We examined the overflow of endogenous norepinephrine with electrical stimulation, the associated pressor response, and rate of initial neuronal uptake of [ 3 H] norepinephrine in perfused mesenteric arteries of 7-and 13-week-old spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. The tissues of two rats, a spontaneously hypertensive and a WKY control rat, were simultaneously processed and subjected to the same electrical stimulation. Both absolute and fractional overflow of endogenous norepinephrine during periarterial nerve stimulation (5 and 10 Hz for 1 minute) in the tissue of 7-week-old SHR was significantly greater whereas overflow of 13-week-old SHR was equivalent as compared with that of the age-matched WKY rats. The tissue content of norepinephrine was 20-25% higher in SHR of both ages. There was significantly enhanced [ 3 H] norepinephrine uptake in the tissues of young SHR, but no difference was observed in the older SHR. The pressor response to periarterial nerve stimulation was significantly enhanced in 7-week-old SHR and much more so at the older age as compared with the WKY control rats. Exogenous norepinephrine dose-response curves in the tissues of 7-week-old SHR exhibited a parallel leftward shift, characteristic of a change in sensitivity, whereas that of 13-week-old SHR showed a much steeper slope as compared with the respective WKY control rats. This finding suggests that in addition to smooth muscle supersensitivity, structural alterations had occurred in vasculature of 13-week-old SHR. These data indicate that in SHR both the exocytotic release of norepinephrine and the responsiveness of the vascular smooth muscle cells are enhanced in the developmental stage of hypertension whereas smooth muscle supersensitivity to norepinephrine and nonspecific structural alterations primarily contribute to the maintenance of hypertension at 13 weeks of age. {Hyperten-sion 1989;14:44-53)

No abstract

Nuclear matrices containing residual DNA were isolated from chicken erythrocytes after extraction of purified nuclei with buffered 2 M NaCI. After further purification of this residual DNA, it was found to contain high concentrations of -Wglobin gene sequences as assayed by dot hybridization with 32P-labeled nick-translated pHB1001. Electron microscopy of a random sample of this residual DNA fraction shows the DNA to be intimately associated with protein at various intervals. A hypothesis for enrichment of active genes in residual DNA from purified chromatin or in nuclear matrix DNA is also discussed.During the past decade many diverse experimental strategies have been applied to the study of eukaryotic transcriptional regulation by the nonhistone chromosomal proteins (1). In spite of all of these efforts, the nonhistones presumably responsible for tissue-specific transcription remain elusive. Studies on DNA sequences have provided evidence suggesting that the nucleotide sequences offlanking and intervening sequences are essential for correct gene expression (2). Nevertheless, analysis of restriction enzyme digests of chicken DNA for ,-globin (3), ovalbumin (4), conalbumin (5), and lysozyme (6) have shown that these genes appear to be indistinguishable between tissues where the genes are either active or inactive. Furthermore, comparison of the sequences around the putative promoter sites of the ovalbumin gene (7) cloned from the DNA of producer and nonproducer tissues revealed no differences. Thus it is reasonable to suggest that the nucleotide sequence alone is insufficient for genomic activation of tissue-specific transcription. Although gene-specific nonhistone proteins have not yet been found in chromatin obtained from specialized tissues, results supporting that possibility have been reported (8)(9)(10)(11)(12)(13).Of the total nuclear proteins, the insoluble nonhistones are significant in their content of tissue-specific proteins (14), in the structure of the nuclear matrix (15), and in their association with transcriptionally active genes (16). Recently, studies by Pettijohn's group also suggested that an insoluble nonhistone protein of high molecular weight appears to be specific to cells undergoing active proliferation (17). Previous results from our laboratory have shown that it is possible to isolate from purified chromatin a DNA fraction significantly enriched in tissue-specific gene sequences (18)(19)(20). We suspect that this DNA, which we have designated DNA-P, is similar to that DNA found associated with the nuclear matrix. Transcribed sequences are associated with the nuclear matrix (21), and these sequences may form the base of the DNA loops in which they reside (22). We show by dot hybridization that the insoluble DNA fraction isolated from chicken erythrocyte nuclear matrices contains high concentrations of f3-globin gene sequences, although this gene is known to be inactive in mature chicken erythrocytes (23). MATERIALS AND METHODSIsolation of DNA Associated with Nonhistones from th...

