Myostatin, a profibrotic factor and the main inhibitor of striated muscle mass, is present in the penile and vascular smooth muscle.

Myostatin is present in striated myofibers but, except for myometrial cells, has not been reported within smooth muscle cells (SMC). We investigated in the rat whether myostatin is present in SMC within the penis and the vascular wall and, if so, whether it is transcriptionally expressed and associated with the loss of corporal SMC occurring in certain forms of erectile dysfunction (ED). Myostatin protein was detected by immunohistochemistry/fluorescence and western blots in the perineal striated muscles, and also in the SMC of the penile corpora, arteries and veins, and aorta. Myostatin was found in corporal SMC cultures, and its transcriptional expression (and its receptor) was shown there by DNA microarrays. Myostatin protein was measured by western blots in the penile shaft of rats subjected to bilateral cavernosal nerve resection (BCNR), that were left untreated, or treated (45 days) with muscle-derived stem cells (MDSC), or concurrent daily low-dose sildenafil. Myostatin was not increased by BCNR (compared with sham operated animals), but over expressed after treatment with MDSC. This was reduced by concurrent sildenafil. The presence of myostatin in corporal and vascular SMC, and its overexpression in the corpora by MDSC therapy, may have relevance for the stem cell treatment of corporal fibrosis and ED.

Muscle Derived Stem Cells Stimulate Muscle Myofiber Repair and Counteract Fat Infiltration in a Diabetic Mouse Model of Critical Limb Ischemia.

BACKGROUND: Critical Limb Ischemia (CLI) affects patients with Type 2 Diabetes (T2D) and obesity, with high risk of amputation and post-surgical mortality, and no effective medical treatment. Stem cell therapy, mainly with bone marrow mesenchymal, adipose derived, endothelial, hematopoietic, and umbilical cord stem cells, is promising in CLI mouse and rat models and is in clinical trials. Their general focus is on angiogenic repair, with no reports on the alleviation of necrosis, lipofibrosis, and myofiber regeneration in the ischemic muscle, or the use of Muscle Derived Stem Cells (MDSC) alone or in combination with pharmacological adjuvants, in the context of CLI in T2D. METHODS: Using a T2D mouse model of CLI induced by severe unilateral femoral artery ligation, we tested: a) the repair efficacy of MDSC implanted into the ischemic muscle and the effects of concurrent intraperitoneal administration of a nitric oxide generator, molsidomine; and b) whether MDSC may partially counteract their own repair effects by stimulating the expression of myostatin, the main lipofibrotic agent in the muscle and inhibitor of muscle mass. RESULTS: MDSC: a) reduced mortality, and b) in the ischemic muscle, increased stem cell number and myofiber central nuclei, reduced fat infiltration, myofibroblast number, and myofiber apoptosis, and increased smooth muscle and endothelial cells, as well as neurotrophic factors. The content of myosin heavy chain 2 (MHC-2) myofibers was not restored and collagen was increased, in association with myostatin overexpression. Supplementation of MDSC with molsidomine failed to stimulate the beneficial effects of MDSC, except for some reduction in myostatin overexpression. Molsidomine given alone was rather ineffective, except for inhibiting apoptosis and myostatin overexpression. CONCLUSIONS: MDSC improved CLI muscle repair, but molsidomine did not stimulate this process. The combination of MDSC with anti-myostatin approaches should be explored to restore myofiber MHC composition.

Oral Bisphenol A (BPA) given to rats at moderate doses is associated with erectile dysfunction, cavernosal lipofibrosis and alterations of global gene transcription.

