The physiological regulation of pacing strategy during exercise: a critical review

The regulation of the pacing strategy remains poorly understood, because much of classic physiology has focused on the factors that ultimately limit, rather than regulate, exercise performance. When exercise is self-paced and work rate is free to vary in response to external and internal physiological cues, then a complex system is proposed to be responsible for alterations in exercise intensity, possibly through altered activation of skeletal muscle motor units. The present review evaluates the evidence for such a complex system by investigating studies in which interventions such as elevated temperature, altered oxygen content of the air, reduced fuel availability and misinformation about distance covered have resulted in alterations to the pacing strategy. The review further investigates how such a pacing strategy might be regulated for optimal performance, while ensuring that irreversible physiological damage is not incurred.

The effects of different air velocities on heat storage and body temperature in humans cycling in a hot, humid environment

AIM

The purposes of this study were to determine (i) the effects of different facing air velocities on body temperature and heat storage during exercise in hot environmental conditions and (ii) the effects of ingesting fluids at two different rates on thermoregulation during exercise in hot conditions with higher air velocities.

METHODS

On five occasions nine subjects cycled for 2 h at 33.0 +/- 0.4 degrees C with a relative humidity of 59 +/- 3%. Air velocity was maintained at 0.2 km h(-1) (0 WS), 9.9 +/- 0.3 km h(-1) (10 WS), 33.3 +/-2.2 km h(-1) (100 WS) and 50.1 +/- 3.2 km h(-1) (150 WS) while subjects replaced 58.8 +/- 6.8% of sweat losses. In the fifth condition, air velocity was maintained at 33.7 +/- 2.2 km h(-1) and subjects replaced 80.0 +/- 6.8% of sweat losses (100.80 WS).

RESULTS

Heat storage, body temperature and rating of perceived exertion were higher in 0 and 10 WS compared with all other conditions. There were no differences in any measured variable between 100 and 150 WS, or between 100 and 100.80 WS. Thus, the evaporative capacity of the environment is increased with higher air velocities, reducing heat storage and body temperature. At higher air velocities, a higher rate of fluid ingestion did not influence heat storage, body temperature or sweat rate.

CONCLUSION

The finding of previous laboratory studies showing a beneficial effect of high rates of fluid ingestion on thermoregulation during exercise in hot, humid, windstill conditions cannot be extrapolated to out-of-doors exercise in which facing air velocities are seldom lower than the athlete's rate of forward progression.

Survival and neonatal morbidity at the limits of viability in the mid 1990s: 22 to 25 weeks

OBJECTIVE

We determined neonatal survival and morbidity rates based on both fetal (stillborn) and neonatal deaths for infants delivered at 22 to 25 weeks' gestation.

STUDY DESIGN

Two hundred seventy-eight deliveries at 22 to 25 weeks' completed gestation were analyzed by gestational age groups between January 1993 and December 1997. Logistic regression models were used to identify maternal and neonatal factors associated with survival.

RESULTS

The rate of fetal death was 24%; 76% of infants were born alive and 46% survived to discharge. Survival rates including fetal death at 22, 23, 24, and 25 weeks were 1.8%, 34%, 49%, and 76%; and survival rates excluding fetal death were 4.6%, 46%, 59%, and 82%, respectively. Logistic regression analyses showed that higher gestational age (P<.0002), higher birth weight (P<.001), female sex (P<.005), and surfactant (P<.003) were associated with neonatal survival. Cesarean section was associated with decreased survival (P <.006).

CONCLUSION

Hospital neonatal survival rates of infants at the limits of viability are significantly lower with the inclusion of fetal deaths. This information should be considered when providing prognostic advice to families when mothers are in labor at 22 to 25 weeks' gestation.

