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M D Wheeler

Publications and source records attributed to M D Wheeler.

At least 37 records · Page 2Linked to original sources
PubMed2000

Medium-chain triglycerides inhibit free radical formation and TNF-alpha production in rats given enteral ethanol.

This study determined whether free radical formation by the liver, tumor necrosis factor (TNF)-alpha production by isolated Kupffer cells, and plasma endotoxin are affected by dietary saturated fat. Rats were fed enteral ethanol and corn oil (E-CO) or medium-chain triglycerides (E-MCT) and control rats received corn oil (C-CO) or medium-chain triglycerides (C-MCT) for 2 wk. E-CO rats developed moderate fatty infiltration and slight inflammation; however, E-MCT prevented liver injury. Serum aspartate aminotransferase levels, gut permeability, and plasma endotoxin doubled with E-CO but were blunted approximately 50% with E-MCT. In Kupffer cells from E-CO rats, intracellular calcium was elevated by lipopolysaccharide (LPS) in a dose-dependent manner. In cells from E-MCT rats, increases were blunted by approximately 40-50% at all concentrations of LPS. The LPS-induced increase in TNF-alpha production by Kupffer cells was dose dependent and was blunted by 40% by MCT. E-CO increased radical adducts and was reduced approximately 50% by MCT. MCT prevent early alcohol-induced liver injury, in part, by inhibition of free radical formation and TNF-alpha production by inhibition of endotoxin-mediated activation of Kupffer cells.

Animals↗
PubMed2000

Gender differences in early alcohol-induced liver injury: role of CD14, NF-kappaB, and TNF-alpha.

The purpose of this study was to determine whether early alcohol-induced liver injury (ALI) in females is associated with changes in CD14 on Kupffer cells, activation of hepatic nuclear factor (NF)-kappaB, and expression of tumor necrosis factor (TNF)-alpha mRNA. Male and female rats were given high-fat control or ethanol-containing diets for 4 wk using the intragastric enteral protocol. Physiological parameters were similar in both genders. Ethanol was increased as tolerance developed with higher blood levels than previously observed, resulting in a fourfold increase in aspartate aminotransferase (males 389 +/- 47 IU/l vs. females 727 +/- 66 IU/l). Hepatic pathology developed more rapidly and was nearly twofold greater and endotoxin levels were significantly higher in females after ethanol. Also, expression of CD14 on Kupffer cells was 1.5-fold greater and binding of transcription factor NF-kappaB in hepatic nuclear extracts and TNF-alpha mRNA expression were threefold greater in females. These data are consistent with the hypothesis that elevated endotoxin after ethanol triggers more activation of Kupffer cells via enhanced CD14 expression in females. NF-kappaB is activated in this process, leading to increases in TNF-alpha mRNA expression in the liver and more severe liver injury in females. It is concluded that gender differences in ALI are dependent on endotoxin and a signaling cascade leading to TNF-alpha.

Animals↗
PubMed2000

Dietary glycine blunts lung inflammatory cell influx following acute endotoxin.

Mortality associated with endotoxin shock is likely mediated by Kupffer cells, alveolar macrophages, and circulating neutrophils. Acute dietary glycine prevents mortality and blunts increases in serum tumor necrosis factor-alpha (TNF-alpha) following endotoxin in rats. Furthermore, acute glycine blunts activation of Kupffer cells, alveolar macrophages, and neutrophils by activating a glycine-gated chloride channel. However, in neuronal tissue, glycine rapidly downregulates chloride channel function. Therefore, the long-term effects of a glycine-containing diet on survival following endotoxin shock were investigated. Dietary glycine for 4 wk improved survival after endotoxin but did not improve liver pathology, decrease serum alanine transaminase, or effect TNF-alpha levels compared with animals fed control diet. Interestingly, dietary glycine largely prevented inflammation and injury in the lung following endotoxin. Surprisingly, Kupffer cells from animals fed glycine for 4 wk were no longer inactivated by glycine in vitro; however, isolated alveolar macrophages and neutrophils from the same animals were sensitive to glycine. These data are consistent with the hypothesis that glycine downregulates chloride channels on Kupffer cells but not on alveolar macrophages or neutrophils. Importantly, glycine diet for 4 wk protected against lung inflammation due to endotoxin. Chronic glycine improves survival by unknown mechanisms, but reduction of lung inflammation is likely involved.

