Antihypertensive effect of volume depletion: interrelation with renal prostaglandins

Since the original studies of Patak et al. in 1975 revealed that the antihypertensive and natriuretic effects of furosemide were markedly blunted or abrogated by indomethacin in both normotensive and hypertensive man, it has been postulated that the ameliorative effects of furosemide in human essential hypertension might be mediated by release of intrarenal prostaglandins. To study the direct effects of furosemide on prostaglandin biosynthesis and release, slices of rabbit renal medulla were incubated in Krebs-Ringer bicarbonate buffer, glucose 10 mM, 1-14C-arachidonic acid (AA) 10 microM, HSA /g/100 ml, 30 min 37 degrees C. Measurements were made of radioactive AA leads to PGE2, and total endogenous immunoreactive PGE2 production (iPGE2) with and without the addition of furosemide (10 microgram/ml) to the media. In the absence of furosemide AA leads to PGE2 was 73 +/- 22 nmol/30 min/g and in the presence of furosemide it fell to 30 +/- 4 nmol/30min/g. iPGE2 was 33 +/- / ng/30 min/mg and decreased to 25 +/- 3 mg with furosemide. These results indicate that the natriuresis and antihypertensive effect of furosemide in vivo, which is associated with a significant increase in urinary PGE2, is not the result of a direct stimulation of furosemide on prostaglandin synthesis but may result from a decrease in PGE metabolism, conversion to another biologically active prostaglandin or possibly be a reflection of events secondary to a direct effect of furosemide on renal hemodynamics and electrolyte excretion.

Efficient electrotransformation of corynebacterium diphtheriae with a mini-replicon derived from the Corynebacterium glutamicum plasmid pGA1

Efficient transformation of the human pathogen Corynebacterium diphtheriae was achieved with novel cloning vectors consisting of a mini-replicon from the cryptic C. glutamicum plasmid pGA1 as well as of the aph(3')-IIa or tetA(Z ) antibiotic resistance genes. Plasmid-containing transformants of C. diphtheriae were recovered at frequencies ranging from 1.3 x 10(5) to 4.8 x 10(6) colony forming units (cfu)/microg of plasmid DNA. Vector DNA was directly transferred from Escherichia coli into C. diphtheriae with frequencies up to 5.6 x 10(5) cfu/microg of plasmid DNA. On the basis of the pGA1 mini-replicon, an expression vector system was established for C. diphtheriae by means of the P(tac) promoter and the green fluorescent reporter protein. In addition, other commonly used vector systems from C. glutamicum, including the pBL1 and pHM1519 replicons, and the sacB conditionally lethal selection marker from Bacillus subtilis, were shown to be functional in C. diphtheriae. Thus, the ability to apply the standard methods of C. glutamicum recombinant DNA technology will greatly facilitate the functional analysis of the recently completed C. diphtheriae genome sequence.

Calcium-alginate gel bead cross-linked with gelatin as microcarrier for anchorage-dependent cell culture

Valuable products obtainedfrom the cultivation of anchorage-dependent mammalian cells require large-scale processes to obtain commercially useful quantities. It is generally accepted that suspension culture is the ideal mode of operation. Because anchorage-dependent cells need surfaces to be able to attach and spread, the incorporation of microcarriers to suspension culture is indispensable. Since the dextran-based microcarrier wasfirst introduced, many different types of microcarriers have been developed and commercialized. In this study, alginate-based microcarriers were made in the following order: (i) calcium-alginate gel beads prepared by dropping a blend of sodium alginate and propylene glycol alginate (PGA) into calcium chloride solution, (ii) the PGA section of gel beads cross-linked with gelatin in alkaline solution (i.e., via the transacylation reaction between the ester group of PGA and amino group of gelatin), and (iii) gelatin membrane around the beads further cross-linked by glutaraldehyde. The glutaraldehyde-treated gelatintransacylated PGA/alginate microcarrier showed superior features in high stability under phosphate-containing solution, density close to that of culture medium, and transparency. Moreover, the Chinese hamster ovary CHO-KI and amphotropic retrovirus producer PA317 cells cultivated on the newly synthesized microcarriers exhibited similar growth kinetics of these two types of cell lines cultured on commercial polystyrene microcarriers. However, cell morphology was easily monitored on the transparent microcarriers made in this study.

