Levels of recombinant human granulocyte colony-stimulating factor in serum are inversely correlated with circulating neutrophil counts.

Recombinant human granulocyte colony-stimulating factor (rhG-CSF) is effective in countering chemotherapy-induced neutropenia. However, serum rhG-CSF levels cannot be maintained throughout the course of rhG-CSF therapy. The drop in serum rhG-CSF levels may vary with the duration of rhG-CSF administration or with the circulating neutrophil counts. We investigated the relationship between serum G-CSF levels and circulating neutrophil counts and the pharmacokinetics of rhG-CSF for patients with lung cancer who had been treated with myelosuppressive chemotherapy and then with subcutaneous rhG-CSF (lenograstim, 2 micrograms per kg of body weight per day). Twelve patients were randomly assigned to four groups with different rhG-CSF therapy schedules. Serum G-CSF levels were measured by an enzyme immunoassay method. Serum G-CSF levels during the rhG-CSF therapy greatly exceeded endogenous G-CSF levels and were mainly due to the presence of exogenous rhG-CSF rather than increased levels of endogenous G-CSF. Despite the duration of rhG-CSF administration, serum G-CSF levels during rhG-CSF therapy were inversely correlated with circulating neutrophil counts (r2 = 0.73, P < 0.0001). The value for the area under the concentration-time curve of rhG-CSF on the day of neutrophilia was lower than that on the day of neutropenia (P < 0.05). Our results suggest that the fall in serum G-CSF levels during rhG-CSF therapy may result from increased clearance and/or decreased absorption of rhG-CSF, two processes related to circulating neutrophil counts.     

Prostacyclin Reversal of Lethal Endotoxemia in Dogs

Severe endotoxemia, a condition where microembolization and intravascular coagulation are thought to play important roles, was treated experimentally with prostacyclin (PGI₂). In a study of 24 dogs, 8 control animals injected with 1.75 mg·kg⁻¹ of endotoxin died within 24 h. Six animals given intravenous aspirin 100 mg/kg, 30 min after endotoxin died. 9 of 10 dogs infused with 100 ng PGI₂·kg⁻¹·min⁻¹ for 3 h, given 30 min after the injection of endotoxin survived 24 h (P < 0.025). Injection of endotoxin resulted in a: (a) maximal 62% fall in mean arterial pressure (P < 0.001); (b) transient doubling of mean pulmonary arterial pressure (P < 0.001); (c) initial 70% drop in cardiac index (P < 0.001); (d) decline in blood platelets from 213,700 to 13,700/mm³ (P < 0.001), and leukocytes from 7,719 to < 750/mm³ (P < 0.001); (e) depressed urine output (P < 0.001); (f) 34% decrease in blood fibrinogen (P < 0.01) and an increase in fibrin degradation products > 50 μg/ml (P < 0.001); (g) fivefold increase in circulating cathepsin D titer (P < 0.005) and (h) increase in blood norepinephrine (P < 0.005), dopamine (P < 0.005), and epinephrine (P < 0.001). Aspirin treatment led to an increase in mean arterial pressure (P < 0.001) and mean pulmonary arterial pressure (P < 0.005), but cardiac index, urine flow, platelets, leukocytes, fibrin degradation products, and cathepsin D levels remained similar to untreated controls. After infusion of PGI₂ there was a: (a) prompt increase of cardiac index to base-line levels; (b) late increase in mean arterial pressure (P < 0.005) after the discontinuation of PGI₂ treatment (c) restoration of urine output; (d) increase in circulating platelets to levels still below base line but above untreated control animals (P < 0.05); (e) no effect on circulating leukocyte levels; (f) fall in fibrin degradation products to 11.2 μg/ml (P < 0.05); (g) decline in cathepsin D levels to values 60% lower than the untreated controls (P < 0.025); and (h) reduction in plasma norepinephrine levels to base line at 4 h (P < 0.005). Although the mode of PGI₂ action is not clear, it is effective in the treatment of experimental endotoxemia.     

