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M Poth

Publications and source records attributed to M Poth.

At least 19 recordsLinked to original sources
PubMed2001

Nitrate in polluted mountainous catchments with Mediterranean climates.

The mountains of southern California receive some of the highest rates of nitrogen (N) deposition in the world (approximately 40 kg ha(-1) year(-1)). These high rates of deposition have translated into consistently high levels of nitrate (NO3-) in some streams of the San Bernardino Mountains. However, not all streams are exhibiting these high levels of NO3-. Perennial streams have high NO3- concentrations (approximately 200 micromoles l(-1)) while ephemeral streams do not (approximately 20 micromoles l(-1)). This difference points to groundwater as the source of the NO3- observed in streams. Furthermore, the evidence indicates a differential impact of N deposition on terrestrial and aquatic systems in Mediterranean climates, with aquatic systems being impacted more quickly. The primary reason for this difference involves the asynchrony between the time that atmospheric deposition occurs (summer), the time period of maximum soil NO3- availability and leaching (winter), and the time of maximum plant N demand (spring). Our results indicate that semiarid Mediterranean climate systems behave differently from more humid systems in that, because of this asynchrony, aquatic systems may not be indicative of changes in terrestrial ecosystem response. These differences lead us to the conclusion that the extrapolation of impacts from humid to Mediterranean climates is problematic and the concept of N saturation may need to be revisited for semiarid and seasonally dry systems.

Climate↗
PubMed2000

Endocrine response to high-intensity exercise: dose-dependent effects of dexamethasone.

We recently reported that in 30-50% of healthy men and women the release of ACTH and cortisol stimulated by exercise is not suppressed by prior administration of a 4-mg dose of dexamethasone (DEX). We now explore other potential differences between these subjects and those whose exercise response was suppressed by examining the effect of a smaller, 1-mg, dose of DEX on exercise-stimulated ACTH and cortisol. Men (n = 15) and women (n = 9) were studied during three high intensity exercise tests: one after taking placebo, one after taking 1 mg DEX, and one after taking 4 mg DEX. Before participation, subjects underwent a test for classification as either a high (HR; n = 10) or low (LR; n = 14) reactor and a maximal exercise test to assess maximal aerobic capacity. Distinct dose-related reductions in plasma concentrations of ACTH, cortisol, and dehydroepiandrosterone (DHEA) were noted for HR under the treatment conditions, whereas both doses of DEX blocked ACTH, cortisol, and DHEA release in LR. Furthermore, basal plasma cortisol, DHEA, and DHEA sulfate were significantly higher in HR compared to LR. Thus, there are inherent basal and stress-reactive differences in HR and LR, and these differences may be useful in constructing a model for the mechanisms and physiological regulation of hypothalamic-pituitary-adrenal axis activation. The question of whether these differences in reactivity of the ACTH-cortisol axis between the HR and LR groups have implications for individual short term function or long term health remains to be answered.

Adrenocorticotropic Hormone↗
PubMed1995

Evidence to suggest nitric oxide is an interstitial regulator of Leydig cell steroidogenesis.

Recent studies have suggested that nitric oxide (NO) may function as both an intracellular and intercellular signal that affects neural and immunological activity, vascular tone, platelet adhesion, and production of some hormones. Arginine analogs such as NG-monomethyl-L-arginine (L-NMMA) and N omega-nitro-L-arginine methyl ester (L-NAME) act to inhibit the intracellular formation of NO and have been used to study the effects of decreased NO formation on physiological systems. A single in vivo study has suggested that a similar analog, NG-nitro-L-arginine, increases serum testosterone (T), but the organ site and mechanism of action were not investigated. The present study was performed to investigate the effects of NO synthase inhibitors on Leydig cell function. L-NMMA and L-NAME, but not the inactive enantiomer (D-NMMA), increased both basal and human chorionic gonadotropin (hCG)-stimulated T production while decreasing guanosine 3':5'-cyclic monophosphate (cGMP). There was no effect on either adenosine 3':5'-cyclic monophosphate (cAMP) accumulation or specific hCG binding. These results suggest that NO formation, which is inhibited by L-NMMA and L-NAME, is important in the regulation of Leydig cell T production by interstitial cells of the testis, and that changes in cGMP levels might be involved in this process.

