Biomedical subjects
Publications and source records attributed to H Zucker.
In the course of experiments to study the minimal protein requirement of common marmosets by nitrogen balance methods, coprophagy was observed. It occurred in most animals fed diets either with a protein content below 6% or lacking histidine/arginine. The protein level of 6% had previously been evaluated as being the minimal protein requirement for maintenance of marmosets.
The degree of atresia of the follicle had no influence on the intrafollicular concentrations of beta-carotene, vitamin E and cholesterol. This might result from the passive transfer of these substances from blood to follicular fluid bound to high density lipoproteins. However, concentrations of vitamin A in follicular fluid were significantly (P less than 0.001) influenced by follicle quality, with highest concentrations (0.32 microgram/ml) in non-atretic follicles and lowest values (0.15 microgram/ml) in greatly atretic follicles. The higher concentrations of vitamin A in healthy follicles might be due to a local conversion of beta-carotene into vitamin A in follicular structures. By influencing hormone and protein synthesis, vitamin A may have a potential for local modulation of follicular development and therefore be one of the factors controlling recruitment, selection and growth of the dominant follicle in cattle.
The protein requirement for maintenance of the marmoset Callithrix jacchus was investigated by factorial calculation via the N balance technique. Six adult male marmosets were fed a protein-free pelleted diet for 22 days. When a low protein diet (6%) was fed in the preperiod, only 7 days were necessary and when fed a higher protein diet (18%) 10 days were necessary to reach a minimum of N excretion during protein depletion. Body weight losses averaged 11% and food intake was 21% lower in the protein free period. The average endogenous urine N (EUN) was 62.1 mg N and endogenous fecal N (EFN) 49.2 mg N/kg W0.75. Body surface losses (BSN) were assumed to be 20 mg N/kg W0.75. The total endogenous loss of 131.3 mg N/kg W0.75 is similar to that of other species. Net protein utilization (NPU) of well balanced proteins, determined near the N equilibrium, was 51.8%. The calculated net protein requirement amounts to 313.6 mg N/kg W0.75, which corresponds to a dietary protein content of 6% in a diet of high caloric density, (about 19-20 MJ/kg dry matter) when the food intake is 3.3% of body weight.
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Marmosets can tolerate an ascorbic acid (AA) deficiency for several weeks without clinical symptoms. After being fed an AA-free diet for 3 months, nonspecific deficiency symptoms became obvious. Different dietary levels of AA resulted in corresponding serum ascorbate levels. The kidney threshold of AA in marmosets is comparable to that in humans. When the minimal AA requirement is defined as the amount that is necessary to maintain a serum AA level above the kidney threshold, then about 20 mg AA/kg body weight is needed. This intake was achieved in our trial with a diet containing 500 ppm AA. Thus, the AA requirement of marmosets is severalfold higher than the AA requirement of humans.
Serum levels of 25(OH)D, alkaline phosphatase (AP), and parathormone (PTH) were evaluated to investigate the vitamin D requirement of Saguinus fuscicollis. Diets with various vitamin D content were fed 4 weeks and longer. The values of 25(OH)D (30-300 nmol/l), AP (less than 300 U/l), and PTH (less than or equal to 1,000 equl/l) considered as normal were obtained with 2,000 IU D3/kg diet, or 33 IU/animal/day, which we regard as the level required. Animals depleted of vitamin D for 215 days developed a secondary hyperparathyroidism.
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In one species each of the subfamilies marmosets and tamarins of the New World monkey family Callithricidae, serum levels of ascorbic acid were compared. Although the feeding regimen had been the same for both species for several years, the average concentration of serum ascorbate in the tamarins Saguinus fuscicollis (n = 21; 0.54 +/- 0.29 mg/100 ml) was only one-fifth that of the marmosets Callithrix jacchus (n = 19; 2.56 +/- 1.07 mg).
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Vitamin A and beta-carotene concentrations in serum, liver and blubber fat were investigated in 65 grey seals of different age and sex in the pupping colony on Sable Island, Canada to determine the vitamin A status. In none of the investigated samples could beta-carotene be detected. There were no differences in the concentration of vitamin A in serum, liver and blubber between male (213 micrograms/l, 376 micrograms/g, 22 micrograms/g respectively) and female (205 micrograms/l, 319 micrograms/g, 19 micrograms/g respectively) juveniles. In adult males concentrations of vitamin A in serum, liver and blubber were higher (260 micrograms/l, 503 micrograms/g, 34 micrograms/g respectively) than in juveniles indicating an age dependent increase of vitamin A in liver and blubber. Contrary to this in lactating females concentrations of vitamin A in serum, liver and blubber were significantly different than in the other animals. While the level of vitamin A in serum and blubber was two times higher with 413 micrograms/1 and 62 micrograms/g respectively, the concentration of vitamin A in liver was much lower (265 micrograms/g) compared to juveniles and adult males. It is possible that the intensified lipid metabolism during lactation, necessary to match the energy requirements of the rapidly growing pup, causes these extreme differences in vitamin A concentrations in serum, liver and blubber of lactating females compared to juveniles and adult males. Due to high concentration of vitamin A in blubber and the high proportion in blubber to total body weight, the blubber represents approximately 40% of total body reserves of vitamin A.
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The biological activity of two fluorinated analogs of 1,25(OH)2D3 was compared with 1,25(OH)2D3 in various vitamin D assays. The effect of 24,24-F2-1,25(OH)2D3 on plasma calcium, bone weight and duodenal calcium binding protein in chicken, on calcium excretion via egg shell in Japanese quails and on mobilization of calcium from the bone in rats was twice as high as the effect of the most potent naturally occurring vitamin D3 metabolite 1,25(OH)2D3. In contrast, 24R-F-1,25(OH)2D3 has less than 50% of the potency of 1,25(OH)2D3. Due to the wider therapeutic dosage range, this compound might be of clinical value.
