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Biomedical subjects

T M Lee

Publications and source records attributed to T M Lee.

At least 145 records · Page 8Linked to original sources
PubMed1986

Circannual variations in circadian rhythms of ground squirrels.

There was a circannual rhythm in the times of activity onset (psi o) and activity termination (psi T) and in the duration of the active phase (alpha) in female ground squirrels (Spermophilus lateralis) maintained in a light-dark (LD) 14:10 photoperiod for 22 mo. Activity onset occurred 2.3 h after light onset in the 4 mo before estrus, 0.5 h before light onset during the month encompassing estrus, and progressively later during each of the ensuing 4 mo. Termination of activity occurred later during the month of estrus than in the 4 mo preceding estrus; alpha nearly doubled during the month of estrus and decreased gradually over the next 3 mo. The psi o and psi T remained entrained to the daily illumination cycle, but the phase angles of activity onset and offset and the duration of the active phase varied seasonally and recurred with a circannual period of 9-11 mo. The LD 14:10 photoperiod entrained the circadian activity rhythm throughout the year; however, circannual variations in activity as well as in estrus and body mass were not entrained by this photoperiod but free-ran with periods of less than 12 mo.

Activity Cycles↗
PubMed1986

Female rats in a laboratory display seasonal variation in fecundity.

Female laboratory rats housed in controlled environments of two separate laboratories displayed seasonal variation in fecundity. Fecundity peaked between May and August and reached a trough between December and February, as measured by oestrous cycle length, variability and regularity, as well as number of animals mating and the percentage of litters reared to weaning. The percentage of mated animals giving birth remained constant throughout the year. Seasonal variations in the laboratory coincided with the seasonal cycle reported for wild rats in natural conditions. Several environmental variables, e.g. food, water, humidity and airborne factors, were evaluated as putative cues for seasonal variation.

Animals↗
PubMed1986

Modified antigens in the treatment of allergic disease.

In summary, effects at improvement upon conventional immunotherapy by antigen modification have taken three major directions. First, methods designed primarily to impede allergen release from the site of deposition have been only modestly successful. An example is alum-precipitated extracts which require somewhat fewer injections. Second, attempts to suppress specific IgE production have been unsuccessful in human trials, although antigen-specific IgG levels have increased in a manner similar to that produced by conventional allergen immunotherapy. The third major avenue of antigen modification, to reduce allergenicity while retaining immunogenicity, appears, at present, to be the most promising. Clinical studies of polymerized allergens summarized above have shown that patients can be given a course of polymerized allergen immunotherapy in a few weeks, while a course involving a comparable quantity of unmodified allergen would require years. With the use of polymerized pollen extracts, degree of symptom reduction, persistence of benefit, and magnitude of IgG-blocking antibody induction are comparable to that achieved with unmodified allergens, while the incidence of systemic reactions is greatly reduced. The development of polymerized allergens appears to represent a significant advance which may be expected to expand the clinical utility of allergen immunotherapy.

Allergens↗
PubMed1985

At what age do rat young stop responding to the maternal pheromone?

We tested postweanling rat young to see if they would continue to respond to the maternal pheromone when pheromone-containing feces were made available in the home cage. We found that they do, and that the consumption of pheromone-containing feces is important for such sustained responsiveness. Nonetheless, interest in the pheromone does not continue past 50 days of age. The possible adaptive significance of the continuation and cessation of pheromonal responsiveness was discussed.

Adaptation, Biological↗
PubMed1984

The relation between the internal phosphorylation potential and the proton motive force in mitochondria during ATP synthesis and hydrolysis.

Using 31P NMR and a potassium ion distribution method, the internal phosphorylation potential and the transmembrane electrical potential of intact rat liver mitochondria were measured simultaneously during ATP synthesis and ATP hydrolysis. The ATPase was shown to quickly equilibrate the internal phosphorylation potential with the proton motive force across the mitochondrial membrane. Upon oxygenation of anaerobic mitochondria, there was a very fast increase of delta pH and a quick uptake of inorganic phosphate prior to the buildup of the internal ATP. Consistent with the chemiosmotic theory, these results showed the presence of proton pumping by the respiratory system from the bulk internal aqueous phase to the bulk external aqueous phase. There was, in the measured energetic parameters, no indication of direct energy coupling or short circuiting protons between the respiratory energy input and the ATP synthesis.

Adenosine Diphosphate↗
PubMed1984

The maternal pheromone and brain development in the preweanling rat.

Preweanling rats selectively approach and consume pheromone-containing maternal feces. This selectivity suggests that the consumption of maternal feces might be important for the growing pup. Previous research suggested that such feces might promote brain development. A series of experiments was carried out in which pups were denied access to maternal feces. These pups were clearly inferior to control pups in brain growth and neurobehavioral maturation, as well as in the quantity of brain myelin.

