Vasomotor control: functional hyperemia and beyond

Historically, functional hyperemia has been viewed largely as an interaction between a parenchymal cell and its associated microvasculature. Locally released metabolites have been thought to produce relaxation of the smooth muscle and a vasodilation that increases blood flow in proportion to metabolic need. This symposium report presents evidence from a variety of disciplines and a number of different types of biological preparations that demonstrates that functional hyperemia is a complex process involving several classes of microvessels including capillaries, arterioles, and small arteries. These vessels do not function independently but are coordinated by a complex set of interrelations involving at least three different modes of interaction between parenchymal cells and the various segments of the vascular bed. These are local metabolic effects, propagated effects extending over long segments of the vasculature, and flow-dependent vasodilation induced by local changes in blood flow. In addition to these acute responses to metabolic demand it appears that tissues may be capable of more long-term structural alterations of the arterial and arteriolar network in response to sustained changes in the relationship between supply and demand. The vascular bed appears to be able to adapt either by increasing the maximal anatomic diameter of the large arteries or by inserting new arterioles into the parenchyma. Thus, classical functional hyperemia appears to be but one manifestation of a multifaceted process leading to highly coordinated responses of many vascular elements, resulting finally in vascular patterns that are optimized to meet parenchymal cell demands.     

蚕豆叶片发育与衰老过程中超氧物歧化酶活性与丙二醛含量变化

蚕豆植株叶片随茎节自上而下表现出明显的发育与衰老顺序,可作为衰老特征的是叶绿素和蛋白质含量明显下降。蚕豆叶中SOD活性主要定位于12 000× g离心后所得的上清液和叶绿体组分。衰老叶片的SOD总活性和叶绿体组分的相对活性都有所下降,SOD同工酶谱也发生了改变。O_2~ 产生速率随叶龄增大而稍上升;而MDA含量在叶片外观表现枯黄衰老征兆前就急剧上升。可能因为衰老叶片过氧化氢酶活性大幅度下降与SOD之间的不平衡,致使O_2~ 代谢中间产物累积而引起膜的损伤.     

Influence of protein conditioning films on binding of a bacterial polysaccharide adhesin from Hyphomonas MHS-3

A putative polysaccharide adhesin which mediates non-specific attachment of Hyphomonas MHS-3 (MHS-3) to hydrophilic substrata has been isolated and partially characterized. A polysaccharide-enriched portion of the extracellular polymeric substance (EPS(P)) from MHS-3 was separated into four fractions using high performance size exclusion chromatography (HPSEC). Comparison of chromatograms of EPS(P) from MHS-3 and a reduced adhesion strain (MHS-3 rad) suggested that one EPS(P) fraction, which consisted of carbohydrate, served as an adhesin. Adsorption of this fraction to germanium (Ge) was investigated using attenuated total reflection Fourier transform infrared (ATR/FT-IR) spectrometry. Binding curves indicated that the isolated fraction had a relatively high affinity for Ge when ranked against an adhesive protein from Mytilis edulis, mussel adhesive protein (MAP) and an acidic polysaccharide (alginate from Macrocystis pyrifera). Spectral features were used to identify the fraction as a polysaccharide previously reported to adsorb preferentially out of the EPS(P) mixture. Conditioning the Ge substratum with either bovine serum albumin (BSA) or MAP decreased the adsorption of the adhesive polysaccharide significantly. Conditioning Ge with these proteins also decreased adhesion of whole cells.     

Arterial adaptations to altered blood flow

Arterial remodeling in response to altered blood flow is believed to be critical to vascular adaptations to developmental, physiological, pathological, and therapeutically induced changes in blood flow. To assess this remodeling, we used left-to-right carotid anastomosis to increase blood flow in the right common carotid arteries of adult rabbits by 60%. After 2 months, these vessels exhibited no compensatory enlargement. In contrast, the same procedure performed in 5- to 6-week-old weanling rabbits resulted in accelerated growth of the vessels: diameters exceeded those of control arteries by 19% after 2 months. Common carotid arteries in adult rabbits remodeled to produce a diameter reduced by 23% when blood flow was reduced by 63% by external carotid ligation. This adaptation restored shear stress exerted on the vessel wall to control levels. The reduced diameter was not reversed when the vessels were maximally dilated with nitroprusside, adenosine, and forskolin; however, normal diameters were restored within 1 week when normal blood flows were reestablished. Thus, the adult arteries did not respond to increased blood flow produced by the anastomosis, but this procedure did reverse adaptations to decreased flow. In contrast, immature arteries were responsive to this increase in blood flow, even in the absence of prior flow modulation.     

