A new relationship between cholesterolemia and cholesterol synthesis determined in rats fed an excess of cystine

The present study deals with an attempt to describe how the plasma cholesterol level is related to input into the plasma of cholesterol synthesized in the liver and in the intestine. It has previously been shown in our laboratory that, for a given absorption of alimentary cholesterol, the rat plasma cholesterol level decreases when internal secretion of cholesterol (cholesterol synthesized in the organs and poured into the plasma) increases. This relationship was established using rats in which the major source of cholesterol synthesis was the intestine. We used rats fed a cystine-enriched diet (5%) which was previously shown to increase cholesterolemia and internal secretion of cholesterol. It was first demonstrated that a significant positive linear correlation exists between individual values of cholesterolemia and those of internal secretion of cholesterol. Secondly, using [14C]acetate as the cholesterol precursor it was shown that ingestion of the cystine-enriched diet increased hepatic but not intestinal cholesterogenesis. Individual values of cholesterolemia were linearly correlated to those of [14C]acetate incorporation into the hepatic sterols. Results obtained by this method were validated by determining the 13C-labeling pattern of cholesterol synthesized de novo by the liver and the intestine after [13C]acetate infusion. Indeed, this labelling indicated that the dilution of exogenous acetyl-CoA in the liver was not changed by cystine feeding, whereas that in the intestine was enhanced. It is concluded that the plasma cholesterol level varies with internal cholesterol secretion, depending on the organ which determines the variations of this secretion: it decreases when intestinal cholesterogenesis increases, whereas it increases when hepatic cholesterogenesis increases. Finally, the use of [14C]acetate coupled with lipoprotein analysis in rats fed the cystine-enriched diet, in control rats and in rats fed a cholesterol-enriched diet, allowed a new linear correlation to be demonstrated: between cholesterol concentration in LDL2 (lipoproteins of density 1.040-1.063 g/ml) and [14C]acetate incorporation into liver sterols. Our results suggest that LDL2 are produced by the liver in relation to cholesterogenesis in this organ.     

Conditions of formation of the heparin-fibronectin-collagen complex and the effect of plasmin

The formation and composition of the insoluble heparin-fibronectin-collagen complex and its degradation by proteolysis was investigated. At fixed concentrations of the other molecular components of the complex, the maximal rate of complex formation, measured turbidimetrically, was reached at a concentration of 4 microM heparin and 0.9 microM collagen, while the rate of complex formation was linearly related to concentrations of fibronectin as high as 3 microM. Heparin was incorporated into the complex in a saturable manner, and was released in active anticoagulant form by plasmin but not by urokinase. The complex formation was inhibited by 5 mM calcium or 250 mM NaCl as well as by polybrene or spermin. It is suggested that fibronectin binds both heparin and collagen cooperatively to form an insoluble ternary complex of the extracellular matrix.     

Arterial supply of the choriocapillaris of anuran amphibians (Rana temporaria,Rana esculenta)

Summary The pattern of the vascular supply to the choroid of the frog eye was studied in toto with the use of the injection-replication-SEM technique. The choroid of anuran amphibians is composed mainly of the choriocapillaris. In both species studied (Rana temporaria, Rana esculenta), an independent arterial supply to the choriocapillaris supplemented that from the ciliary arteries. This additional vascular route arises from the optic artery, a separate branch of the arteria infundibularis superficialis. The optic artery, accompanied by its vein within the vascular sheath of the optic nerve, joins the rich arterial capillary network of the choriocapillaris and supplies the posterior pole of the ocular bulb. The superficial capillary network displays a dense collar around the entrance of the optic nerve into the eye and is composed of a circular meshwork of small capillaries, several layers deep. More peripherally, however, it becomes single layered. This capillary network, as a whole, establishes numerous connections with the adjacent choriocapillaris at the posterior pole of the ocular bulb. In anuran amphibians the complex arrangement of both arterial systems supporting the choriocapillaris may be regarded as a more complete equivalent of the short posterior ciliary arteries of mammals.     

The superficial vascular hyaloid system in the eye of the frogs,Rana temporaria and Rana esculenta

Summary The angioarchitecture of the superficial vascular hyaloid system (membrana vasculosa retinae) of the frog eye was studied by means of scanning electron microscopy of vascular corrosion casts. The terminal vessels form a single-layered sheath intimately adjacent to the vitreal side of the avascular retina. The hyaloid system is subdivided by the ventral venous trunk into three central areas: the dorsal, the temporo-ventral, and the naso-ventral area. Toward the ora serrata, the hyaloid system is bordered by an arterial ring, and by nasal and temporal venous branches forming more or less complete hemicircles. A vascular zone composed of several tongue-like sectors establishes an inter-connection between the peripheral vascular rings and the central areas of the fundus. The arterial blood is supplied from the arterial ring. The drainage of the hyaloid system is provided via two routes: (1) the Y-shaped ventral trunk collects blood from the central areas, (2) the two peripheral venous branches drain the tongue-like sectors. The vessels within the dorsal area follow preferentially a dorso-ventral meridional direction. This densely capillarized territory corresponds in localization to the area centralis retinae. The ultrastructure of microvessels of the hyaloid system is characterized by features typical for capillaries of the central nervous system.     