Intracellular calcium alterations in response to increased external calcium in normal and neoplastic keratinocytes

Normal keratinocytes proliferate when cultured in medium with 0.02-0.10 mM calcium and terminally differentiate when medium calcium is increased to greater than 0.1 mM. In contrast, neoplastic keratinocyte cell lines maintain the potential for continued cell renewal and survive when external calcium is increased. In order to determine whether elevation of extracellular calcium produced changes in intracellular free calcium (Cai) levels, Cai was measured in individual living keratinocytes by use of the fluorescent calcium probe fura-2. Most normal keratinocytes responded to increased extracellular calcium by a gradual 2- to 3-fold increase in Cai lasting for at least 28 min. A subpopulation displayed a sharp peak of Cai at 2 min. In contrast, the Cai level in neoplastic cells in either low or high calcium medium was 2- to 3-fold higher than that in normal cells, and all cells in the population showed a transient 4- to 9-fold elevation of Cai 2 min after external calcium was increased. Thus normal and neoplastic keratinocytes differ in the level of Cai under low calcium conditions and in their response to elevated external calcium. The regulation of Cai in keratinocytes may be important in determining their potential for terminal differentiation.

Effects of maternal gestational diabetes on offspring adiposity at 4-7 years of age

OBJECTIVE

The purpose of this study was to assess the long-term effects of maternal prenatal factors, including gestational diabetes mellitus (GDM), adiposity, and weight gain during pregnancy, on adiposity of offspring from 4 to 7 years of age. A second purpose was to investigate the relationships among childhood adiposity, blood pressure, and 2-h postprandial glucose level.

RESEARCH DESIGN AND METHODS

Prospective observational study of four groups of children including large-for-gestational-age (LGA) offspring of mothers with gestational diabetes (OGDM); appropriate-for-gestational-age (AGA) OGDM; LGA control subjects; and AGA control subjects. Anthropometrics including skin-fold measurements, blood pressure measurements, and a 2-h postprandial glucose measurement were obtained at each visit. Repeated measures analysis of variance models were used to detect different patterns of longitudinal change among the groups.

RESULTS

LGA OGDM were more likely to be heavier, have larger circumferences and skin-fold measurements, and have a higher BMI than AGA OGDM and control subjects, and these findings increased with increasing age. Blood pressures and postprandial glucose values were similar for OGDM and control subjects at 4-7 years. Multivariable analyses showed that infant BMI and maternal prepregnant BMI predicted 7-year BMI for OGDM, whereas for control subjects, maternal prepregnancy BMI and weight gain during pregnancy were positive predictors with a small negative contribution from birth BMI.

CONCLUSIONS

We conclude that LGA OGDM have evidence of increasing body size and adiposity with increasing age and that maternal GDM and maternal prepregnant adiposity are significant predictors of their unique growth patterns.

Interaction of BCG-activated macrophages with neoplastic and nonneoplastic cell lines in vitro : quantitation of the cytotoxic reaction by release of tritiated thymidine from prelabeled target cells

Peritoneal cells from mice infected ip with Mycobacterium bovis, strain BCG, were cytotoxic to syngeneic tumor cells in vitro. Cytotoxicity was estimated by measurement of release of tritiated-thymidine (3-H-TDR) from prelabeled target cells. The cell responsible for tumor cytotoxicity was the macrophage. Macrophages from uninfected mice or from oil-, starch-, or thioglycollate-induced peritoneal exudates had little effect on labeled tumor monolayers. Tumoricidal macrophages were present at 3-7 days and persisted through 6 weeks after a single BCG injection. Two neoplastic/nonneoplastic cell-line pairs, all four of the cell lines derived from a cloned syngeneic embryo cell line, were used as target cells for BCG-activated macrophages. Both tumor cell lines released significantly more 3-H-TDR than did the two nonneoplastic lines. In a mixed neoplastic/nonneoplastic target cell population, BCG-activated macrophages selectively destroyed the neoplastic cells; nonneoplastic cells were not affected as "innocent bystanders".

Effect of anticipation during unknown or unexpected exercise duration on rating of perceived exertion, affect, and physiological function

OBJECTIVES

To determine the effect of unknown exercise duration and an unexpected increase in exercise duration on rating of perceived exertion (RPE), affect, and running economy during treadmill running.

