Rat renal arcade segment expresses vasopressin-regulated water channel and vasopressin V2 receptor

The arcades are long, branched renal tubules which connect deep and mid-cortical nephrons to cortical collecting ducts in the renal cortex. Because they are inaccessible by standard physiological techniques, their functions are poorly understood. In this paper, we demonstrate that the arcades are a site of expression of two proteins, aquaporin-2 (the vasopressin-regulated water channel) and the V2 vasopressin receptor, that are important to regulated water transport in the kidney. Using a peptide-derived polyclonal antibody to aquaporin-2, quantitative ELISA in microdissected segments showed that aquaporin-2 is highly expressed in arcades and that the expression is increased in response to restriction of fluid intake. Immunocytochemistry revealed abundant aquaporin-2 labeling of structures in the cortical labyrinth in a pattern similar to that of the Na(+)-Ca2+ exchanger and kallikrein, marker proteins expressed in arcades but not in cortical collecting ducts. RT-PCR experiments demonstrated substantial aquaporin-2 and V2 receptor mRNA in microdissected arcades. In situ hybridization, using 35S-labeled antisense cRNA probes for the V2 receptor demonstrated strong labeling of both arcades and cortical collecting ducts. Thus, these results indicate that the arcades contain the specific proteins associated with vasopressin-regulated water transport, and may be a heretofore unrecognized site of free water absorption.

Isolated, electrically-stimulated airway preparations--their use in determining beta-adrenoceptor agonist activity

We have assessed the suitability of electrically-stimulated superfused preparations of guinea-pig trachea, cat trachea and human bronchus for investigating the relaxant activity of the beta-adrenoceptor agonist, isoprenaline. Superfused strips of guinea-pig trachea, cat trachea and human bronchus all contracted in response to electrical stimulation. Guinea-pig trachea possesses inherent tone, and in its presence, electrical stimulation caused biphasic responses, comprising a modest, transient contraction, usually followed by a longer lasting relaxation. Human bronchus also possesses inherent tone, but responses were variable, generally monophasic, comprising a transient contraction of variable magnitude, but a longer lasting relaxation was occasionally observed after the transient contraction. Cat trachea possesses no inherent tone, and electrical stimulation of this preparation caused simple monophasic contractile responses. On guinea-pig trachea, addition of indomethacin (2.8 microM) abolished the inherent tone, and under these conditions, electrical stimulation caused monophasic contractile responses similar to those observed in cat trachea. On human bronchus, however, indomethacin enhanced inherent tone, which tended to uncover or exaggerate any relaxant component in the responses to electrical stimulation. The 5-lipoxygenase inhibitor, zileuton (10 microM), reduced, but did not abolish, the tone and converted the electrically-induced response to a monophasic contraction. In all preparations in which inherent tone was low or absent, whether naturally (cat trachea) or through pharmacological intervention (guinea-pig trachea with indomethacin, or human bronchus with zileuton), isoprenaline (1-100 nM) inhibited electrically-stimulated contractions in a concentration-related fashion (EC50s: 9-100 nM). In preparations exhibiting inherent tone (guinea-pig trachea with indomethacin or human bronchus with or without indomethacin), this tone was inhibited by isoprenaline. This relaxant activity, on guinea-pig trachea at least, was concentration-related (EC50: 5.4 nM). Such isoprenaline-induced relaxations complicated the analysis of inhibitory effects against electrically-induced contractions. Thus, in such experiments, only at higher concentrations did isoprenaline reliably inhibit these contractions (EC50: 23-119 nM), lower concentrations of isoprenaline often resulting in an apparent enhancement. The enhancement was probably artefactual, resulting from the fact that the electrically-induced contractions originated from a lower baseline. These data suggest that electrically-stimulated airway preparations are suitable for evaluating the relaxant activity of beta-adrenoceptor agonists, but the relaxant potency should be assessed in preparations lacking inherent tone, such as cat trachea, guinea-pig trachea in the presence of cyclo-oxygenase inhibition, or human bronchus in the presence of 5-lipoxygenase inhibition.

Metabolism of fenbufen by cultured 3T3-L1 adipocytes: synthesis and metabolism of xenobiotic glycerolipids

The storage of xenobiotic compounds as glycerolipids and their subsequent mobilization was studied using fenbufen and differentiated 3T3-L1 cells in culture. Fenbufen was taken up from the incubation medium and incorporated into triacylglycerol, diacylglycerol, and phospholipids. The triacylglycerol was susceptible to digestion by pancreatic lipase. The xenobiotic phospholipid contained three species, one of which behaved as fenbufenoyl phosphatidylcholine as judged by TLC, HPLC, choline analysis, and mass spectroscopy. After incubation with radioactive fenbufen for 18 h, the cells were transferred to a chase medium where radioactivity was lost from the cells and appeared in the medium. The rate was three times higher when 10 microM isoproterenol was present; insulin had no effect. Non-esterified fenbufen and analogues of mono- and di-acylglycerol were secreted. Monofenbufenoylglycerol was characterized by its ability to be used as a substrate by purified monoacylglycerol acyltransferase. When oleic acid was used in place of fenbufen, the majority of the radioactivity released in a chase experiment was the non-esterified acid (over 90%) and neither mono- nor di-acylglycerol was detected. These data indicate that 3T3-L1 adipocytes can synthesize fenbufen-containing lipids and release them into the medium on hormonal stimulation. The secretion of mono- and di-acylglycerols may have unforeseen pharmacological or toxicological implications.

