Biomedical subjects

R D Stith

Publications and source records attributed to R D Stith.

At least 19 recordsLinked to original sources

PubMed1994

Pressor and endocrine responses to lesions of canine rostral ventrolateral medulla.

To understand the mechanism(s) of reduction in arterial pressure (AP) after kainic acid cytotoxic lesions in the rostral ventrolateral medulla (RVLM), recordings of AP, cardiac output (CO), heart rate (HR), plasma catecholamines, and cortisol were obtained from awake relaxed dogs. Mongrels (n = 12) were instrumented with a solid-state pressure transducer in the descending aorta and a pulse transit-time ultrasonic flowmeter on the aortic arch. After the dogs recovered from thoracotomy, AP, CO, HR, and plasma levels of epinephrine, norepinephrine, and cortisol were recorded periodically or measured at rest over 2-3 wk followed by unilateral, cytotoxic lesion placement in the rostral C1 area of the RVLM. After the dogs recovered from lesion surgery, the measurements were repeated, and, compared with prelesion control values, they showed significantly decreased AP (-23.1 mmHg) and total peripheral resistance (-0.014 peripheral resistance units) but no significant changes in CO or HR. The reduction in AP may be caused partially by significant reductions in plasma epinephrine (-47%), norepinephrine (-34%), and cortisol (-66%) levels. Lesion sites corresponded to the rostral C1 area, immunocytochemically positive for phenylethanolamine-N-methyltransferase (PNMT). These observations support the concept that a discrete site in the RVLM, demarcated by a rostral subgroup of PNMT-immunoreactive cell bodies, contributes to direct sympathoexcitatory support of resting AP. The neurotransmitter responsible for vasomotor tone, however, remains unknown. This study also provides new information suggesting a role for catecholamine and cortisol regulation from this putative vasomotor center.

Animals↗

PubMed1994

Relative contribution of type I and II corticosterone receptors in VMH lesion-induced obesity and hyperinsulinemia.

Ventromedial hypothalamic (VMH) lesion-induced obesity is accompanied by hyperinsulinemia and hyperphagia, which are dependent upon corticosterone (Cort) for their expression. Whether Cort exerts these actions through its stimulation of type I or II Cort receptor populations is unknown. Therefore, food intake and weight gain were measured in obese adrenalectomized VMH-lesioned rats given continuous infusion of various doses of either a type I-receptor agonist (aldosterone), a type II-receptor agonist (RU-28362), or several combination doses. Similarly, the receptor population responsible for lesion-induced hyperinsulinemia was identified. Type II receptor stimulation restored the hyperphagia, weight gain, and hyperinsulinemia of adrenalectomized VMH-lesioned animals, while type I receptor stimulation blocked their weight loss.

Adrenalectomy↗

PubMed1994

Peripheral endocrine and metabolic responses to centrally administered interleukin-1.

It is becoming increasingly apparent that interleukin-1 (IL-1) acts systemically and centrally to play an important role in regulating the hormonal and metabolic response to stress, infection, and trauma. The aim of this study was to observe the peripheral metabolic and endocrine responses to 15, 25, and 50 ng intracerebroventricular (i.c.v.) recombinant IL-1 beta in awake, freely moving rats over a 6-hour period. The rate and duration of elevation of temperature and plasma corticosterone and glucose were dose-dependent and did not return to control levels until 6 or more hours later. Hepatic glycogen content 6 h after i.c.v. IL-1 was 58, 52 and 78% of control after 15, 25, and 50 ng, respectively. The plasma insulin response to elevated plasma glucose in rats treated with 15 ng was absent in those treated with 25 and 50 ng. Responses of plasma glucagon to each dose of IL-1 were not significantly different from control responses. PEPCK enzyme activity was diminished to 60, 66, and 81% of control after 15, 25, and 50 ng IL-1, respectively. No changes of body temperature or plasma corticosterone were observed when 25 or 50 ng IL-1 were injected intravenously. These results are strong evidence that central actions of IL-1 significantly affect peripheral glycemia via classical hepatic and endocrine adjustments.

Animals↗

PubMed1994

Endocrine and carbohydrate responses to interleukin-6 in vivo.