METHODS

Sixteen well trained male and female runners completed three bouts of treadmill running at 75% of their peak treadmill running speed. In the first trial, they were told to run for 20 minutes and were stopped at 20 minutes (20 MIN). In another trial, they were told to run for 10 minutes, but at 10 minutes were told to run for a further 10 minutes (10 MIN). In the final trial, they were not told for how long they would be running but were stopped after 20 minutes (unknown, UN). During each of the running bouts, RPE, oxygen consumption (ml/kg/min), heart rate (beats/min), stride frequency (min(-1)), affect scores (arbitrary units), and attentional focus (percentage associative thought scores) were recorded.

RESULTS

RPE increased significantly between 10 and 11 minutes in the 10 MIN compared with the 20 MIN and UN trials (p<0.05). The affect score decreased significantly between 10 and 11 minutes in the 10 MIN compared with the 20 MIN trial (p<0.05). Running economy, as measured by oxygen consumption, was significantly lower in the UN compared with the 20 MIN trial from 10 to 19 minutes (p<0.05).

CONCLUSIONS

The change in RPE between 10 and 11 minutes in the 10 MIN trial suggests that RPE is not purely a measure of physical exertion, as treadmill speed was maintained at a constant pace both before and after the unexpected increase in exercise duration. The associated changes in affect score at similar times in the 10 MIN trial supports the hypothesis that RPE has an affective component.

Chelation of intracellular Ca2+ inhibits murine keratinocyte differentiation in vitro

The role of intracellular Ca2+ in the regulation of Ca(2+)-induced terminal differentiation of mouse keratinocytes was investigated using the intracellular Ca2+ chelator 1,2-bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA). A cell permeable acetoxymethyl (AM) ester derivative BAPTA (BAPTA/AM) was loaded into primary mouse keratinocytes in 0.05 mM Ca2+ medium, and then the cells were induced to differentiate by medium containing 0.12 or 0.5 mM Ca(2+) Intracellular BAPTA loaded by BAPTA/AM (15-30 microM) inhibited the expression of epidermal differentiation-specific proteins keratin 1 (K1), keratin 10 (K10), filaggrin and loricrin as detected by immunoblotting. The differentiation-associated redistribution of E-cadherin on the cell membrane was delayed but not inhibited as determined by immunofluorescence. BAPTA also inhibited the expression of K1, K10 and loricrin mRNA. Furthermore, BAPTA prevented the decrease in DNA synthesis induced by 0.12 and 0.5 mM Ca2+, indicating the drug was inhibiting differentiation but was not toxic to keratinocytes. To evaluate the influence of BAPTA on intracellular Ca2+, the concentration of intracellular free Ca2+ (Cai) in BAPTA-loaded keratinocytes was examined by digital image analysis using the Ca(2+)-sensitive fluorescent probe fura-2, and Ca2+ influx was measured by 45Ca2+ uptake studies. Increase in extracellular Ca2+ (Cao) in the culture medium of keratinocytes caused a sustained increase in both Cai and Ca2+ localized to ionomycin-sensitive intracellular stores in keratinocytes. BAPTA lowered basal Cai concentration and prevented the Cai increase. After 12 hours of BAPTA treatment, the basal level of Cai returned to the control value, but the Ca2+ localized in intracellular stores was substantially decreased. 45Ca2+ uptake was initially (within 30 min) increased in BAPTA-loaded cells. However, the total 45Ca2+ accumulation over 24 hours in BAPTA-loaded cells remained unchanged from control values. These results indicate that keratinocytes can maintain Cai and total cellular Ca2+ content in the presence of increased amount of intracellular Ca2+ buffer (e.g., BAPTA) by depleting intracellular Ca2+ stores over a long period. The inhibition by BAPTA of keratinocyte differentiation marker expression may result from depletion of the Ca(2+)-stores since this is the major change in intracellular Ca2+ detected at the time keratinocytes express the differentiation markers. In contrast, the redistribution of E-cadherin on the cell membrane may be more directly associated with Cai change.