Bisphenol A (BPA), a suspected reproductive biohazard and endocrine disruptor, released from plastics is associated with ED in occupationally exposed workers. However, in rats, despite the induction of hypogonadism, apoptosis of the penile corporal smooth muscle (SM), fat infiltration into the cavernosal tissue and changes in global gene expression with the intraperitoneal administration of high dose BPA, ED was not observed. We investigated whether BPA administered orally rather than intraperitoneally to rats for longer periods and lower doses will lead to ED. Main outcome measures are ED, histological, and biochemical markers in rat penile tissues. In all, 2.5-month-old rats were given drinking water daily without and with BPA at 1 and 0.1 mg kg(-1) per day. Two months later, erectile function was determined by cavernosometry and electrical field stimulation (EFS) and serum levels of testosterone (T), estradiol (E2) and BPA were measured. Penile tissue sections were assayed by Masson (SM/collagen), Oil Red O (fat), terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) (apoptosis), immunohistochemistry for Oct4 (stem cells), and α-SM actin/calponin (SM and myofibroblasts), applying quantitative image analysis. Other markers were assayed by western blotting. DNA microarrays/microRNA (miR) assays defined transcription profiles. Orally administered BPA did not affect body weight, but (1) decreased serum T and E2; (2) reduced the EFS response and increased the drop rate; (3) increased within the corporal tissue the presence of fat, myofibroblasts and apoptosis; (4) lowered the contents of SM and stem cells, but not nerve terminals; and (5) caused alterations in the transcriptional profiles for both mRNA and miRs within the penile shaft. Long-term exposure of rats to oral BPA caused a moderate corporal veno-occlusive dysfunction (CVOD), possibly due to alterations within the corporal tissue that pose gene transcriptional changes related to inflammation, fibrosis and epithelial/mesenchymal transition (EMT).

Optimization of oxygen tolerance extension in rats by intermittent exposure.

Optimization of oxygen tolerance extension by intermittent exposure was studied in groups of 20 rats exposed to systematically varied patterns of alternating oxygen and normoxic breathing periods at 4.0, 2.0, and 1.5 ATA. Oxygen periods of 20, 60, and 120 min were alternated with normoxic intervals that provided oxygen-to-normoxia ratios of 4:1, 2:1, 1:1, and 1:3. In general, median survival times had nearly linear relationships to increasing normoxic intervals with oxygen period held constant. Exceptions occurred at 4.0 and 2.0 ATA where a 5-min normoxic interval was too short for adequate recovery even with a 20-min oxygen period, and an oxygen period of 120 min was too long even with a normoxic interval of 30 min. These exceptions did not occur at 1.5 ATA. Survival time for many intermittent exposure patterns was equivalent to that for continuous exposure to an oxygen pressure definable as a time-weighted average of the alternating oxygen and normoxia periods. However, this predictive method underestimated the degree of protection achieved by several of the intermittent exposure patterns, especially those performed at 4.0 ATA. Results provided guidance for selection of intermittent exposure patterns for direct evaluation in humans breathing oxygen at 2.0 ATA. Definition of intermittent exposure patterns and conditions that produced prominent gains in oxygen tolerance can also facilitate the performance of future experiments designed to study potential mechanisms for oxygen tolerance extension by intermittent exposure. Heat shock and oxidation-specific stress proteins that are induced by exposure to oxidant injury are suggested for emphasis in such investigations.

Treatment satisfaction with inhaled insulin in patients with type 1 diabetes: a randomized controlled trial.

OBJECTIVE: In patients with type 1 diabetes, glycemic control can be achieved as effectively with an inhaled insulin regimen, comprising preprandial inhaled intrapulmonary insulin plus a bedtime ultralente injection, as with a conventional subcutaneous insulin regimen involving two to three injections per day. Our objective was to compare patient satisfaction between inhaled insulin and subcutaneous insulin. RESEARCH DESIGN AND METHODS: Subjects with type 1 diabetes participated in a 12-week open-label trial and were randomized to either an inhaled insulin regimen or a subcutaneous insulin regimen. Subjects (n = 69) were asked to complete a 15-item self-administered satisfaction questionnaire, the Patient Satisfaction with Insulin Therapy (PSIT) Questionnaire, at baseline and week 12. Outcomes included mean percentage changes in global (overall) satisfaction and two subscales: convenience/ease of use and social comfort. RESULTS: The mean percentage improvement in overall satisfaction with inhaled insulin (35.1%, 95% CI 18.0-52.2) was greater than with subcutaneous insulin (10.6%, 4.7-16.5) (P < 0.01), as was the improvement in convenience/ease of use: inhaled insulin 41.3% (22.9-59.6) versus subcutaneous insulin 11.2% (4.1-18.3; P < 0.01). Improvement in social comfort was greater with inhaled insulin but was not statistically significant. The 12-week change in HbA(1c) was associated with improved overall satisfaction (r = -0.27, P = 0.04). CONCLUSIONS: Inhaled insulin may offer the first practical, noninvasive alternative to insulin injections. For patients with type 1 diabetes, inhaled insulin maintains glycemic control and provides greater overall satisfaction and convenience/ease of use than subcutaneous insulin.