Animal Population Groups↗
PubMed1984

The maternal pheromone and deoxycholic acid in relation to brain myelin in the preweanling rat.

We examined the lipid composition of blood and myelin in preweanling rats denied access to maternal feces. Levels of triglycerides and free fatty acids in the blood were reduced and in the brain the amount of myelin and the phospholipid concentration in myelin were also reduced. The addition of deoxycholic acid to ordinary laboratory chow prevented these deficiencies. We conclude that response to the maternal pheromone and the subsequent ingestion of deoxycholic acid through maternal feces promotes the deposition of normal brain myelin.

Animal Population Groups↗
PubMed1984

The maternal pheromone and deoxycholic acid in the survival of preweanling rats.

Preweanling rats selectively approach and consume pheromone-containing maternal feces. This selectivity suggests that the consumption of maternal feces might be important for the growing pup. We tested the hypothesis that such feces, because of their high deoxycholic acid content, may protect against acute enteritis. A series of experiments was carried out in which pups were denied access to maternal feces. These pups died more often from acute enteritis than control pups. Additional confirmation of the hypothesis was obtained when feces-denied young fed deoxycholic acid showed a significantly lower mortality than feces-denied young fed laboratory chow alone.

Animals↗
PubMed1984

Altered bile acid physiology during lactation in the rat.

There is evidence that the rate of bile acid secretion increases significantly during lactation in the rat. We show that this increase in secretion rate is accompanied by an expanded bile acid pool and that occasioning the enhancement of both pool size and secretion is an increase in bile acid synthesis. The hypothesis is advanced that maternal prolactin, promoted by suckling young, amplifies cholesterol-7-alpha-hydroxylase, the rate-limiting enzyme in bile acid biosynthesis, and perhaps HMG-CoA reductase, the rate-limiting enzyme in cholesterogenesis.

Animals↗
PubMed1983

The maternal pheromone of the rat: testing some assumptions underlying a hypothesis.

Herein we report four experiments relating to the maternal pheromone of the rat that show (a) preweanling young consume pheromone-containing feces most conspicuously between 14 and 27 days; (b) they consume those feces preferentially; (c) such feces contain high levels of deoxycholic acid; and (d) preweanling young are deficient in deoxycholic acid. The data of these experiments lend support to the hypothesis that in responding to the pheromone the young ingest deoxycholic acid, a steroid believed to promote gut immunocompetence and brain myelination.

Animals↗
PubMed1982

A study on the exchange rate of magnesium with ATP.

The exchange process of Mg2+ with ATP was found to be, in many cases, dominated by Mg2+ exchange between ATP and ATP-Mg (a bimolecular reaction) rather than the Mg2+ off-process from ATP-Mg to solution (a unimolecular reaction). The Mg2+ off-rate from ATP-Mg and the rate constant of the bimolecular reaction were determined at 10 and 25 degrees C at pH 7.3, using 31P-NMR at 145.7 MHz. At this resonance frequency intermediate to slow exchange phenomena with respect to the NMR time scale of 2.5 . 10(3) s-1 were observed in ATP resonances. Various implications of these results to studies of biological systems have been pointed out.

Adenosine Triphosphate↗
PubMed1982

Reduced prolactin binding to liver membranes during pheromonal emission in the rat.

Between 14 and 27 days of lactation, female rats excrete a pheromone in their feces that is cholic-acid dependent and that strongly attracts young. Previous research has shown that high circulating levels of prolactin are necessary before the pheromone can be emitted. However, during the time of pheromonal emission prolactin in serum conspicuously declines, while in hepatic cytosol the hormone reaches peak levels. We were interested in the question of how the liver can show peak cytosolic concentrations of prolactin at a time of falling blood levels of prolactin. Accordingly, we examined the prolactin binding capacity of liver membrane fractions during selected periods of lactation. We also studied the livers of virgin and pregnant females for comparison. Three membrane fractions were separated: the cell membrane, the nuclear membrane and a fraction consisting of the cell membrane and large non-nuclear organelles. In all three fractions, there was an increase in available and total prolactin binding in the liver when pregnant females were compared with nulliparous females. However, during the time of pheromonal emission, when prolactin in hepatic cytosol was elevated, there was a significant reduction in the prolactin binding capacity of the liver. How such a reduction increases the cytosolic concentration of the hormone and in turn heightens cholic acid output and pheromonal emission remains unsolved.

Animals↗
PubMed1981

Two-dimensional TLC analysis of ginsenosides from root of dwarf ginseng (Panax trifolius L.) Araliaceae.

A procedure is reported for the two-dimensional TLC separation of ginsenosides from the root of Panax trifolius L. The solvent systems and spray reagents described are useful for the identification of ginsenosides in various species of Panax. The results of the separation and identification with controls of at least four ginsenosides from the root of P. trifolius L. are reported. The total percentage of ginsenosides was 0.0061%.

Chromatography, Thin Layer↗