Acute Disease↗
PubMed1999

Glycine: a new anti-inflammatory immunonutrient.

The mechanism of the immunosuppressive effects of glycine and its pathophysiological applications are discussed in this review. Glycine has been well characterized in spinal cord as an inhibitory neurotransmitter which activates a glycine-gated chloride channel (GlyR) expressed in postsynaptic membranes. Activation of the channel allows the influx of chloride, preventing depolarization of the plasma membrane and the potentiation of excitatory signals along the axon. Glycine has recently been shown to have similar inhibitory effects on several white blood cells, including hepatic and alveolar macrophages, neutrophils, and lymphocytes. Pharmacological analysis using a GlyR antagonist strychnine, chloride-free buffer, and radiolabeled chloride has provided convincing evidence to support the hypothesis that many white blood cells contain a glycine-gated chloride channel with properties similar to the spinal cord GlyR. Molecular analysis using reverse transcription-polymerase chain reaction and Western blotting has identified the mRNA and protein for the beta subunit of the GlyR in total RNA and purified membrane protein from rat Kupffer cells. Dietary glycine is protective in rat models against endotoxemia, liver ischemia-reperfusion, and liver transplantation, most likely by inactivating the Kupffer cell via this newly identified glycine-gated chloride channel. Glycine also prevents the growth of B 16 melanomas cell in vivo. Moreover, dietary glycine is protective in the kidney against cyclosporin A toxicity and ischemia-reperfusion injury. Glycine may be useful clinically for the treatment of sepsis, adult respiratory distress syndrome, arthritis, and other diseases with an inflammatory component.

Alcohols↗
PubMed1999

Essential role of tumor necrosis factor alpha in alcohol-induced liver injury in mice.

BACKGROUND & AIMS: Tumor necrosis factor (TNF)-alpha is associated with increased mortality in alcoholics, but its role in early alcohol-induced liver injury is not fully understood. Recently, it was shown that injury induced by the enteral alcohol delivery model of Tsukamoto and French was reduced by antibodies to TNF-alpha. To obtain clear evidence for or against the hypothesis that TNF-alpha is involved, we studied TNF receptor 1 (TNF-R1, p55) or 2 (TNF-R2, p75) knockout mice. METHODS: Long-term enteral alcohol delivery was modified for male gene-targeted mice lacking TNF-R1 and TNF-R2. Animals were given a high-fat liquid diet continuously with either ethanol or isocaloric maltose-dextrin as a control for 4 weeks. RESULTS: Ethanol elevated serum levels of alanine aminotransferase nearly 3-fold in wild-type and TNF-R2 knockout mice but not in TNF-R1 knockout mice. Likewise, ethanol caused severe liver injury in wild-type mice (pathology score, 5.5 +/- 0.6) and TNF-R2 knockout mice (pathology score, 5.0 +/- 0.4), but not in TNF-R1 knockout mice (pathology score, 0.8 +/- 0.4; P < 0.001). CONCLUSIONS: Long-term ethanol feeding caused liver injury in wild-type and TNF-R2 knockout mice but not in TNF-R1 knockout mice, providing solid evidence in support of the hypothesis that TNF-alpha plays an important role in the development of early alcohol-induced liver injury via the TNF-R1 pathway. Moreover, the long-term enteral ethanol feeding technique we described for the first time for knockout mice provides a useful new tool for alcohol research.

