PubMed Health⌕ Search

Biomedical subjects

M M Jacobs

Publications and source records attributed to M M Jacobs.

At least 19 recordsLinked to original sources
PubMed1991

Differentiation of type II cells during explant culture of human fetal lung is accelerated by endogenous prostanoids and adenosine 3',5'-monophosphate.

Explant culture of the fetal lung, in the absence of serum or hormones, results in precocious biochemical and morphological differentiation of alveolar epithelial cells. In this study we tested the hypothesis that these maturational events are induced by endogenous cAMP. During culture of human fetal lung the content of tissue cAMP increased 140% from days 3-6. Treatment with isobutylmethylxanthine caused a further doubling of cAMP content, and indomethacin blocked most of the increase in cAMP. Isobutylmethylxanthine accelerated and indomethacin inhibited the increases during culture in surfactant protein-A (SP-A), SP-A mRNA, SP-B mRNA, phosphatidylcholine content, and activity of fatty acid synthetase. There was no effect of these treatments on the content of SP-C mRNA, which did not increase during culture. Increasing concentrations of prostaglandins E1 and E2 in the presence of indomethacin produced a parallel stimulation of cAMP content, SP-A, and fatty acid synthetase activity. The temporal increase in SP-A was also blocked by inhibitors of protein kinase-A. In morphological studies, indomethacin-treated explants appeared less mature, with decreased intralumenal volume and more columnar epithelial cells. We conclude that increased tissue cAMP levels, stimulated by endogenous prostaglandins, accelerate differentiation of alveolar epithelial cells during explant culture.

1-Methyl-3-isobutylxanthine↗
PubMed1990

Simultaneous preparation of paired, syncytial, microvillous and basal membranes from human placenta.

A method for the simultaneous preparation of microvillous and basal membrane vesicles from human placental syncytiotrophoblast is described. Mg2(+)-aggregated basal membranes are separated from microvillous membranes by low-speed centrifugation after initial homogenization and centrifugation steps. Microvillous membranes (MVM) are obtained from the low speed supernatant while basal membranes (BM) contained in the Mg2(+)-aggregated material are resuspended and further purified on a sucrose step gradient. MVM and BM prepared by this method were enriched 20-fold and 11-fold as determined by the membrane marker enzymes, alkaline phosphatase (MVM) and adenylate cyclase (BM). There was minimal cross-contamination of the two isolated plasma membrane fractions and the yields obtained were 26% (MVM) and 21% (BM) compared to the initial homogenate. The MVM and BM fractions were free from contamination by mitochondrial or lysosomal membranes and showed only minor contamination by microsomal membranes. The two membrane fractions were also tested for the presence of non-syncytial plasma membranes by electrophoretic immunoblotting. Contamination of both MVM and BM by fibroblast, endothelial, macrophage and cytotrophoblast plasma membranes amounted to less than 15% of the total membrane protein as determined by immunoblotting. Vesicle orientation, determined from the latency of specific concanavalin A binding, was 88 +/- 4% right-side out for MVM and 73 +/- 12% right-side out for BM. This simple preparative procedure produces a high yield of both MVM and BM from human placenta. The analytical data demonstrates that 'paired' MVM and BM fractions derived from the same placental tissue have a high purity in terms not only of contamination by intracellular membranes, but also in terms of contamination by non-syncytial plasma membranes.

Alkaline Phosphatase↗
PubMed1990

Control of the sodium-proton antiporter in human placental microvillous membranes by transport substrates.