Further evidence that tachykinin-induced contraction of human isolated bronchus is mediated only by NK2-receptors

The tachykinin-receptors mediating contraction of human bronchus have been characterized using both tachykinin-receptor selective agonists and blocking drugs under conditions where tachykinin metabolism by endogenous peptidases has been controlled, and true equilibrium conditions have been established. The findings that neurokinin A (EC50 = 2 nM) is the most potent agonist, and the NK2-receptor selective agonist, GR64349, is only 3-fold weaker, whereas agonists selective for NK1-receptors, substance P methyl ester, or NK3-receptors, senktide, are inactive, suggest that this effect is mediated exclusively by NK2-receptors. This is supported by observations that GR64349 is antagonised by the selective NK2-receptor blocking drugs, MEN10207 (pA2 = 6.7), R396 (pA2 = 6.1), (+/-)SR48968 (pA2 = 8.4) and GR159897 (pA2 = 8.6), but not by the NK1-receptor blocking drug, GR82334 (pA2 < 5). In approximately half of the preparations, the peptidase inhibitors, phosphoramidon (1 microM) and bestatin (100 microM), caused a marked and well-maintained contraction (approximately 20% of neurokinin A maximum), which may indicate a role for endogenous tachykinins in the regulation of tone in this preparation. This is supported by the finding that neurokinin A-immunoreactive nerve fibres are located around intrinsic neurones of local ganglia and within the smooth muscle layer of this preparation.

Sphingosine inhibits rat hepatic monoacylglycerol acyltransferase in Triton X-100 mixed micelles and isolated hepatocytes

Hepatic monoacylglycerol acyltransferase (MGAT), a developmentally-regulated microsomal activity that catalyzes the synthesis of sn-1,2-diacylglycerol, is regulated by anionic phospholipids and sn-1,2-diacylglycerol in Triton X-100 mixed micelles. Spingomyelin stimulated MGAT activity, whereas sphingosine, sphinganine, phytosphingosine, and stearylamine were inhibitors (IC50 of 9, 5.5, 5, and 6 mol %, respectively). Since ceramide and octylamine had relatively little effect, inhibition appears to require a free amino group and a long-chain hydrocarbon. Inhibition by sphingosine was competitive with respect to phosphatidic acid, phosphatidylinositol, or phosphatidylserine, suggesting that anionic phospholipids may activate MGAT at a specific site that is competitively blocked by sphingolipids. Both sphingosine and sphinganine inhibited MGAT activity in cultured hepatocytes from 10-day-old rats in a dose-dependent manner. Stimulation of MGAT activity by diacylglycerol was specific for sn-1,2-stereoisomers that contained two long fatty acyl chains. The diacylglycerol analogs phorbol 12-myristyl 13-acetate and ceramide had no effect. The highly cooperative activation of MGAT by sn-1,2-diacylglycerol was also inhibited by sphingosine. It is unlikely that activation of MGAT by low molar concentrations of anionic phospholipids is solely due to electrostatic interactions between the enzyme and negatively charged lipids because high ionic strength, neomycin, and Ca2+ had similar effects on enzyme activity irrespective of the presence or absence of phosphatidic acid. These data suggest that MGAT activity may be regulated physiologically by specific intermediates of glycerolipid metabolism and that, in neonatal rat liver, signal transduction may be linked to the synthesis of complex lipids via the monoacylglycerol pathway.

Characterization of the prostanoid receptors mediating constriction and relaxation of human isolated uterine artery

1. This study was undertaken to characterize pharmacologically the prostanoid receptor subtypes mediating constriction and relaxation of human isolated uterine artery. 2. U-46619 was a potent constrictor agonist on human uterine artery (EC50 [95% CL] = 3.5 [1.8-6.7] nM). Prostaglandin E2 (PGE2), PGF2 alpha, PGD2 and PGI2 only weakly constricted the uterine artery, being at least 100 times less potent than U-46619. The PGE2 and PGI2 constrictor effects may be modified by the potent dilator effects of these compounds. A number of agonists which show selectivity for FP-, DP- and EP-receptors including ICI 81008, BW 245C, sulprostone, rioprostil and butaprost, failed to cause any constriction at concentrations up to 30 microM. 3. Constrictor responses induced by all agonists tested were reduced or abolished by the TP-receptor blocking drugs, GR 32191 and EP 092. pA2 estimates for both antagonists versus U-46619 were 8.50, values which are consistent with their affinities at TP-receptors. 4. In preparations pre-constricted with phenylephrine (1 microM) both PGI2 and PGE2 were potent relaxant agonists. The selective IP-receptor agonists, cicaprost and iloprost, also dilated human uterine artery and were approximately 10 fold more potent than PGI2. The EP2-receptor agonists, butaprost and rioprostil and the selective DP-agonist, BW 245C, were at least 100 fold weaker than PGI2 and PGE2 suggesting that neither DP- nor EP2 receptors were involved. 5. We conclude that TP-receptors mediate constriction, whereas IP- and possibly EP4-receptors mediate relaxation of human uterine artery.