Influence of Renal Failure on Ciprofloxacin Pharmacokinetics in Rats

Ciprofloxacin pharmacokinetics have been shown to be modified in patients with renal failure (e.g., the intestinal secretion of ciprofloxacin is increased). This study investigated the influence of renal failure on the pharmacokinetics of ciprofloxacin following oral and parenteral administration to rats of a dose of 50 mg/kg of body weight. After parenteral administration, only renal clearance (CL_R) was reduced in nephrectomized rats (5.3 ± 1.4 versus 17.8 ± 4.7 ml/min/kg, P < 0.01, nephrectomized versus control rats). However, nonrenal clearance was increased in nephrectomized rats (32 ± 4 versus 15 ± 5 ml/min/kg, P < 0.01, nephrectomized versus control rats), suggesting compensatory mechanisms for reduced renal function. After oral administration, apparent total clearance and CL_R were reduced (P < 0.01) in nephrectomized rats (117 ± 25 and 6.8 ± 4.4 ml/min/kg, respectively) compared with the values for control rats (185 ± 9 and 22.6 ± 5.3 ml/min/kg, respectively) and the area under the concentration-time curve was higher (P < 0.01) for nephrectomized rats (436.3 ± 90.5 mg · min/liter) than for control rats (271.3 ± 14.3 mg · min/liter). Terminal elimination half lives in the two groups remained constant after oral and parenteral administration. These results suggest an increased bioavailability of ciprofloxacin in nephrectomized rats, which was confirmed by a nonlinear mixed-effect model.     

Extended-spectrum beta-lactamase production is associated with an increase in cell invasion and expression of fimbrial adhesins in Klebsiella pneumoniae

Extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae strains are suggested to possess higher pathogenic potential than non-ESBL producers. Microbial adherence to and invasion of host cells are critical steps in the infection process, so we examined the expression of type 1 and 3 fimbrial adhesins by 58 ESBL-producing and 152 nonproducing isolates of K. pneumoniae and their abilities to invade ileocecal and bladder epithelial cells. Mannose-sensitive hemagglutination of guinea pig erythrocytes and mannose-resistant hemagglutination of ox erythrocytes were evaluated to determine the strains’ abilities to express type 1 and type 3 fimbriae, respectively. Bacterial adhesion to and invasion of epithelial cells were tested by enzyme-linked immunosorbent assay and imipenem killing assay, respectively. The adherence of ESBL- and non-ESBL-producing strains to epithelial cells did not differ significantly (P > 0.05). In contrast, the proportion of strains capable of invading (>5% relative invasion) ileocecal and bladder epithelial cells was significantly higher among ESBL producers (81%, n = 47/58, and 27.6%, n = 16/58, respectively) than among non-ESBL producers (61%, n = 93/152, and 10%, n = 15/152, respectively) (P = 0.0084, odds ratio [OR] = 2.711, 95% confidence interval [CI] = 1.302 to 5.643 and P = 0.0021, OR = 4.79, 95% CI = 1.587 to 7.627). The mean invasion by ESBL producers (5.5% ± 2.8% and 3.3% ± 2.7%, respectively) was significantly higher than that by non-ESBL producers (2.9% ± 2.6% and 1.8% ± 2%, respectively) (P < 0.0001). Likewise, the proportion of ESBL producers coexpressing both fimbrial adhesins was significantly higher (79.3%; n = 46/58) than that of non-ESBL producers (61.8%; n = 94/152) (P = 0.0214; OR = 2,365; 95% CI = 1.157 to 4.834). Upon acquisition of SHV-12-encoding plasmids, two transconjugants switched on to produce type 3 fimbriae while expression of type 1 fimbriae was not affected. The acquisition of an ESBL plasmid appeared to upregulate the phenotypic expression of one or more genes, resulting in greater invasion ability.     

Mechanisms of Epinephrine-induced Glucose Intolerance in Normal Humans: ROLE OF THE SPLANCHNIC BED

