Localization and characterization of prostaglandin E1 receptors in rat small intestine

While prostaglandins of the E series are known to affect several small intestinal functions, their cellular mechanisms are poorly understood. The purposes of our study were to determine whether receptors for PGE are present in rat small intestine and to locate and characterize the receptor binding in the subcellular fractions. Small intestinal binding of prostaglandin E1 was significantly higher than that of prostaglandin E2. Highest receptor binding for prostaglandin E1 was found in the plasma membrane fraction of isolated small intestinal enterocytes. Curvilinearity of prostaglandin E1 binding in plasma membranes upon Scatchard analysis indicated two receptor binding sites in rat small intestine. Competitive binding studies demonstrated that receptor binding was highest for prostaglandins of the E series. These studies are the first to demonstrate specific prostaglandin E1 receptors in different subcellular fractions of rat small intestine. We suggest that receptor binding of prostaglandin E may be an important initial step in the mechanism of prostaglandin-E-induced responses in the small intestine.

Characterization of epidermal growth factor receptors in astrocytic glial and neuronal cells in primary culture

Studies characterized the structure and function of epidermal growth factor (EGF) receptors in astrocytic glial cells and neuronal cells in primary culture from neonatal rat brain. [125I]EGF binding to membranes prepared from glial and neuronal cultures was specific and dependent on protein concentration; however, glial preparations bound 5-fold more [125I]EGF per mg protein. Unlabeled EGF competed for binding to both glial and neuronal membranes with an IC50 of 5 nM, whereas insulin, insulin-like growth factor I, and nerve growth factor failed to compete. Scatchard plot analysis of binding data for glial cells yielded a curvilinear plot with dissociation constants of 7.12 nM for high affinity and 6.2 microM for low affinity sites. The higher level of binding in glial compared to neuronal membranes reflected a greater number of binding sites rather than differences in receptor affinity. In glial membranes, [125I]EGF covalently cross-linked to one major protein with a mol wt of 170,000, and EGF stimulated the phosphorylation of a 170,000 protein which was half-maximal at 20 nM. In contrast, neither covalent cross-linking nor receptor autophosphorylation could be detected in neuronal membranes. Culture of glial cells in the presence of EGF stimulated [35S]methionine incorporation into both cellular and secreted proteins, whereas no effect of EGF was observed in neuronal cultures. The addition of EGF to glial cultures produced a dose-dependent stimulation of [3H]thymidine incorporation as well as the multiplication of cells over a 6-day period. These observations show that functional EGF receptors in the neonatal brain are predominantly localized in glial cells.

Smoking-related alterations in epidermal growth factor and insulin receptors in human placenta

Studies characterized insulin and EGF receptors in human placental tissue from smokers and nonsmokers. Specific binding of 125I-labeled insulin and EGF to placental membranes was not different for nonsmokers compared with smokers. EGF and insulin receptor kinases were further studied using a wheat germ agglutinin-purified preparation of solubilized placental membrane proteins. In extracts from the nonsmoker group, EGF stimulated the active phosphorylation of Mr 170,000 and 140,000 protein bands, which was half-maximal (EC50) at 5 x 10(-8) M. In extracts from the smokers group, however, phosphorylation of these two protein bands was barely detectable over a range of 0 to 10(-6) M EGF. Thus, EGF-stimulated phosphorylation of the 170,000 and 140,000 bands was markedly decreased in placental membranes from smokers. In contrast, insulin stimulated the phosphorylation of a 95,000 protein that was immunoprecipitated with anti-insulin receptor antiserum in membrane preparations from both nonsmokers and smokers. Dose-response curves for autophosphorylation indicate that EC50 values were 2.6 and 7.0 nM insulin for nonsmokers and smokers, respectively. Laser densitometry scan of the 95,000 band on autoradiograms further showed that maximal 32P incorporation was 30% greater in smokers compared with nonsmokers. Analysis of the insulin-dependent phosphorylation of an exogenous substrate, poly(Glu,Tyr) (4:1), showed a similar pattern of values for nonsmokers versus smokers. These results indicate that insulin receptor autophosphorylation and tyrosine kinase activity were normal or increased, whereas EGF-stimulated kinase activity was markedly decreased in placental membrane proteins from smokers. Western blot analysis using an antiserum to the EGF receptor showed the presence of immunoreactive bands of 126,000 and 150,000-170,000 in receptor preparations from nonsmokers, whereas only the 126,000 protein was detected in preparations from smokers. Thus, the smoking-related deficiency in EGF receptor autophosphorylation appeared to be due to the absence of a 150,000-170,000 receptor protein. In conclusion, maternal cigarette smoking is associated with selective alterations in two major receptor-mediated pathways thought to be involved in cell growth and differentiation in human placenta.