Developmental regulation of the catalytic subunit of the apolipoprotein B mRNA editing enzyme (APOBEC-1) in human small intestine

Apolipoprotein (apo) B mRNA editing is a site-specific cytidine deamination reaction responsible for the production of apoB-48 in mammalian small intestine. This process is mediated by an enzyme complex that includes the catalytic subunit, APOBEC-1. In the present study, it is shown that the developmental regulation of apoB mRNA editing in fetal human small intestine is closely mirrored by accumulation of APOBEC-1 mRNA. Similar results were obtained using Caco-2 cells, the data further suggesting that culture of these cells under conditions previously shown to promote differentiation produce an earlier and more marked induction of APOBEC-1 mRNA abundance. Complementary analysis of APOBEC-1 protein accumulation using immunocytochemical localization reveals its appearance to be temporally coordinated with the accumulation of APOBEC-1 mRNA and its distribution to be confined to villus-associated enterocytes. Previous studies demonstrated a close temporal association between the development of triglyceride synthesis and apoB mRNA editing in the rat liver and small intestine. Analysis of fatty acid CoA ligase, monoacylglycerol acyltransferase, and diacylglycerol acyltransferase activity in preparations of human liver and small intestine demonstrates activity of all three enzymes in the late first and early second trimester, suggesting that certain aspects of complex lipid biosynthesis in the human fetal small intestine and liver are regulated developmentally. The cues that modulate the post-transcriptional regulation of fetal human small intestinal apoB gene expression may thus include both temporal programming and events related to the emergence of lipid transport capability.

Linoleic and linolenic acids are selectively secreted in triacylglycerol by hepatocytes from neonatal rats

To determine whether specific fatty acids are metabolized differently by neonatal liver, hepatocyte cultures from neonatal (age: 5, 11, and 21 days) and adult rats were incubated with radiolabeled 18:1, 18:2, or 18:3. At each age, the rate of oxidation was highest for 18:3 and lowest for 18:1. Conversely, esterification was highest for 18:1 and lowest for 18:3. Fatty acid esterification was of the order: day 5 > day 11 > adult > day 21. When incubations contained each of two of the above fatty acids, one radiolabeled and the other not, 18:1 inhibited oxidation of radiolabeled 18:2 by up to 45% in neonatal hepatocytes. In addition, added 18:1 increased glycerolipid accumulation from 18:2 and 18:3. Under these conditions, the relative proportion of triacylglycerol secreted in the medium, compared with that accumulated in the cells, was two- to fourfold higher for day 11 and 21 rat hepatocytes. The results suggest that a specific mechanism exists in the livers of neonatal rats to spare n-3 and n-6 fatty acids from oxidation and instead secrete them in triacylglycerol.

Evidence for functional binding and stable sliding of the TATA binding protein on nonspecific DNA

The TATA binding protein (TBP) is required at RNA polymerase I, II, and III promoters that either contain or lack a TATA box. In an effort to understand how TBP might function at such a wide variety of promoters, we have investigated the specific and nonspecific DNA binding properties of human TBP. We show that TBP has less than a 10(3)-fold preference for binding a TATA box (TATAAAAG) than for an average nonspecific site. In contrast to TBP, which binds to the minor groove of DNA, major groove binding proteins typically display binding specificities in the range of 10(6). Once TBP is bound to DNA, whether it be a TATA box or nonspecific DNA, binding is quite stable with a t1/2 of dissociation in the range of 20-60 min for a 300-base pair DNA fragment. In this binding state, TBP appears to be capable of stable one-dimensional sliding along the DNA. Sequence-specific binding can be accounted for, in part, by different rates of sliding. Additional findings demonstrate that specific and nonspecific DNA impart upon TBP an enormous and equivalent degree of thermal stability, suggesting that the TBP-DNA interface on non-specific DNA is not radically different from that on TATA. Consistent with this notion, we find that nonspecifically bound TBP is competent in establishing pol II transcription complexes on DNA. Together, these finding provide a plausible mechanistic explanation for the ability of TBP to function at TATA-containing and TATA-less promoters.

Dimerization of the TATA binding protein

The TATA binding protein (TBP) is a central component of all eukaryotic transcription machineries. The recruitment of TBP to the promoter is slow and possibly rate limiting in transcription complex assembly. In an effort to understand the nature of this potential rate-limiting step, we have investigated the physical state of TBP prior to DNA binding. By chemical cross-linking, gel filtration chromatography, and protein affinity chromatography, we find that the conserved carboxyl-terminal DNA binding domain of human TBP dimerizes when not bound to DNA. The data completely support the proposed dimeric structure of plant TBP, previously determined by x-ray crystallography. TBP dimers are quite stable, having an approximate equilibrium dissociation constant (KD) in the low nanomolar range. The dimerization interface appears to be dominated by hydrophobic forces, as predicted by the crystal structure. TBP dimers do not bind DNA, but they must dissociate into monomers before stably binding to the TATA box. Dissociation of TBP dimers appears to be relatively slow, and as such has the potential to dictate the kinetics of DNA binding.