The role of interleukin-6 (IL-6) in carbohydrate metabolism beyond its inhibition of hepatic phosphoenolpyruvate carboxykinase has not been widely pursued. To describe such IL-6 effects, we examined in the rat the responses of plasma corticosterone, glucagon, insulin, and glucose levels and the hepatic glycogen content 30, 60, 90, 120, and 180 min after intravenous injection of recombinant human IL-6. The effect to increase plasma corticosterone was consonant with the well-known action of IL-6 on the hypothalamus-pituitary-adrenal cortex. IL-6 produced a transient increase in plasma glucagon that was mirrored by elevated plasma glucose and a depletion of hepatic glycogen. Plasma insulin levels were not elevated within the first hour after IL-6 injection but were significantly elevated 90 min and beyond. We suggest that the stimulus for increased circulating insulin was elevated plasma glucose, rather than a direct effect of IL-6. The results demonstrate that IL-6, acting directly on peripheral organs and/or through the central nervous system (CNS) can alter the hormonal and carbohydrate milieu. We propose that these actions of IL-6 are one aspect of its role in the acute phase response.

Animals↗

PubMed1990

Tocainide and mortality after myocardial infarction: a prospective study in conscious dogs.

The production of an anterior myocardial infarction as part of an experimental animal model for sudden death was burdened by a persistently elevated mortality rate (30%) despite the use of traditional antiarrhythmic drugs. Mortality was reduced when tocainide (600 mg three times daily) was empirically administered for 4 days before and 4 days after myocardial infarction. Retrospective analysis showed that mortality at 4 days after infarction was significantly lower in the tocainide-treated dogs than in the preceding large group of dogs that had not been so treated (5 [9%] of 55, versus 64 [32%] of 199, p less than 0.01). This difference was still evident 30 days after myocardial infarction (13 [24%] of 55 versus 83 [42%] of 199; p less than 0.05). This observation led to the present prospective study in 106 dogs with a similar protocol but with a randomized sequence. At 4 days after myocardial infarction, the mortality rate was 55% lower in the tocainide group than in the control group (7 [12.5%] of 56 versus 14 [28%] of 50; p less than 0.05). During the 10 days after treatment withdrawal 9 (18%) of 49 dogs in the tocainide group died compared with only 2 (5%) of 36 in the control group. This rebound in mortality produced similar survival figures in the two groups at 14 and at 30 days after infarction when mortality was 30% (17 of 56) in the tocainide group and 34% (17 of 50) in the control group. The tocainide plasma levels were 7.4 +/- 4 micrograms/ml the day before infarction and 7.2 +/- 3 micrograms/ml 3 days after infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Mortality and bacteriology of sepsis following cecal ligation and puncture in aged mice.

Epidemiologic data suggest that elderly adults are more susceptible to invasive bacterial infection by indigenous gut flora than are younger adults. The purpose of this investigation was to characterize a murine model of clinically encountered peritonitis in the aged. We subjected three different age groups (young, 16 weeks; mature, 12 months; senescent, 24 months) of C57BL/6NNia mice to surgically induced peritonitis by the cecal ligation and puncture procedure. Senescent mice died in a significantly shorter time following surgery than mature mice (median time to death, 24.4 versus 38.5 h, respectively; P less than or equal to 0.001). Blood, liver, spleen and occasionally, ceca were obtained at 2 and 12 h after the cecal ligation and puncture procedure and immediately following death, to characterize the bacterial kinetics of the model. Qualitative and quantitative aerobic, anaerobic, and coliform cultures were performed. No age-related differences were found in the types of bacteria isolated throughout the time course of progressive sepsis. In mice in the mature and senescent age groups, at 2 and 12 h postsurgery, gram-negative anaerobes and gram-positive aerobes predominated in all tissues that were cultured. At the time of death, however, blood and tissue isolates consisted predominantly of coliform bacteria. The shift from mixed infection during sepsis to predominantly gram-negative bacterial infection reflected a similar progressive shift in bacterial types found in the cecum. At death, senescent mice had 100-fold fewer coliform bacteria in the bloodstream than those found in mature mice (2.5 x 10(9) versus 4.6 x 10(11), respectively). The increased sensitivity of aged mice to invasive bacterial infection documented in this series of experiments accords well with human epidemiologic experience and demonstrates the appropriateness of the model for continued investigations of sepsis in the aged.

