Search PubMed⌕ Search

Biomedical subjects

P M Daniel

Publications and source records attributed to P M Daniel.

At least 37 records · Page 2Linked to original sources
PubMed1978

The effect of age upon the entry of some amino acids into the brain, and their incorporation into cerebral protein.

The way in which the influx of amino acids into the brain changes as the age of rats increases from one to 25 weeks is reported. Most of the amino acids have a very high rate of influx during the first weeks of life, which falls progressively until an adult is reached by about 8 to 10 weeks of age. The high influx in early life is due to carrier-mediated transport systems which act more rapidly in the young than in the adult. These systems can be saturated by raised levels of amino acid in the blood, both in young and adult animals. The high influx in early life is necessary to provide abundant supplies of amino acids for cerebralprotein formation during the period of rapid brain growth. In adult life, influx declines to a level that is adequate to support the synthesis of cerebral protein, which is still being continuously broken down and renewed at a remarkably high rate.

Age Factors↗
PubMed1978

Portal circulations and their relation to counter-current systems.

We have reviewed the distribution of portal circulations throughout the animal body; they are commoner than is generally supposed. Most portal circulations consist of two serial capillary beds connected by one or more larger vessels. We have called these 'convergent' portal circulations: examples are hepatic portal, placental, hypophysial, renal, ovarian and testicular circulations, as are parts of the lymphatic circulation. A second type of portal circulation, which is less common, consists of two serial capillary beds that are not connected by larger vessels. These we have called 'continuous' portal circulations: adrenal and pancreatic circulations are examples of this type. When a countercurrent concentrating mechanism exists in the body it is always part of the primary or secondary bed of a convergent portal circulation, though some convergent portal circulations are not associated with countercurrent mechanisms.

Adrenal Glands↗
PubMed1978

The effect of age upon the influx of glucose into the brain.

1. Rats aged from 1 to 116 weeks were studied. 2. Influx of glucose into the brain is low in suckling rats but rises after weaning, to reach its highest level in the young adult, thenceforward declining slowly as age increases. 3. The blood-brain barrier for glucose is fully developed in the rat by the age of 18 days and glucose enters the brain, at this stage, by carrier-mediated transport, as in the adult. 4. The results show that the low influx of glucose into the brain of the suckling animal is due to a low maximum rate of transport of glucose rather than to a low affinity of the carrier-molecule for glucose. 5. In the young adult rat, efflux of glucose back from the brain into the blood is greater than in either the suckling or the old animals. Thus the margin of safety, i.e. the extent to which the blood glucose can be reduced without affecting the utilization of glucose by the brain, is highest in the young adult. 6. The lower margin of safety in the suckling animals is compensated for by the high influx of the ketone bodies which provide an alternative source of energy at this age. In the old animals there is no alternative source of energy, so that the older brain is at greatest risk in hypoglycaemia.

Aging↗
PubMed1978

The influx of amino acids into the heart of the rat.

1. The influx of nineteen amino acids into the heart of the living rat was studied by a method specially devised for experiments under controlled conditions in vivo. 2. When, in separate experiments, the concentration of each amino acid in turn was artificially raised in the circulation, the influx of that amino acid into the heart increased. 3. Our data indicate that at least ten of these amino acids enter the heart in vivo by means of saturable carrier-mediated transport systems. The transport rates conform, at least approximately, to Michaelis kinetics and the transport systems are clearly, in the cases of many amino acids, active, i.e. energy-dependent. 4. The amino acids which were studied had rates of influx into the heart which differed from each other over a range of more than 10 to 1, even when allowances were made for the difference in their concentration in the circulating blood. These differences in influx were not related to such factors as the molecular size of the individual amino acids. 5. The amino acids which have a high influx into the heart are mainly those which are needed either to re-synthesize contractile protein or as oxidizable substrates.

Amino Acids↗