An experimental model to investigate the dynamics of wound contraction

An excisional wound model in the Hooded Lister rat is described. The methods used to inflict, measure and characterise the process of wound contraction are comprehensively discussed. The model is shown to be reliable, reproducible and capable of detecting the effect of systemically administered prednisolone.

Characterization of the PGE receptor subtype mediating inhibition of superoxide production in human neutrophils

1. The aims of this study were to characterize the EP receptor subtype mediating the inhibition of superoxide anion generation by formyl methionyl leucine phenylalanine (FMLP)-stimulated human neutrophils, and to test the hypothesis that adenosine 3':5'-cyclic monophosphate (cyclic AMP) is the second messenger mediating the inhibition of the neutrophil by prostaglandin (PG)E2. 2. PGE2 (0.001-10 microM) inhibited FMLP (100 nM)-induced O2-generation from human peripheral blood neutrophils in a concentration-dependent manner, with an EC50 of 0.15 +/- 0.03 microM, and a maximum effect ranging from 36-84% (mean inhibition of 68.7 +/- 2.5%, n = 32). 3. The EP2-receptor agonists, misoprostol, 11-deoxy PGE1, AH13205 and butaprost, all at 10 microM, inhibited O2- generation, causing 95.5 +/- 2.9%, 56.8 +/- 5.2%, 37.1 +/- 6.6% and 18.9 +/- 4.4% inhibition respectively, the latter two being much less effective than PGE2. Similarly, the EP1-receptor agonist, 17-phenyl PGE2 (10 microM), and the EP3/EP1-receptor agonist, sulprostone (10 microM), also inhibited O2- generation, causing 32.2 +/- 7.0% and 15.3 +/- 3.4% inhibition respectively. 4. The non-selective phosphodiesterase inhibitor, isobutyl methylxanthine (IBMX, 0.25 mM) inhibited the FMLP response by 54.5 +/- 5.0%. In addition, IBMX shifted concentration-effect curves for PGE2, misoprostol, 11-deoxy PGE1, butaprost, and AH 13205 to the left, to give EC50s of 0.04 +/- 0.03 (n = 13), 0.07 +/- 0.03 (n = 4), 0.08 +/- 0.03 (n = 4), 0.33 +/- 0.13 (n = 4) and 0.41 +/- 0.2 microM (n = 3) respectively, allowing equieffective concentration-ratios (EECs, PGE2 = 1) of 11.5, 5.3, 50.7 and 12.7 to be calculated. This agrees well with the relative potencies of these agonists at EP2 receptors.5. By contrast, even in the presence of IBMX (0.25 mM), sulprostone and 17-phenyl PGE2 were only effective at the highest concentration (10 microM), and gave EECs of > 700 and 486 respectively, suggesting that EP1 or EP3 receptors are not involved.6. The selective type IV phosphodiesterase inhibitor, rolipram at 2 and 10 nM did not inhibit the FMLP response, but at the higher concentration of 50 nM, it decreased the FMLP response by 46.6 +/-7.3%.However, rolipram shifted concentration-effect curves for PGE2 to the left to give EC50s of 0.06 +/-0.022,0.015 +/- 0.0, 0.012 +/- 0.006 microM at 2, 10 and 50 nM respectively, compared to the control EC50 of0.27+/- 0.09 microM for PGE2.7. The EP4/TP receptor blocking drug, AH 23848B (10 microM, 10 min) did not inhibit 02- generation by PGE2, but was found to potentiate significantly the effect of PGE2 at the lower concentrations of PGE2 tested (0.001-0.1 microM).8. The adenylate cyclase inhibitor, SQ 22,536 (0.1 mM, 2 min) reduced PGE2-induced inhibition of 02-production, giving an EC50 in the absence of SQ 22,536 of 0.24 +/- 0.1, and 1.9 +/- 1.1 AM in its presence.9. These results suggest that inhibition of superoxide generation by PGE2 is mediated by stimulation ofEP2 receptors and activation of adenylate cyclase, leading to the elevation of intracellular levels of cyclic AMP.

