Effect of saturated and unsaturated lipid on the composition of mesenteric triglyceride-rich lipoproteins in the rat

The effect of saturated and unsaturated lipids on the composition of mesenteric lymph triglyceride-rich lipoproteins was studied in rats. A short-term steady-state infusion model was developed in mesenteric lymph fistula rats. Micellar solutions of linoleate, oleate, or palmitate were infused intraduodenally. Steady-state conditions of lymph flow, triglyceride, and apoA-I and apoB secretion rates were achieved in hours 3-5 after the start of the infusion. During this steady-state period, triglyceride-rich lipoproteins were prepared and characterized. With lipid infusion there were the expected increases in secretion rates of triglyceride, apoB, and apoA-I both in whole lymph and in the d less than 1.006 g/ml lipoproteins. Compositional analysis of d less than 1.006 g/ml lipoproteins revealed no difference in the ratios of phospholipid or apoA-I (surface) to triglyceride (core) constituents between saturated and unsaturated lipids, suggesting a similar particle size. This was directly verified by agarose gel filtration and electron microscopy carried out at 27 degrees C, which showed no difference in particle size between linoleate and palmitate chylomicrons. When these lipoproteins were prepared at 4 degrees C, palmitate lipoproteins exhibited dramatically changed gel filtration elution profiles, suggesting a shift to smaller or at least distorted particles and questioning earlier results suggesting a smaller size for saturated fat d less than 1.006 g/ml lipoproteins. Despite the similarity of size between saturated and unsaturated chylomicrons, the apoB content of unsaturated linoleate chylomicrons was significantly lower than that of palmitate chylomicrons. This difference was present whether chylomicrons were prepared by centrifugation or by gel filtration. The clearance of palmitate chylomicrons from the circulation of recipient rats was slightly more rapid than that of linoleate chylomicrons. The mechanism for this apparently selective increase in the apoB content of saturated fat chylomicrons is unknown but the present studies suggest that these changes may be of physiologic significance, perhaps relating to the potential atherogenicity of saturated lipids.     

Exercise training and responsiveness of isolated coronary arteries.

Exercise is associated with release of catecholamines and vasoactive intestinal polypeptides. Recurrent exposure to catecholamines modifies the sensitivity of adrenoceptors. To test the hypothesis that exercise training may affect the sensitivity of the epicardial coronary arteries, we performed studies on isolated coronary arteries from male dogs capable of running on a treadmill. The animals were separated randomly into two groups: sedentary and exercise training. After 11 wk, rings of left circumflex and left anterior descending coronary arteries were studied in vitro. Contractions to alpha 1-adrenergic agonists (norepinephrine and phenylephrine) were not affected by exercise training. During contractions with prostaglandin F2 alpha, endothelium-dependent relaxations to alpha 2-adrenergic agonists (norepinephrine and UK 14304) were not reduced significantly by exercise training. The concentration-relaxation curves to beta-adrenergic agonists (norepinephrine, isoproterenol, and epinephrine) were shifted to the right after training. The concentration-response curves to vasoactive intestinal polypeptide, but not that to substance P, were shifted to the right in rings with endothelium from exercise-trained animals. These findings demonstrate a decrease in responsiveness of canine vascular smooth muscle to beta-adrenergic agonists and to vasoactive intestinal polypeptide after exercise training.     

BEHAVIORAL SIGNIFICANCE OF UNDERWATER VOCALIZATIONS OF CAPTIVE LEOPARD SEALS, HYDURGA LEPTONYX

Two groups of underwater vocalizations were identified in a three-year study of two captive leopard seals, Hydurga leptonyx (one female and one male at Taronga Zoo, Sydney). This was supplemented by recordings over three months from a male at Marineland, New Zealand. The sexual state of the seals at Taronga was deduced from serum hormonal concentrations: the female was considered to be in estrus at specific times during the breeding season. The seal at Marineland, New Zealand was assumed to be sexually mature on the basis of size and age. Of 12 different underwater sound types recorded, six were produced by the seals at Taronga Zoo during agonistic interactions (local calls) and were heard through most of the year. The other six sound types were produced by lone seals. These broadcast calls were produced by the female only when sexually receptive, and by the mature male during December and January, months believed to be the breeding season of wild leopard seals. We propose that underwater acoustic behavior is important in the mating system of this species, and that broadcast calls are used by mature females to advertise their sexual receptivity, and possibly by mature males in search of mates.     

How were introns inserted into nuclear genes?

There is now abundant evidence that many introns have been inserted into nuclear genes after the divergence of multigene families, sometimes in a semi-regular pattern with respect to pre-existing domains. This note examines ways in which these insertions might have occurred using known molecular mechanisms.     

High-performance liquid chromatographic methods for the determination of a new carbapenem antibiotic, L-749,345, in human plasma and urine

A column-switching, reversed-phase high-performance liquid chromatographic (HPLC) method for the determination of a new carbapenem antibiotic assay using ultraviolet detection has been developed for a new carbapenem antibiotic L-749,345 in human plasma and urine. A plasma sample is centrifuged and then injected onto an extraction column using 25 mM phosphate buffer, pH 6.5. After 3 min, using a column-switching valve, the analyte is back-flushed with 10.5% methanol–phosphate buffer for 3 min onto a Hypersil 5 μm C₁₈ BDS 100×4.6 mm analytical column and then detected by absorbance at 300 nm. The sample preparation and HPLC conditions for the urine assay are similar, except for a longer analytical column 150×4.6 mm. The plasma assay is specific and linear from 0.125 to 50 μg/ml; the urine assay is linear from 1.25 to 100 μg/ml.     

The role of Eh, pH and iron in the bactericidal power of human plasma

The bactericidal power of fresh human plasma against Klebsiella pneumoniae and Escherichia coli was extremely sensitive to changes in Eh and pH. At a high Eh (approx. +200 mV) the bacteria were destroyed, but rapid regrowth occurred when the Eh was lowered to approx. -400 mV. Abolition of the bactericidal effect was also produced by adding ferric iron at a high Eh (approx. +200 mV). Lowering the pH to 6.50 reduced or prevented the bactericidal effect. These results are probably related to the availability of iron for bacterial growth, and could be important for understanding the development of infection in injured or diseased tissue.