesis in the suckling rats beginning with the 9th day of life. This phenomenon became more pronounced with the age of the rats.     

Metabolic DNA in the hepatocyte nuclei in newborn rats.

The behaviour in time of labelled nuclear DNA in the hepatocytes of newborn rats was studied using autoradiographic and biochemical techniques in two groups of experiments. In the first group H-3-thymidine was injected to the mothers at the 16th day of pregnancy and the amount of labelled DNA was evaluated in the newborns after delivery. In the second group H-3-thymidine was injected to the newborns two hours after birth and the labelled DNA was studied at the same time intervals as the first group. The amount of labelled thymidine incorporated into the first group of animals remains constant for the first three days of life, thereafter a reduction in specific activity of DNA is observed concomitant with an increase of the percentage of labelled nuclei and a decrease of the number of grains per nucleus. These results show that mitotic divisions, which are absent during the first three days of life, take place between the third and sixth days of life. The decrease of the specific activity is therefore due to dilution and not to loss of labelled DNA. In the second group of experiments the DNA labelled with H-3-thymidine shows a decrease by about 30--40% per day during the first three days of life accompanied by a decrease in the number of grains per nucleus without changes in the percentage of labelled nuclei. These data show that DNA synthesized during the first day after birth is metabolically unstable, unlike that synthesized during foetal life.     

The regulation of pineal serotonin N-acetyltransferase activity in newborn rats.

Rat pineal serotonin N-acetyltransferase activity increases 2–3 hr after birth and then decreases again. The activity at night is higher than that during the day in rats as young as 1 to 2 days old. Administration of the beta adrenergic blocker trimepranol to newborn or 2-day old rats at night lowers the elevated serotonin N-acetyltransferase activity. Hence, the activity is under adrenergic control even in the not yet innervated pineal gland of the newborn rats.     

Atrial natriuretic peptide in heart and specific binding in organs from fetal and newborn rats

To assess the possibility that atrial natriuretic peptide plays a role in salt and water balance during early mammalian development, we examined hearts from fetal and neonatal rates for the presence of this peptide and presumed target tissues for their ability to bind the hormone. Immunohistochemistry was used to localize and radioimmunoassay to quantify this peptide in heart. Immunoreactive atrial natriuretic peptide was visualized in the fetal heart on day 17.5 post-conception. It was distributed throughout the atrial appendages and free wall and, in ventricle, in the trabeculae carnae and chordae tendineae. The concentrations of immunoreactive atrial natriuretic peptide in atria of rats on day 19.5 post-conception were one-tenth of those in the adult. Levels of this peptide in fetal ventricle were low and virtually absent from the adult tissue. Specific binding of radiolabelled atrial natriuretic peptide measured by whole organ counting occurred in several organs from 19.5-day fetal and neonatal rats. A number of these tissues, including the kidney, ileum, adrenal, lung and liver, are targets for and/or bind the peptide in adult rats. Specific binding in these tissues was localized using autoradiography at anatomical sites similar to those in adult organs. Specific binding was also seen in fetal but not neonatal skin. In the kidney, binding was associated with immature as well as mature glomeruli. These findings support the proposition that atrial natriuretic peptide may function in the perinatal rat as it does in the adult and, in addition, may play a unique role during fetal life.     

Space flight effects on haemopoietic stem cells of the bone marrow of rats

Abstract. Changes in the number of haemopoietic stem cells (CFU-s) were studied in rats during the recovery day and selected post-recovery days after an 18–19-day flight on biosatellites Cosmos 936 and Cosmos 1129 . There was a decrease in the CFU-s number of the bone marrow of rats on the recovery day. On the 6th day post-recovery the CFU-s number was still depressed, while on the 25th day post-recovery it was elevated above control value. The differentiation ratio of transplanted bone marrow cells was not altered by space flight.     

Glucose turnover rate in newborn rats.

In starved newborn rats an increase in glucose turnover rate was observed 4 and 6h after birth, but a dramatic fall occurred at 16h. In suckling newborn rats, no decrease in glucose turnover rate was observed at 16h. The metabolic clearance of glucose did not change in fed or starved animals. The results are discussed in relation to metabolic adaptation to extra-uterine life.     

Chronic early leucine administration induces behavioral deficits in rats.

Sustained levels of leucine comparable to those of human Maple Syrup Urine Disease (MSUD) were achieved in blood and brain of rats by subcutaneous leucine administration twice a day from the 6th to the 28th day of life. Control rats were treated with saline in the same volumes. Behavioral studies using aversive and nonaversive tasks were performed during adult age. Chronic early leucine treatment impaired acquisition of a two-way shuttle avoidance task and altered habituation to an open field. Our results suggest that early postnatal leucine administration induces long-lasting behavioral deficits.     