To evaluate the role of the splanchnic bed in epinephrine-induced glucose intolerance, we selectively assessed the components of net splanchnic glucose balance, i.e., splanchnic glucose uptake and hepatic glucose production, and peripheral glucose uptake by combining infusion of [3-³H]glucose with hepatic vein catheterization. Normal humans received a 90-min infusion of either glucose alone (6.5 mg/kg⁻¹ per min⁻¹) or epinephrine plus glucose at two dose levels: (a) in amounts that simulated the hyperglycemia seen with glucose alone (3.0 mg/kg⁻¹ per min⁻¹); and (b) in amounts identical to the control study. During infusion of glucose alone, blood glucose rose twofold, insulin levels and net posthepatic insulin release increased three- to fourfold, and net splanchnic glucose output switched from a net output (1.65±0.12 mg/kg⁻¹ per min⁻¹) to a net uptake (1.56±0.18). This was due to a 90-95% fall (P < 0.001) in hepatic glucose production and a 100% rise (P < 0.001) in splanchnic glucose uptake (from 0.86±0.14 to 1.71±0.12 mg/kg⁻¹ per min⁻¹), which in the basal state amounted to 30-35% of total glucose uptake. Peripheral glucose uptake rose by 170-185% (P < 0.001). When epinephrine was combined with the lower glucose dose, blood glucose, insulin release, and hepatic blood flow were no different from values observed with glucose alone. However, hepatic glucose production fell only 40-45% (P < 0.05 vs. glucose alone) and, most importantly, the rise in splanchnic glucose uptake was totally blocked. As a result, splanchnic glucose clearance fell by 50% (P < 0.05), and net splanchnic glucose uptake did not occur. The rise in peripheral glucose uptake was also reduced by 50-60% (P < 0.001). When epinephrine was added to the same dose of glucose used in the control study, blood glucose rose twofold higher (P < 0.001). The initial rise in splanchnic glucose uptake was totally prevented; however, beyond 30 min, splanchnic glucose uptake increased, reaching levels seen in the control study when severe hyperglycemia occurred. Splanchnic glucose clearance, nevertheless, remained suppressed throughout the entire study (40%-50%, P < 0.01).     

Comparison of Aryl Hydrocarbon Hydroxylase Induction in Cultured Blood Lymphocytes and Pulmonary Macrophages

Aryl hydrocarbon hydroxylase induction was studied in cultured peripheral blood lymphocytes and pulmonary alveolar macrophages from 15 smokers and 8 nonsmokers with a variety of pulmonary diseases. Enzyme levels in lymphocytes from cigarette smokers cultured in medium without an inducing agent were 57±6 mU/10⁶ cells (mean±SEM), while enzyme levels in lymphocytes from nonsmokers were 20±2 mU/10⁶ cells (P < 0.001). When lymphocytes were cultured in the presence of the inducing agent, benzo-(a)anthracene, enzyme activity was increased to 168±23 mU/10⁶ cells in smokers' cells and 99±22 mU/10⁶ cells in lymphocytes from nonsmokers (P < 0.04). When noninduced enzyme values in cultured macrophages were compared, smokers' cells had enzyme levels of 45±5 mU/10⁶ cells, whereas nonsmokers had enzyme activity of 24±2 mU/10⁶ cells (P < 0.002). However, pulmonary macrophages from smokers or nonsmokers, cultured in the presence of benzo(a)-anthracene, had similar levels of induced enzyme activity (P > 0.1). A positive correlation was observed for nonsmokers (r = 0.596, P > 0.1 <0.2) or smokers (r = 0.640, P < 0.04), when enzyme values for noninduced cultures of macrophages and lymphocytes from individual patients were simultaneously compared. Enzyme values for macrophages and lymphocytes cultured in the presence of an inducer also revealed a positive correlation for individual smokers (r = 0.801, P < 0.001) or nonsmokers (r = 0.785, P < 0.01). Inducibility (expressed as fold-induction) for macrophages and lymphocytes from individual patients was also positively correlated (r = 0.889, P < 0.001 for nonsmokers and r = 0.942, P < 0.001 for smokers). These results indicate that the capacity for aryl hydrocarbon hydroxylase induction is similar whether tested in lymphocytes or pulmonary macrophages from this group of pulmonary disease patients.     

Reversal of Secondary Hyperparathyroidism by Cimetidine in Chronically Uremic Dogs

Chronic cimetidine therapy has been shown to suppress circulating concentrations of immunoreactive parathyroid hormone (iPTH) in hemodialysis patients. To evaluate the long-term metabolic effects of cimetidine treatment, we studied seven chronically uremic dogs for 20 wk. The dogs were studied under metabolic conditions before, during, and after cimetidine therapy. iPTH fell progressively in the five treated dogs from 536±70 μleq/ml (mean±SE) (nl < 100 μleq/ml) before treatment to 291±25 μleq/ml at 12 wk (P < 0.001) and 157±32 μleq/ml at 20 wk (P < 0.001). The control dogs showed no consistent change in iPTH. The fall in iPTH was not associated with a change in serum ionized calcium. However, serum phosphorus decreased from 5.7±0.9 mg/dl to 3.4±0.2 mg/dl by the 20th wk (P < 0.05). By contrast, the serum concentration of 1,25-dihydroxycholecalciferol increased in all treated dogs from 33.4±4.3 pg/ml to 51.8±2.4 pg/ml during treatment (P < 0.01). Calcium balance was negative in all seven dogs before cimetidine (−347±84 mg/72 h) and remained so in the control dogs; it became positive in the five treated dogs after 12 wk (1,141±409 mg/72 h) (P < 0.05). Phosphorus balance, 24-h fractional phosphate excretion, and creatinine clearance remained unchanged. Pooled samples of serum obtained during the control and 20th wk of therapy were fractionated by gel filtration and the eluates assayed for immunoreactivity. The decrease in iPTH was associated with a decrease in all the immunoreactive species, indicating suppression of parathyroid gland secretion.     