Efficacy of inhaled human insulin in type 1 diabetes mellitus: a randomised proof-of-concept study.

BACKGROUND: Effective glycaemic control in type 1 diabetes mellitus usually requires two or more insulin injections daily. Inhaled intrapulmonary delivery of insulin offers a potential new way to deliver meal-related insulin, eliminating the need for preprandial injections. METHODS: 73 patients with type 1 diabetes mellitus were studied in an open-label, proof-of-concept, parallel-group randomised trial. Patients in the experimental group received preprandial inhaled insulin plus a bedtime subcutaneous ultralente insulin injection. Patients in the control group received their usual insulin regimen of two to three injections per day. Participants monitored their blood glucose four times daily, and adjusted insulin doses weekly to achieve preprandial glucose targets of 5.6-8.9 mmol/L. The primary outcome measure was change in glycosylated haemoglobin (HbA1c) after 12 weeks. Secondary outcomes were fasting and postprandial glucose response to a mixed meal; hypoglycaemia frequency and severity; pulmonary function; and patients' satisfaction. FINDINGS: Changes in HbA1c were indistinguishable between groups (difference 0.2% [95% CI -0.2 to 0.5]). Changes in fasting and postprandial glucose concentrations, and occurrence and severity of hypoglycaemia were also similar between groups. Inhaled insulin was well tolerated and had no effect on pulmonary function (ie, spirometry, lung volumes, diffusion capacity, and oxygen saturation). INTERPRETATION: This proof-of-concept study shows that preprandial insulin can be given by inhalation in individuals with insulin-deficient type 1 diabetes as a less invasive alternative to conventional preprandial insulin injections.

Inhaled human insulin treatment in patients with type 2 diabetes mellitus.

BACKGROUND: Despite demonstrated benefits, intensive insulin therapy has not gained widespread clinical acceptance for several reasons: Multiple daily injections are inconvenient, adherence is a concern, and the time-activity profile may not mimic normal insulin secretion. As such, alternate means of administering insulin are being evaluated. OBJECTIVE: To assess the efficacy and safety of pulmonary delivery of insulin in type 2 diabetic patients who require insulin. DESIGN: Randomized, open-label, 3-month study consisting of a screening visit, a 4-week baseline lead-in phase, and a 12-week treatment phase. SETTING: General clinical research center and outpatient research clinics. PATIENTS: 26 patients (16 men, 10 women) with type 2 diabetes (average age, 51.1 years; average duration of diabetes, 11.2 years). INTERVENTION: Patients received inhaled insulin before each meal plus a bedtime injection of ultralente insulin, performed home glucose monitoring, and had weekly adjustment of insulin dose; target level for preprandial plasma glucose was 5.55 to 8.88 mmol/L (100 to 160 mg/dL). MEASUREMENTS: Glycemic control (hemoglobin A(1c) level) obtained at baseline and monthly for 3 months. Pulmonary function tests were done at baseline and at the end of the study. RESULTS: Inhaled insulin treatment for 3 months significantly improved glycemic control compared with baseline: Mean hemoglobin A(1c) levels decreased by 0.0071 +/- 0.0072 (0.71% +/- 0.72%). Patients experienced an average of 0.83 mild to moderate hypoglycemic event per month; no severe events were recorded. Patients showed no significant weight gain or change in pulmonary function compared with baseline. CONCLUSIONS: Pulmonary delivery of insulin in type 2 diabetic patients who require insulin improved glycemic control, was well tolerated, and demonstrated no adverse pulmonary effects. Larger-scale studies are ongoing to provide long-term efficacy and safety data.