Animals↗
PubMed1995

Growth response of bigcone Douglas fir (Pseudotsuga macrocarpa) to long-term ozone exposure in southern California.

Long-term radial growth of bigcone Douglas fir (Pseudotsuga macrocarpa) was studied throughout its range in the San Bernardino Mountains of southern California, where ambient ozone has been high for approximately the past 40 years. A gradient of both ozone concentration and precipitation exists from west (high) to east (low). Growth rates of bigcone Douglas fir are considerably lower since 1950 throughout the San Bernardino Mountains, with the largest growth reductions in the western part of the range where ozone exposure is highest. Needle retention is also somewhat lower at high ozone sites. Lower annual precipitation since 1950 may have some impact on long-term growth reductions, and short-term growth reductions induced by drought are an important component of long-term growth reductions at sites with high ozone exposure. An ozone-climate stress complex may be responsible for recent reductions in the growth of bigcone Douglas fir.

Air Pollutants↗
PubMed1995

Hormone-containing cosmetics may cause signs of early sexual development.

Exogenous hormone exposure can cause early sexual development, but only one report suggests that this may occur secondary to the use of hair-care products. This study evaluated the usage frequency and biological effects of hormone-containing hair-care products. We reviewed the records of 102 consecutive dependent children referred for evaluation of sexual precocity. Eight children (7.8%) were using these products. All eight were black (100%), compared to 57 (61%) of the 94 patients not using such products (p < 0.05). There was no significant difference between these two groups in mean age, sex distribution, height, height standard deviation score, bone age:chronologic age ratio, or serum estradiol level. We conclude that exposure to hormones in hair-care products may be more frequent than expected and should be considered in the differential diagnosis of early sexual development in children.

Child↗
PubMed1993

The effects of dorsal raphe administration of eltoprazine, TFMPP and 8-OH-DPAT on resident intruder aggression in the rat.

To evaluate the role of somatodendritic 5-HT1A receptors in the mediation of aggressive behaviour, eltoprazine, TFMPP (1-(3-trifluoromethylphenyl)piperazine hydrochloride) and 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin) were administered locally into the dorsal raphe nucleus of rats. 8-OH-DPAT (1 and 10 micrograms) and eltoprazine (10 and 30 micrograms) reduced aggression, but concomitantly reduced social interest and increased inactivity. TFMPP (1 and 10 micrograms) did not reduce aggression. As 8-OH-DPAT and to a lesser extent eltoprazine affect 5-HT1A receptors, it is proposed that a general reduction of serotonergic neurotransmission by activation of somatodendritic serotonergic autoreceptor leads to a non-specific reduction of aggression. As TFMPP has a significantly lower affinity for 5-HT1A receptors than 8-OH-DPAT or eltoprazine, the lack of effect of TFMPP supports this view.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1993

Effects of somatostatin and captopril on glomerular prostaglandin E2 production in normal and diabetic rats.

Somatostatin (SRIH) has recently been shown to be effective in reversing many of the early changes of diabetic nephropathy. It is unknown whether SRIH exerts its protective effects via its ability to suppress growth hormone (GH) or via other direct renal effects. Since changes in glomerular prostaglandin (PG) E2 production are thought to be an important part of the underlying pathophysiology of diabetic nephropathy, we sought to determine if SRIH altered glomerular PG E2 production in the rat. Whole glomeruli isolated from streptozotocin-diabetic rats and from controls were incubated with either saline, captopril, or varying concentrations of SRIH, and PG E2 production was determined by direct radioimmunoassay of media. Incubation with captopril (10(-4) M) resulted in equivalent increases in PG E2 production in glomeruli from both control and diabetic rats (140.8 +/- 12.8% and 150.2 +/- 18.9% respectively). Incubation with high concentrations of SRIH (10(-6) M) also resulted in significant increases in glomerular PG E2 production in both diabetic and control rats. However, at low SRIH concentrations (10(-10) M), glomerular PG E2 production was increased only in the diabetic rats (167.0 +/- 11.4% vs 95.3 +/- 9.2% in normals). We conclude that SRIH increases glomerular PG E2 production, and that glomeruli from diabetic rats appear to be more sensitive to lower concentrations of SRIH when compared to normal rats. It is possible that this effect on PG E2 production may underlie the favorable effects of SRIH on the glomerulus in diabetes.