[Prostaglandin regulation of ionic conductivity of model membranes]

Electrical conductivity of model membranes of lecithin, cardiolipin, gangliosides and lecithin-gangliosides mixture under the effect of PGE1, PGA1, PGI2 were investigated for a number of ions. Property of prostaglandins to increase membrane conductivity within a wide range of concentrations (10(-5) M--10(-10) M) was discovered. Cation selectivity of the membranes under the effect of prostaglandins was found. Ability of prostaglandins to change conformation of lipid membranes was indicated.

Chemical instability of 15-keto-13,14-dihydro-PGE2: the reason for low assay reliability

The spontaneous degradation of 15-keto-13,14-dihydro-PGE2 was studied under various conditions. In aqueous media, dehydration rapidly occurred, particularly at high or very low pH. The acid catalyzed dehydration product was identified as 15-keto-13,14-dihydro-PGA2. This compound was also formed at alkaline pH, however, at higher pH a bicyclic compound, 11-deoxy-13,14-dihydro-15-keto-11,16-cyclo-PGE2, was formed in addition (cf. Fig. 1). The amounts of the latter compound increased with time and with increasing pH. In samples containing albumin, 15-keto-dihydro-PGE2 was degraded even more rapidly than in buffer of the same pH. In addition to the formation of the dehydration products, a considerable part of the metabolite was bound to albumin to yield water soluble adducts. A similar binding occurred to a low molecular weight fraction of plasma. The compound that was bound was 15-keto-dihydro-PGA2, whereas both 15-keto-dihydro-PGE2 and the bicyclic product were relatively inert in this respect. Due to its chemical stability, the bicyclic degradation product, 11-deoxy-13,14-dihydro-15-keto-11,16-cyclo-PGE2, is suggested as a suitable target for measurements instead of the labile parent compound, 15-keto-dihydro-PGE2, or the reactive dehydration product, 15-keto-dihydro-PGA2.

Mass spectrometric determination of new prostaglandin derivatives (series A and E)

The reaction of prostaglandins E1, E2, A1 and A2 with a 1:1 mixture of N,O-bis-trimethylsilyltrifluoroacetamide and piperidine favours the quantitative enolization of the 9-keto group of prostaglandins E, thus giving the corresponding tetrakis-TMS derivatives with molecular ions at m/e 642 and m/e 640 for prostaglandins E1 and E2, respectively, and also gives a new type of prostaglandin A-piperidyl-TMS derivative characterized by very strong base peaks at m/e 464 and 462, with molecular ions at m/e 637 and 635 for prostaglandins A1 and A2, respectively. The probable reaction mechanisms prevailing in both cases are discussed in accordance with the low and high resolution mass spectral data presented.

The effect of sodium restriction and prostaglandin inhibition on the renin-angiotensin system in man

To investigate the possible interrelationship between the renin-angiotensin and prostaglandin systems, two groups of normal men were evaluated under conditions of varied sodium intake and after indomethacin, an inhibitor of prostaglandin synthesis. Eight subjects were placed on a 200 mEq Na diet and given 45 min infusions of prostaglandin A1 (PGA1) at 0.075 microng/kg/min and angiotensin II at 10 ng/kg/min on separate mornings. PGA1 produced a significant rise in both plasma renin activity (PRA) and aldosterone. Angiotensin II caused a similar rise in aldosterone. The patients were then placed on a 10-20 mEq Na diet and the infusions repeated. PGA1 again induced a further increase in both PRA and aldosterone. Angiotensin II produced the expected increase in aldosterone while PRA decreased. Body weight and 24 h sodium excretion were not different from control days on either diet. When indomethacin was administered to patients on the low sodium diet, PRA fell significantly and there was an increased pressor responsiveness to angiotensin. In a separate group of 4 patients on a low salt intake, basal PRA fell significantly during a 4 day period of indomethacin administration and returned to control values within 48 h after discontinuing the drug. These studies suggest that PGA1 infusions stimulate renin release independently of sodium balance. Inhibition of prostaglandin synthesis lowers PRA and increases pressor responsiveness to angiotensin. The data provide further evidence that vasodepressor prostaglandins may play a role in renin release and blood pressure homeostasis.