Intragenomic polymorphism of the primary structure of 5S rRNA gene variants of the loach (Misgurnus fossilis L.). Determination of the transcriptional activity

The primary structure of 12 cloned repeats of loach oocyte 5S rRNA genes was determined. The heterogeneity of nucleotide sequences was revealed in the coding regions and spacer of the genes. The results of the study on in vivo transcriptional activity of the cloned 5S rRNA gene variants are consistent with the localisation of site specific base substitutions in the coding part affecting the transcription. We have compared the nucleotide sequences of loach 5S rRNA gene variants and of Xenopus laevis, X. borealis and Bombyx mori 5S genes which can be actively transcribed in X. laevis oocyte nuclei. As a result we could propose a consensus nucleotide sequence in the internal control region (from 45-th up to 100-th nucleotide) of the eukaryotic 5S rRNA gene. This sequence comprises a RNA-polymerase III promotor and stretches interacting with transcriptional factors. We have considered the base substitutions in the nucleotide sequences of 5S gene variants exerted on the experimental model of loach 5S rRNA secondary structure. All base substitutions in actively transcribed genes do not influence the general double-stranded structures of the transcripts. However in 5S RNA transcripts from genes with low transcriptional activity base substitutions affecting the box c RNA-polymerase III promoter destroy hairpin II interacting with ribosomal proteins. We have concluded that two factors can restrict the divergency of 5S rRNA genes: (1) conservation of the nucleotide sequence in the gene internal control region, and (2) conservation of the general double stranded structures in 5S rRNA transcripts.     

N.m.r. and c.d. studies of the DNA fragments d(TATATATA) and d(TATATA) in solution

DNA fragments d(TATATATA) and d(TATATA) were studied in low-salt aqueous solutions and found to coexist in more than one conformer. 1H-n.m.r. demonstrates that single-stranded and double-stranded states are involved in the conformational coexistence. Circular dichroism spectroscopy indicates a global B-DNA stacking of bases in the fragments. 31P-n.m.r. resonances of the TpA and ApT phosphodiester bonds are substantially separated in the spectra of both d(TATATATA) and d(TATATA) duplexes to suggest an alternating architecture of their backbones. In fact, the oligonucleotide duplexes are much more alternating than the corresponding polynucleotide under the same solution conditions. The alternating character of the d(TATATATA) double helix is further enhanced in molar caesium fluoride solutions. The oligonucleotide isomerization into X-DNA is, however, accompanied by gel formation, which makes high resolution n.m.r. measurements impossible.     

The effect of (+) cyanidanol-3 on the Na+-K+-ATP-ase and Mg++-ATP-ase activities of the rat brain in the presence and absence of ascorbic acid

The authors investigated the effects of (+) cyanidanol-3-(Catergen) in vitro on the activities of rat brain plasma membrane and microsomal Na+-K+-ATP-ase and Mg++-ATP-ase, in the presence and absence of ascorbic acid. Due to lipid peroxidation induced by low concentration of ascorbid acid, activity of both ATP-ase decreased. (+) cyanidanol-3 proved to be an effective antioxidant in this system. It inhibited the decrease of ATP-ase activity which occurred as a result of lipid peroxidation promoted by ascorbic acid.     

Tachykinins and calcitonin gene-related peptide: co-existence in sensory nerves of the nasal mucosa and effects on blood flow

The presence and co-existence of calcitonin gene-related peptide (CGRP)- and substance P (SP)-like immunoreactivity (-LI) in sensory neurons of the nasal mucosa and trigeminal ganglion in several vertebrate species, including man, were established using immunohistochemistry. In the nasal mucosa the CGRP- and SP-immunoreactive (IR) nerve fibers were localized within the epithelium, around arteries, arterioles, venules, venous sinusoids and close to exocrine elements, mainly ducts. Double-staining experiments revealed that the CGRP-LI-containing nerve profiles and cell bodies also contained SP-LI. In the pig, CGRP- and SP-IR fibers were also detected in the maxillary portion of the trigeminal nerve and around the sphenopalatine artery and vein, as well as around the nasal dorsal vein. The nasal mucosal content of CGRP-LI, as determined by radioimmunoassay, was almost 5-fold higher in the pig and guinea pig compared to man. The nasal CGRP-IR nerves disappeared after capsaicin pretreatment in the guinea pig. In the cat, local intra-arterial infusions of capsaicin, SP, neurokinin A (NKA), neuropeptide K (NPK) and CGRP caused a concentration-dependent increase in nasal blood flow. CGRP caused a longer-lasting vasodilatation than the tachykinins. In conclusion, the morphological findings of co-localization of CGRP-LI and SP-LI in capsaicin-sensitive nerve fibers of the nasal mucosa and trigeminal ganglia of different species including man, coupled with the in vivo description of the high vasodilator potency of CGRP and tachykinins, imply co-release of several vasoactive agents upon activation of the nasal sensory nerves. Furthermore, the similarity of the morphological findings among the different species indicates that experimental data from animals may reflect the existence of similar mechanisms in humans.     

Temperature jump study of charge translocation during the bacteriorhodopsin photocycle

Temperature jump experiments were carried out on purple membranes oriented and fixed in polyacrylamide gel. With green background illumination a relaxation of the photocurrent after an infrared laser pulse could be observed. To simulate the temperature jump signals different models of the bacteriorhodopsin photocycle were tested. The parameters of these models were obtained by measuring absorbance changes and photocurrent after excitation with a 575-nm laser flash.

A model with a temperature-dependent branching before the M state turned out to be satisfying. Other models, especially those with a late branching or without branching, could not reproduce the temperature jump measurements.