Animals↗
PubMed1993

A comparison of NO and N2O production by the autotrophic nitrifier Nitrosomonas europaea and the heterotrophic nitrifier Alcaligenes faecalis.

Soil microorganisms are important sources of the nitrogen trace gases NO and N2O for the atmosphere. Present evidence suggests that autotrophic nitrifiers such as Nitrosomonas europaea are the primary producers of NO and N2O in aerobic soils, whereas denitrifiers such as Pseudomonas spp. or Alcaligenes spp. are responsible for most of the NO and N2O emissions from anaerobic soils. It has been shown that Alcaligenes faecalis, a bacterium common in both soil and water, is capable of concomitant heterotrophic nitrification and denitrification. This study was undertaken to determine whether heterotrophic nitrification might be as important a source of NO and N2O as autotrophic nitrification. We compared the responses of N. europaea and A. faecalis to changes in partial O2 pressure (pO2) and to the presence of typical nitrification inhibitors. Maximal production of NO and N2O occurred at low pO2 values in cultures of both N. europaea (pO2, 0.3 kPa) and A. faecalis (pO2, 2 to 4 kPa). With N. europaea most of the NH4+ oxidized was converted to NO2-, with NO and N2O accounting for 2.6 and 1% of the end product, respectively. With A. faecalis maximal production of NO occurred at a pO2 of 2 kPa, and maximal production of N2O occurred at a pO2 of 4 kPa. At these low pO2 values there was net nitrite consumption. Aerobically, A. faecalis produced approximately the same amount of NO but 10-fold more N2O per cell than N. europaea did. Typical nitrification inhibitors were far less effective for reducing emissions of NO and N2O by A. faecalis than for reducing emissions of NO and N2O by N. europaea.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerobiosis↗
PubMed1992

The effects of intraventricular administration of eltoprazine, 1-(3-trifluoromethylphenyl)piperazine hydrochloride and 8-hydroxy-2-(di-n-propylamino)tetralin on resident intruder aggression in the rat.

Various serotonergic agents may reduce aggression in rats, but how they act in different parts of the brain is unknown. This study attempted to unravel part of this question by application of different serotonergic ligands into the lateral ventricle (i.c.v.) of male rats (resident-intruder aggression). 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin; 1 and 10 micrograms), a specific 5-HT1A agonist, affected neither aggression nor any other behaviour. The mixed 5-HT1A,B,C agonist, TFMPP (1-(3-trifluoromethylphenyl)piperazine hydrochloride), and the 5-HT1A/1B agonist, eltoprazine ((1-(2,3)-dihydro-1,4-benzodioxin-5-yl)piperazine hydrochloride), suppressed aggression at i.c.v. doses of 10 and 30 micrograms. This reduction was not caused by sedation. These data suggest a role of postsynaptic 5-HT1B receptors in mediating the anti-aggressive effects of mixed 5-HT1 agonists.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1991

Inhibition of TSH activation of human cultured thyroid cells by tumor necrosis factor: an explanation for decreased thyroid function in systemic illness?

Thyroidal economy in systemic nonthyroidal illness (the sick euthyroid syndrome) is marked by reductions in both thyroid function and peripheral T4 to T3 conversion, presumed to reflect a homeostatic mechanism to conserve energy. TSH levels tend to be normal in these patients, and the mechanism underlying reduced thyroidal secretion is unknown. Since increased blood levels of tumor necrosis factor (TNF) are found in many of the conditions associated with the sick euthyroid syndrome, we hypothesized that TNF might affect the function of the thyroid gland. We, therefore, explored the effects of TNF on TSH stimulation of the thyroid, employing a human thyrocyte cell culture model. Cells were incubated with various concentrations (0-1000 pg/mL) of recombinant human TNF-alpha and bTSH (1 mU/mL), with measurement of secreted thyroglobulin (Tg) and cyclic AMP (cAMP) as the end points of stimulation. TNF had no effect on either basal or TSH-stimulated cAMP generation, but significantly blunted TSH-stimulated Tg secretion. No loss of cell viability and growth was observed based on trypan blue exclusion and thymidine incorporation by cells. These studies demonstrated an inhibitory effect on TNF on human thyrocytes in concentrations comparable to blood levels seen in humans during systemic illness. We conclude that increases in serum TNF may be responsible for reduced thyroid function in patients with the sick euthyroid syndrome.