The microvillous membrane of the human placental syncytiotrophoblast contains an amiloride-inhibitable, electroneutral, Na+/H+ antiporter. The kinetic characteristics of this antiporter have been investigated to determine its response to alterations in intracellular and extracellular H+ and Na+ concentrations. Antiporter activity was measured using a pH-sensitive fluorescent probe entrapped in placental microvillous vesicles. We report here on the kinetic characterization of the antiporter, a transporter which displays simple, saturable kinetics for the external site but complex kinetics at the internal site. Measurement of the external Na+ and H+ dependences demonstrated that Na+ and H+ compete for binding to a single external binding site which displays saturation kinetics. The external Km determined for Na+ was 8.2 +/- 4.0 mM, while the external pK was 7.29 +/- 0.02. The Vmax calculated from these experiments was 0.57 +/- 0.10 nequiv./s per mg membrane protein. By contrast, the internal dependences for both Na+ and H+ showed significant deviations from simple linear kinetics. Decreasing internal pH to 6.0 stimulated Na+/H+ exchange to a greater degree than predicted for a single-site saturable binding model, in a manner which suggested allosteric activation. At the other extreme, Na+/H+ exchange ceased above an internal pH of 7.1, despite the existence of an inwardly-directed Na+ gradient. Increasing intracellular Na+ caused inhibition of Na+/H+ exchange but the intracellular Na+ dependence showed that the effect is due to a mechanism more complex than simple, competitive inhibition between Na+ and H+. These results show that the microvillous Na+/H+ antiporter is insensitive to changes in extracellular Na+ and H+ concentrations in the physiological range. Changes in intracellular Na+ and H+ however are likely to cause marked changes in antiporter activity. These characteristics suggest that cellular Na+ and H+ concentrations are tightly controlled in the placental syncytiotrophoblast and that the Na+/H+ antiporter may play a significant role in their regulation.

Amiloride↗
PubMed1990

Potassium inhibition of DMH-induced small intestinal tumors in rats.

This is a preliminary report that shows that supplemental potassium partially prevents 1,2-dimethylhydrazine (DMH) induction of tumors of the small intestine in Sprague-Dawley rats. Male rats were injected weekly with 20 mg DMH/kg body wt for 20 weeks. Potassium chloride was provided in the drinking water one week before the first DMH treatment and was continued until sacrifice 14 weeks after the last DMH treatment. There were four groups of rats and they were identified as follows: DMH, DMH + K, K, and untreated control. Based on 24-hour food and water consumption data and food and water compositions, rats provided 0.5% potassium (from KCl in the drinking water) were ingesting 287.5 +/- 9.2 mg potassium per 24 hours (K/Na = 4.18) and the unsupplemented groups were ingesting 180.3 +/- 18.4 mg potassium per 24 hours (K/Na = 2.62). At sacrifice, the incidence of DMH-induced small intestinal tumors was significantly (p less than 0.05) reduced from 46% (6/13) in the DMH group to 6% (1/17) in the DMH + K group (p less than 0.05). The potassium supplement also significantly (p less than 0.05) reduced the cumulative small intestinal tumor incidence from 40% (8/20) in the DMH group to 5% (1/20) in the DMH + K group. The incidence of colon tumors and of zymbal gland tumors appeared to be reduced by the potassium supplement; however, these were not statistically significant observations (p greater than 0.05). Based on the complete blood count and other blood parameters measured, the level of potassium supplement used induced no apparent toxic effects.(ABSTRACT TRUNCATED AT 250 WORDS)

1,2-Dimethylhydrazine↗
PubMed1990

Metabolism of the potent carcinogen 3-methylcholanthrylene by rat liver microsomes.

The products formed in the metabolism of 3-methylcholanthrylene (3MCE), either in the presence or in the absence of an epoxide hydrolase inhibitor, 3,3,3-trichloropropylene 1,2-oxide (TCPO), with an NADPH-regenerating system and liver microsomes from 3-methylcholanthrene (3MC)-treated male Sprague-Dawley rats were separated by reversed-phase and normal-phase HPLC. The metabolites were characterized by UV-visible absorption spectral analysis, and by comparing their retention times on reversed-phase and normal-phase HPLC with authentic 3MC derivatives whenever available. In addition to 3MC trans-1,2-diol, 3MC-1-one, and 3MC-2-one reported earlier by other investigators, 3-hydroxymethylcholanthrylene (3-OHMCE), 3-OHMCE trans-11,12-dihydrodiol, 3MCE trans-11,12-dihydrodiol, 3MCE trans-9, 10-dihydrodiol. 9- and 10-hydroxy-3MCE. 3MC-2-one trans-9,10-dihydrodiol, and a chemically unstable 3MCE 1,2-epoxide were identified as metabolites of 3MCE. 3MC cis-1,2-diol, a previously reported metabolite of 3MCE, was not detectable. In the presence of TCPO, metabolites that have been identified include 3-OHMCE, 3-OHMCE 11,12-epoxide. 3MCE 11,12-epoxide, 3MC-2-one, 3MC-1-one, 9-hydroxy-3MCE, 10-hydroxy-3MCE, and an unstable metabolic intermediate 3MCE 1,2-epoxide. The results suggest that 3MCE 1,2-epoxide, 3MCE 9,10-diol-7,8-epoxide, and 3MC-2-one 9,10-diol-7,8-epoxide may be involved in the metabolic activation of 3MCE to carcinogenic form.