Signal transduction for proliferation and differentiation in keratinocytes

In mouse and human epidermis, the Ca2+ environment of the basal cell layer is substantially below serum Ca2+, while that of the granular cell layer is unusually high. Reduction of extracellular Ca2+ concentration (Cao) in the medium of keratinocyte cultures maintains a basal cell phenotype while serum Ca2+ concentrations induce terminal differentiation. Measurements of intracellular Ca2+ (Cai) by the use of Fura 2 and digital imaging technology reveal that Cai increases 10-20-fold in response to an increase in Cao and remains elevated. Concomitant with the rise in Cai is an increase in the metabolism of phosphatidylinositol (PI) to yield inositol phosphates and diacylglycerol. PI metabolism is also stimulated by calcium ionophores suggesting that a rise in Cai is directly responsible. The consequent increase in diacylglycerol and Cai would activate protein kinase C, an event known to trigger epidermal differentiation. Specific Cao and Cai determine the expression of individual markers of keratinocyte differentiation in vitro. These findings may account for the importance of the Ca2+ gradient for maintaining regulated growth and differentiation of the epidermis in vivo.

Histologic localization of indocyanine green dye in aging primate and human ocular tissues with clinical angiographic correlation

OBJECTIVE

This study aimed to histologically localize indocyanine green (ICG) dye in the geriatric primate and human eye and to correlate these findings with clinical ICG angiography.

DESIGN

The study design was a clinicopathologic correlation.

PARTICIPANTS

Six eyes of three geriatric monkeys (Maccaca mulatta) with macular drusen, 19 to 29 years of age, housed at the California Primate Research Center and an enucleated human eye from a 66-year-old patient with choroidal melanoma were examined.

INTERVENTION

All six monkey eyes and the human eye underwent clinical ICG angiography. Five monkey eyes were enucleated at varying intervals after intravenous ICG dye injection for histologic examination. One monkey eye was removed without prior ICG injection as an age-matched control. The human eye was enucleated after intravenous injection of ICG dye.

MAIN OUTCOME MEASURES

Infrared fluorescence microscopy of freeze-dried tissue sections was performed to detect ICG fluorescence. Histologic sections were stimulated with an 810-nm diode laser, and the fluorescence emitted was detected with a Hamamatsu infrared camera. The images were digitally recorded. The distribution of fluorescence on histologic examination was correlated with the fluorescence of the clinical ICG angiogram.

RESULTS

Infrared fluorescence microscopy of monkey sections localized fluorescence within retinal and choroidal vessels early after injection of ICG dye. The ICG fluorescence was seen in the extravascular choroidal stroma within 10 minutes after injection. The stromal fluorescence persisted in sections obtained 50 minutes after injection of ICG. The retinal pigment epithelium (RPE)-Bruch's membrane complex was brightly fluorescent in the middle- and late-stage histologic sections. Drusen deposits were brightly fluorescent at all timepoints examined. Similar findings were observed in freeze-dried tissue sections of the human eye. The fluorescence detected on histologic sections correlated closely with the fluorescence of the clinical ICG angiograms for the same interval.

CONCLUSIONS

The ICG dye does not remain solely within the choroidal intravascular space but extravasates into the choroidal stroma and accumulates within the RPE. Extravascular ICG binds to drusen material. These findings will enhance the interpretation of clinical ICG angiography.

Child, parent, and family mental health and functioning in Australia during COVID-19: comparison to pre-pandemic data

The COVID-19 pandemic presents significant risks to population mental health. Despite evidence of detrimental effects for adults, there has been limited examination of the impact of COVID-19 on parents and children specifically. We aim to examine patterns of parent and child (0-18 years) mental health, parent substance use, couple conflict, parenting practices, and family functioning during COVID-19, compared to pre-pandemic data, and to identify families most at risk of poor outcomes according to pre-existing demographic and individual factors, and COVID-19 stressors. Participants were Australian mothers (81%) and fathers aged 18 years and over who were parents of a child 0-18 years (N = 2365). Parents completed an online self-report survey during 'stage three' COVID-19 restrictions in April 2020. Data were compared to pre-pandemic data from four Australian population-based cohorts. Compared to pre-pandemic estimates, during the pandemic period parents reported higher rates of parent depression, anxiety, and stress (Cohen's d = 0.26-0.81, all p < 0.001), higher parenting irritability (d = 0.17-0.46, all p < 0.001), lower family positive expressiveness (d = - 0.18, p < 0.001), and higher alcohol consumption (22% vs 12% drinking four or more days per week, p < 0.001). In multivariable analyses, we consistently found that younger parent age, increased financial deprivation, pre-existing parent and child physical and mental health conditions, COVID-19 psychological and environmental stressors, and housing dissatisfaction were associated with worse parent and child functioning and more strained family relationships. Our data suggest wide-ranging, detrimental family impacts associated with the COVID-19 pandemic; and support policy actions to assist families with financial supports, leave entitlements, and social housing.