Cyclic AMP↗
PubMed1991

Dehydroepiandrosterone antagonizes the suppressive effects of dexamethasone on lymphocyte proliferation.

Administration of dehydroepiandrosterone (DHEA) appears to have physiological effects opposing those of glucocorticoids in several animal models. Recently, immunomodulatory effects of treatment with DHEA have been described. This paper reports the effects of DHEA treatment on splenocyte blastogenic responses as well as thymic and spleen weights in C3H/HeN mice. Pretreatment of mice with sc DHEA (60 mg/kg.day) for 3 days in vivo antagonized the profound suppression of in vitro blastogenic responses seen in T- and B-lymphocytes after a single injection of dexamethasone (DEX; 60 mg/kg). Pretreatment with DHEA also significantly reduced dexamethasone-induced thymic and splenic atrophy. Splenic lymphocytes from DHEA-treated mice were markedly more resistant to in in vitro suppression of blastogenesis by DEX at 10(-6)-10(-8) M compared to lymphocytes from control mice. However, DHEA added to lymphocyte cultures in vitro over a concentration range from 10(-7)-10(-8) M failed to protect against suppression of mitogenic responses caused by addition of DEX to cultures. In summary, DHEA given in vivo antagonizes the suppressive actions of DEX on lymphoid target tissues in mice.

Animals↗
PubMed1990

Protection from glucocorticoid induced thymic involution by dehydroepiandrosterone.

Dehydroepiandrosterone (DHEA), the most abundantly secreted human adrenal steroid, has no known specific function. In spite of this fact there is an abundance of data associating DHEA with "health" in both man and experimental animals. Research in our laboratory has demonstrated evidence for an antagonistic interaction between DHEA and glucocorticoids (GC) in liver and brown adipose tissue. We hypothesized that DHEA also antagonized effects of GC on the immune system and that this "immune protective effect" might explain the diffuse positive effects of DHEA reported in the literature. Effects of GC on the immune system include involution of the thymus when given in animals in vivo and death of thymic lymphocytes in vivo with exposure to these steroids. We hypothesized that DHEA would block this GC mediated thymocyte destruction in vivo and in vitro. Pretreatment with DHEA for three days blocked approximately 50% of the thymic involution seen with dexamethasone. Results of in vitro experiments confirmed protective effects of DHEA in pretreated animals. (less than 50% of cell death in lymphocytes from pretreated mice compared with lymphocytes from control mice.) We conclude from these studies that DHEA protects against at least one GC anti-immune effect, thymic lymphocyte lysis.

Animals↗
PubMed1990

Effects of photochemical smog and mineral nutrition on ponderosa pine seedlings.

Two-year-old seedlings of ponderosa pine (Pinus ponderosa Dougl. ex Laws) were exposed to ambient concentrations of photochemical smog (AA) and clean air (CA) during a single field season at Tanbark Flat of the San Gabriel Mountains in the Los Angeles Basin. The seedlings were grown in a perlite-vermiculite medium with full supply of nutrients (based on modified Hoagland solution); reduced to 50% supply of N; reduced to 50% supply of Mg; and reduced to 50% supply of N+Mg. No significant effects of air pollution exposures on injury development, stem growth and concentrations of plant pigments were determined. The seedlings in the AA treatment had decreased N concentration in current year needles compared with CA seedlings; however, the needle concentrations of other elements did not change. Reduction of N supply in the growing medium caused decreased N, P, Ca, K and chlorophyll a concentrations in needles. Stem growth of the seedlings with reduced N supply was significantly decreased as well. No changes in stem growth or chemical composition of plants with reduced Mg supply were noted. Reduction of supply of nutrients did not change responses of trees to the air pollution exposures.

Journal Article↗
PubMed1987

Determination of substituted indole derivatives by ion suppression-reverse-phase high-performance liquid chromatography.