Aging↗

PubMed1989

Effect of interleukin-6/interferon-beta 2 on glucocorticoid action in rat hepatoma cells.

Reuber hepatoma cells (RHC) were treated 4 h with dexamethasone (dex), with and without simultaneous fibroblast-conditioned medium (cIL-6). A cytosol fraction, prepared in the presence of molybdate and dithiothreitol, was analyzed for [3H]dex (20 nM) binding in the presence and absence of 1 microM dex at 4 degrees C. Receptor levels declined from 76.0 fmol/mg at zero dex to 28.8 fmol/mg at 10 nM dex, and to 11.8 fmol/mg at 1 microM dex (P less than or equal to 0.05). cIL-6 plus 10 nM dex lowered binding to 18.3 fmol/mg (P less than or equal to 0.05), and treatment with cIL-6 alone diminished binding to 9.8 fmol/mg (P less than or equal to 0.05). Thus, cIL-6 diminished the number of available glucocorticoid receptors.

Animals↗

PubMed1989

Changes in myocardial contractile protein ATPases in chronically adrenalectomized rats with and without glucocorticoid replacement.

Studies were conducted to examine the effects of chronic adrenalectomy (Adx) and adrenalectomy plus glucocorticoid replacement therapy on rat cardiac contractile protein ATPase activities. The Ca2+-dependent Mg-ATPase activity of myofibrils isolated from rat ventricles 3 weeks postadrenalectomy (Adx) was significantly decreased at all pCa2+ concentrations (P less than 0.01), compared to sham-operated (SO) rats. Similarly, Ca2+-, K+-EDTA, and actin-activated myosin ATPase activities of Adx rat hearts were markedly decreased below that of SO rats (P less than 0.01). Dexamethasone administration to Adx rats prevented the decrease of Ca2+- and K+-ATPase activities of myosin, but not of myofibrillar Ca2+-dependent Mg-ATPase or actin-activated myosin Mg-ATPase activities. These studies suggest that glucocorticoid insufficiency induced by adrenalectomy results in altered myocardial contractile protein ATPase activity which may underlie impaired cardiac performance.

Adenosine Triphosphatases↗

PubMed1989

Cardiovascular changes in chronically adrenalectomized conscious rats.

Mean arterial blood pressure (MABP), heart rate (HR), stroke volume index (SVI), cardiac index (CI), systemic vascular resistance index (SVRI), and central venous pressure (CVP) were measured in conscious, freely moving, sham-operated (SO) and chronically adrenalectomized (ADX) rats. After 3 weeks of ADX, the rats exhibited hypotension, tachycardia, and diminished SVI and CI. From 3 to 6 weeks after surgery, the HR decreased and SVRI increased. These changes were obscured when the same measurements were obtained in the same rats under enflurane anesthesia. Cardiovascular responses to an epinephrine (0.4 microgram/kg/min) infusion were measured in conscious SO and ADX rats. The magnitude of change from baseline to peak was similar in all groups, indicating that ADX did not alter the responsiveness of the cardiovascular system to epinephrine. The peak MABP response to epinephrine in ADX rats was significantly below that of SO control rats, suggesting that ADX impaired the ability of the cardiovascular system to maintain normal arterial blood pressure. No differences were found in plasma concentrations of Na+, K+, Cl-, PO4 =, or hematocrit that would help to explain the effect of long-term adrenalectomy. The data underscore the cardio-depressant effect of enflurane anesthesia, demonstrate the importance of a conscious rat model in studying the effects of ADX on the cardiovascular system, and emphasize that the full effects of ADX occur over a period of several weeks.

Adrenal Insufficiency↗

PubMed1988

Human recombinant IL-1 alters glucocorticoid receptor function in Reuber hepatoma cells.