Alanine Transaminase↗
PubMed1999

Production of superoxide and TNF-alpha from alveolar macrophages is blunted by glycine.

Glycine blunts lipopolysaccharide (LPS)-induced increases in intracellular calcium concentration ([Ca(2+)](i)) and tumor necrosis factor-alpha (TNF-alpha) production by Kupffer cells through a glycine-gated chloride channel. Alveolar macrophages, which have a similar origin as Kupffer cells, play a significant role in the pathogenesis of several lung diseases including asthma, endotoxemia, and acute inflammation due to inhaled bacterial particles and dusts. Therefore, studies were designed here to test the hypothesis that alveolar macrophages could be inactivated by glycine via a glycine-gated chloride channel. The ability of glycine to prevent endotoxin [lipopolysaccharide (LPS)]-induced increases in [Ca(2+)](i) and subsequent production of superoxide and TNF-alpha in alveolar macrophages was examined. LPS caused a transient increase in intracellular calcium to nearly 200 nM, with EC(50) values slightly greater than 25 ng/ml. Glycine, in a dose-dependent manner, blunted the increase in [Ca(2+)](i), with an IC(50) less than 100 microM. Like the glycine-gated chloride channel in the central nervous system, the effects of glycine on [Ca(2+)](i) were both strychnine sensitive and chloride dependent. Glycine also caused a dose-dependent influx of radiolabeled chloride with EC(50) values near 10 microM, a phenomenon which was also inhibited by strychnine (1 microM). LPS-induced superoxide production was also blunted in a dose-dependent manner by glycine and was reduced approximately 50% with 10 microM glycine. Moreover, TNF-alpha production was also inhibited by glycine and also required nearly 10 microM glycine for half-inhibition. These data provide strong pharmacological evidence that alveolar macrophages contain glycine-gated chloride channels and that their activation is protective against the LPS-induced increase in [Ca(2+)](i) and subsequent production of toxic radicals and cytokines.

Animals↗
PubMed1998

A choline-rich diet improves survival in a rat model of endotoxin shock.

This study investigated whether dietary choline can prevent endotoxin shock. Female Sprague-Dawley rats fed chow or chow plus choline chloride (0.025-0.4%) for 3 days were given lipopolysaccharide (LPS) via the tail vein. Eighty-three percent and 56% of chow-fed rats survived after 2.5 or 5.0 mg/kg LPS, respectively. Choline increased survival in a dose-dependent manner, with maximal effects observed at 0.4%; this dose of choline prevented mortality completely after 2.5 or 5 mg/kg LPS. Choline also improved the microscopic appearance of the lungs and blunted increases in serum aspartate aminotransferase levels. Intracellular Ca2+ was monitored in liver and lung macrophages during LPS exposure. Ca2+ increases in macrophages from choline-fed rats were blunted by 40-60% compared with chow-fed controls. Feeding choline also blunted tumor necrosis factor-alpha production. Feeding glycine, which prevents macrophage activation via a chloride channel, in addition to choline was even more effective than feeding choline alone, suggesting that glycine and choline act via distinct sites. These data are consistent with the hypothesis that choline diminishes endotoxin shock by preventing macrophage activation.

Animals↗
PubMed1997

Growth retardation in premenarchial female rhesus monkeys during chronic administration of GnRH agonist (leuprolide acetate).

Leuprolide acetate in depot form (0.75 mg/kg body weight/month, i.m.) was administered to four female rhesus monkeys from 18-30 months of age, a period that includes the premenarchial growth spurt. They were compared to eight age matched controls. As anticipated, sexual maturation was blocked in the Leuprolide group and menarche did not occur. Growth was also severely retarded; no weight gain occurred during the study in the Leuprolide group as compared to a 25% weight gain (P = .044) in the control group. The Leuprolide group also lost muscle mass. Food intake normalized for body weight was not affected. Linear growth averaged 35% less in the Leuprolide group. Serum IGF-1 concentrations increased from 486 +/- 84 to 965 +/- 47 ng/mL (P = .0025) in the Leuprolide group and from 838 +/- 139 to 3,006 +/- 545 ng/mL (P = .0016) in the control group. These data suggest that premenarchial pituitary/gonadal suppression results in a distinctive pattern of growth retardation in monkeys.