Animals↗
PubMed1990

Beta-adrenergic receptors and cAMP response increase during explant culture of human fetal lung: partial inhibition by dexamethasone.

We studied beta-adrenergic receptors and responses in human fetal lung (15-25 wk gestation) maintained in explant culture with and without added dexamethasone. To determine beta-adrenergic receptor concentration, we performed radioligand binding assays with [125I]-iodocyanopindolol. We also examined the ability of isoproterenol to stimulate cAMP generation as a measure of response to beta-adrenergic receptor occupancy. In control cultures, beta-receptor concentration increased significantly from d 0 to 3 of culture and thereafter remained stable. The kd (approximately 24 pM) of [125I]-iodocyanopindolol did not change with time in culture. The ability of isoproterenol to stimulate cAMP generation over basal levels increased in controls throughout the 5 d in explant culture. Addition of dexamethasone (10 nM) to the culture medium partially blocked the increase in beta-receptor concentration and decreased both cAMP content and generation (basal and stimulated) in a dose-dependent manner (median effective concentration approximately 1 nM). In these same explants, dexamethasone increased the activity of fatty acid synthetase, an enzyme important in surfactant synthesis, more than 2-fold. Our results indicate that beta-adrenergic receptors and isoproterenol stimulation of cAMP generation increase spontaneously in human fetal lung grown in explant culture. Dexamethasone, which accelerates other aspects of human lung development in vitro, decreases beta-adrenergic receptor concentration and inhibits beta-adrenergic responses.

Cyclic AMP↗
PubMed1989

Prevention, recognition, and treatment of perinatal asphyxia.

Management of perinatal asphyxia is one of those rare opportunities in clinical medicine when death or life-long disability can be prevented with several minutes of skillful and judicious action. Fetal and neonatal asphyxia is approached most successfully as a joint obstetric, pediatric, and anesthetic effort. This article reflects the team approach to perinatal asphyxia.

Asphyxia Neonatorum↗
PubMed1989

Ontogeny of fetal adenylate cyclase; mechanisms for regulation of beta-adrenergic receptors.

Transmembrane second messenger signalling systems regulate differentiation, growth and homeostatic responses during fetal development. The beta-adrenergic adenylate cyclase system is the best studied of these and has been used as a model to investigate the control of developmental processes. In tissues such as lung, heart and parotid, beta-adrenergic responsiveness of adenylate cyclase increases during development. In the developing fetal lung beta-receptor concentration increases during gestation or after glucocorticoid treatment, but cannot fully explain enhanced adrenergic responsiveness. To probe developmental and hormonal effects on beta-receptor function, we asked if advancing gestation or glucocorticoid treatment alters beta-receptor-Gs interactions in fetal rabbit lung membrane particulates. Before 25 days gestation, 1-isoproterenol competes for 3H-dihydroalprenolol (DHA), a radiolabelled beta-antagonist, with a single low affinity, later in gestation, high and low affinities of isoproterenol for the beta-receptor are present which can be shifted to the lower affinity by addition of guanyl nucleotide. High affinity binding is precociously induced in 25 days--fetal lung particulates as early as 3 h after maternal betamethasone treatment, but beta-adrenoreceptor concentration in treated fetuses was increased over controls only after 24 h of treatment. Cholera toxin catalyzed ADP ribosylation of membrane particulates showed cholera toxin substrate (Gs) was not altered by glucocorticoid treatment. Stimulation of adenylate cyclase activity with isoproterenol (100mM) and GTP (100mM) resulted in no incremental increase over that produced by GTP (100mM) alone in glucocorticoid treated or control particulates, either early or late in gestation. These data demonstrate that beta-receptor-Gs interactions are not sufficient to produce full agonist responses. Although both beta-adrenergic receptors and Gs are present in fetal rabbit lung early in gestation, interaction of these two adenylate cyclase components appears subsequently. This developmental event can be rapidly induced by maternal betamethasone treatment.