Effects of beta-naphthoflavone on insulin receptor binding and protein kinase activity in rat liver and placenta

Studies investigating the effects of beta-naphthoflavone (beta NF) on insulin receptor binding and its intrinsic protein kinase activity in rat liver and placenta were performed. Membranes were prepared from maternal liver and placenta on gestation day 11 and used for [125I]insulin radioreceptor assay. Scatchard analysis showed that association constants (Ka) for high affinity binding sites were similar for placental and liver membrane. The administration of beta NF, 15 mg/kg, 1 day before study did not alter the specific binding of insulin to liver membranes, whereas ligand binding to placental preparations was decreased 40% from control. Scatchard analysis of binding to placental membranes suggests that beta NF treatment was associated with a change in the number of high affinity binding sites. In further studies membrane receptors were solubilized and partially purified by wheat germ agglutinin affinity chromatography for protein kinase assay. Insulin stimulated the phosphorylation of the Mr 95,000 subunit of the receptor in lectin-purified membrane proteins from liver and placenta. In liver receptor preparations, beta NF treatment was associated with a nearly 3-fold increase in the insulin-stimulated phosphorylation of the 95-kD protein. In contrast, placental receptor preparations showed a 40% decrease in the extent of autophosphorylation following beta NF treatment. Insulin-stimulated phosphorylation of an exogenous substrate poly(Glu4, Tyr) also showed a divergent pattern of changes in liver and placental receptors following beta NF treatment. In studies during late gestation (day 18), beta NF treatment was also associated with an increase in liver receptor kinase activity, whereas placental receptors showed a decrease in autophosphorylation. Thus, acute treatment with beta NF during mid and late gestation was associated with significant alterations in insulin receptor protein kinase activity, and data suggest that fetal insulin receptors may respond in a different manner than maternal receptors to polyaromatic compounds like beta NF. The observed effects of beta NF on liver and placental receptor kinase activity may be related to alterations in insulin function in the regulation of pregnancy and fetoplacental growth.

Ontogeny of insulin receptors in the rat hemochorial placenta

Binding of 125I-insulin to rat placental membranes was time and protein concentration dependent, reversible, and specific. Unlabeled porcine insulin competed for 125I-insulin binding with an IC50 of 65 nM, while IGF-I was much less potent with an IC50 of 2.12 mM. Specific binding of 125I-insulin decreased during the second half of gestation from Days 11 to 19. Scatchard analysis of the binding data for membranes prepared from Gestation Days 11 and 19 yielded typical curvilinear plots which showed a marked decrease in the number of binding sites in late gestation placenta. Beginning on Day 14, insulin binding was characterized with isolated labyrinth and basal zone portions of the hemochorial placenta. There was no evidence for differences in Kd values or the number of binding sites in these two functionally distinct portions of the rat placenta. Crosslinking of 125I-insulin followed by SDS-PAGE showed a single protein with a molecular weight of 130,000 from placental tissues on Gestation Days 11 and 19 and confirmed a gestational decrease in the number of insulin receptors. In solubilized, lectin-purified preparations from placenta and liver membranes, insulin stimulated the phosphorylation of a Mr 95,000 protein. 32P-incorporation into this 95,000 protein was stimulated fivefold by insulin in Day 11 placenta receptor, whereas no detectable 32P-incorporation was found in Day 19 placenta. Thus, while the alpha- and beta-subunits of insulin receptors in mid and late gestation placenta have molecular weights which are similar to receptors in maternal liver, data indicate the presence of a functional difference in insulin-stimulated kinase activities.

Metabolic and immune effects of dietary arginine supplementation after burn

The effect of supplemental dietary arginine on metabolism and immunity was studied in 36 burned guinea pigs (30% of total body surface area) with previously placed catheter gastrostomies. The animals were randomized into four groups. After an initial three-day adaptation period, all groups received continuous isonitrogenous, isocaloric (175 kcal [735 kJ]/kg/d), and isovolemic intragastric tube feedings until postburn day (PBD) 14. Groups A, B, C, and D received 0%, 1%, 2%, and 4%, respectively, of total energy intake as arginine given in the form of crystalline arginine hydrochloride with 22%, 21%, 20%, and 18%, respectively, of total energy as whey protein. The average body weight after burn decreased equally in all groups. Resting metabolic expenditure on PBD 6 was higher in groups B (151% +/- 6% of preburn) and C (156% +/- 7%) than in groups A (131% +/- 4%) and D (136% +/- 3%). Ear-thickness response to dinitrofluorobenzene challenge on PBD 12 showed the best response in group C. The mortality rates of groups A, B, C, and D were 56%, 29%, 22%, and 56%, respectively. This study suggests that oral dietary arginine supplementation up to 2% of energy intake may be beneficial after burn injury.