SUMMARY Noreplnephrine (NE) incorporation by portal-mesenteric veins (P-M) reins) and atria of spontaneously hypertensive rats (SHR) were compared with that of age-matched Wistar Kyoto controls (WKY).Tissues were incubated in the presence of tritiated norepinephrine (*H-NE), and fractions were isolated by means of differential and sucrose density gradient centrifugation. The peak of radioactivity was located in the 0.4-0.5 M sucrose region that contained vesicular materials, as shown by electron micrographs. NE incorporation (picomoles/mg tissue) into the P, subtraction of SHR atria and P-M veins was reduced; in atria, the reduction was statistically significant. These results contrasted with the enhanced 'H-NE incorporation by SHR mesenteric artery, and point out regional differences in this process. shows that altered activity of the sympathetic nervous system plays a role in the development of high arterial pressure in genetically hypertensive rats.

There is still controversy concerning the primary site of RNA synthesis in the cell.' When tissues are radioautographed after administration of radioactive inorganic phosphorus or radioactive RNA2 precursors such as tritiated uridine or cytidine, it is commonly observed that radioactivity appears in the nucleus first and in the cytoplasm later. It has furthermore been shown that isolated nuclei of both animal' and plant4 material are able to synthesize RNA in vitro but that enucleated cytoplasm is unable to carry on such synthesis., Although the problem of whether or not RNA is synthesized in both nucleus and cytoplasm is not completely understood,6-8 there is increasing cytological evidence that a substantial portion of the cytoplasmic RNA is synthesized in the nucleus9-'7 and subsequently migrates to the cytoplasm.The site of RNA synthesis in the nucleus, however, is variously proposed to be the nucleolus,'3 16, 18 the chromatin,'9-2' or both.22 23 It has been suggested that cytoplasmic RNA is derived from either the nucleolus'3 16, 18 or from the chromatin after passage through the nucleolus'9' 20 or from both.'3 The autoradiographic data heretofore obtained are inconclusive on these points. Autoradiographs of nuclei labeled with radioactive RNA precursors are only rigorously interpretable in the case of isolated nuclei or nucleoli because of the background otherwise created by radioactive cytoplasm or by chromatin closely associated with the nucleolus. In the present work the more direct approach, of the physical fractionation of previously labeled, isolated nuclei has been used. Large quantities of nuclei have. bten isolated, incubated under suitable conditions with labeled precursors of RNA, the subnuclear components then separated from one another, and the amounts of radioactivity contained in the RNA of chromatin, nucleoli, and other nuclear components estimated directly. It has in this way been possible to arrive at reasonably firm conclusions concerning the site of RNA synthesis in the nucleus.Materials and Methods.-Plant tissues: Pea seedlings, Pisum sativum, were grown in vermiculite in the dark for 4 days at 250C. From these seedlings, apical tips, 1.0-~l.0 cm in length, were cut, freed of vermiculite, and then washed with 0.5% clorox for 3 min. These stem sections were then used for isolation of nuclei.Chemicals: Cytidine-H3, specific activity: 4,900 mc per mM, used as RNA precursor and obtained from New England Nuclear Corporation, Boston, was added to the incubation medium in a final concentration of 25 Itc per ml. Phosphocreatine kinase was prepared from rabbit muscle according to the procedure described by Kuby et al.24 Penicillin powder, specific activity 1,000 units per mg was used as manufactured by Chas. Pfizer & Co., Inc., New York. Other chemicals were of reagent grade.Isolation and incubation of nuclei: Nuclei were isolated from pea seedlings by a new method which consists in passing the plant tissue through a set of counter-rotating rollers with simultaneous addition of a sucrose-CaCl2 ...