Adenylyl Cyclases↗
PubMed1988

Estrogen reduces beta-adrenoceptor-mediated cAMP production and the concentration of the guanyl nucleotide-regulatory protein, Gs, in rabbit myometrium.

The uterine contractile response to adrenergic agonists or sympathetic stimulation is influenced dramatically by the hormonal milieu. Rabbit uterine contraction is mediated by alpha 1-adrenoceptors, whereas relaxation in response to the same stimulus is mediated by beta 2-adrenoceptors. Whether uterine contractility is increased or decreased by adrenergic stimulation is determined by the gonadal steroids estrogen and progesterone: uterine contraction prevails in the estrogen-dominant or the ovariectomized animal, but in the progesterone-dominant rabbit, uterine relaxation is observed. In previous studies, we have demonstrated that changes in the concentration or agonist affinity of these adrenoceptors cannot account for the changes in contractile response. In the present studies, we tested whether sex steroids might alter beta-adrenergic response by acting on events distal to receptor occupancy, and whether this could explain the conversion of contractile response. We found that myometrial cAMP generation is potently stimulated by beta-agonists in progesterone-treated and also in ovariectomized animals, but this stimulation is absent after estrogen treatment. Similar, but smaller, changes were observed for cAMP generation in response to prostaglandin E2 and forskolin. Stimulation of adenylate cyclase in uterine particulates by agents which act on the guanyl nucleotide-sensitive stimulatory transducer, Gs, is unchanged after estrogen treatment. However, specific labeling of Gs catalyzed by cholera toxin is reduced in membrane particulates from estrogen-treated animals. Recombination of extracts of uterine membranes from the differently treated animals also suggested qualitative differences in Gs. We conclude that at least one component of the adenylate cyclase cascade beyond the beta-adrenoceptor, i.e., Gs, is a target for ovarian steroids; estrogen reduces Gs labeling and beta-adrenoceptor-mediated cAMP production. However, uterine Gs labeling and cAMP production are similar in ovariectomized and in progesterone-treated rabbits. Since these uteri exhibit different contractile responses, the observed changes are not sufficient to explain sex steroid-mediated conversion of myometrial contractile response.

Adenosine Diphosphate Ribose↗
PubMed1988

Respiratory diseases in pregnancy.

Pregnant women with respiratory problems pose a special challenge. Pregnancy alters lung function and the natural history of common pulmonary disorders. Respiratory problems in pregnancy must be approached with an understanding of the unique, inter-dependent physiologic and psychological status of mother and fetus.

Asthma↗
PubMed1987

Selenium inhibition of benzo[a]pyrene, 3-methylcholanthrene, and 3-methylcholanthrylene mutagenicity in Salmonella typhimurium strains TA98 and TA100.