Development and factor analysis of a questionnaire to measure patient satisfaction with injected and inhaled insulin for type 1 diabetes.

OBJECTIVE: To develop a self-administered questionnaire to address alternative delivery routes of insulin and to investigate aspects of patient satisfaction that may be useful for subsequent assessment and comparison of an inhaled insulin regimen and a subcutaneous insulin regimen. RESEARCH DESIGN AND METHODS: Attributes of patient treatment satisfaction with both inhaled and injected insulin therapy were derived from five qualitative research studies to arrive at a 15-item questionnaire. Each item was analyzed on a five-point Likert scale so that higher item scores indicated a more favorable attitude. There were 69 subjects with type 1 diabetes previously taking injected insulin therapy who were enrolled in a phase II clinical trial. Their baseline responses on the questionnaire were evaluated and subjected to an exploratory factor analysis. Meaningful factors were retained and interpreted based on their psychometric properties. RESULTS: Exploratory factor analysis suggested a two-factor solution accounting for 66 and 20% of the variance, respectively. The first factor contained 10 reliable items (Cronbach's alpha = 0.89) relating to convenience and ease of use, and the second contained 5 reliable items (Cronbach's alpha = 0.82) relating to social comfort. CONCLUSIONS: Among patients with type 1 diabetes, this analysis highlighted and quantified two key factors contributing to patient satisfaction: convenience/ease of use and social comfort. The questionnaire underwent rigorous development, had reliable properties, and an interpretable and rich factor structure. This report is intended to help advance, in subsequent investigations, the understanding and measurement of treatment satisfaction with novel and existing forms of insulin delivery.

Effects of prolonged oxygen exposure at 1.5, 2.0, or 2.5 ATA on pulmonary function in men (predictive studies V).

As part of a study of human organ O2 tolerance, lung flow-volume and spirometric measurements were performed repeatedly before, during, and after continuous O2 exposures at 1.5, 2.0, and 2.5 ATA for average durations of 17.7, 9.0, and 5.7 h, respectively (effects of O2 breathing at 3.0 ATA for 3.5 h were reported previously; J. M. Clark, R. M. Jackson, C. J. Lambertsen, R. Gelfand, W. D. B. Hiller, and M. Unger. J. Appl. Physiol. 71: 878-885, 1991). Additional measurements of pulmonary mechanical function, gas exchange, and alveolar inflammatory cells were obtained before and after O2 exposure. Rates of pulmonary symptom development and lung volume reduction increased progressively with elevation of O2 pressure. Average rates of vital capacity reduction over a useful range of O2 pressures provided a valuable general description of pulmonary O2 tolerance in humans. However, the existence of multiple pulmonary effects of O2 toxicity and the complexity of their interactions require awareness that deviations from the average relationships may occur in different individuals or under varying conditions of O2 exposure and subsequent recovery. The associated pulmonary function deficits may represent responses to a composite of direct and indirect effects of O2 poisoning, along with related consequences and subsequent reactions to those effects.

Hypoxic ventilatory sensitivity in men is not reduced by prolonged hyperoxia (Predictive Studies V and VI).

Potential adverse effects on the O2-sensing function of the carotid body when its cells are exposed to toxic O2 pressures were assessed during investigations of human organ tolerance to prolonged continuous and intermittent hyperoxia (Predictive Studies V and VI). Isocapnic hypoxic ventilatory responses (HVR) were determined at 1.0 ATA before and after severe hyperoxic exposures: 1) continuous O2 breathing at 1.5, 2.0, and 2.5 ATA for 17.7, 9.0, and 5.7 h and 2) intermittent O2 breathing at 2.0 ATA (30 min O2-30 min normoxia) for 14.3 O2 h within 30-h total time. Postexposure curvature of HVR hyperbolas was not reduced compared with preexposure controls. The hyperbolas were temporarily elevated to higher ventilations than controls due to increments in respiratory frequency that were proportional to O2 exposure time, not O2 pressure. In humans, prolonged hyperoxia does not attenuate the hypoxia-sensing function of the peripheral chemoreceptors, even after exposures that approach limits of human pulmonary and central nervous system O2 tolerance. Current applications of hyperoxia in hyperbaric O2 therapy and in subsea- and aerospace-related operations are guided by and are well within these exposure limits.

