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Biomedical subjects

I Schmidt

Publications and source records attributed to I Schmidt.

At least 91 records · Page 5Linked to original sources
PubMed1993

Onset of excess fat deposition in Zucker rats with and without decreased thermogenesis.

To study the first stages of excess fat deposition in Zucker rats, we artificially fed littermates with identical amounts of milk from 4 to 15-16 days of age while continuously recording oxygen consumption (VO2) and deep body temperature. Under intermittent cold loads simulating the periodic thermoregulatory stimulation experienced in the nest, differences between the amounts of body fat deposited by artificially reared fatty (fa/fa) and lean (Fa/-) pups were as large as those seen in mother-reared pups. The decreased VO2 of the cold-reared fatty pups could account for 90-100% of their extra fat deposition. At thermoneutrality, 16-day-old littermates reared with low feeding rates showed small but significant genotype differences in body fat that were not energetically accounted for by differences in VO2 or lean body mass. Slightly but significantly lower fecal energy losses indicated that differences in resorption might account for the positive energy balance of thermoneutrally reared fa/fa pups. Reduced energy expenditure thus efficiently fuels excess fat deposition but is not essential for the onset of excess fat deposition in fa/fa pups. Other factors than reduced sympathetic activation of brown adipose tissue must be considered as a primary cause for the development of fa/fa obesity.

Adipose Tissue↗
PubMed1993

Rapid changes in metabolic cold defense and GDP binding to brown adipose tissue mitochondria of rat pups.

To determine developmental changes of brown adipose tissue (BAT) thermogenic activity at defined circadian and thermal states, we evaluated the time course of cold-induced increases of in vitro guanosine 5'-diphosphate (GDP) binding in parallel with whole body metabolism (oxygen consumption, VO2) and core temperature (Tc) in 1- to 11-day-old rat pups. During the maximum phase of the juvenile diurnal cycle, Tc of littermates was recorded continuously and VO2 alternately until 2 min before animals were killed for removal of interscapular BAT. GDP binding after 1.5 h at thermoneutrality and its increase during physiologically comparable cold loads were significantly lower in 1-day-old pups than in 5- and 11-day-old pups. Cold defense was activated more rapidly in the older pups, but GDP binding in even the 1-day-old pups was significantly increased during the second 10-min period of cold exposure. We conclude that rapid changes in thermogenic activity, in connection with the known developmental changes in the dependence of the suckling rat's metabolic cold defense on maternal and sibling contact and circadian phase, will distort longitudinal studies of any fast-changing BAT parameter when the conditions immediately before tissue removal are not thoroughly controlled.

Adipose Tissue, Brown↗
PubMed1992

An expression vector system providing plasmid stability and conditional suicide of plasmid-containing cells.

A cloning vector system was constructed on the basis of the pBR322 derivative pEG1 by introducing the whole parB locus of plasmid R1 cloned behind the promoter of the alkaline phosphatase gene (phoA) of Escherichia coli. The parB locus in combination with the phoA promoter ensures both (i) plasmid stabilization due to the post-segregational killing of plasmid-free cells during growth and (ii) killing of the cells induced by the potential environmental signal phosphate limitation. This vector, therefore, appears to be a model system for increasing the stability of recombinant plasmids and for decreasing the potential risks in the application of recombinant bacteria in industrial fermentations.

Alkaline Phosphatase↗
PubMed1992

Circadian changes of brown adipose tissue thermogenesis in juvenile rats.

The aim of this study was to determine whether the circadian cycle of core temperature (Tc) and oxygen consumption (VO2) in juvenile rats is correlated with changes in the thermogenic activity of brown adipose tissue (BAT). Nine-day-old rat pups derived from two colonies with 12:12 h light-dark cycles 180 degrees out of phase were artificially reared in continuous light for 12-48 h while Tc and VO2 were recorded. For measurement of GDP binding half the pups from each colony were killed during the maximum phase of their circadian Tc cycle and the other half during the minimum phase. During the maximum phase (0.5-2 h after lights-off in the colony of origin), when Tc was 36.1 +/- 0.1 degrees C, GDP binding (pmol/mg protein) was 575 +/- 31 (n = 19). During the minimum phase (0.5-2 h after lights-on), when Tc was 32.9 +/- 0.5 degrees C, GDP binding was 361 +/- 47 (n = 19). Moreover, the correlations between Tc, VO2, and GDP binding determined during the maximum plateau of the circadian cycle differ substantially from those determined during the minimum phase. Consequently, developmental studies of thermoregulation and BAT activity in suckling pups are seriously compromised if circadian phase is neglected.

