Role of sodium and water excretion in the antihypertensive effect of vasopressin in the spontaneously hypertensive rat.

Mean arterial pressure (mmHg (1 mmHg = 133.322 Pa)), sodium excretion rate (mumol.kg-1.min-1), and urine flow (microL.kg-1.min-1) were measured in conscious unrestrained spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) before, during, and after a 3-h intravenous infusion of arginine vasopressin (20 ng.kg-1.min-1), an equipressor dose of phenylephrine, or an infusion of the vehicle. Cessation of the phenylephrine infusion was associated with a return of arterial pressure to preinfusion control values in both SHR and WKY. Cessation of the vasopressin infusion was also associated with a return of arterial pressure to preinfusion values in WKY. In contrast, in the SHR, arterial pressure fell from a preinfusion control level of 164 +/- 6.2 to 137 +/- 4 mmHg within 1 h of stopping the vasopressin infusion. Five hours after stopping the infusion, pressure was 134 +/- 3 mmHg (29 +/- 5 mmHg below preinfusion levels). Similar to the WKY, cessation of a vasopressin infusion was associated with a return of arterial pressure to preinfusion values in Sprague-Dawley rats. Thus, the failure to observe a hypotensive response in normotensive rats was not a peculiarity of the WKY strain. Sodium excretion rates increased during the infusions of vasopressin to a greater extent in SHR than in WKY. However, the natriuresis induced by phenylephrine was not significantly different from that generated by vasopressin in SHR, and in WKY, the natriuresis was greater for phenylephrine than for vasopressin. Urine output increased to a greater extent during the infusions of phenylephrine in both SHR and WKY than during vasopressin infusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Molecular dynamics computations and solid state nuclear magnetic resonance of the gramicidin cation channel.

This paper reports on a coupled approach to determining the structure of the gramicidin A ion channel, utilizing solid state nuclear magnetic resonance (NMR) of isotopically labeled gramicidin channels aligned parallel to the magnetic field direction, and molecular dynamics (MD). MD computations using an idealized right-handed beta-helix as a starting point produce a refined molecular structure that is in excellent agreement with atomic resolution solid state NMR data. The data provided by NMR and MD are complementary to each other. When applied in a coordinated manner they provide a powerful approach to structure determination in molecular systems not readily amenable to x-ray diffraction.     

Transbilayer distribution and mobility of phosphatidylinositol in human red blood cells

The present studies describe the distribution of phosphatidylinositol (PI) within the membrane bilayer of the human red blood cell (RBC) as well as its transbilayer mobility. The membrane bilayer distribution was determined by measuring the hydrolysis of PI in the exterior leaflet of the RBC membrane using a PI-specific phospholipase C and by extraction of PI from the exterior leaflet using bovine serum albumin. The transbilayer mobility of PI was measured by following the fate of radiolabeled PI which was first incorporated into the outer leaflet of the RBC membrane. Our results indicate that PI is asymmetrically distributed in the membrane, with approximately 80% located in the inner and 20% in the outer leaflet of the bilayer. The rate of transbilayer mobility of PI is similar to that for certain molecular species of phosphatidylcholine and much slower than that reported for the aminophospholipids in the RBC membrane.     

Induction of F9 cell differentiation by transient exposure to retinoic acid.

The F9 cell is a mouse embryonal teratocarcinoma which can be induced to differentiate into visceral endoderm by treatment with retinoic acid (RA). Treatment with RA in conventional studies was carried out in the constant presence of RA. Here we demonstrate that treatment with RA can be as short as 3 hrs to induce differentiation of F9 cells. Morphology, alpha-fetoprotein gene activity, and temporal patterns of F9 cell differentiation are the same with both short- and long-term treatment with RA.     