Inhibiting cholesterol absorption with CP-88,818 (beta-tigogenin cellobioside; tiqueside): studies in normal and hyperlipidemic subjects.

CP-88,818 (beta-tigogenin cellobioside; tiqueside) is a synthetic saponin developed to treat hypercholesterolemia by inhibiting the absorption of biliary and dietary cholesterol. Two studies are reported here: one in patients to assess safety and efficacy, and one in normal volunteers to explore the mechanism of action. The former included 15 hypercholesterolemic outpatients [low-density lipoprotein cholesterol (LDL-C) > or = 160 mg/dl] treated with 1, 2, and 3 g of tiqueside daily (b.i.d.) in a crossover design for three 2-week treatment periods, each separated by a 3-week placebo period. The mechanistic study was conducted with 24 healthy male subjects who were randomized in a parallel group design to either placebo (n = 6) or tiqueside (2 or 4 g/day; n = 9 each) once daily for 3 weeks. All subjects in this study were fed a low-fat, low-cholesterol diet [National Cholesterol Education Program (NCEP) Step 1]. Fecal steroid excretion rates and plasma lipid levels were determined at baseline and after 3 weeks of treatment. Fractional cholesterol absorption was measured before and after treatment by the continuous feeding, dual-isotope method. Tiqueside produced a dose-dependent reduction in plasma LDL cholesterol levels in the hypercholesterolemic patients. In the mechanistic study, it decreased fractional cholesterol absorption rates and increased fecal neutral sterol excretion rates, changes associated with trends toward lower LDL cholesterol levels. Other lipoprotein levels were unaffected, as were fecal fat and bile acid excretion and fat-soluble vitamin absorption. Thus tiqueside dose-dependently inhibits cholesterol absorption in humans, resulting in a reduction in serum LDL cholesterol levels.

Inhibition of cholesterol absorption with CP-148,623 lowers serum cholesterol in humans.

OBJECTIVE: To determine the effects of the reduction of intestinal cholesterol absorption with CP-148,623 on serum cholesterol levels in men with mild hyperlipidemia. METHODS: In an outpatient study in a university medical center, healthy male volunteers (n = 25) with borderline-high serum cholesterol levels participated in a double-blind, placebo-controlled parallel-group study. A 3-week dietary run-in period was followed by 2 weeks of treatment with either CP-148,623 (300 mg twice a day; n = 12) or placebo (n = 13). RESULTS: Fractional cholesterol absorption (by the dual-isotope, continuous-feeding technique), fecal neutral sterol excretion, and serum lipids were measured after the diet run-in and after the treatment periods. CP-148,623 caused a marked inhibition (by 38%) of fractional cholesterol absorption (50% +/- 2% [baseline] to 31% +/- 1%) and a 71% increase in fecal neutral sterol excretion (481 +/- 39 mg/day [baseline] to 804 +/- 55 mg/day), compared with negligible changes in the placebo group (p < 0.0001 for both). Mean percent reductions from baseline in serum low-density lipoprotein (LDL) cholesterol levels were 11.6% with CP-148,623 (119 +/- 17 mg/dl to 104 +/- 13 mg/dl) versus a nonsignificant 1.8% reduction with placebo (change with CP-148,623 versus placebo, p < 0.0002). CONCLUSIONS: In healthy male volunteers with mild hypercholesterolemia, treatment for 2 weeks with 600 mg/day CP-148,623 inhibited fractional cholesterol absorption by 35% to 40%, increased fecal neutral sterol excretion by 60% to 70%, and reduced serum LDL cholesterol by 10% to 12%.