Changes in blood flow distribution during the perinatal period in fetal sheep and lambs.

We have measured total blood flows and blood flows per 100 g tissue to major tissues at 120 and 140 days gestation in fetal sheep and at 3 and 21 days of age in lambs (gestation period = 144 +/- 2 days). Between 120 and 140 days gestation, flow per 100 g tissue increased by 74, 150, and 317% in the renal, intestinal, and hepatic arterial beds, but no further significant change in flow was observed at 3 or 21 days postpartum. Blood flows per 100 g to cerebral hemispheres and cerebellar tissues also increased dramatically during late gestation (142 and 121%, respectively), but declined sharply by 3 days postpartum (73 and 75%, respectively). Brain blood flows at 21 days postpartum remained substantially below late gestational levels. Adrenal blood flows per 100 g more than doubled during late gestation, fell by more than half at birth, and only partially recovered by 21 days of age. Blood flows to carcass tissues did not change in late gestation, fell at birth, then partially recovered. Pre- and post-natal increases in brain blood flows were almost entirely attributable to increased perfusion rather than tissue growth, whereas large perinatal increases in flow to the diaphragm paralleled tissue growth. Tissue growth and increased perfusion per 100 g contributed almost equally to increased blood flows to kidneys postnatally, and to adrenal glands and the gastrointestinal tract prenatally.     

Biosynthesis of lysosomal hydrolases: their synthesis in bound polysomes and the role of co- and post-translational processing in determining their subcellular distribution

By in vitro translation of mRNA’s isolated from free and membrane-bound polysomes, direct evidence was obtained for the synthesis of two lysosomal hydrolases, β-glucuronidase of the rat preputial gland and cathespin D of mouse spleen, on polysomes bound to rough endoplasmic reticulum (ER) membranes. When the mRNA’s for these two proteins were translated in the presence of microsomal membranes, the in vitro synthesized polypeptides were cotranslationally glycosylated and transferred into the microsomal lumen. Polypeptides synthesized in the absence of microsomal membranes were approximately 2,000 daltons larger than the respective unglycosylated microsomal polypeptides found after short times of labeling in cultured rat liver cells treated with tunicamycin. This strongly suggests that nascent chains of the lysosomal enzymes bear transient amino terminal signals which determine synthesis on bound polysomes and are removed during the cotranslational insertion of the polypeptides into the ER membranes. In the line of cultured rat liver cells used for this work, newly synthesized lysosomal hydrolases showed a dual destination; approximately 60 percent of the microsomal polypeptides detected after short times of labeling were subsequently processed proteolytically to lower molecular weight forms characteristic of the mature enzymes. The remainder was secreted from the cells without further proteolytic processing. As previously observed by other investigations in cultured fibroblasts (A. Gonzalez-Noriega, J.H. Grubbs, V. Talkad, and W.S. Sly, 1980, J Cell Biol. 85: 839-852; A. Hasilik and E.F. Neufeld, 1980, J. Biol. Chem., 255:4937-4945.) the lysosomotropic amine chloroquine prevented the proteolytic maturation of newly synthesized hydrolases and enhanced their section. In addition, unglycosylated hydrolases synthesized in cells treated with tunicamycin were exclusively exported from the cells without undergoing proteolytic processing. These results support the notions that modified sugar residues serve as sorting out signals which address the hydrolases to their lysosomal destination and that final proteolytic cleavage of hydrolase precursors take place within lysosome itself. Structural differences in the carbohydrate chains of intracellular and secreted precursors of cathespin D were detected from their differential sensitivity to digestion with endoglycosidases H and D. These observations suggest that the hydrolases exported into the medium follow the normal secretory route and that some of their oligosaccharides are subject to modifications known to affect many secretory glycoproteins during their passage through the Golgi apparatus.     