Animals↗
PubMed1994

Breast-feeding in the management of the newborn with phenylketonuria: a practical approach to dietary therapy.

Guidelines introduced in 1979 for breast-feeding infants with phenylketonuria included a formula containing low amounts of phenylalanine (PHE) as part of the dietary prescription. Although the guidelines were revised in 1988, new PHE-free products were not included. In addition, the guidelines recommend infant weight checks before and after feeding to ensure correct dietary intake of breast milk. In this study, we present data based on treatment of 13 infants for the first 6 months of life using a PHE-free product and human milk (n = 9) or commercial formula (n = 4). The study began with nine breast-fed infants; five were weaned before 6 months of age and were discontinued from the study. Published estimates of volume and energy of daily human milk consumption were used to prescribe and assess intake of breast milk. No differences were noted between the groups in blood levels of PHE at initiation of dietary therapy, age at initiation of dietary therapy, or length of time to achieve metabolic control. Furthermore, blood levels of PHE and growth parameters for each month up to 6 months of age were similar for both groups. These data support the efficacy of PHE-free formula and estimation of breast milk volumes in managing the diet of infants with phenylketonuria.

Bottle Feeding↗
PubMed1994

Update on therapy for precocious puberty.

The onset of pubertal development before age 8 years in girls or 9 years in boys indicates precocious puberty. The numerous causes of precocious puberty can be classified as central or peripheral. CPP arises from premature activation of the hypothalamic-pituitary axis; therefore, it has hormonal and physical characteristics similar to normal puberty. PPP results from production of sex steroids independent of the hypothalamic-pituitary axis. All types of precocious puberty are characterized by rapid growth and skeletal advancement, leading to the paradox of the tall child becoming a short adult secondary to early epiphyseal fusion. The choice of therapy for precocious puberty is dependent on the underlying etiology with differing strategies employed for central and peripheral causes (Table 3). Long-acting GnRH-a provide effective, selective, and reversible therapy for CPP. GnRH-agonists are not effective in PPP; however, other agents such as testolactone, spironolactone, and ketoconazole can be used to manage the premature sexual maturation associated with these conditions.

Adolescent↗
PubMed1991

Growth hormone regulation by growth hormone-releasing hormone in infant rhesus monkeys.

To study the relationship of endogenous GHRH to the changes seen in serum GH concentration in neonatal primates, we administered antiserum to GHRH (GHRH-Ab) or GHRH antagonist, (N-Acetyl-Tyr1,D-Arg2)GHRH-(1-29)-NH2, to unanesthetized, fasted rhesus monkeys, 1-31 days of age, via an acutely placed venous catheter. The administration of GHRH-Ab resulted in a significant decrease in serum GH concentration at 1-2 and 7-9 days, but not at 28-31 days of age. The administration of GHRH antagonist resulted in a significant decrease in serum GH concentrations at 1-2 days, but not at 7 or 14 days of age. These results imply that basal serum GH is more dependent on endogenous GHRH at 1-2 days than after 7-28 days of age. This suggests developmental changes in the hypothalamic regulation of GH secretion with advancing age in the neonatal period.

Animals↗
PubMed1991

Drug treatment in precocious puberty.