Relationship of 133Xe cerebral blood flow to middle cerebral arterial flow velocity in men at rest.

Cerebral blood flow (CBF) was measured by 133Xe clearance simultaneously with the velocity of blood flow through the left middle cerebral artery (MCA) over a wide range of arterial PCO2 in eight normal men. Average arterial PCO2, which was varied by giving 4% and 6% CO2 in O2 and by controlled hyperventilation on O2, ranged from 25.3 to 49.9 mm Hg. Corresponding average values of global CBF15 were 27.2 and 65.0 ml 100 g min-1, respectively, whereas MCA blood-flow velocity ranged from 42.8 to 94.2 cm/s. The relationship of CBF to MCA blood-flow velocity over the imposed range of arterial PCO2 was described analytically by a parabola with the equation: CBF = 22.8 - 0.17 x velocity + 0.006 x velocity2 The observed data indicate that MCA blood-flow velocity is a useful index of CBF response to change in arterial PCO2 during O2 breathing at rest. With respect to baseline values measured while breathing 100% O2 spontaneously, percent changes in velocity were significantly smaller than corresponding percent changes in CBF at increased levels of arterial PCO2 and larger than CBF changes at the lower arterial PCO2. These observed relative changes are consistent with MCA vasodilation at the site of measurement during exposure to progressive hypercapnia and also during extreme hyperventilation hypocapnia.

Metabolic effects of darglitazone, an insulin sensitizer, in NIDDM subjects.

Insulin resistance is a significant pathogenetic factor in the development of non-insulin-dependent diabetes mellitus (NIDDM). A new class of drugs, the thiazolidinediones, have been shown to lower blood glucose levels without stimulating insulin secretion. We report the metabolic effect of the thiazolidinedione, darglitazone, in obese NIDDM subjects. Nineteen subjects were enrolled in a double-blind placebo-controlled study in which 25 mg of darglitazone was given once a day for 14 days. Nine subjects received the active drug and ten subjects received placebo. Darglitazone-treated subjects showed; 1) a decrease in 24-h plasma glucose area under the curve from 292.8 +/- 31.2 to 235.2 +/- 21.6 mmol.h-1.l-1 p = 0.002; 2) a decrease in 24-h serum insulin area under the curve from 1027.2 +/- 254.4 to 765.6 +/- 170.4 microU.h-1.l-1 p = 0.045; 3) a decrease in 24-h non-esterified fatty acid area under the curve from 1900 +/- 236 to 947 +/- 63 g.h-1.l-1 p = 0.002; 4) a decrease in mean 24-h serum triglyceride by 25.9 +/- 6.2% as compared to -3.9 +/- 4.8% for the placebo-treated group, p = 0.012. Placebo-treated subjects showed no change in their metabolic parameters after treatment. Thus, darglitazone is effective in increasing insulin effectiveness in obese NIDDM subjects. The potential for this and similar drugs to treat or prevent NIDDM as well as the insulin-resistance syndrome needs to be explored.

Overnight branched-chain amino acid infusion causes sustained suppression of muscle proteolysis.

Short-term (3 to 4 hours) infusion of branched-chain amino acids (BCAA) has been shown to suppress muscle protein breakdown. Whether these effects are sustained with chronic elevations of BCAA is not known. In the present study, we examined the effect of an overnight (16-hour) systemic BCAA infusion on whole-body and skeletal muscle amino acid metabolism, as assessed by simultaneously measured 3H-phenylalanine and 14C-leucine kinetics in eight normal volunteers; 10 overnight-fasted subjects studied during a 4-hour saline infusion served as controls. Overnight BCAA infusion increased plasma BCAA concentrations by fivefold to eightfold, and this was associated with a 20% to 60% decline in arterial concentrations of other amino acids. For Phe, this decline was mediated by a reduction in the systemic rate of appearance ([Ra] 0.38 +/- 0.03 v 0.60 +/- 0.01 mumol/kg/min for BCAA and saline, respectively, P < .001). Endogenous Leu Ra, calculated more indirectly as the difference between the total Leu Ra and the unlabeled Leu infusion rate, did not differ between groups. In the forearm, overnight BCAA infusion resulted in a diminished net release of Phe (-3 +/- 2 v -18 +/- 4 [saline] nmol/min/100 mL, P < .02), and BCAA balance became markedly positive (751 +/- 93 v -75 +/- 30, P < .001). The diminished net forearm Phe release was accounted for by a decrease in local Phe Ra (P < .02). As with the systemic endogenous Leu Ra, forearm Leu Ra was not reproducibly affected by infused BCAA.(ABSTRACT TRUNCATED AT 250 WORDS)