Exposure of Reuber hepatoma cells (RHC) to 30 and 300 fM human rIL-1 (hurIL-1) for 4 h significantly decreased cytosolic glucocorticoid binding. Scatchard analysis indicated that the 30 and 300 fM doses of hurIL-1 significantly decreased the Bmax (maximum number of available binding sites), but did not alter the Kd (affinity of the glucocorticoid receptor for ligand). The decrease in cytosolic glucocorticoid binding, expressed relative to cytosol protein, did not result from increased intracellular protein in hurIL-1-treated RHC. In addition, the receptor binding reaction in RHC treated with 300 fM hurIL-1 could be resolved only by computer application of a three-parameter model. Sucrose density gradient ultracentrifugation analysis confirmed significantly less untransformed (8 to 10S) receptor-ligand complexes in hurIL-1-treated RHC, which is biologically significant because hurIL-1 (300 fM) also inhibited the glucocorticoid induction of the gluconeogenic enzyme, phosphoenolpyruvate carboxykinase (PEPCK). Altered transformation of the receptor-ligand complex, a possible mechanism of action for hurIL-1-mediated inhibition of PEPCK induction, was examined. However, receptor transformation, verified by in vitro activation by high salt (0.3 M KCl) of glucocorticoid receptor-ligand complexes and subsequent sucrose density gradient ultracentrifugation analysis, was not affected by hurIL-1. Furthermore, cytoplasmic glucocorticoid binding, determined in intact cell dexamethasone uptake experiments, was decreased in hurIL-1-treated RHC. The decrease in cytoplasmic glucocorticoid binding was reflected subsequently in decreased nuclear binding. The results support our hypothesis that, during acute infection and inflammation, mediators alter metabolic pathways in the liver by interfering with glucocorticoid action.

Carcinoma, Hepatocellular↗

PubMed1988

Failure of glucagon to induce hepatic phosphoenolpyruvate carboxykinase in endotoxic shock.

We have determined that one reason for diminished PEPCK activity during endotoxemia is the inhibition of glucocorticoid action in hepatic cells. Since glucocorticoid and glucagon hormones act cooperatively to regulate the expression of PEPCK mRNA, we examined whether endotoxin also inhibits the action of glucagon to induce this enzyme. Treated mice were injected intraperitoneally with endotoxin and glucose after a 24 hr fast and given ad libitum access to food and water. Control mice received the same amount of glucose and access to food and water. All mice were given intravenous injections of glucagon for 3 consecutive hours before euthanasia. Blood was analyzed for glucose concentrations, and the liver was assayed for PEPCK activity. Refeeding control mice after a 24 hr fast increased plasma glucose levels to 173 +/- 14 mg/dL and decreased PEPCK activity to 20.6 +/- 2.0 units/mg liver. Subsequent administration of exogenous glucagon further increased plasma glucose to 224 +/- 17 mg/dL and hepatic PEPCK to 31.4 +/- 1.4 units/mg liver. Refeeding endotoxin-treated mice after a 24 hr fast slightly increased plasma glucose levels to 75 +/- 4 mg/dL but had no effect on PEPCK activity. Subsequent glucagon administration had no effect on plasma glucose levels (75 +/- 1.0 mg/dL) or hepatic PEPCK activities (18.8 +/- 5.0 units/mg liver). Therefore, glucagon action to increase liver PEPCK activity and plasma glucose levels was inhibited in endotoxin-treated mice.

Animals↗

PubMed1987

Monokines mediate decreased hepatic glucocorticoid binding in endotoxemia.

The purpose of this study was to determine whether endotoxin decreased hepatic glucocorticoid binding by the action of mediator(s). Steroid binding in liver cytosol, plasma glucose levels, and plasma corticosterone levels were assayed in C3HeB/FeJ LPS normoresponsive and C3H/HeJ LPS hyporesponsive mice. In C3HeB/FeJ mice, endotoxin significantly depressed the maximum number of steroid binding sites (Bmax) to 30% of control. Plasma glucose levels were decreased to 50% of control, and plasma corticosterone levels increased 4-fold. No changes in these parameters were seen in C3H/HeJ mice given endotoxin, except for decreased plasma glucose levels at the highest dose of endotoxin. Decreased steroid binding was observed in C3H/HeJ mice 4-6 hours after receiving C3HeB/FeJ peritoneal exudate cells (elicited with thioglycolate) and endotoxin. No change in steroid binding was observed in C3H/HeJ mice that received C3H/HeJ peritoneal exudate cells and endotoxin. Mediator-rich plasma was produced in CF-1 mice by infecting them with 1 X 10(7) BCG and by challenging them with endotoxin (2 micrograms) 2 weeks later for 2 h. Transfer of BCG-endotoxin plasma to C3H/HeJ mice also resulted in decreased steroid binding and plasma glucose. These results indicate that perturbation of glucocorticoid action during endotoxin shock is mediated by soluble factor(s) other than endotoxin. A likely source of mediator(s) is the mononuclear phagocyte.