Tubulin and actin in paired nonneoplastic and spontaneously transformed neoplastic cell lines in vitro: fluorescent antibody studies

Pairs of nonneoplastic and spontaneously transformed neoplastic cells were derived from rat, mouse and hamster embryos. The neoplastic cells of each pair had poorly spread cellular morphology, grew in agarose in vitro and produced invasive sarcomas in vivo; the nonneoplastic cells exhibited none of these properties. The distribution of microtubules and microfilament bundles (stress fibers or actin cables) was examined in five such paired lines and in 3T3 and SV40-transformed 3T3 cells by indirect immunofluorescent microscopy of fixed cells treated with rabbit antibody prepared against bovine brain tubulin or guinea pig smooth muscle actin, respectively. Actin cables in all the neoplastic cells appeared thinner and more sparse than in the paired nonneoplastic cells. These differences were also observed in living cells with polarization microscopy. In contrast, microtubules appeared similar in neoplastic and nonneoplastic cells, both in areas of thin peripheral lamellar cytoplasm which allowed a clear visualization of fine, curving microtubules and in regions of thick, central endoplasm which obsecured individual microtubules. In fact, the main morphological difference between neoplastic and nonneoplastic cells was the relative amount of lamellar cytoplasm or endoplasm, rather than the appearance of microtubles in either region. Thus the distinctive growth properties and retracted cellular morphology of neoplastic cells in this study did not correlate with decreased or disorganized microtubules, but with thin and sparse actin cables.

Fluid regimens in the first week of life may increase risk of patent ductus arteriosus in extremely low birth weight infants

BACKGROUND

High fluid volumes may increase neonatal morbidity. However, evidence supporting fluid restriction is inconclusive and restricting fluids may restrict caloric intake.

OBJECTIVE

To determine if higher fluid intake was associated with increased risk of patent ductus arteriosus (PDA) or bronchopulmonary dysplasia (BPD) in extremely low birth weight (ELBW) infants.

STUDY DESIGN

A total of 204 ELBW (<or=32 weeks, <or=1250 g) infant survivors were grouped into low-, intermediate- and high-fluid groups. chi2 analyzed proportions of subjects with and without morbidities across groups. Logistic regression quantified increased risk of PDA or BPD associated with fluid intake while controlling for confounders. Analysis of variance compared differences in caloric intake across groups.

RESULT

After controlling for gestational age, severity of illness and weight change, fluid intake on day 2 (odds ratio (OR) 1.014; confidence interval (CI) 1.001 to 1.028) and day 3 (OR 1.022; CI 1.004 to 1.040) was associated with increased risk of PDA.

CONCLUSION

High fluid intake (>170 ml kg(-1) day(-1)) in the first days of life is associated with increased risk of PDA.

Autoantibody production by severe combined immunodeficient mice reconstituted with synovial cells from rheumatoid arthritis patients