Formation of benzo[a]pyrene-DNA adducts by microsomal enzymes: comparison of maternal and fetal liver, fetal hematopoietic cells and placenta

The formation of benzo[a]pyrene (BP)-DNA adducts was studied in vitro in the presence of microsomes prepared from the isolated labyrinth zone of the rat placenta, the hematopoietic erythroblast cells of the fetal liver, the fetal liver, as well as the maternal liver. Pregnant rats received beta-naphthoflavone (beta NF; 15 mg/kg, i.p.) on day 17 gestation. One day later, placentae, fetal and maternal livers were obtained and hematopoietic erythroblast cells were separated from hepatocytes in the fetal livers. The respective microsomal fractions were incubated in the presence of calf thymus DNA, NADPH-regenerating system and [3H]BP (300 microCi) at 37 degrees C for 30 min. Following beta NF pretreatment, the levels of covalent binding (pmol/mg DNA/mg microsomal protein) for maternal liver, fetal liver, placenta and erythroblast cells were: 28.4, 2.4, 0.31 and 3.9, respectively, with the hematopoietic erythroblast cells being the most active among fetal tissue preparations. The extent of transplacental induction compared to control was greatest in the hematopoietic cells (18-fold) followed by fetal liver (16-fold) and labyrinth zone (5-fold). Further experiments characterized the BP-DNA adducts formed by induced microsomes. DNA was isolated, purified and digested sequentially with DNase I, snake venom phosphodiesterase type II and alkaline phosphatase type III. The deoxynucleoside-BP adducts were purified on a Sephadex LH-20 column and then separated on HPLC and the adducts were quantitated radiometrically. Seven distinct adducts were separated on HPLC and named A-G in order of elution. Adduct B was prominent in all preparations (22-55% total radioactivity). The adduct profile and retention time for peak B is similar to that reported for the adduct formed by microsomal activation of 9-hydroxy BP. Peak D constituted a major fraction (19%) in maternal liver profiles in comparison with the three fetal tissue preparations (8%). In subsequent experiments, peak D was shown to be derived from reaction of (+/-)7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) with DNA. Peak C was unique to erythroblast cell and labyrinth profiles, while peak G was specific for maternal liver and fetal liver profiles. These results demonstrate that fetal liver and its hematopoietic cells are significant sites of BP bioactivation which may contribute to the fetal toxicity of polyaromatic hydrocarbons.

Positional metabolism of benzo(a)pyrene in rat placenta and maternal liver. Comparison of induction effects

The biotransformation of [14C]benzo(a)pyrene (BP) was studied in vitro in the presence of microsomes prepared from isolated labyrinth and basal zone tissues of the rat placenta, as well as from maternal liver. Pregnant rats, day 14 of gestation, received beta-naphthoflavone (beta NF; 15 mg/kg, ip) or 3-methyl-cholanthrene (3MC; 30 mg/kg, ip). On day 15, placentae were dissected and microsomes were incubated with 17 microM [14C]BP and 2 mM NADPH. Metabolites formed in the incubation flasks were extracted and separated by HPLC utilizing a reverse phase column. Only trace BP metabolism occurred in basal zone microsomes from control, beta NF-, or 3MC-pretreated animals, as well as in labyrinth microsomes from control animals. In contrast, the preadministration of beta NF and 3MC increased labyrinth microsomal BP metabolism by 10- to 15-fold. Labyrinth and maternal liver microsomes from beta NF- and 3MC-treated animals actively converted BP to eight separate metabolites which co-chromatographed primarily with quinones and phenols. The overall formation of BP diol and phenolic metabolites by labyrinth microsomes was appreciably less than was observed for liver preparations. The very low activity of BP-4,5-oxide hydrolase in labyrinth microsomes compared to liver may in part explain the low level of formation of BP diols in placental microsomes. Labyrinth microsomes catalyzed the covalent binding of [3H]BP to calf thymus DNA, and this activity increased 5-fold following beta NF pretreatment. A comparison of induced tissues indicates that the amount of DNA binding in labyrinth microsomes is more extensive than would be expected by the level of total BP metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and identification of rat hepatic cytosolic enzymes responsible for defluorination of methoxyflurane and fluoroacetate