Selenium (Se) decreased the mutagenicity of benzo[a]pyrene (BP), 3-methylcholanthrene (3MC), and 3-methylcholanthrylene (3MCE) in Salmonella typhimurium strains TA98 and TA100. Metabolism of BP, 3MC and 3MCE to mutagens was accomplished with the liver S9 fraction from Aroclor 1254-treated male Sprague-Dawley rats. Exposure of the bacteria to 4 nmoles BP, 10 nmoles 3MC, or 10 nmoles 3MCE in the presence of S9, and up to 200 nmoles Se as Na2SeO3 resulted in decreased mutagenicities up to 39, 66 and 60% of their respective control activities without Se in TA98 and up to 46, 52 and 64% of their respective control activities without Se in TA100. Se (200 nmoles) alone was not mutagenic in strains TA98 or TA100 with or without S9. BP, 3MC and 3MCE were not mutagenic in either strain without S9. None of the tested concentrations of BP, 3MC, 3MCE and Se were cytotoxic. Assays of the aryl hydrocarbon hydroxylase (AHH) activity in the S9 preparation revealed decreased AHH activity with increase in Se concentration. The decreased mutagenicity and AHH activity were Se (as Na2SeO3) dependent and could not be duplicated by sulfur (S as Na2SO3). Inhibition of AHH activity by Se provides an explanation of the mechanism of Se inhibition of BP, 3MC and 3MCE mutagenicities in S. typhimurium TA98 and TA100.

Animals↗
PubMed1985

Human myometrial adrenergic receptors during pregnancy: identification of the alpha-adrenergic receptor by [3H] dihydroergocryptine binding.

The radioactive alpha-adrenergic antagonist [3H] dihydroergocryptine binds to particulate preparations of term pregnant human myometrium in a manner compatible with binding to the alpha-adrenergic receptor (alpha-receptor). [3H] Dihydroergocryptine binds with high affinity (KD = 2 nmol/L and low capacity (receptor concentration = 100 fmol/mg of protein). Adrenergic agonists compete for [3H] dihydroergocryptine binding sites stereo-selectively ([-]-norepinephrine is 100 times as potent as [+]-norepinephrine) and in a manner compatible with alpha-adrenergic potencies (epinephrine approximately equal to norepinephrine much greater than isoproterenol). Studies in which prazosin, an alpha 1-antagonist, and yohimbine, and alpha 2-antagonist, competed for [3H] dihydroergocryptine binding sites in human myometrium indicated that approximately 70% are alpha 2-receptors and that 30% are alpha 1-receptors. [3H] dihydroergocryptine binding to human myometrial membrane particulate provides an important tool with which to study the molecular mechanisms of uterine alpha-adrenergic response.

Dihydroergotoxine↗
PubMed1979

Selenium effects on the carcinogenicity and metabolism of 2-acetylaminofluorene.

Addition of 4 ppm Se to the drinking water of male albino rats fed diets containing 0.03% 2-acetylaminofluorene (AAF) provided protection against hepatic damage and also resulted in at least 50% reduction in liver tumor incidence. An in vitro assay system utilizing microsomes from Se supplemented or non-supplemented 3-methylcholanthrene (MC) induced rats was used to determine the effect of oral Se intake on the metabolism of AAF. Oral Se administration led to an increase in ring hydroxylation and a decrease in N-hydroxylation. Addition of Se to the microsomal assay system increased 3-OH AAF formation and decreased N-OH AAF formation, thus shifting the balance of metabolism toward detoxification pathways.

2-Acetylaminofluorene↗
PubMed1978

Effect of sodium selenite and methyl methanesulfonate or N-hydroxy-2-acetylaminofluorene co-exposure on sister-chromatid exchange production in human whole blood cultures.

Sodium selenite (Na2SeO3) was tested for its sister-chromatid exchange (SCE)-inducing ability in human whole blood cultures and for the effect of its co-exposure with methyl methanesulfonate (MMS) or N-hydroxy-2-acetylaminofluorene (N-OH-AAF) on SCE frequency. Long exposure times (77 h and 96 h) to 3.95 X 10(-6) M Na2SeO3 resulted in cell death as measured by mitotic indices, but mitotic figures were present after exposure to higher concentrations for a shorter time (19 h). High Na2SeO3 concentrations (7.90 X 10(-6) and 1.19 X 10(-5) M) resulted in a three-fold increase in the SCE frequency above background level (6--7 SCEs/cell). Exposure of lymphocytes to 1 X 10(-4) M MMS for the last 19 h of culture yielded an average SCE frequency of 30.17 +/- 0.75 while a similar exposure to 2.7 X 10(-5) M N-OH-AAF resulted in 13.61 +/- 0.43 SCEs/cell. Simultaneous addition of the high Na2SeO3 concentrations and MMS or N-OH-AAF to the cultures resulted in SCE frequencies that were 25--30% and 11--17%, respectively, below the sum of the SCE frequencies produced by the individual compounds.