Precocious puberty, as defined by the onset of pubertal development before the age of 8 years in girls or 9 years in boys, can be classified into central and peripheral aetiologies. Central precocious puberty (CPP) results from early activation of the hypothalamic-pituitary-gonadal axis and has similar physical and hormonal characteristics to normal puberty. Extrapituitary gonadotrophin secretion or independent sex steroid secretion results in peripheral precocious puberty (PPP). Precocious puberty is characterised by rapid growth and advancement of skeletal age. The skeletal advancement is greater than the growth increase, so that final adult height is compromised. Long-acting gonadotrophin releasing hormone (GnRH) agonists are the current therapy of choice for central precocious puberty, having demonstrated effectiveness in halting the precocious development associated with this condition with minimal side effects. GnRH agonists are not effective as therapy for peripheral precocious puberty, but a number of other agents have been used with some success. These include androgen antagonists, testolactone, ketoconazole, and medroxyprogesterone acetate. The use of GnRH agonists has been associated with an increase in predictions of final height; however, continuing studies in treated cohorts are necessary to determine the true benefit of any of these agents on increasing ultimate height.

Adolescent↗
PubMed1991

The treatment of precocious puberty.

Long-acting GnRH agonists are the treatment of choice for central precocious puberty. GnRH agonists are not effective in peripheral precocious puberty, but a number of other agents, including medroxyprogesterone acetate, ketoconazole, testolactone, and androgen antagonists, may be useful.

Androgen Antagonists↗
PubMed1991

Physical changes of puberty.

Normal pubertal development is characterized by major physical alterations: sexual maturation, changes in body composition, and rapid skeletal growth. Breast development is the first manifestation of puberty in approximately 85% of girls; the normal age for initial breast development is 8 to 13 years. Menarche generally occurs within 2 years of the onset of breast development, with a mean age in American girls of 12.8 years. In boys, the first manifestation of puberty is testicular enlargement; the normal age for initial signs of puberty is 9 to 14 years in males. Pubic hair in boys generally appears 18 to 24 months after the onset of testicular growth and is often conceived as the initial marker of sexual maturation by male adolescents. Skeletal growth is one of the most striking characteristics of puberty. Linear-growth velocity begins to increase in males at genital stage III and pubic-hair stage II, but peak height velocity is not attained until age 14 years in boys and 12 years in girls. Lean body mass, which primarily reflects muscle mass, begins to increase during early puberty in both boys and girls. Fat mass increases during the late stages of puberty in girls. Sex differences in the adolescent growth spurt produce the characteristics sexual dimorphism in shape and proportions seen in young adults.

Adolescent↗
PubMed1990

Diagnosis and management of precocious puberty.

The onset of pubertal development before the age of 8 years in girls or 9 years in boys constitutes precocious puberty. There are numerous causes of precocious puberty, which can be classified as central or peripheral precocious puberty. Central precocious puberty results from premature activation of the hypothalamic-pituitary-gonadal axis and thus presents with physical and hormonal findings similar to those found in normal puberty. Peripheral precocious puberty results from extrapituitary gonadotropin secretion or secretion of sex steroids independent of pituitary gonadotropins. All types of precocious puberty are characterized by rapid growth and advancement of skeletal age, leading to the paradox of the tall child becoming a short adult as a result of premature epiphyseal fusion. Long-acting GnRH agonists afford effective, selective, and reversible therapy of central precocious puberty without significant toxicity. GnRH agonists are not effective in managing the premature sexual maturation associated with peripheral precocious puberty, but a number of other agents have been used with some success. These agents include testolactone, ketoconazole, and medroxyprogesterone acetate. GnRH agonist treatment leads to an increase in predicted final height. To determine the true benefit of any of these agents in increasing ultimate height, there is a need for continuing studies in treated cohorts to follow growth patterns until adult stature is achieved.

Child↗
PubMed1990

Longitudinal changes in growth hormone response to growth hormone-releasing hormone in neonatal rhesus monkeys.