Mitotic activity changes in the corneal epithelium of rats of different ages following exposure to pain]

A study was made of pain stimulus (amputation of 1/3 of the tail) on the mitotic activity in the corneal epithelium of 21-day fetuses, 1-, 3-, 4-, 5-, 7-, 10-, 15-, 20- and 25-day rats. In 45 minutes after the infliction of trauma no significant change was seen in the cornea of the fetuses and of the one-day-old ratlings. A gradual establishment of the reactive inhibition of mitoses in response to pain occurred between the 3rd and the 10th day of postnatal development. This reaction became more intense after the 10th day, reaching the maximum by the 25th day. Reactive inhibition of the mitotic activity was connected with the inhibition of the entrance of cells into mitosis.     

Respiratory adaptation to chronic hypercapnia in newborn rats

We asked 1) whether newborn rats respond to chronic hypercapnia with a persistent increase in ventilation and 2) whether changes in lung mass were accompanying the respiratory adaptation to chronic hypercapnia, as previously observed during neonatal chronic hypoxia. Five litters of rats were kept in 7% CO2 (with 21% O2) from day 1 to 7 after birth (CO2exp) and compared with six litters of control rats growing in normocapnia-normoxia (C). Body weight was similar between the two groups. Ventilation, measured by flow plethysmography, increased in CO2exp from day 2 and remained steadily elevated, and at day 7 it almost doubled (174%) the C value because of the large increase in tidal volume and mean inspiratory flow (192 and 189%, respectively) with no changes in respiratory frequency. Two days after return to normocapnia, ventilation was still 33% higher than in C; at this time, acute exposure to hypercapnia increased ventilation relatively less in the CO2exp than in C because of a lower increase in tidal volume. Neither the lung weight-to-body weight nor the heart weight-to-body weight ratios increased in CO2exp. We conclude that 1) chronic hypercapnia in newborn rats induces a steady increase in ventilation, which persists at least 2 days after return to normocapnia with a reduction in the acute response to CO2, and 2) hyperventilation per se is not the cause of the increased lung mass observed during chronic neonatal hypoxia.     

Changes in the properties of photostimulated cyclic nucleotide phosphodiesterase from the retina of rats with hereditary retinal degeneration

A degree of extractability and activation of cGMP-phosphodiesterase (PDE) (EC. 3.1.4.17) from the rod outer segment membranes was studied in Campbell rats with inherited retinal degeneration and control Wistar rats as compared to the control, the PDE extractability in the diseased rats was found to be considerably lower, which manifested as early as the 15th day of the postnatal life. Changes in the GTP-stimulated and basal PDE activity were observed in Campbell rats. Beginning from the 25th day of the postnatal life the GTP-stimulated PDE of degenerative retina decreased and by the 60th day it reached the basal activity level in these animals. In the diseased rats the first 57 days of postnatal life the basal activity of PDE was sufficiently higher, followed by a sharp decrease reaching the basal activity level of the control rats. The obtained data on the changed PDE activity are likely to be a result of the disturbance in the protein-lipid interaction and a change in the external layer of the photoreceptor membranes in rats with inherited retinal degeneration.     

Circannual variation of mortality rate following a single injection of hydrocortisone in newborn rats

Under constant experimental conditions of room temperature and illumination, a highly significant seasonal difference was observed in the mortality rate of rats which received hydrocortisone on the first day of life. The rate was high in winter and low in summer. Inborn circannual variation of the susceptibility to exogenous corticosteroid was shown to exist in newborn rats.     

The hypothalamic magnocellular neurosecretory system in developing rats

Studies concerning the development of the magnocellular system are scarce and discordant in literature. We carried out an immunohistochemical study on supraotic and paraventricular hypothalamic nuclei using antivasopressin and antioxytocin antibodies in developing rats between the 15th day of intrauterine life and the 6th day of postnatal life. In addition, we performed RT-PCR experiments to establish the stage at which these hormones appear and neurosecretory activity commences. The results showed that supraoptic and paraventricular nuclei appear, respectively, on the 16th and the 18th day of intrauterine life and both immediately synthetize vasopressin neurohormone. By contrast, synthesis of oxytocin takes place from the 2nd day after birth. Probably, these nuclei synthetize oxytocin in conjunction with the decline of placental maternal oxytocin.     

Hepatocyte chromosomal non-histone proteins in developing rats.

Rat hepatocytes taken a different stages of the perinatal period were partially purified. On sodium dodecylsulphate acrylamide electrophoresis chromosomal non-histone proteins showed important variations in complexity during development. Chromosomal phosvitin kinase strongly increased during the last days of fetal life; it strongly decreased just after birth and increased again for a short time, while the cytosol phosvitin kinase increased more significantly after birth. Chromosomal non-histone proteins prepared at varoius stages were incubated with [gamma-32P]ATP and resolved on polyacrylamide gel. The incorporation was very low in sample taken at the 15th say of the fetal life. A dramatic increase was observed at the 17th day. This incorporation strongly decreased in the samples taken thereafter and it was negligible in proteins from adult rats. The variations in protein kinase and in 32P incorporation into non-histone proteins were correlated with the pattern of appearance of enzymes in this period of life, with cell growth and with the hormone-induced maturation.     