A method for the separation of substituted indole derivatives has been developed by the use of ion suppression-reversed-phase high-performance liquid chromatography (IS-HPLC). Signal response, selectivity (alpha), retention times (tR), and capacity factors (k') were monitored by varying the mobile phase with respect to methanol composition and pH. Chromatographic parameters including tR, k', K (distribution coefficients), alpha, number of theoretical plates, height equivalent to theoretical plates, and column resolution were calculated and assessed in regard to the suitability of four stationary phases in the analysis of 20 substituted indole derivatives. This work has established the chromatographic foundation needed to analyze over 10 specific enzyme reactions involved in the microbial and plant metabolism of auxins. Quantitative studies on the stability of auxins were possible by employing IS chromatography (ISC). The application of the developed IS chromatographic technique was employed to detect indole-3-acetic acid derived from L-tryptophan in a fluorescent pseudomonad culture.

Chromatography, High Pressure Liquid↗
PubMed1987

Biosynthesis of Indole-3-Acetic Acid by the Pine Ectomycorrhizal Fungus Pisolithus tinctorius.

Previous work has indicated that anatomical and morphological changes (stunting and dichotomy) in roots of various conifers may be influenced by plant-growth-regulating substances secreted by mycorrhizae. Indole-3-acetic acid (IAA) has been tentatively identified as a major auxin produced by some selected ectomycorrhizae. We report the isolation and detection of IAA as a secondary metabolite from Pisolithus tinctorius by thin-layer chromatography, high-performance liquid chromatography (HPLC), enzyme-linked immunosorbent (monoclonal antibody) assay (ELISA), and unequivocal identification by gas chromatography-mass spectrometry (GC-MS). The thin-layer chromatography methods for auxin isolation described here are novel, with the use of heptane-acetone-glacial acetic acid as the migrating solvent and formaldehyde, H(2)SO(4), and vanadate in detection. The acidic extract of the culture supernatant was methylated with ethereal diazomethane to detect IAA as methyl-3-IAA by HPLC, ELISA, and GC-MS. The quantitative amount of IAA detected ranged from 4 to 5 mumol liter by HPLC and ELISA. Another unidentified metabolite was detected by GC-MS with a typical indole nucleus (m/z = 130), indicating that it could be an intermediate in auxin metabolism. Plant response (Pseudotsuga menziesii, Douglas fir) was monitored upon inoculation of P. tinctorius and l-tryptophan. There was a consistent increase in plant height and stem diameter as a result of the two treatments, with statistical differences in dry weights of the shoots and roots.

Journal Article↗
PubMed1987

Increased Effectiveness of Competitive Rhizobium Strains upon Inoculation of Cajanus cajan.

A field study was conducted in lysimeters containing N-enriched soil to determine the effects of four competitive rhizobium strains upon yield parameters of pigeon peas (Cajanus cajan). The greatest differences observed were in seed yields; strain P132 effected the highest seed yield (121 +/- 20 g per plant), and the control strain (indigenous rhizobia) effected the lowest yield (43.9 +/- 8 g per plant). With the exception of seeds and pods, the dry matter weights were not different. Although there appeared to be no effect by inoculum strains on the fractional content of N derived from biological nitrogen fixation when the total plant biomass was considered, strains P132 and 401 partitioned more of the N derived from fixation into seeds and leaves than did the other strains. Because the seeds comprised the major portion of plant N, more total N and more N derived from biological nitrogen fixation (about half of total N) were found in plants inoculated with P132, whereas the smallest amount was found in the uninoculated controls. P132 was also the best competitor with respect to indigenous rhizobia and acounted for all of the nodules found on the plants in which it was inoculated.

Journal Article↗
PubMed1986

Dinitrogen production from nitrite by a nitrosomonas isolate.

A chemolithotrophic ammonium-oxidizing bacterium that was able to reduce NO(2) to N(2) (m/z 30) while oxidizing ammonium under conditions of oxygen stress was isolated from stream sediments. Energy was derived from ammonium oxidation, as evidence by growth, with CO(2) serving as the sole C source. The organism was a gram-negative, motile, short rod that failed to grow either aerobically or anaerobically in heterotroph media. The organism was identified as a Nitrosomonas sp.

Journal Article↗