Animals↗

PubMed1986

Interleukin 1: a regulatory role in glucocorticoid-regulated hepatic metabolism.

The purpose of this study was to investigate the effect of interleukin 1 (IL 1) on glucocorticoid-regulated hepatic metabolism. Steroid binding in liver cytosol, plasma glucose, plasma corticosterone, and phosphoenolpyruvate carboxykinase (PEPCK) activity were assayed in C3H/HeJ mice after IL 1 administration. Mice received 5 pyrogenic U (PU) of rabbit IL 1 i.p. and were sacrificed 4 hr later. In adrenal-intact mice, steroid binding and plasma glucose were significantly decreased (63 and 64% of control) and plasma corticosterone was significantly elevated threefold. In adrenalectomized mice, IL 1 (5 PU) treatment produced similar results in steroid binding (66% of control) and plasma glucose (71% of control). PEPCK was measured in intact mice fasted overnight and treated with 5 PU of IL 1. PEPCK was induced in fasted control animals (23.1 +/- 1.4 U/mg) vs fed control animals (15.9 +/- 0.7 U/mg). IL 1 treatment inhibited the induction of PEPCK in fasted animals (13.4 +/- 2.0 U/mg) and caused a significant decrease in steroid binding (78% of fasted control) and plasma glucose (82% of fasted control). No difference in plasma corticosterone was seen in IL 1-treated mice and fasted control mice. These data indicate that IL 1 decreases intracellular steroid receptors, resulting in decreased induction of PEPCK and subsequent reduced gluconeogenesis and plasma glucose. We propose that IL 1 plays a regulatory role in glucocorticoid-regulated hepatic metabolism.

Adrenalectomy↗

PubMed1986

General effect of endotoxin on glucocorticoid receptors in mammalian tissues.

Considering the ubiquitous nature of glucocorticoid actions and the fact that endotoxin inhibits glucocorticoid action in the liver, we proposed to examine whether endotoxin affected extrahepatic actions of glucocorticoids. Fasted C57BL/6J mice were injected intraperitoneally with endotoxin (LD50) at 0800 and were killed 6 h later. Control mice were injected with an equal volume of saline. 3H-dexamethasone binding, measured by a new cytosol exchange assay utilizing molybdate plus dithiothreitol, in liver, kidney, skeletal muscle, spleen, lung, and heart tissue was significantly lower in treated than in control mice. The equilibrium dissociation constants were not significantly different, but the number of available binding sites in each tissue was reduced by endotoxin treatment. Phosphoenolpyruvate carboxykinase activity was significantly reduced in liver but not in kidney. Endotoxin treatment lowered glycogen content in liver but not in skeletal muscle. The reduction observed in the "a" form of liver glycogen synthase due to endotoxin was not seen in skeletal muscle glycogen synthase "a." These data support the proposal that endotoxin or a mediator of its action inhibits systemic glucocorticoid action. The results also emphasize the central role of the liver in the metabolic disturbances of the endotoxin-treated mouse.

Animals↗

PubMed1985

Effects of aging and endotoxin on hepatic glucocorticoid action and glucose metabolism in mice.

Hepatic binding of [3H] dexamethasone, phosphoenolpyruvate carboxykinase activity, glycogen levels, and plasma glucose and corticosterone concentrations were measured in young, mature, and old mice given either endotoxin or vehicle. Endotoxin treatment differentially lowered plasma glucose concentration, hepatic glycogen content, PEPCK activity and specifically bound [3H] dexamethasone, but increased plasma corticosterone concentration by a magnitude dependent upon the age of the animal.

Aging↗

PubMed1983

Influence of endotoxin treatment on dexamethasone induction of hepatic phosphoenolpyruvate carboxykinase.