Compensatory renal hypertrophy after nephrectomy in newborn rats]

The process of the kidney compensatory hypertrophy in young rats has been studied after nephrectomy on the 2nd day of life. The intact kidney was investigated by morphometrical and electron microscopical methods from the 1st day till the 3rd month after operation. The kidney compensatory hypertrophy in the early postnatal ontogenesis is accompanied by the acceleration of growth and differentiation of renal structures. The hypertrophy involves three successive steps: (1) functional tension of ultrastructures; (2) expressed hyperplasia and hypertrophy of cells; (3) structural-functional specialization. Among the cellular factors of the kidney compensatory growth at this age, the main role is played by the process of cell hyperplasia.     

Aflatoxin B1 induced hepatocarcinogenesis in neonatal rats.

Role of cell replication on aflatoxin B1 (AFB1) induced hepatocarcinogenesis was investigated in neonatal rats showing persistence of cell replication in the liver for 21 days of post natal life. Adult (8-10 weeks old) rats displaying no hepatocytic proliferation served as controls. Three doses of AFB1 were administered to both the groups at intervals of 48 hr with the doses starting on 10th day of age in the neonatal group. Appearance of phenotypically altered preneoplastic hepatocytes was quantitated in both the groups. A significantly higher incidence of preneoplastic foci was recorded in neonatal rats as compared to adult animals. The results suggest that presence of cell replication in neonatal rats at the time of AFB1 administration enhances the process of hepatocarcinogenesis.     

The modulating role of essential and non-essential amino acids in organotypic tissue culture in rats of different ages

The effect of amino acids L-lysin, L-asparagin, L-arginin, L-glutamate was investigated in organotypic tissue culture of spleen, liver and brain cortex of rats at different age. The amino acids in concentration 0.05 ng/ml are active inducing a less intensive growth zone, as compared to control, in 1-day and in older rats--an intensive growth zone, as compared to control in 21-day rats. The data obtained suggest a modulating role of amino acids in the tissues at different stages of maturation.     

Serum lipids in 8- to 35-day-old Zucker rats

The serum concentrations of triacylglycerols, cholesterol, and phospholipids were measured in 8- to 35-day-old Zucker rats. The animals were killed at 35 days of age. and their phenotype is determined on the basis of the weight of their inguinal subcutaneous fat pads. The serum lipid concentrations in all the rats increased from the 8th day of life, reaching a maximum at day 17 to 21. Weaning produced a large decrease in the concentrations of all three types of lipids. In the obese rats, the serum concentration of triacylglycerols was significantly raised from day 35 of life, that of cholesterol from day 21, and that of phospholipids from as early as day 8. At this age this latter concentration nevertheless cannot be used as a factor for detecting the obese phenotype.     

Cholinesterase activity of the hypothalamo-hypophysial neurosecretory system in rats during the ontogenetic development

Summary The hypothalamic region and the neural lobe of rats from the 16th foetal day to adult animals have been studied for acetylcholinesterase and cholinesterase activity after Karnovsky. The attention was focused on the magnocellular nuclei-supraoptic and paraventricular, the median eminence and the neural lobe. Acetylcholinesterase activity appears in the paraventricular nucleus on the 18th foetal day, i.e. prior to that in the supraoptic nucleus. Heterochronic development and heteromorphism of paraventricular neurosecretory cells have been noticed. The median eminence shows no clear acetylcholinesterase activity. There are acetylthiocholine and butyrylthiocholine positive structures in the posterior pituitary. These structures are especially pronounced in 30–47-day rats. The cholinergic mechanism of release of neurohormones from the neural lobe is suggested. The results are discussed in functional and phylogenetic aspects.     

Dynamics of calcium levels and changes SERCA content in muscle fibers of rats and Mongolian gerbils during hind limb unloadings of various duration

In this study, it was shown that calcium levels in the fibers of m. soleus of Mongolian gerbils after one day of unloading increased four and a half times in comparison with the control. In rats, the situation differed: 2.8 times increase after the 1st day of hypogravity persisted until the 3rd day and then calcium levels slightly decreased to the 12th day. However, the base concentrations of calcium in the control group of gerbils were significantly lower than in control rats, thus there was larger shift of this parameter during the first day. Probably, this was the reason for an earlier start of the protein phenotype shift in gerbils: statistically significant increase in the number of fibers with "fast" SERCA isoforms was detected after one day of unloading and therefore slow-to-fast shift in myosin phenotype was observed on the 3rd day of unloading. The same changes in rat muscle could be detected only after the 7th and the 12th day, respectively. In both species, there was a tendency to restore their initial parameters to the 12th day but in gerbils it was much more intensive.     

In vitro oxidation of [U-14C] palmitate, [1-14C] and [6-14C] glucose in newborn and adult rats and pigs

Studies have been made on the intensity of oxidation of [U-14C]-palmitate, [1-14C]- and [6-14C]-glucose by slices of the liver and skeletal muscles of new-born, 1-day, 5-day and adult Wistar rats and domestic pigs. It was found that the level of 14CO2 production from these substrates is higher in tissues of rats than in those of pigs. At early stages of ontogenesis, in tissues of both species intensive oxidation of glucose is observed together with oxidation of fatty acids. In the course of ontogenetic development, the intensity of glucose utilization significantly decreases, whereas the level of fatty acid catabolism remains relatively unaffected.