In an attempt to characterize the heterogeneity of the human autoantibody response, mice with severe combined immunodeficiency were reconstituted with synovial or blood lymphocytes from patients with rheumatoid arthritis (RA). Mononuclear cells extracted from synovial fluid or tissue (SMC) were a greatly enriched source of IgM rheumatoid factor (RF)-producing cells compared to the peripheral blood mononuclear cells (PBMC) of rheumatoid arthritis patients or normal donors. Six to nine weeks after reconstitution of mice with synovial mononuclear cells, 0%-39.3% (mean = 11.4%) of total IgM consisted of IgM RF compared to 0%-0.15% (mean = 0.02%) in mice given RA PBMC and 0%-1.2% (mean = 0.34%) in mice given normal PBMC. Detectable levels of IgM RF were maintained in some mice for as long as 20 weeks after transfer. Mice reconstituted with synovial membrane or synovial fluid lymphocytes produced a heterogeneous mixture of immunoglobulins. These included other autoantibodies, such as anti-nuclear and anti-cytoplasmic antibodies, and antibodies to exogenous antigens such as the Epstein-Barr virus nuclear antigen-1 (EBNA-1). This heterogeneity is further illustrated by the demonstration that the sera from mice given synovial cells also contained IgG antibodies possessing all three major VH families (VH1, VH3 and VH4) and the four major V kappa families (V kappa 1 to V kappa 4). Autoantibody production gradually decreased with time even under circumstances where total immunoglobulin levels increased, and elevated production could not be induced by antigenic stimulation. These findings describe a new model for the analysis of human autoantibody production.

Regulation of intracellular free calcium in normal murine keratinocytes

Cultured normal murine keratinocytes maintain a basal cell phenotype in medium with a Ca2+ concentration of 0.05 mM and differentiate when exposed for 28-48 h to medium supplemented with extracellular Ca2+ greater than 0.10 mM. Previous studies have documented Ca2+ activation of signaling pathways in the plasma membrane and tightly regulated cellular responses to small incremental changes in extracellular Ca2+. To determine if changes in free cytosolic calcium (Cai) are associated with these early signaling events, digital image analysis of fura-2-loaded keratinocytes was used to measure Cai in individual cells. Basal keratinocytes in 0.05 mM Ca2+ display a biphasic Cai increase when exposed to greater than 0.1 mM Ca2+ in serum-containing medium. These separate phases were controlled by different media components. Initial peak Cai occurred rapidly (within 60 s), was transient (lasting less than 5 min), and resulted from release of 10-20% of total intracellular Ca2+ stores. Peak Cai depended on serum concentration and was independent of extracellular Ca2+. This transient Cai response was lost as keratinocytes differentiated. Plateau Cai level was sustained (greater than 24 h) and depended on extracellular Ca2+, but not serum. The magnitude of plateau Cai increased incrementally following increases in extracellular Ca2+ as small as 0.02 mM. A similar biphasic Cai increase was noted in cultures of murine dermal fibroblasts stimulated by 1.2 mM Ca2+ and serum. However, fibroblasts did not lose the serum response in high-Ca2+ medium, and plateau Cai was not sensitive to small changes in extracellular Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-random fluctuations in power output during self-paced exercise

OBJECTIVES

To analyse the power output measured during a self-paced 20-km cycling time trial, during which power output was free to vary, in order to assess the level and characteristics of the variability in power output that occurred during the exercise bout.

METHODS

Eleven well-trained cyclists performed a 20-km cycling time trial, during which power output was sampled every 200 m. Power spectrum analysis was performed on the power output data, and a fractal dimension was calculated for each trial using the Higuchi method.

RESULTS

In all subjects, power output was maintained throughout the trial until the final kilometre, when it increased significantly, indicating the presence of a global pacing strategy. The power spectrum revealed the presence of 1/f-like scaling of power output and multiple frequency peaks during each trial, with the values of the frequency peaks changing over the course of the trial. The fractal dimension (D-score) was similar for all subjects over the 20-km trial and ranged between 1.5 and 1.9.

CONCLUSIONS

The presence of an end spurt in all subjects, 1/f-like scaling and multiple frequency peaks in the power output data indicate that the measured oscillations in power output during cycling exercise activity may not be system noise, but may rather be associated with system control mechanisms that are similar in different individuals.