Cell Survival↗
PubMed1978

Studies on ovarian and uterine weight responses to follicle stimulating hormone.

A uterine weight response may potentially provide a plausible qualitative method for detection of "asialo" follicle stimulating hormone (FSH). Asialo FSH is a biologically inert species of FSH when assayed for ovarian weight response by the hCG augmentation method. Numerous experiments have been performed under a uniform set of conditions for normalization of ovarian and uterine weight responses. The influence of several hormones and 2 injection routes on the gonadal responses to FSH have been assessed. Immature female, 24--25 day old Sprague-Dawley rats were injected subcutaneously (sc) or intraperitoneally (ip) twice daily for 3 days. On the 4th day the rats were sacrificed, the ovaries and uterus were removed, cleaned and weighed. Uterine weights were obtained before and after removal of the fluid. NIH-FSH-S9 and its asialo derivative prepared by neuraminidase digestion were the species of follicle-stimulating hormone (FSH) used in all experiments. Addition of either 21 IU prolactin or 0.05 mg histone to FSH did not significantly alter the ovarian weight response augmented by hCG (P = 0.2). Addition of histone to 90 and 180 microgram FSH elicited neither a uterine weight response when injected sc nor an ovarian weight change when injected ip. Both routes of injection of the 2 dose levels of FSH had little effect on the uterine weight. In marked contrast, 90 and 180 microgram asialo FSH injected either sc or ip gave increased uterine weight responses in the presence of hCG. On further examination the uterine weight increase in response to asialo FSH injections proved to be statistically significant (sc. P = 0.02; ip, P = 0.05). Use of the uterine weight response might be exclusively proposed as a qualitative method for detecting asialo FSH. Such biologically inactive species, which elicit no increased ovarian weight response in the hCG augmentation assay, are frequently generated in the preparation of FSH. Determination of the uterine weights may provide meaningful use of auxiliary data from the hCG ovarian augmentation assay of putative FSH preparations which fail to elicit the desired ovarian weight responses.

Animals↗
PubMed1977

Inhibitory effects of selenium on 1,2-dimethylhydrazine and methylazoxymethanol colon carcinogenesis: correlative studies on selenium effects on the mutagenicity and sister chromatid exchange rates of selected carcinogens.

Selenium (Se) inhibition of either the activation of test compounds and/or mutagenic events elicited by activated compounds is suggested by experimental rat assays, mutagenesis assays, and assays with human lymphocytes in culture. The colon tumor incidence in 1,2-dimethylhydrazine (DMH)-treated rats was reduced from 87% to 40% by 4 ppm Se supplements in the drinking water. Supplemental Se decreased the total number of colon tumors induced by DMH more than three-fold and by methylazoxymethanol (MAM) almost two-fold. Coexposure of Salmonella typhimurium TA 1538 to an effective molar ratio of Se/2-acetylaminofluorene=10, Se/N-OH-acetylaminofluorene=10 and SE/N-OH-aminofluorene=300 reduced the mutagenicity to 65, 68, and 61% of their respective controls with mutagen alone. With a molar ratio of Se/N-OH-AAF=100, Se reduced the activity to 28% of the mutagenicity of N-OH-AAF alone. Preliminary data indicating MAM is mutagenic in S. typhimurium TA 1535 and His G 46(6837) are presented. In toxicity studies exposure of human lymphocyte cultures to 1.3 X 10(-9) to 1.6 X 10(-5) M Se yielded sister chromatid exchange (SCE) rates equivalent to background levels of 6--7 SCE per cell. The SCE frequencies of lymphocytes cultured with Se and selected carcinogens are discussed.

Animals↗