The role of 24,25(OH)2D3 in calcium homeostasis is still controversial. In the present study the administration of low doses of 1,25(OH)2D3 and of higher doses of 24,25(OH)2D3 either alone or in conjunction with each other, were studied in rachitic chicks and in Japanese quails. Whereas 24,25(OH)2D3 alone had no significant effect on duodenal CaBP and on alkaline phosphatase in chick serum, it increased the influence of 1,25(OH)2D3 on these two parameters strongly. Also, when 1,25(OH)2D3 and 24,25(OH)2D3 were given simultaneously to Japanese quails, calcium excretion via the egg shell was clearly higher than when either metabolite had been administered alone. These results indicate that 1,25(OH)2D3 and 24,25(OH)2D3 exert a strong synergistic effect in rachitic animals.
The influence of zinc content in the diet on cadmium retention in the liver and kidney was studied in growing chicks. Cadmium and zinc concentrations used were similar to those occurring in normally feeds. Increasing cadmium levels in feeds resulted in increasing cadmium concentrations in organs. The cadmium levels in liver were about half as high as in kidneys. Physical conditions and growth rate of the chicks remained unaffected by the cadmium feeding. Cadmium retention in liver and kidneys was related to the zinc content of the diet. Feeding zinc-deficient diets resulted in a 40% higher cadmium retention than feeding adequate zinc diets (50 mg/kg). Excessive zinc levels had no additional effect on cadmium retention.
4 protein sources were tested for palatability, digestibility, influence on bodyweight and consistency of faeces in Callithrix jacchus and Saguinus fuscicollis. The protein sources were incorporated at crude protein levels of 12, 17 and 22% in a pelleted diet. A banana supplement was also fed which reduced the total protein content to 10.7, 14.7 and 18.3%. The test diets, fed for 3 weeks, were well accepted with the milk proteins being slightly preferred. Consumption of the 12% protein pellets was greater than their 22% equivalents. True protein digestibility was calculated to be 97% for lactalbumin, 96% for casein, 90% for soy protein concentrate and 83% for soyabean meal. Changes in bodyweight were negligible. Dry matter of faeces varied between 25% (lactalbumin diets) and 28% (casein diets), but did not change with increasing protein intake. Increasing levels of cellulose, from 2.4 to 7.2% total crude fibre lowered the apparent protein digestibility from 84.3 to 79.2% and the digestibility of dry matter from 82.2 to 76.5%.
The biological activity of the three mono-beta-D-glucopyranosides (mono-glucosides) of 1,25-dihydroxycholecalciferol [1,25(OH)2D3] synthesized chemically has been studied in chicks and Japanese quails. While the 1- and the 3-glucoside showed no or only little effect on serum calcium, bone weight, calcium binding protein (CaBP) or calcium deposition in the egg shell, the 25-glucoside was found to be more than half as active as the aglycone 1,25(OH)2D3. The bioactivity of this glucoside parallels a higher binding constant to the intestinal 1,25(OH)2D3 receptor compared to those of the two other glucosides.
An increase in the number of nerve branches of the unmyelinated axon terminals with increasing age was observed in normal adult mouse motor endplates. In addition, ultrastructural investigation revealed signs of nerve retraction. A combined light and electron microscopic investigation was performed on zinc-iodine-osmium stained endplates in soleus muscles. The number of branch points in a synapse, endplate length and muscle fiber diameter were evaluated in "young adult" (3 months) and adult (6 and 11 months) mice. For all 3 parameters, 3-month-old animals had the lowest values. Eleven-month-old animals had more branch points and larger endplate lengths than 6-month-old animals while there was no significant difference in fiber diameters. Branch point numbers and endplate length were correlated in each muscle while fiber diameters did not correlate with any of the other parameters. The ultrastructure of 15 thin nerve branches--likely candidates for new branches--was investigated in serial section and in 14 of them synaptic contacts were found. Near such contacts, empty gutters, possibly abandoned former synaptic sites, were present in several cases. It is concluded that there is continual nerve sprouting in synapses of adult mice and that sprouts form synaptic contacts. The possible signs of nerve retraction observed indicate that, as in the frog, synaptic contacts in mouse muscles undergo some continual remodeling.
At frog neuromuscular junctions spontaneous miniature end-plate potentials (m.e.p.p.s) were recorded from several isolated spots within single synapses. This was done by consecutively placing an extracellular glass micro-electrode (focal electrode) at different recording sites, while the intracellular electrode remained in one place. After each set of recordings, muscles were stained to reveal both axon terminals and cholinesterase (ChE) such that the exact position of each recording site could be determined. In many nerve terminal branches a similar quantum size was found at several different spots. In other instances, however, mean quantum amplitudes varied by 10-60% at different spots along the same terminal branches. As a control, individual spots were recorded from repeatedly after repositioning the focal electrode. In these recordings mean m.e.p.p. amplitude varied by only 5-10%. It is concluded that quantum size within a single junction is similar at many spots, but deviates markedly at others. Correlation of this variation with the stained preparations suggested that spots where quanta significantly larger or smaller than normal were recorded were either at ChE rings or at the distal ends of nerve branches, respectively; at different nerve terminal branches within the same junction, quantum amplitudes were similar in many cases but deviated in others. The results are consistent with ultrastructural evidence that frog neuromuscular junctions are non-homogeneous structures which undergo continual remodelling.