Data are summarized about digestion and absorption of carbohydrates, lipids and proteins during mammalian perinatal development including human fetuses. Corresponding with the high fat intake in suckling rats, absorption of triglycerides was found to be approximately 2-3 times higher in suckling than in adult rats. Carnitine contents of the small intestinal mucosa of rats decrease postnatally, reaching adult levels at the time of weaning. Other studies suggested that gluconeogenesis may occur in the small intestine in the neonatal period. The intestinal mucosa of infant rats produces ketones; it was suggested that ketone production is to a large extent due to a breakdown of long-chain fatty acids. Studies dealing with the development of colonic sodium transport in rats are described. Other studies on the developing colon showed that the proximal colon resembles ileum during the early postnatal period. Developmental changes of the "specialization" of intestinal segments are reviewed. In all studies attention is given to the maturative effects of hormones of the adrenal cortex and thyroid gland (88 references).
It was confirmed that the main source of energy for growth and development in the neonatal period was fat. Considerable attention was paid to the development of both white adipose tissue (WAT) and brown adipose tissue (BAT) in the rat and human newborn. Cholesterol metabolism during development was studied in the liver, the small intestine and both WAT and BAT. Brown adipose tissue of rats and adipose tissue from human newborns require carnitine for optimum respiration and fatty acid oxidation. Surprisingly, carnitine enhanced lipolysis in human newborn adipose tissue, Intravenously-fed newborn patients exhibited a rapid decrease of plasma level of carnitine and its esters, indicating a greater requirement for exogenous carnitine than in adult subjects (52 references)
Effects of early neonatal interventions on metabolic parameters later in life (s.c. late effects) were studied in rats using two models; namely, (a) the effects of premature weaning and (b) the effects of "dietary" manipulations during the suckling period (s.c. small vs. large litters), (a) Premature weaning of rats caused an earlier degeneration of spermiogenesis and elevated plasma cholesterol levels in adult animals when compared to levels found in animals weaned 12 days later (on day 30 after birth). In adult rats, radioiodine uptake in thyroid glands was lower in the group weaned prematurely. Premature weaning was followed by a decrease of corticosterone production in adrenal glands in adult animals; in female adult prematurely weaned rats, an elevated response of adrenal cortex to stressors was observed. Several other studies explored the "immediate" effects of early, premature weaning, (b) Early exposure to high fat diet evoked a hypercholesterolaemic response in adulthood following brief exposure to HF diet. Rats from litters reduced to 3 or 4 pups per mother on postnatal day 3 exhibited 2 days later plasma levels of cholesterol higher than in rats raised in large litters of 8 or 14. The difference between small and large litters was preserved for the whole lifespan of the animals. In adulthood, rats from small litters were fatter and had higher levels of plasma cholesterol and insulin. Other studies suggester that early dietary experience may regulate the pattern of drug metabolism in adult life. An inhibition of diurnal plasma corticosterone variation was found in rats overfed during the neonatal period and an increased stimulation of lipolysis by norepinephrine and lipogenesis by insulin was demonstrated in neonatally underfed rats. Interesting studies were reported in longitudinally studies in children: at the age of 9-12 year brest-fed children (for more than 6 months) had the highest cholesterol levels; on the other hand significantly increased levels of APO B, Apo Al, ATH index and Apo/B Apo A1 quotient (p<0.05) were found in the nonbreast-fed group (27 references).
Early studies suggested endocrine type mother-pup interaction: 13M administered to suckling rats appeared via the urine of the suckling and mother's milk in the circulation of litter mates who were not injected with iodine; levels of thyroxin in rat milk were influenced by the status of the thyroid gland of the lactating rat. Administration of TRH (thyrotropin releasing hormone) to lactating mothers led to an appearance of unaltered hormones in the milk and stomach content of sucklings. TSH (thyroid stimulating hormone) or ACTH (adrenocorticotropic hormone) when given orogastrically to suckling rats increased thyroid hormones and corticosterone serum levels in suckling rats. Functional effects of gastrointestinal administration of insulin, bombesin (mammalian analog of gastrin-releasing peptide) and epidermal growth factor (EGF) are reviewed in detail (32 references).
During our studies on gastrointest-inal motility in suckling rats using 51Cr or 51Cr-EDTA as markers, we noticed that these markers - in contrast to studies in adult rats "adhered" to the gastrointestinal wall of sucklings. We therefore decided to test the use of another non-absorbable marker Poly R-478 (an acetylated anthrapyridone chromophore linked to an polyamino-ethylene-sodium ethylene sulfonate copolymer backbone developed by the Dynapol Corporation (Palo Alto, CA). This new method has appeared to be useful.
Since the beginning of the 19th century, the comparative and ontogenetic branches of developmental physiology were cultivated in our country. Evidence was given that development of the gastrointestinal tract in tadpoles is dependent on the quality of proteins in their food. A complete metamorphosis of Amblystoma mexicanum, was entirely accomplished by feeding with powderized thyroid gland. The definition and chronological delimitation of both the suckling and weaning period in experimental animals opened the investigation of the effect of disturbance of the natural environment caused by premature weaning on the ensuing development of an individual. A new term was coined "late effects of early adaptations". Analysis was provided by impressive research of the development of energetic metabolism and development of gastrointestinal tract functions, water and electrolyte exchange and endocrine functions including the role of the pineal gland in control of circadian rhythms (12 references).