Interactions between Antibiotics and Human Neutrophils in the Killing of Staphylococci: STUDIES WITH NORMAL AND CYTOCHALASIN B-TREATED CELLS

Normal and antibiotic-pretreated staphylococci were incubated with human neutrophils to determine the interactions between cells and antimicrobials in the killing of the organisms. Staphylococcus aureus 502A pretreated during log-phase growth with subinhibitory (¼ minimum inhibiting concentration) (MIC) concentrations of penicillin G were more susceptible to killing by normal neutrophils than untreated bacteria (intracellular survival 0.17±0.04 vs. 1.5±0.38%, mean±SEM, respectively, at 35 min in 14 experiments; P < 0.01 by t test). Furthermore, this enhanced susceptibility to killing was observed even when phagosome formation was inhibited by cytochalasin B (65.6±4.6% pencillintreated vs. 30.5±4.5% untreated killed at 30 min in 14 experiments, P < 0.001). Pretreatment of S. aureus with vancomycin similarly enhanced susceptibility to killing by cytochalasin B-treated polymorphonuclear leukocytes (PMN), whereas pretreatment with gentamicin did not.     

Effect of captopril on uterine blood flow and prostaglandin E synthesis in the pregnant rabbit

Captopril, 5 mg/kg, administered to pregnant rabbits caused a reduction in mean arterial pressure (MAP) from 106±2 to 87±2 mmHg (P<0.01) without change in cardiac output or renal blood flow. Uterine blood flow fell from 31.9±2.5 to 21.3±3.4 ml/min (P<0.01) as uterine vein prostaglandin E series level (PGE) decreased from 127±23 ng/ml to 26±8 ng/ml (P<0.01). Saralasin also caused a reduction in MAP from 110±5 to 92±4.3 (P<0.01), a reduction in uterine blood flow from 28.8±1.6 to 21.8±1.7 ml/min (P<0.01) as uterine vein PGE decreased from 121.3±14.4 to 63.5±14.2 ng/ml (P<0.01). Plasma renin activity (PRA) was higher in the uterine vein, 11±3 ng/ml per h, than peripheral vein, 6±1.6 ng/ml per h, (P<0.05), before Captopril and rose in the uterine vein to 90±19 ng/ml per h (P<0.01) as peripheral vein PRA rose to 62±15 ng/ml per h (P<0.05) after Captopril. After saralasin uterine vein PRA rose from 4.6±1.5 to 14.8±6.3 ng/ml per h (P<0.05) and peripheral vein PRA rose from 3.7±1 to 6.5±2.1 (P<0.05).     

Stimulation of Monovalent Cation Active Transport by Low Concentrations of Cardiac Glycosides: ROLE OF CATECHOLAMINES

The stimulatory effect of low concentrations of ouabain on the Na-K pump in isolated guinea pig left atria was studied in vitro by assessing active transport of the K⁺ analog Rb⁺. Active transport of Rb⁺ was stimulated 20±8% (SEM, P < 0.05) above control values by 3 nM ouabain, but was inhibited by concentrations >10 nM. Preincubation with the β-adrenergic antagonist propranolol (1 μM) completely blocked stimulation of active transport of Rb⁺ by 3 nM ouabain. Norepinephrine, 10 nM, increased Rb⁺ active transport 29±10% (P < 0.02) above control values. The β-adrenergic agonist l-isoproterenol, 10 nM, increased active transport of Rb⁺ by 33±10% (P < 0.01) above control levels. This stimulatory effect was abolished if tissues were first exposed to propranolol. Tyramine (0.1 μM), a stimulator of endogenous catecholamine release, increased active transport of Rb⁺ 26±12% (P < 0.05) above control values. Rb⁺ active transport was not significantly changed when left atrial tissues were incubated with α-adrenergic agonists or antagonists. Ouabain stimulation of Rb⁺ active transport was prevented by in vivo depletion of myocardial endogenous catecholamines by either reserpine or 6-hydroxydopamine. These findings indicated that in myocardial tissue, Na-K pump stimulation by low concentrations of ouabain is mediated at least in part through β-adrenergic effects of endogenous catecholamines.     