Beta 2-adrenoceptors mediate a reduction in endothelial permeability in vitro

The permeability of bovine pulmonary artery endothelial (CPAE) monolayers to Evans blue-labelled albumin (Evans blue-albumin) has been measured in vitro. Thrombin caused a concentration-dependent increase in Evans blue-albumin clearance across endothelial monolayers. Isoprenaline inhibited thrombin-induced Evans blue-albumin clearance in a concentration-dependent manner (EC50 21 nM). This effect was mimicked by the selective beta 2-adrenoceptor agonists salbutamol (EC50 64 nM) and salmeterol (EC50 2.7 nM), but not by the selective beta 1-adrenoceptor agonist, RO-363 ((1-[3',4'-dihydroxyphenoxy]-2-hydroxy-[3",4"- dimethoxyphenethylamino]-propane)oxalate), nor by the selective beta 3-adrenoceptor agonist, CL-316,243 (disodium (R,R)-5-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]-amino]propyl]-1,3- benzodioxole-2,2-dicarboxylate). Isoprenaline, salbutamol and salmeterol, but not RO-363 or CL-316,243 produced small, but significant reductions in Evans blue-albumin clearance across unstimulated endothelial monolayers. Inhibition of the response to thrombin by isoprenaline was antagonised by the selective beta 2-adrenoceptor antagonist, ICI-118,551 ((erythro-DL-1(7-methylindan-4- yloxy)3-isopropylaminobutan-2-ol), pKB 8.4). Salmeterol also inhibited hydrogen peroxide-stimulated Evans blue-albumin clearance. Hence, the widely used beta 2-adrenoceptor agonists, salbutamol and salmeterol, are able to reduce endothelial permeability at nanomolar concentrations.

GR159897, a potent non-peptide antagonist at tachykinin NK2 receptors

GR159897 ((R)-1-[2-(5-fluoro-1H-indol-3-yl)ethyl]-4-methoxy-4- [(phenylsulfinyl)methyl]piperidine) is a novel, highly potent and selective non-peptide antagonist at tachykinin NK2 receptors. GR159897 inhibited binding of the NK2 receptor antagonist radioligand [3H]cyclohexylcarbonyl-Gly-Ala-(D)Trp-Phe-NMe2 ([3H]GR100679) to human ileum NK2 receptors transfected into Chinese hamster ovary cells (pKi 9.5) and to rat colon membranes (pKi 10.0). GR159897 was a competitive antagonist of contractions induced by the NK2 receptor agonist [Lys3,Gly8-R-gamma-lactam-Leu9]neurokinin A-(3-10) (GR64349) in guinea-pig trachea (pA2 8.7), and had negligible activity at human NK1 receptors transfected into Chinese hamster ovary cells (pKi 5.3), NK1 receptors in guinea-pig trachea (pKB < 5) or NK3 receptors in guinea-pig cerebral cortex (pKi < 5). In vivo, in the anaesthetised guinea-pig, GR159897 (0.12 mg.kg-1 i.v.) potently antagonised bronchoconstriction induced by GR64349 (dose-ratio = 28), with a long duration of action (3 h). GR159897 should be a useful tool for studying the physiological and pathophysiological role of tachykinin NK2 receptor activation.

Evidence for the presence of AH 13205-sensitive EP2-prostanoid receptors in the pregnant baboon but not in the pregnant sheep myometrium near term

OBJECTIVE

Our purposes were to assess the effects of prostaglandin (PG) E2 and PGF2 alpha on myometrial contractility in pregnant sheep and baboons in an in vitro superfusion study, and to characterize further the PGE-sensitive (EP) receptor subtype involved in the myometrial response to PGE2 by using the selective prostanoid EP2 agonist AH 13205.

METHODS

Strip preparations of uterine muscle from 15 sheep (107-145 days' gestational age) and ten baboons (158-185 days' gestation) were studied. Cumulative concentration-response curves (CRC) were constructed to oxytocin (4.2 pmol/L to 0.42 mumol/L, PGE2 (0.1 nmol/L to 1 mumol/L), and PGF2 alpha (1 nmol/L to 100 mumol/L), and 50% effective concentration (EC50) values (mean and 95% confidence interval) were calculated. We also tested the hypothesis that PGE2-induced myometrial relaxation in pregnant baboons could be mediated by EP2-prostanoid receptors. Myometrial strips were stimulated by oxytocin (0.42 nmol/L), and CRCs to the EP2-agonist AH 13205 (0.1 nmol/L to 10 mumol/L) were constructed.

RESULTS

Prostaglandin F2 alpha stimulated myometrial activity in a concentration-related fashion in all preparations from both sheep and baboons. The EC50 in the sheep myometrium for PGF2 alpha (52 nmol/L, 95% confidence interval [CI] 25-110) was significantly (P < .05) lower than that in baboon myometrium (183 nmol/L, 95% CI 93-355). Oxytocin stimulated myometrial activity in preparations of both sheep (EC50 = 0.29 nmol/L, 95% CI 0.11-0.71) and baboon (EC50 = 0.31 nmol/L, 95% CI 0.18-0.52). In contrast, responses to PGE2 were species-related: PGE2 caused concentration-related stimulation of myometrial activity in sheep tissue (EC50 = 3.2 nmol/L, 95% CI 2.0-5.0), but induced concentration-related inhibition of activity in baboon myometrium (50% inhibitory concentration [IC50] = 21 nmol/L, 95% CI 2.2-203). A concentration-related inhibitory response to AH 13205 (IC50 = 3.56 nmol/L, 95% CI 1.28-5.99) was obtained in the baboon. In contrast, AH 13205 failed to inhibit comparable myometrial strip preparations from pregnant sheep.

CONCLUSIONS

The present studies suggest that both sheep and baboon myometrium contain prostanoid receptors that mediate stimulation. In addition, baboon myometrium, like that from the human, contains AH 13205-sensitive EP receptors (EP2 receptors), which mediate inhibition. The pregnant baboon may therefore represent a suitable animal model for investigations into the use of EP2 agonists for the prevention of premature labor in humans.