Arsenic in orchard and potato soils and plant tissue

Summary The total and water soluble arsenic contents of orchard and potato field soils are significantly higher where arsenic has been applied. Orchards with a record of past and present applications show average values as high as 99.57 ppm total arsenic and 1.99 ppm water-soluble arsenic. Orchards with a low or no arsenic application show 27.21 ppm total and 0.20 ppm water-soluble arsenic. Potato fields situated on ex-orchard plantings have an average of 38.70 ppm total and 0.32 ppm water-soluble arsenic, whereas those on non-orchard soils showed values of 9.63 and 0.04 ppm respectively. Highest soil arsenic concentrations were found in the 0–10 cm surface layer and at a distance of one meter from the tree trunk. In plant tissue the apple leaf, peel and pulp all were significantly higher for recently arsenic treated orchards, while only the apple pulp showed significance where applications had been discontinued for the past 10–15 years. Potato leaf and peel were significantly higher in arsenic on exorchard soil while the pulp was not.     

Mechanical stretch and progesterone differentially regulate activator protein-1 transcription factors in primary rat myometrial smooth muscle cells

During pregnancy, stretch of the uterus, imposed by the growing fetus, is an important signal for the induction of genes involved in the onset of labor. In this study, the expression of activator protein-1 (AP-1) family mRNAs in response to in vitro stretch was investigated in myometrial cells. Rat primary myometrial smooth muscle cells were plated onto collagen I-coated Flex I culture plates and subjected to 25% static stretch on day 4 of culture. Static stretch induced an increase in the expression of c-fos, fosB, fra-1, c-jun, and junB. The expression of both c-fos and junB was maximally induced at 30 min by static stretch. The peak induction for fosB and c-jun occurred at 1 h, whereas the peak of fra-1 induction occurred between 1 and 2 h after application of stretch. Treatment of myometrial cells with progesterone (100 nM, 400 nM, 1 microM) for 1 or 6 h before the application of static stretch did not affect the magnitude of the c-fos response. However, 24 h of progesterone exposure reduced the magnitude of c-fos and fosB stretch induction at both the 400 nM and 1 microM doses. These data indicate that several members of the AP-1 family are stretch-responsive genes in myometrial smooth muscle cells. This response can be attenuated by pretreatment with progesterone; however, the requirement for longer pretreatment times suggests that the inhibitory actions of progesterone do not occur through a direct action of the progesterone receptor within the promoter regions of AP-1 genes.     

Thermomechanical analysis of collagen crosslinking in the developing ovine thoracic aorta

We have used hydrothermal isometric tension (HIT) techniques in a sheep model to assess collagen crosslink stability and its contribution to the mechanical properties of the ovine thoracic aorta during perinatal and postnatal development. Aortic tissue was studied from fetal sheep, lambs, and adult sheep. Strips of tissue were loaded under isometric tension and heated to a 90 degrees C isotherm which was sustained for 3 hours. The decrease in load at this temperature is associated with collagen peptide bond hydrolysis and chain slippage, and the rate of this decrease is an inverse indicator of collagen crosslinking. The half-time of load decay (t1/2) was computed before and after tissue was treated with NaBH4 which stabilizes immature, reducible crosslinks. We observed a two-fold increase in t1/2 of untreated tissue from the lamb to the adult, indicating that aortic collagen crosslinking increased during postnatal development. Furthermore, the t1/2 of NaBH4-stabilized lamb tissue was similar to that of the untreated adult tissue, suggesting that much of the immature crosslinking in the lamb is stabilized during postnatal development. These observations suggest (a) increased crosslinking occurs during postnatal development and (b) that this increase is largely due to a conversion of immature crosslinks into their mature heat stable form.