Nucleophilic addition of bisulfite ion to prostaglandins E2 and A2: implication in aqueous stability

Evidence is presented to indicate that the bisulfite ion (HSO3-) adds across the C-9 carbonyl group of dinoprostone (prostaglandin E2) and across the delta 10,11- bond of prostaglandin A2. At room temperature, the apparent equilibrium constant, determined by phase solubility analysis, circular dichroism, UV spectroscopy, and partitioning, for the formation of the bisulfite adduct of dinoprostone is about 7.5 M-1 at neutral pH. From this result and a free energy relationship reported in the literature for the thermodynamics of nucleophilic addition to carbonyl groups, it is concluded that the chemical reactivity of the C-9 carbonyl group of dinoprostone is not high enough to improve aqueous stability through reversible one-step nucleophilic reactions. However, from a series of kinetic experiments, it is concluded that the equilibrium is extremely favorable for the formation of the bisulfite adduct of prostaglandin A2 over pH 4-8 at room temperature. The second-order rate constant for the attack of sulfite ion (SO3 2-) to prostaglandin A2 is 1.75 sec-1 M-1.

Molecular conformation prostaglandin A1 monoclinic crystalline polymorph

The molecular conformation of the monoclinic crystalline polymorph of prostaglandin A1 has been determined by X-ray diffraction techniques. The space group is P21 with a = 13.637(2), b = 7.567(1), c = 10.576(2) A, beta = 107.37(3) degrees; Dc = 1.073 g.cm-3 for Z = 2. The molecular conformation is characterized by the nearly parallel arrangement of the C1-C7 and C13-C20 side chains, with a general flattening of the overall structure when compared with the orthorhombic polymorph. The cyclopentenone moiety assumes a C8 envelope conformation with C8 and O9 displaced +0.29 A and -0.18 A from the C9-C10=C11-C12 plane respectively. Concerted, small varations of the torsion angles, primarily about the C8-C12, C14-C15 and C16-C17 bonds, bring the monoclinic and orthorhombic conformations into coincidence.

RENOMEDULLARY VASODEPRESSOR SUBSTANCE, MEDULLIN: ISOLATION, CHEMICAL CHARACTERIZATION AND PHYSIOLOGICAL PROPERTIES

The chemical and physiological properties of renomedullary depressor substances were investigated utilizing the normotensive, vagotomized, pentolinium-treated rat for assay. By a combination of solvent extraction, column chromatography, and thin-layer chromatography, three biologically active acidic lipids were isolated from rabbit renal medulla. The first compound, called medullin, is an acidic lipid with potent vasodepressor and relatively weak nonvascular smooth muscle-stimulating properties. Ultraviolet analysis revealed spectra closely resembling that of prostaglandin E-1 (PGE-1). Infrared analysis showed the presence of carbonyl, methylene, and hydroxyl groups in addition to trans ethylene bonds. Although closely resembling PGE-1, medullin appears to be a more unsaturated carboxylic lipid with less polar (hydroxyl) groups.

The hypotensive action of medullin is attributable to a direct effect on peripheral arteriolar beds without cardiac depression, because intra-arterial and intravenous injections of medullin reduced peripheral resistance markedly and increased cardiac output simultaneously. In addition, no effect on cardiac rate or contractility was observed in the isolated rabbit heart preparation. Comparative studies of medullin and PGE-1 indicated that the hypotensive activity of these compounds is similar with respect to potency and mechanism of action. The only biological difference between crystalline PGE-1 and medullin was a fiftyfold greater stimulation of nonvascular smooth muscle by PGE-1 in comparison to medullin. A second biologically active acidic lipid isolated from rabbit medulla was tentatively identified as PGE-1, and was found to possess both vasodepressor and nonvascular smooth muscle-stimulating properties. The third isolate from rabbit medulla possessed potent intestinal stimulating activity but weak to absent vasodepressor effects, properties similar to those of prostaglandin F compounds.