Human tolerance and physiological responses to exercise while breathing oxygen at 2.0 ATA.

Multiple physiological functions were monitored in ten men who performed two 30-min periods of 150-W ergometer exercise during 120-min exposures to O2 at 2.0 ATA. There were no convulsions or electroencephalographic manifestations of increased excitability. Sequential measurements of peripheral visual fields, pulmonary mechanical function, mental performance, and cardiovascular function during the resting recovery after each of the two exercise periods were not detectably altered from pre-exercise control values. Pre- and post-exposure measurements of visual acuity, accommodation, pupil diameter, visual cortical activity, and retinal electrical activity also revealed no significant differences. While CNS symptoms were absent, average arterial PCO2 rose by about 5 mm Hg during both exercise periods. This finding was confirmed in six subjects who performed four 6-min periods of continuous exercise at 50, 100, 150, and 200 W while breathing O2 at 2.0 ATA. Average arterial PCO2 rose nearly linearly from 34.3 mm Hg at rest to 44.0 mm Hg at 200 W. Arterial PCO2-related increments in brain blood flow and PO2 may explain part or all of the known detrimental influence of exercise on CNS O2 tolerance.

Prostaglandin E2 induces up-regulation of murine macrophage beta-endorphin receptors.

Cultured murine bone marrow macrophages specifically bound 125I-labeled beta-endorphin. Binding was displaceable by 100 times molar excess of full-length beta-endorphin but was insensitive to the opioid receptor antagonist, naloxone. Binding was inhibited by beta-endorphin's C-terminal tetrapeptide, lys-lys-gly-glu, but not by the truncated N-terminal 27 amino acid fragment, indicating that binding of beta-endorphin to this receptor is dependent on its C-terminus. Macrophages incubated for 24 h with 10(-8)-10(-5) M prostaglandin E2 showed a dose-dependent increase in beta-endorphin binding, implying receptor up-regulation. This was also observed in response to the phosphodiesterase inhibitor, isobutylmethylxanthine, indicating that regulation of these receptors may be mediated through a cAMP-dependent process. This is the first demonstration that beta-endorphin receptor expression can be positively regulated.

Effects of epinephrine on human muscle glucose and protein metabolism.

Systemic epinephrine infusion causes hypoaminoacidemia and inhibits whole body leucine flux (proteolysis) in humans. Its specific action on muscle protein is not known and is difficult to assess during systemic epinephrine infusions, which affect plasma insulin, amino acid, and free fatty acid concentrations. During a steady-state infusion of L-[ring-2,6-3H]phenylalanine, we examined the effect of locally infused epinephrine on the metabolism of protein and glucose in forearm muscle of 10 healthy human volunteers. During local epinephrine infusion, systemic concentrations of glucose, phenylalanine, insulin, and epinephrine were unchanged and lactate declined (P < 0.02). Compared with baseline, epinephrine induced significant increases in forearm blood flow (P < 0.01) and net lactate release (P < 0.001) and a decrease in glucose uptake (P < 0.01) at both 2 and 4 h. At 2 and 4 h phenylalanine release from muscle proteolysis was suppressed (P < 0.01), and at 4 h the net phenylalanine balance was less negative than baseline (P < 0.02), indicating an anticatabolic effect on muscle protein. We conclude that in human forearm muscle epinephrine, at physiological concentrations, has a catabolic effect on muscle glycogen but an anticatabolic action on muscle protein. The mechanism of this latter effect is not known.