Function of B cells expressing a human immunoglobulin M rheumatoid factor autoantibody in transgenic mice

We have generated transgenic mice that express the immunoglobulin (Ig)M heavy chain and kappa light chain genes coding for a human IgM rheumatoid factor (RF), Les. Transgenic B cells expressing human IgM RF show striking similarities to their counterparts in normal humans. They comprise a significant proportion of the adult B cell population, but secrete only low levels of RF into the serum. The RF transgene-expressing B cells localize to primary B cell follicles and the mantle zone regions of secondary follicles in the spleen. Using these mice we have been able to show that one of the central functions of normal RF-expressing B cells may be to act as highly efficient antigen-presenting cells for low concentrations of immune-complexed antigen. High levels of secretion of IgM RF can not be induced under normal circumstances, although RF-expressing B cells proliferate well in vitro to both aggregated human IgG and anti-human IgM antibodies. However, these mice are not intrinsically secretion deficient. By crossing the RF transgenic mice with the autoimmune MRL/lpr background, we find a dramatic increase, > 200-fold, in levels of serum RF. The results strongly suggest that a major function of normal resting RF B cells is unrelated to antibody secretion. Rather, the RF B cells in the follicles may play a role in antigen presentation and regulation of immune responses to antibody-bound nonself-, and possibly self-antigens. This physiologic role of RF B cells may be disrupted in RF-associated autoimmune disease.

Phase I study of twice-weekly gemcitabine and concurrent thoracic radiation for patients with locally advanced non-small-cell lung cancer

PURPOSE

To determine the maximum tolerated dose (MTD) and dose-limiting toxicity of twice-weekly gemcitabine and concurrent thoracic radiation in patients with Stage IIIa/IIIb non-small-cell lung cancer (NSCLC).

METHODS AND MATERIALS

Seventeen patients with histologically confirmed Stage IIIa and IIIb NSCLC were studied. Gemcitabine was administered via a 30-min i.v. infusion twice weekly for 6 weeks concurrent with 60 Gy of thoracic radiation. Gemcitabine, starting at a twice-weekly dose of 10 mg/m2 (20 mg/m2/week), was escalated in 10-15 mg/m2 increments in successive cohorts of 3 to 6 patients until dose-limiting toxicity was observed.

RESULTS

Of the 17 patients entered, 16 were evaluable for toxicity. The dose-limiting toxicity at 50 mg/m2 given twice weekly (100 mg/m2/week) was Grade 3 pneumonitis observed in 1 patient, Grade 3 pulmonary fibrosis in a second patient, and Grade 4 esophagitis observed in two additional patients. Twice-weekly gemcitabine at a dose of 35 mg/m2 was determined to be the MTD. The overall response rate for the 16 evaluable patients was 88%. The median survival for the entire group is 16.0 months.

CONCLUSIONS

The MTD of twice-weekly gemcitabine is 35 mg/m2 (70 mg/m2/week) given with thoracic radiation. A Phase II study within the Cancer and Leukemia Group B to ascertain the potential efficacy of this treatment regimen is in development.

Regulation of the Balb/c-3T3 cell cycle-effects of growth factors

The platelet-derived growth factor (PDGF), which is found in serum but not in plasma, has been purified to homogeneity; it stimulates replication at a concentration of 10(-10) M. Brief treatment with PDGF causes density-inhibited Balb/c-3T3 cells to become competent to synthesize DNA; pituitary fibroblast growth factor (FGF) or precipitates of calcium phosphate also induce competence. Continuous treatment with plasma allows competent, but not incompetent, cells to synthesize DNA. A critical component of plasma is somatomedin, a group of hormones with insulin-like activity; multiplication-stimulating activity (MSA) or insulin replace plasma somatomedin in promoting DNA synthesis. We have studied the molecular correlates of competence and the role of SV40 gene A products in regulating DNA synthesis. Treatment of quiescent cells with pure PDGF or FGF causes the preferential synthesis of five cytoplasmic proteins (approximate molecular weight 29,000, 35,000, 45,000, 60,000, and 72,000 detected by SDS-PAGE under reducing conditions). Two of these competence-associated proteins (29,000 and 35,000 daltons) are insulin, or epidermal growth factor (EGF). PDGF, FGF, or calcium phosphate induce an ultrastructure change within the centriole of 3T3 cells; this ultrastructural modification of the centriole is detectable by immunofluorescence within 2 h or PDGF treatment. Plasma, EGF, or MSA do not modify the centriole. SV40 induces replicative DNA synthesis in growth-arrested 3T3 cells but does not cause this alteration in centriole structure. Gene A variants of SV40, including a mutant with temperature-sensitive (ts) T-antigen (ts A209), a deletion in t-antigen (dl 884), and several ts A209 strains containing t-antigen deletions were used to induce DNA synthesis in Balb/c-3T3 cells. Like wild type SV40, all strains induced DNA synthesis equally well under permissive or nonpermissive conditions. Addition of PDGF or plasma had little effect on SV40-induced DNA synthesis. Thus, the viral function that induces replicative DNA synthesis in Balb/c-3T3 cells. Like wild type SV40, all strains induced DNA synthesis equally well under permissive or nonpermissive conditions. Addition of PDGF or plasma had little effect on SV40-induced DNA synthesis. Thus, the viral function that induces replicative DNA synthesis in Balb/c-3T3 cells is not t and is not temperature sensitive. This SV40 gene function overrides the cellular requirement for hormonal growth factors. It does not induce transient centriole deciliation, a hormonally regulated event.