Biosynthesis of Prostacyclin in Rat Cerebral Microvessels and the Choroid Plexus

Abstract: Microvessels, predominantly capillaries, were isolated from rat cerebrum by a modification of published procedures. The morphology and purity of the preparations were monitored by light and electron microscopy and by enrichment in alkaline phosphatase, γ-glutamyl transpeptidase, and prostacyclin synthetase. A reversed-phase high-pressure liquid chromatographic method was used in the purification of prostaglandins after extraction from aqueous incubation solutions. Prostacyclin synthesis in brain is localized in cerebral blood vessels and capillaries. The endogenous biosynthetic capacity of the isolated cerebral capillary fractions for prostacyclin, measured as its chemically stable breakdown product, 6-keto-prostaglandin F_1α, was 11 ng/mg protein/10 min. Choroid plexus and intact surface vessels synthesized 6-keto-prostaglandin F_1α at 37 and 35 ng/mg protein/10 min, respectively. The prostacyclin-synthesizing enzyme of the cerebral capillaries also converted the exogenously added prostaglandin endoperoxides to 6-keto-prostaglandin F_1α. Comparison of the synthesis of prostaglandins 6-keto-F_1α, E₂, and F_2α showed that 6-keto-prostaglandin F_1α was the major prostaglandin formed in the microvessels, in the larger surface vessels, and in the choroid plexus. Prostaglandin D₂ was not detected. Prostacyclin synthesis by the cerebral vasculature is similar to that in other blood vessels and cultured human endothelial cells. Possible physiological roles of prostacyclin in the cerebral microvasculature are discussed with special regard to the autoregulation of cerebral blood flow.     

Intermediate Filaments from Bovine, Rat, and Human CNS: Mapping Analysis of the Major Proteins

Abstract: Intermediate filaments were isolated by an axon-flotation method from bovine, rat, and human CNS. Gel electrophoresis showed four major proteins, having molecular weights of about 50,000, 70,000, 160,000, and 210,000, to be present in filaments of all three species. Small differences in molecular weights and major differences in relative distribution of the filament proteins were observed among species. In bovine and rat brain the predominant protein was the 50,000 band, but in human brain the 70,000 band was present in greatest amount. Each filament protein of the three species was studied by peptide mapping using limited proteolysis and cyanogen bromide cleavage. Within the same molecular weight group, filament proteins from different species gave similar maps with both techniques. Some degree of heterogeneity was also observed. However, filament proteins of different molecular weights of the same species gave distinctly different maps. These studies rule out the possibility that filament proteins from different molecular weight groups are related to each other by oligomerization; nor is it likely that the lower molecular weight proteins are derived from the subunit of molecular weight 210,000.     

Molar proportions and relative rates of synthesis of histones in rat testis

The molar proportions and relative rates of synthesis of histones in normal and hypophysectomized rat testis seminiferous epithelial cells were determined. After hypophysectomy the molar proportions of histones H1, H2B and (H2A + protein A24) in seminiferous epithelial cells of rat testis increased while their corresponding variants TH1-x, TH2B-x and X₂ decreased, but the molar proportions of major-class histones (i.e., sum of subfractions) remained relatively constant and similar to the proportions in somatic cells. The apparent molar proportions of the labeled histones, determined immediately after 2-h periods of [³H]leucine incorporation, were much higher relative to H4 than the proportions of total histones determined by dye binding. The values, however, approached the molar proportions of total histones when rats were killed 11 days after the [³H]leucine injection. Two-dimensional gel electrophoresis confirmed that the high initial molar proportions relative to H4 by [³H]leucine incorporation were not due to the possible contamination by highly-labeled non-histone proteins. The specific activity of histone H4 relative to the specific activity of DNA, determined immediately after 3-h periods of [³H]leucine and [¹⁴C]thymidine incorporations was similar to the value when rats were killed 13 days after the injections. It is proposed that histones of seminiferous epithelial cells are synthesized disproportionally relative to H4 and in excess of the quantities required for polynucleosome assembly. The excess histones are subsequently displaced or degraded slowly.