Fluconazole Pharmacokinetics in Burn Patients

The pharmacokinetics of fluconazole in nine adult patients with severe (30 to 95% total body surface area) burns were studied. There was no significant difference in half-life (t_1/2), clearance (CL), or volume of distribution (V) over time in five patients on days 3 and 8 of the study (P > 0.05). Combined parameter estimates (means ± standard deviations) for all nine patients for the two study periods were as follows: t_1/2, 24.4 ± 5.8 h; CL, 0.36 ± 0.09 ml/min/kg; and V, 0.72 ± 0.12 liters/kg. These estimates of t_1/2 and CL in burn patients were approximately 13% shorter and 30% more rapid, respectively, than the most extreme estimates reported for other populations.     

Cell-surface protein disulfide isomerase catalyzes transnitrosation and regulates intracellular transfer of nitric oxide

Since thiols can undergo nitrosation and the cell membrane is rich in thiol-containing proteins, we considered the possibility that membrane surface thiols may regulate cellular entry of NO. Recently, protein disulfide isomerase (PDI), a protein that catalyzes thio–disulfide exchange reactions, has been found on the cell-surface membrane. We hypothesized that cell-surface PDI reacts with NO, catalyzes S-nitrosation reactions, and facilitates NO transfer from the extracellular to intracellular compartment. We observed that PDI catalyzes the S-nitrosothiol–dependent oxidation of the heme group of myoglobin (15-fold increase in the rate of oxidation compared with control), and that NO reduces the activity of PDI by 73.1 ± 21.8% (P < 0.005). To assess the role of PDI in the cellular action of NO, we inhibited human erythroleukemia (HEL) cell-surface PDI expression using an antisense phosphorothioate oligodeoxynucleotide directed against PDI mRNA. This oligodeoxynucleotide decreased cell-surface PDI content by 74.1 ± 9.3% and PDI folding activity by 46.6 ± 3.5% compared with untreated or “scrambled” phosphorothioate oligodeoxynucleotide–treated cells (P < 0.0001). This decrease in cell-surface PDI was associated with a significant decrease in cyclic guanosine monophosphate (cGMP) generation after S-nitrosothiol exposure (65.4 ± 26.7% reduction compared with control; P < 0.05), with no effect on cyclic adenosine monophosphate (cAMP) generation after prostaglandin E₁ exposure. These data demonstrate that the cellular entry of NO involves a transnitrosation mechanism catalyzed by cell-surface PDI. These observations suggest a unique mechanism by which extracellular NO gains access to the intracellular environment.     

Effect of protein binding on the pharmacological activity of highly bound antibiotics

During antibiotic drug development, media are frequently spiked with either serum/plasma or protein supplements to evaluate the effect of protein binding. Usually, previously reported serum or plasma protein binding values are applied in the analysis. The aim of this study was to evaluate this approach by experimentally measuring free, unbound concentrations for antibiotics with reportedly high protein binding and their corresponding antimicrobial activities in media containing commonly used protein supplements. Free, unbound ceftriaxone and ertapenem concentrations were determined in bacterial growth medium with and without bovine/human serum albumin, as well as adult bovine serum and human plasma using in vitro microdialysis. The corresponding antimicrobial activity was determined in MIC and time-kill curve experiments using Escherichia coli ATCC 25922 and Streptococcus pneumoniae ATCC 6303 as test strains. A semimechanistic maximum effect model was simultaneously fitted to the data and respective EC₅₀ (concentration at half-maximum effect) values compared. Protein binding differed significantly for ceftriaxone (P < 0.05) between human plasma (76.8 ± 11.0%) and commercially available bovine (20.2 ± 8.3%) or human serum albumin (56.9 ± 16.6%). Similar results were obtained for ertapenem (human plasma, 73.8 ± 11.6%; bovine serum albumin, 12.4 ± 4.8%; human serum albumin, 17.8 ± 11.5%). The MICs and EC₅₀s of both strains were significantly increased (P < 0.05) for ceftriaxone when comparing human and bovine serum albumin, whereas the EC₅₀s were not significantly different for ertapenem. Free, unbound antibiotic concentrations differed substantially between plasma and protein supplements and correlated well with antimicrobial efficacy. Therefore, free, active concentrations should be measured in the test system instead of correcting for literature protein binding values.     