Galactose consumption, metabolism, and follicle-stimulating hormone concentrations in women of late reproductive age

OBJECTIVE

To test the hypothesis that high galactose consumption and low activity of galactose-1-phosphate uridyl transferase (transferase) is associated with early ovarian senescence among nongalactosemic women.

DESIGN

Cross-sectional study. Data collection consisted of a self-administered questionnaire with sections on diet (food frequency data to measure galactose consumption), reproductive, and medical histories. One blood sample was collected to measure FSH and transferase activity; FSH was used as a measure of ovarian senescence. Among women who were having menstrual periods at least every 8 weeks, the blood sample was drawn in the early follicular phase (days 2 to 4) of a menstrual cycle.

PARTICIPANTS

Two hundred ninety-five women volunteers ages 38 to 49 years who had not had a hysterectomy or oophorectomy were recruited through posters and advertisements.

MAIN OUTCOME MEASURE

Serum FSH concentrations.

RESULTS

Controlling for age, smoking, and body mass, transferase activity and FSH were unrelated. However, FSH levels were 29% higher (95% confidence intervals, 9% to 52%) among women who reported consuming > or = 6 g galactose/d.

CONCLUSION

These data do not support the hypothesis that low transferase activity represents a genetic predisposition for early ovarian senescence, as measured by FSH levels in women ages 38 to 49 years. However, the hypothesized positive association between galactose consumption and FSH was supported.

Adipose monoacylglycerol:acyl-coenzyme A acyltransferase activity in the white-throated sparrow (Zonotrichia albicollis): characterization and function in a migratory bird

Although migrating birds use stored triacylglycerol as their primary fuel for flight, they must retain sufficient stores of omega 6 and omega 3 fatty acids to sustain reproduction after the spring migration. Hepatic monoacylglycerol:acyl-coenzyme A acyltransferase (EC 2.3.1.22) (MGAT) activity is associated with physiological periods in which lipolysis and beta-oxidation are prominent, and it may also play a role in the selective retention of certain essential fatty acids. Therefore, we characterized MGAT activity in adipose tissue from the white-throated sparrow (Zonotrichia albicollis), a migratory bird. MGAT specific activity from adipose tissue and liver, respectively, was 22.2 +/- 7.27 and 0.79 +/- 0.35 nmol/min/mg of total particulate protein. Activity did not vary seasonally or between male and female birds. Specific activity increased 4.3-fold in the presence of 75 micrograms of phosphatidylcholine and phosphatidylserine (1:1, w/w). MGAT acylated sn-1(3)-monooleoylglycerol, sn-2-monooleylglycerol ether and sn-1(3)-monooleylglycerol ether at 7.5, 5.7 and 1.7%, respectively, of the rate observed with sn-2-monooleoylglycerol. An initial lag phase observed at low concentrations of palmitoyl-CoA was corrected by adding 2 mM MgCl2, Mg(NO3)2 or CaCl2, suggesting a requirement for divalent cations. MGAT acylated sn-2-monolinolenoylglycerol and sn-2-monolinoleoylglycerol in preference to sn-2-monooleoylglycerol. Specificity of MGAT for sn-2-monoacylglycerols and the probable enhanced affinity fo sn-2-monoacylglycerols of specific acyl chains may allow selected omega 6 and omega 3 fatty acids to be retained within the adipocyte, while nonessential fatty acids are released for beta-oxidation in flight muscles.

Characterization of dilator prostanoid receptors in the fetal rabbit ductus arteriosus

The purpose of this study was to determine which receptors mediate the dilator effects of prostaglandins (PGs) on the ductus arteriosus of the fetal rabbit. Isolated rings of the vessel from fetal New Zealand White rabbits were precontracted with indomethacin (1 microM) and potassium (25 mM) in 100 to 110 mmHg oxygen, and the dilator effects of a range of synthetic prostanoids were quantified by cumulative relaxant concentration-effect curves. The potencies of agonists were quantified with reference to PGE2 by the equieffective molar ratio (EMR): EC50 test agonist/EC50 PGE2. The effects on these responses of available antagonists were also studied. None of a range of synthetic prostanoids with selective agonism of EP1, EP2 or EP3 receptors was as potent as PGE2. The rank order of potency was as follows: PGE2 (EC50 = 0.36 nM [95% confidence intervals [CI] = 0.32-0.41, n = 44], EMR = unity) >> misoprostol (EMR 145, 95% CI 73-217) > [1R-[1 alpha (Z),2 beta (R*),3 alpha]]-4-(benzoyl-amino)phenyl 7-[3 hydroxy-2(2-hydroxy-3-phenoxypropoxy)-5- oxocyclopentyl]-4-heptenoate, single enantiomer (GR 63799K) (EMR 685, 95% CI 427-944) >> ((+/-)-trans-2-[4[(1-hydroxphenyl) phenyl]-5-oxocylopentaneheptanoic acid (AH13205) (EMR > 100,000) > or = sulprostone (EMR > 10,000) > or = 0. The EP1 antagonists, 6-isopropoxy-9-oxoxanthine-2-carboxylic acid (AH6809) (10 microM) and 8-clorodi-benz[b,f][1,4]oxazepine-10 (11H)-carboxylic acid, 2-acetylhydrazide (SC19220) (30 microM), had no significant effect on the sensitivity of the ductus to PGE2.(ABSTRACT TRUNCATED AT 250 WORDS)