Enzymes responsible for the defluorination of methoxyflurane (MOF) and fluoroacetate (FAc) were separated and purified from rat liver cytosol. Both hepatic cytosolic enzymes with defluorination activity were labile and addition of 2-mercaptoethanol had little effect on the stability of these enzymes. Glutathione S-transferase (GT) activity of the same cytosolic fractions was stable for at least 11 days. Separation of defluorination and GT enzymatic activities on DEAE-Sephadex A-50 and reduced glutathione-affinity columns revealed that the defluorinations of MOF and FAc were primarily catalyzed by anionic proteins which also exhibited GT activity. Further identification by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed protein bands with pl values of approximately 6.5 and 6.9 and molecular weights of approximately 20,000. However, other proteins that exhibited no GT activity also defluorinated MOF and FAc, but accounted for only 10% of the total defluorination activity present in anionic proteins. Results from a separate purification experiment using a CM-cellulose column also indicated that the enzymes responsible for defluorination coeluted with cationic GTs. Collectively, these cationic enzymes were responsible for about 20% of the recovered cytosolic defluorination activities. The results suggest that the cytosolic defluorinations of both MOF and FAc are primarily the result of a dehalogenation reaction catalyzed by one or more species of rat liver cytosolic GTs.

The effect of the thromboxane synthetase inhibitor Dazmegrel (UK-38,485) on wound healing, dermal ink perfusion and skin blood flow measurements in deep partial thickness burns

A guinea-pig model was used to evaluate the effect of Dazmegrel (UK-38,485), a new highly selective inhibitor of thromboxane synthetase, on burn wound healing. Dazmegrel had a beneficial effect on wound healing when given systemically at a dosage of 3.4 mg kg-1 day-1 but higher doses had no effect. There was no change in dermal perfusion measured by India ink injection or by 133Xe injection in any of the groups receiving parenteral Dazmegrel. Neither was the number of hair follicles in the healing burn wound significantly different between the treated and control animals. When Dazmegrel was applied topically, it inhibited wound healing. These findings are consistent with previous reports from different laboratories that prostaglandin inhibitors impair healing of the burn wound when applied topically but improve wound healing when given parenterally. The present study further suggested that the improvement in wound healing in this model was not mediated by improved dermal perfusion.

Effect of Dazmegrel (UK-38,485) on immune function in a burned guinea-pig model

We investigated the effects of Dazmegrel, a highly effective and selective thromboxane synthetase inhibitor, on the immune system in a bilateral 5 per cent total body surface area (TBSA) deep partial thickness scald in a guinea-pig model. The animals were randomized into two groups: one received Dazmegrel at 3.4 mg kg-1 day-1 by i.m. injection; the other received the same volume of saline. Cell-mediated immunity was evaluated by the response to the hapten dinitrofluorobenzene (DNFB), as measured by ear swelling in response to cutaneous application. The ear swelling of the Dazmegrel-treated group was 52.8 +/- 3.8 per cent, compared to 41.4 +/- 2.4 per cent for the control group (P less than 0.02). Neutrophil bactericidal function was determined on post-burn day (PBD) 7 and opsonic function on both post-burns days 7 and 22. The serum opsonic indices were nearly identical at both times, but the Dazmegrel-treated animals had a significantly improved neutrophil bactericidal index (1.15 +/- 0.05 v. 1.68 +/- 0.17, P less than 0.01). Dazmegrel exerted a stimulating effect on the immune system in this burn model, improving neutrophil antibacterial function and cell-mediated immunity.

Renal responses to atrial natriuretic factor during converting enzyme inhibition

The effect of converting enzyme inhibitor (CEI) on the renal response to atrial natriuretic factor (ANF) was determined in the rat. In the absence of CEI, ANF produced rapid and significant increases in sodium, potassium, calcium, and urine excretions while blood pressure declined transiently. In the presence of CEI, ANF enhanced the excretion of sodium and potassium but not of calcium and urine. The activity of CEI was documented by observing that, in the presence of CEI, the elevation of blood pressure produced by angiotensin I was significantly attenuated. The potentiating effect of CEI on the natriuretic response to ANF supports the hypothesis that converting enzyme may be involved in the metabolism of ANF.