Better lactate clearance associated with good neurologic outcome in survivors who treated with therapeutic hypothermia after out-of-hospital cardiac arrest

Introduction

Several methods have been proposed to evaluate neurological outcome in out-of-hospital cardiac arrest (OHCA) patients. Blood lactate has been recognized as a reliable prognostic marker for trauma, sepsis, or cardiac arrest. The objective of this study was to examine the association between initial lactate level or lactate clearance and neurologic outcome in OHCA survivors who were treated with therapeutic hypothermia.

Methods

This retrospective cohort study included patients who underwent protocol-based 24-hour therapeutic hypothermia after OHCA between January 2010 and March 2012. Serum lactate levels were measured at the start of therapy (0 hours), and after 6 hours, 12 hours, 24 hours, 48 hours and 72 hours. The 6 hour and 12 hour lactate clearance were calculated afterwards. Patients’ neurologic outcome was assessed at one month after cardiac arrest; good neurological outcome was defined as Cerebral Performance Category one or two. The primary outcome was an association between initial lactate level and good neurologic outcome. The secondary outcome was an association between lactate clearance and good neurologic outcome in patients with initial lactate level >2.5 mmol/l.

Results

Out of the 76 patients enrolled, 34 (44.7%) had a good neurologic outcome. The initial lactate level showed no significant difference between good and poor neurologic outcome groups (6.07 ±4 .09 mmol/L vs 7.13 ± 3.99 mmol/L, P = 0.42), However, lactate levels at 6 hours, 12 hours, 24 hours, and 48 hours in the good neurologic outcome group were lower than in the poor neurologic outcome group (3.81 ± 2.81 vs 6.00 ± 3.22 P <0.01, 2.95 ± 2.07 vs 5.00 ± 3.49 P <0.01, 2.17 ± 1.24 vs 3.86 ± 3.92 P <0.01, 1.57 ± 1.02 vs 2.21 ± 1.35 P = 0.03, respectively). The secondary analysis showed that the 6-hour and 12-hour lactate clearance was higher for good neurologic outcome patients (35.3 ± 34.6% vs 6.89 ± 47.4% P = 0.01, 54.5 ± 23.7% vs 25.6 ± 43.7% P <0.01, respectively). After adjusting for potential confounding variables, the 12-hour lactate clearance still showed a statistically significant difference (P = 0.02).

Conclusion

The lactate clearance rate, and not the initial lactate level, was associated with neurological outcome in OHCA patients after therapeutic hypothermia.     

Neuroendocrine responses to glucose ingestion in man. Specificity, temporal relationships, and quantitative aspects

The mechanisms of postprandial glucose counterregulation—those that blunt late decrements in plasma glucose, prevent hypoglycemia, and restore euglycemia—have not been fully defined. To begin to clarify these mechanisms, we measured neuroendocrine and metabolic responses to the ingestion of glucose (75 g), xylose (62.5 g), mannitol (20 g), and water in ten normal human subjects to determine for each response the magnitude, temporal relationships, and specificity for glucose ingestion. Measurements were made at 10-min intervals over 5 h. By multivariate analysis of variance, the plasma glucose (P < 0.0001), insulin (P < 0.0001), glucagon (P < 0.03), epinephrine (P < 0.0004), and growth hormone (P < 0.01) curves, as well as the blood lactate (P < 0.0001), glycerol (P < 0.001), and β-hydroxybutyrate (P < 0.0001) curves following glucose ingestion differed significantly from those following water ingestion. However, the growth hormone curves did not differ after correction for differences at base line. In contrast, the plasma norepinephrine (P < 0.31) and cortisol (P < 0.24) curves were similar after ingestion of all four test solutions, although early and sustained increments in norepinephrine occurred after all four test solutions. Thus, among the potentially important glucose regulatory factors, only transient increments in insulin, transient decrements in glucagon, and late increments in epinephrine are specific for glucose ingestion. They do not follow ingestion of water, xylose, or mannitol.