ADH-induced recycling of fluid-phase marker from endosomes to the mucosal surface in toad bladder

In the toad urinary bladder, the reversal of antidiuretic hormone (ADH) stimulation results in the endocytosis of apical membrane water channels, along with any fluid-phase marker present in the mucosal bathing solution. We have loaded vesicles with horseradish peroxidase (HRP), then restimulated the bladders and measured the reappearance of endocytosed HRP in the mucosal bath. HRP-loaded bladders that were restimulated showed HRP release that peaked sharply within 15 min after restimulation. Varying the interval between loading and restimulation did not vary HRP release significantly. Restimulation with forskolin gave HRP release values similar to ADH. The amount of HRP released correlated with the magnitude of water permeability induced. The demonstration that fluid-phase markers can be recycled from endosomes to the apical surface in a hormone-dependent fashion indicates that endocytosed membrane, containing water channels, is able to rapidly recycle back to the surface in response to hormone restimulation. In addition, marker release declined progressively with repeated restimulation, totaling < 30% of the retrieved amount. This result indicates that a relatively large proportion of the retrieved marker reaches a nonrecycling compartment.

Hepatic monoacylglycerol acyltransferase is regulated by sn-1,2-diacylglycerol and by specific lipids in Triton X-100/phospholipid-mixed micelles

The lipid cofactor requirement of hepatic monoacylglycerol acyltransferase (MGAT) (EC 2.3.1.22) was studied in Triton X-100/lipid-mixed micelles. Anionic phospholipids and anionic lysophospholipids stimulated MGAT activity, whereas fatty acids and sphingosine inhibited enzyme activity. Phosphatidic acid was a potent activator, stimulating MGAT 11-fold at 4.2 mol %. Kinetic studies revealed that phosphatidic acid, with an apparent Ka of 0.26 mol %, was a better activator than phosphatidylserine, phosphatidylinositol, or cardiolipin. Of the anionic lysophospholipids, lysophosphatidic acid was a better activator than lysophosphatidylserine, stimulating maximally at less than 3 mol %. Oleate was a more potent inhibitor (Ki, 2.4 mol %) than sphingosine (Ki, 18.3 mol %). The dependence of MGAT on sn-2-monoacylglycerol was not cooperative in the absence or presence of anionic phospholipids, oleic acid, or sphingosine. The apparent Km for sn-2-monoC18:1-glycerol was 1.24 mol % in the presence of maximally activating phospholipid and 0.19 mol % when phospholipid was omitted. MGAT's product sn-1,2-diacylglycerol was a weaker activator than the anionic phospholipids, but the effects of diacylglycerol and phospholipid were additive. Activation by sn-1,2-diC18:1-glycerol was highly cooperative with a Hill coefficient of 3.6. Activation was specific for the sn-1,2-stereoisomer; neither 1,3-diacylglycerol nor the ether analogs of sn-1,2- or 1,3-diacylglycerol were activators. Since several of the lipid modulators of MGAT activity are intracellular second messengers, these data suggest the possibility that regulatory links exist between signal transduction and the synthesis of complex lipids via the monoacylglycerol pathway.

Long-term regulation of collecting duct water permeability: freeze-fracture analysis of isolated perfused tubules

Terminal inner medullary collecting duct (IMCD) segments from water-restricted rats have high osmotic permeabilities despite the absence of vasopressin (AVP). We performed freeze-fracture analysis of individual IMCD segments from such animals following measurement of their water permeability (Pf). IMCD segments from control rats did not have a high Pf in the absence of AVP (88 +/- 15 microns/s) and had a low incidence of E-face intramembrane particle (IMP) clusters (9.6 +/- 2.7 clusters/100 microns 2). Segments exposed to 0.1 nM AVP in vitro had enhanced Pf (1,060 +/- 210 microns/s) and cluster incidence (122 +/- 33 clusters/100 microns 2). IMCD segments isolated from rats dehydrated for 48 h and perfused without AVP exposure had an elevated Pf (605 +/- 71 microns/s) and a high incidence of clusters (166 +/- 36 clusters/100 microns 2). There also was an increase in the number of single particles between clusters in tubules from dehydrated rats (2.5-fold) and in AVP-treated tubules (3.6-fold). These findings indicate that IMP clusters are associated with high water permeability in tubules from dehydrated animals independent of continued AVP exposure. The increased incidence of particles between clusters suggests that water channels may also occur outside of cluster domains.