To determine whether differential response to growth hormone-releasing hormone (GHRH) could cause the developmental changes seen in growth hormone (GH) secretion, we administered 10 micrograms/kg GHRH (1-44 NH2) to a group of four unanesthetized, fasted, rhesus monkeys via acutely placed venous catheters at 1, 7, 14, and 28 d postnatal age. Serum GH was assayed by hGH RIA in sera collected at -60, -30, 0, 15, 30, 45, 60, and 90 min relative to the GHRH bolus. Serum cortisol was measured by ELISA in the 0-, 30-, and 60-min samples. Differences between age groups were analyzed by repeated measures analysis of variance and paired t tests. Mean basal GH levels were higher at 1 d (9.4 +/- 1.2 micrograms/L, mean +/- SEM) than at 7 (5.5 +/- 0.4), 14 (5.6 +/- 0.5), and 28 d (5.3 +/- 0.5) of age. There were no other significant differences in mean basal GH values between the age groups. Mean post-GHRH GH concentrations decreased significantly with each age after 1 d (22.6 +/- 1.6): 7 d (16.4 +/- 1.3); 14 d (11.3 +/- 1.0); and 28 d (7.9 +/- 0.9). Similarly, mean delta-GH values decreased with each increase in age from 1 d (15.0 +/- 1.9): 7 d (10.9 +/- 1.6); 14 d (5.9 +/- 1.1); and 28 d (2.7 +/- 0.8). Serum cortisol was not correlated with serum GH at any age. Our study demonstrates decreasing basal GH concentration and GH responses to GHRH with advancing age from 1 to 28 d in the rhesus monkey.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1990

Changes in basal and stimulated growth hormone secretion in the aging rhesus monkey: a comparison of chair restraint and tether and vest sampling.

We studied basal serum GH and GH responses to iv clonidine and insulin-induced hypoglycemia in a group of four young (5-7 yr old) and four older (10-14 yr old) adult male rhesus monkeys under two restraint conditions, chair adaptation and a tether and vest system, to determine what changes in GH secretion occur with aging. The serum GH response to iv administration of GH-releasing hormone (GHRH) was also studied in the groups under tether and vest restraint. Serum samples were collected every 15 min and assayed for GH using a human GH RIA and for cortisol using an enzyme-linked immunosorbant assay. GH and cortisol concentrations in the young and older groups were analyzed with analysis of variance (ANOVA). In the chaired studies the older animals had a lower mean 6-h basal GH concentration than did the younger animals (2.7 +/- 0.8 vs. 3.5 +/- 0.5 micrograms/L; P = 0.0002). Prestimulation GH was lower before clonidine and insulin in the older chaired group (1.1 +/- 0.5 and 2.3 +/- 0.6 micrograms/L, respectively) compared to the younger group (3.6 +/- 0.8 and 3.8 +/- 0.7 micrograms/L, respectively; P less than 0.001). Poststimulation GH was lower after clonidine and insulin in the older chaired group (3.2 +/- 2.4 and 7.1 +/- 2.8 micrograms/L, respectively) compared to the younger chaired group (6.3 +/- 2.2 and 10.3 +/- 3.0 micrograms/L, respectively; P less than 0.05), but the differences in GH increments were not statistically significant. In the tether and vest studies the older animals had a lower mean 6-h basal GH concentration than did the younger animals (1.7 +/- 0.4 vs. 3.5 +/- 1.2 micrograms/L; P less than 0.0001). Prestimulation GH concentrations were also lower in the older tethered animals before clonidine (2.1 +/- 0.3 micrograms/L) and GHRH (1.4 +/- 0.2 micrograms/L) compared to levels in the younger animals (3.1 +/- 0.9 and 3.2 +/- 0.7 micrograms/L; P = 0.0023 and P = 0.0001, respectively). The younger tethered animals had greater poststimulation responses to clonidine (8.7 +/- 3.0 micrograms/L), insulin (8.8 +/- 3.6 micrograms/L), and GHRH (6.0 +/- 2.4 micrograms/L) than the older animals (3.8 +/- 0.9, 3.9 +/- 2.5, and 2.9 +/- 0.7 micrograms/L; P less than 0.0001, P = 0.0025, and P less than 0.03, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