Following glucose ingestion, plasma glucose rose to peak levels of 156±6 mg/dl at 46±4 min, returned to base line at 177±4 min, reached nadirs of 63±3 mg/dl at 232±12 min, and rose to levels comparable to base line at 305 min, which was the final sampling point. Plasma insulin rose to peak levels of 150±17 μU/ml (P < 0.001) at 67±8 min. At the time glucose returned to base line, insulin levels (49±12 μU/ml) remained fourfold higher than base line (P < 0.01); thereafter they declined but never fell below base line. Plasma glucagon decreased from 95±14 pg/ml to nadirs of 67±11 pg/ml (P < 0.001) at 84±9 min and then rose progressively to peak levels of 114±17 pg/ml (P < 0.001 vs. nadirs) at 265±12 min. Plasma epinephrine, which was 18±4 pg/ml at base line, did not change initially and then rose to peak levels of 119±20 pg/ml (P < 0.001) at 271±13 min.

These data indicate that the glucose counterregulatory process late after glucose ingestion is not solely due to the dissipation of insulin and that sympathetic neural norepinephrine, growth hormone, and cortisol do not play critical roles. They are consistent with, but do not establish, physiologic roles for the counterregulatory hormones—glucagon, epinephrine, or both—in that process.

     

Triiodothyronine-induced Thyrotoxicosis Increases Mononuclear Leukocyte β-Adrenergic Receptor Density in Man

β-Adrenergic receptors are increased in some tissues of experimentally thyrotoxic animals but are reported to be unchanged in mononuclear leukocytes of spontaneously thyrotoxic humans. We examined the effects of triiodothyronine (100 μg/d for 7 d) and placebo on high-affinity mononuclear leukocyte β-adrenergic receptors in 24 normal human subjects, using a double-blind design. β-Adrenergic receptors were assessed by specific binding of the antagonist (-)[³H]dihydroalprenolol. Triiodothyronine administration resulted in objective evidence of moderate thyrotoxicosis and an increase in mean (-)[³H]dihydroalprenolol binding from 25±3 to 57±9 fmol/mg protein (P < 0.001). The latter was attributable, by Scatchard analysis, to an increase in β-adrenergic receptor density (967 ± 134 to 2250 ± 387 sites per cell, P < 0.01); apparent dissociation constants did not change. Placebo administration had no effects. Marked inter- and intraindividual variation in mononuclear leukocyte β-adrenergic receptor density was also noted. Because this was approximately threefold greater than analytical variation, it is largely attributable to biologic variation. Thus, we conclude: (a) The finding of a triiodothyronine-induced increase in mononuclear leukocyte β-adrenergic receptor density in human mononuclear leukocytes, coupled with similar findings in tissues of experimentally thyrotoxic animals, provides support for the use of mononuclear leukocytes to assess receptor status in man. (b) There is considerable biologic variation in β-adrenergic receptor density in man. (c) The findings of thyroid hormone-induced increments in β-adrenergic receptor density provide a plausible mechanism for the putative enhanced responsiveness to endogenous catecholamines of patients with thyrotoxicosis.     

Comparative Pharmacology of Cefaclor and Cephalexin

Two cephalosporin antibiotics, cefaclor and cephalexin, were administered orally to healthy, adult male volunteers for comparison of their pharmacological properties. In doses of 250 mg orally, cefaclor produced a peak serum concentration of 6.01 ± 0.55 (standard deviation [SD]) μg/ml compared with 9.43 ± 2.36 μg/ml for cephalexin (P < 0.01). The half-lives were 0.58 ± 0.07 (SD) h and 0.80 ± 0.12 (SD) h, and elimination constants were 1.22 ± 0.15 and 0.88 ± 0.13 h⁻¹ for cefaclor and cephalexin, respectively (P < 0.001). Neither drug showed accumulation over the dosing period, and both were well tolerated.     