Erythromycin, lincosamides, peptidyl-tRNA dissociation, and ribosome editing

Inaccurate protein synthesis produces unstable beta-galactosidase, whose activity is rapidly lost at high temperature. Erythromycin, lincomycin, clindamycin, and celesticetin were shown to counteract the error-inducing effects of streptomycin on beta-galactosidase synthesized in the antibiotic-hypersensitive Escherichia coli strain DB-11 Met-. Newly synthesized beta-galactosidase was more easily inactivated by high temperatures when synthesized by bacteria partially starved for arginine, threonine, or methionine. Simultaneous treatment with erythromycin or lincomycin yielded beta-galactosidase that was inactivated by high temperatures less easily than during starvation alone, an effect attributed to stimulation of ribosome editing. When synthesized in the presence of canavanine, beta-galactosidase was inactivated by high temperature more easily but this effect could not be reversed by erythromycin. The first arginine in beta-galactosidase occurs at residue 13, so the effect of erythromycin during arginine starvation is probably to stimulate dissociation of erroneous peptidyl-tRNAs of at least that length. Correction of errors induced by methionine starvation is probably due to stimulation of dissociation of erroneous peptidyl-tRNAs bearing peptides at least 92 residues in length. All the effects of erythromycin or the tested lincosamides on protein synthesis are probably the result of stimulating the dissociation from ribosomes of peptidyl-tRNAs that are erroneous or short.

Glycogen storage disease in adults

OBJECTIVE

To identify complications amenable to prevention in adults with glycogen storage disease (GSD) types Ia, Ib, and III and to determine the effect of the disease on social factors.

DESIGN

Case series and clinical review.

SETTING

Referral medical centers in the United States and Canada.

PATIENTS

All patients with GSD-Ia (37 patients), GSD-Ib (5 patients), and GSD-III (9 patients) who were 18 years of age or older.

MEASUREMENTS

Ultrasound or radiographic studies identified liver adenomas, nephrocalcinosis, or kidney stones. Radiographic studies identified osteopenia. Reports of the clinical examination, serum chemistry results, and social data were obtained.

RESULTS

For patients with GSD-Ia, problems included short stature (90%), hepatomegaly (100%), hepatic adenomas (75%), anemia (81%), proteinuria or microalbuminuria (67%), kidney calcifications (65%), osteopenia or fractures or both (27%), increased alkaline phosphatase (61%) and gamma-glutamyltransferase (93%) activities, and increased serum cholesterol (76%) and triglyceride (100%) levels. Hyperuricemia was frequent (89%). Patients with GSD-Ib had severe recurrent bacterial infections and gingivitis. In patients with GSD-III, 67% (6 of 9) had increased creatinine kinase activity. Four of these patients had myopathy and cardiomyopathy.

CONCLUSIONS

For GSD-Ia, hyperuricemia and pyelonephritis should be treated to prevent nephrocalcinosis and additional renal damage. For GSD-Ib, granulocyte-colony-stimulating factor may prevent bacterial infections. For GSD-III, more data are required to determine whether the myopathy and cardiomyopathy can be prevented. Most of the patients with GSD-I and GSD-III had 12 or more years of education and were either currently in school or employed.

A novel inhibitory prostanoid receptor in piglet saphenous vein

A range of prostanoid agonists were tested for activity on isolated ring preparations of piglet saphenous vein. The selective TxA2-mimetic (TP-receptor agonist), U-46619, contracted the preparation in a concentration-related fashion. These contractions were inhibited by the TP-receptor blocking drug, GR32191B, producing a pA2 of 7.8 (slope = 1.6). Prostanoid-induced relaxant responses were studied on preparations which had been pre-contracted using an EC60 concentration of phenylephrine (mean EC60 = 0.97 microM), in the presence of GR32191B (1 microM), to block contractile TP-receptors. Under these conditions, PGD2, PGE2, PGF2 alpha, PGI2, and U-46619, all caused concentration-related relaxation. PGE2 was the most potent agonist (EC50 = 0.23nM), whereas, all of the other agonists were at least 1,000-fold weaker, providing strong evidence for the presence of inhibitory EP-receptors. The selective synthetic EP-agonists, sulprostone (EP1/EP3) and AH13205X (EP2), were next tested for relaxant activity. While both compounds caused concentration-related relaxant activity, they were respectively 6,000 and 11,000-fold less potent than PGE2. The potent TP-receptor blocking drugs, AH22921X and AH23848B, were both weak antagonists of PGE2 but not isoproterenol-induced relaxant responses of piglet saphenous vein in a concentration-related fashion. These two compounds had pA2 values against PGE2 of 5.3 and 5.4 respectively, with regression slopes not significantly different from unity. In contrast, neither compound at a concentration of 30 microM had any antagonist activity against prostanoid-induced effects on guinea-pig fundus (EP1), rabbit ear artery (EP2) or guinea-pig vas deferens (EP3). In conclusion, the piglet saphenous vein contains TP-receptors mediating smooth muscle contraction, and a PGE2-specific (EP) receptor mediating relaxation. The inhibitory EP-receptor does not appear to be of the EP1, EP2 or EP3-subtypes, and appears therefore to be a novel subtype which we tentatively term EP4, and the potent TP-receptor blocking drugs, AH22921X and AH23848B, appear to be weak, but specific EP4-receptor blocking drugs.