Adipose Tissue, Brown↗
PubMed1990

Defective thermoregulatory thermogenesis does not cause onset of obesity in Zucker rats.

To test whether or not the onset of obesity in fatty (fa/fa) Zucker rats is caused by decreased thermoregulatory thermogenesis, pups were artificially reared above their lower critical temperature from 3 or 4 days of age. Littermates were continuously fed identical amounts of synthetic rat milk while body temperature (Tc) and oxygen consumption rate (VO2) were continuously recorded. When the daily mean Tc of all pups was held greater than 37 degrees C, neither Tc nor VO2 differed between fa/fa and genetically lean (Fa/-) pups during the first 2 wk of life. Tc and VO2 were significantly elevated in Fa/- pups during the third postnatal week. At both 16 and 21 days of age, fa/fa pups were identified by their low Tc during a brief cold exposure. Body fat and fat-free dry mass of fa/fa and Fa/- littermates differed at 21 but not at 16 days of age. The excess energy deposited as fat was partly derived from decreased nonthermoregulatory energy expenditure and decreased synthesis of lean body mass. Calculations support the speculation that a greater extraction of energy from the synthetic diet additionally supports the excess fat deposition. Decreased thermoregulatory thermogenesis and excess fat storage appear to be secondary and independent consequences of the primary genetic lesion.

Animals↗
PubMed1990

Development of circadian cycle of core temperature in juvenile rats.

To find out whether or not juvenile rats can sustain circadian rhythms of core temperature (Tc) in the absence of diurnal cues, we continuously recorded Tc for 12 days in isolated pups artificially reared in continuous dim light. Possible effects of uncontrolled environmental 24-h cycles were excluded by simultaneously studying pups born on the same day to two mothers entrained to 12:12 h light-dark cycles 180 degrees out of phase. Age-dependent changes were discriminated from the effects of sustained isolation by comparing Tc records between pups isolated from 10 or from 4 days of age (late- or early-isolated pups). Both groups of pups showed Tc cycles in phase with the light cycle in the colony of origin and with highest amplitudes from 10 to 13 days of age. Tc cycles with a period length close to 24 h could be seen through the 12th day of artificial rearing for early-isolated pups but only until the 6th day for late-isolated pups. In the third postnatal week the rhythm faded gradually. Self-sustained circadian Tc rhythms observed in isolated 1- to 2-wk-old pups demonstrate a functional endogenous clock in the juvenile rat.

Animal Husbandry↗
PubMed1989

Endogenous 24-hour cycle of core temperature and oxygen consumption in week-old Zucker rat pups.

Experiments were designed to test whether or not the 24-h core temperature fluctuations in week-old rat pups are of endogenous origin. Lean (Fa/-) Zucker rat pups born on the same day to mothers maintained in two different colonies with light/dark cycles 12 h out of phase with each other were mother-reared through the first 3-4 days of life and then artificially reared simultaneously in constant dim light. Continuous, automatic measurement of core temperature and oxygen consumption during artificial rearing showed clear 24-h rhythms in 5- to 8-day-old pups. Each rhythm reached a daily minimum at a time corresponding to the beginning of the light period in the colony of origin. The amplitude of these rhythms did not diminish during artificial rearing, nor did the phase difference between the rhythms of pups originating in the two colonies systematically change. The persistent 12-h phase differences between these two groups of pups prove that the observed rhythms are not caused by exogenous stimuli. We conclude that the rat pup possesses an endogenous time-keeping mechanism that permits the expression of overt rhythmicity at the age of 1 week.

Animals↗
PubMed1989

[Kidney function in the course of compensatory hypertrophy following unilateral nephrectomy in the Wistar rat].

Unilateral nephrectomy was performed in 109 male Wistar rats, 35 animals served as controls. Determinations of glomerular filtration rate (GFR) using slope clearance of 99mTc-DTPA and of tubular function using an orally water-loading test were made. The tests were performed 2 and 5 days as well as 2, 4, 5 and 6 weeks after nephrectomy. In all examinations the GFR was more than 50% of the level of two-kidney control animals. Fractional maximum diuresis was increased in the first 2 examinations after nephrectomy from 8.9 +/- 2.1 to 15.4 +/- 4.2% of the GFR and fractional clearance of osmotically free water from 6.8 +/- 1.9 to 10.9 +/- 3.5%. In the fourth and sixth week the proximal tubular reabsorption was increased and the glomerulo-tubular balance had been recovered. However, the minimal urine osmolarity was increased to 107.8 +/- 17.7 mmol/l and the osmotic load of the nephrons remained elevated. Possible clinical implications of the results are discussed.

Animals↗