Role of Plasma Vasopressin in Impaired Water Excretion of Glucocorticoid Deficiency

In the present study, the effect of selective glucocorticoid deficiency on renal water excretion was investigated in conscious, trained, adrenalectomized dogs. The animals were studied before and after a water load while on replacement therapy of desoxycorticosterone acetate, 5 mg/day, and dexamethasone, 0.8 mg/day (group I), and while off dexamethasone for 5-9 days (group II). Before the water load the weight, inulin space, cardiac output, blood pressure, glomerular filtration rate, renal blood flow, plasma osmolality, and plasma antidiuretic hormone measured by radioimmunoassay were similar in both groups I and II. However, after a 40 ml/kg water load a marked impairment in renal water excretion in the glucocorticoid deficient dogs became apparent. Maximal free water clearance was −0.046±0.16 vs. 6.51±0.72 ml/min (P < 0.001) and minimal urinary osmolality was 425±56 vs. 82±3.5 mosmol/kg H₂O (P < 0.001) in group II as compared to group I. Plasma antidiuretic hormone was maximally suppressed during the water load in group I to 0.34±0.08 pg/ml but remained elevated at 9.18±1.79 pg/ml (P < 0.005) in group II. This nonsuppressibility of plasma antidiuretic hormone during water loading in group II was associated with a significant tachycardia of 145±6 vs. 87±6 beats/min (P < 0.001) in group I and a significantly lower stroke volume of 27±0 vs. 59±0.5 ml/beat (P < 0.001). In conclusion, our results implicate a persistent secretion of antidiuretic hormone as an important factor in the impaired water excretion of glucocorticoid deficiency. A deleterious effect of glucocorticoid deficiency on cardiac function was observed and this hemodynamic alteration could be involved in initiating a nonosmolar, baroreceptor-mediated release of vasopressin.     

Renal Extraction of Gentamicin in Anesthetized Dogs

The tubular handling of gentamicin (G) and its intrarenal distribution were determined to elucidate the mechanism of G accumulation in the kidney. At a serum level of 11.1 ± 0.5 μg/ml (10 animals), as maintained by constant infusion for 5 h, serum Na⁺ and K⁺, arterial pressure, effective renal plasma flow and glomerular filtration rate remained undisturbed. The clearance values in milliliters per minute for G, inulin, and p-aminohippuric acid were 40.3 ± 1.8, 49.9 ± 2.8, and 132 ± 14, respectively. The ratio of clearance of G to clearance of inulin was 0.82 ± 0.04 (P < 0.005), suggesting net reabsorption of G by the renal tubules. The renal cortex/serum ratio for G was 11.9 ± 2.1, and the medulla/serum ratio was 2.7 ± 0.4, indicating greater uptake of G by the cortex. The extraction ratio of p-aminohippuric acid was 0.74 ± 0.03. In contrast, the extraction ratio of G was 0.20 ± 0.03, which was significantly lower than that of inulin (0.30 ± 0.04). It is concluded that the accumulation of G in the cortex was due to tubular reabsorption. Probably some of the reabsorbed G became trapped in the epithelial cells after crossing the luminal membrane, whereas some returned to the circulation.     

Comparison of Acute Alterations in Left Ventricular Relaxation and Diastolic Chamber Stiffness Induced by Hypoxia and Ischemia: ROLE OF MYOCARDIAL OXYGEN SUPPLY-DEMAND IMBALANCE

To clarify conflicting reports concerning the effects of ischemia on left ventricular chamber stiffness, we compared the effects of hypoxia at constant coronary perfusion with those of global ischemia on left ventricular diastolic chamber stiffness using isolated, perfused rabbit hearts in which the left ventricle was contracting isovolumically. Since chamber volume was held constant, increases in left ventricular end diastolic pressure (LVEDP) reflected increases in chamber stiffness. At a control coronary flow rate (30 ml/min), 2 min of hypoxia and pacing tachycardia (4.0 Hz) produced major increases in postpacing LVEDP (10±1 to 24±3 mm Hg, P < 0.01) and the relaxation time constant, T, (40±4 to 224±37 ms, P < 0.001), while percent lactate extraction ratio became negative (+ 18±2 to −48±15%, P < 0.001). Coronary perfusion pressure decreased (72±5 to 52±3 mm Hg, P < 0.01), and since coronary flow was held constant, the fall in coronary perfusion pressure reflected coronary dilation and a decrease in coronary vascular resistance. Following an average of 71±6s reoxygenation and initial heart rate (2.0 Hz), LVEDP and relaxation time constant T returned to control. Hypoxia alone (without pacing tachycardia) produced similar although less marked changes (LVEDP, 10±1 to 20±3 mm Hg; and T, 32±3 to 119±22 ms; P < 0.01 for both) and there was a strong correlation between LVEDP and T (r = 0.82, P < 0.001).