Decreased glucocorticoid binding has been observed at a time after endotoxin (3 to 6 h) when imparied liver enzyme induction is known to occur. This study was undertaken to characterize the early time course of hypoglycemia and decreased liver phosphoenolpyruvate carboxykinase (PEPCK) activity in intact and adrenalectomized mice given endotoxin. In addition, altered steroid induction of hepatic PEPCK was examined in adrenalectomized mice given dexamethasone at intervals before and after a median lethal dose of endotoxin. Intact mice demonstrated a dramatic hyperglycemia at 1 h after endotoxin treatment, a response absent in adrenalectomized mice. Plasma glucose levels were significantly reduced from control values at 3 and 6 h posttreatment, with the most pronounced endotoxin-induced hypoglycemia seen in adrenalectomized mice. Hepatic PEPCK activity in intact mice given endotoxin was decreased at 3 and 6 h after treatment, although no change from basal, noninduced levels was seen in poisoned adrenalectomized mice. The increased increment in hepatic PEPCK activity due to fasting of intact control mice was reproduced in adrenalectomized control mice by the administration of dexamethasone. Furthermore, the induction of hepatic PEPCK by dexamethasone was inhibited by 1 h after endotoxin treatment, with enzyme activity falling to basal, noninduced levels by 6 h posttreatment. At these same time intervals after endotoxin treatment, no evidence of histopathology in the liver or adrenal glands was seen. These results coincide with changes in steroid binding seen previously and indicate that endotoxin treatment produces significant alterations in glucocorticoid action at the subcellular or molecular level.

Adrenal Glands↗

PubMed1983

Down regulation of hepatic glucocorticoid receptors after endotoxin treatment.

The mechanism by which endotoxin administration results in hypoglycemia was evaluated by characterizing [3H]dexamethasone binding and phosphoenolpyruvate carboxykinase activity in hepatic cytosol preparations from treated and control mice. Starved mice were given Escherichia coli O111:B4 endotoxin or saline intraperitoneally on day 3 after bilateral adrenalectomy. [3H]dexamethasone binding was measured by the charcoal method after the incubation of cytosol preparations with [3H]dexamethasone in the presence or absence of unlabeled dexamethasone. Changes in [3H]dexamethasone binding were found to be time and dose dependent in treated mice. When mice given different doses of endotoxin reached the same stage of morbidity, as indicated by the average time of death, significantly lower glucocorticoid binding was measured. Scatchard analysis of binding isotherms defined a single class of binding sites. Association and dissociation rate constants and the equilibrium dissociation constant (Kd) were not altered, but the maximum number of binding sites was depressed by endotoxin. The rank order of potency of competitors for [3H]dexamethasone binding, dexamethasone greater than hydrocortisone = corticosterone greater than deoxycorticosterone greater than progesterone greater than testosterone = estradiol, was consistent with a glucocorticoid receptor, although the competition was not altered by endotoxin. Endotoxin treatment prevented the glucocorticoid-induced increase in hepatic phosphoenolpyruvate carboxykinase activity. We conclude that the hypoglycemia of endotoxin poisoning is effected, in part, by the inhibition of the glucocorticoid-mediated induction of phosphoenolpyruvate carboxykinase via the down regulation of hepatic glucocorticoid receptors.

Animals↗

PubMed1982

Effect of central catecholamine depletion on 3H-dexamethasone binding in the dog.

Dogs were bilaterally adrenalectomized (Adx) or sham adrenalectomized 2 weeks after the administration of 6-hydroxydopamine (6-OHDA) or saline-ascorbic acid vehicle directly into the third ventricle (3V). Hypothalamic and hippocampal cytosols were assayed in vitro for high affinity binding of 3H-dexamethasone (3H-DM). 6-OHDA treatment resulted in a significant reduction of norepinephrine concentration in the hypothalamus, but not in the hippocampus, when measured 2 weeks after the second dose. Treatment with this neurotoxin also caused a decrease in 3H-DM binding in the hypothalamus that was detectable after adrenalectomy. A statistically significant reduction in bound DM was not observed in the hypothalamus after 6-OHDA treatment of dogs with intact adrenals, perhaps because of a masking effect of endogenous corticosteroids. No change was observed in the hippocampus. Saturation analysis of binding data revealed the total maximum number of available binding sites in hypothalamic cytosol was lower after 6-OHDA treatment, compared to saline-injected controls. Calculated values for dissociation constants revealed no differences between dogs treated with Adx, saline and Adx, and 6-OHDA. The data support the suggestion that catecholamines may act, in part, by altering the specific binding of a glucocorticoid to its hypothalamic receptor.

Adrenalectomy↗