Alleviation of fatty liver in dairy cows with 14-day intravenous infusions of glucagon

Twenty multiparous cows were fed additional concentrate during the final 30 d prepartum to cause susceptibility to fatty liver. From 14 to 42 d postpartum, all cows were subjected to a protocol to induce fatty liver and ketosis. To test glucagon as a treatment for fatty liver, either glucagon at 10 mg/d or excipient was infused via the jugular vein from 21 to 35 d postpartum. All cows had fatty liver at 14 d postpartum and became ketonemic and hypoglycemic during the induction of ketosis. Glucagon increased plasma glucose to 142% of that of controls throughout the 14-d treatment. The hypoinsulinemia present in cows with fatty liver was not affected by glucagon. Plasma beta-hydroxybutyrate and nonesterified fatty acids were decreased by glucagon. At 6 d postpartum, liver triacylglycerol averaged 12.9% of liver (wet weight basis). Glucagon had decreased triacylglycerol content of livers by 71% at d 35. Glycogen was 1.0% of the wet weight of livers at 6 d in milk, but it was decreased by glucagon to 0.5% at 2 d after glucagon began. Glycogen then increased in cows treated with glucagon until at 38 d in milk liver glycogen was 3.7% versus 1.6% in controls. Our results document that glucagon decreases the degree of fatty liver in early lactation dairy cows, which also decreases the incidence of ketosis after alleviation of fatty liver.

Calcium mediates expression of stress-response genes in prostaglandin A2-induced growth arrest

We have explored the mechanisms involved in the induction of five stress-response genes (heme oxygenase [HO], c-fos, Egr-1, gadd153, and HSP70) in human diploid fibroblasts growth-arrested by treatment with the antiproliferative prostaglandin A2 (PGA2). The kinetics of c-fos and Egr-1 induction were found to be rapid with maximum expression occurring within 60 min of treatment, whereas maximum expression of HO, gadd153, and HSP70 occurred between 4 and 8 h of treatment. Nuclear run-on assays and measurements of mRNA clearance in the presence of actinomycin D demonstrated that increases in both the rates of gene transcription and/or mRNA stability contribute to the genetic response to PGA2. Although the mechanisms responsible for increasing the mRNA levels differ for the individual genes, additional experiments provided evidence that alterations in intracellular calcium ([Ca2+]i) levels were important in initiating the genetic response to PGA2. PGA2 treatment resulted in a rapid increase in [Ca2+]i with the dose-response relationship for Ca2+ mobilization consistent with that seen for the induction of all five genes. [Ca2+]i chelators that attenuate Ca2+ mobilization by PGA2 also blocked the mRNA induction by PGA2 treatment. Density-inhibited confluent cells were less responsive than proliferating subconfluent cells with respect to Ca2+ mobilization after PGA2 treatment. This was correlated with a lower level of gene induction. These studies support the hypothesis that increased Ca2+ mobilization is an early and central event in the signal transduction pathway (or pathways) mediating the activation of genes in response to PGA2 treatment.