Influence of long-term oxygen therapy on cardiac acceleration and deceleration capacity in hypoxic patients with chronic obstructive pulmonary disease

BACKGROUND

There is increasing interest in cardiovascular co-morbidities of chronic obstructive pulmonary disease (COPD). Heart rate turbulence (HRT) and phase-rectified signal averaging (PRSA) techniques quantify the heart's acceleration/deceleration capacities. We postulated that these methods can help assess the integrity of cardiac control in hypoxic COPD.

METHODS

Eight hypoxic stable COPD patients, nine healthy age-matched older adults and eight healthy young adults underwent ECG monitoring for 24 h. Patients with COPD were also monitored following 4 weeks of standardized oxygen therapy. HRT measures [turbulence onset (TO), turbulence slope (TS)] and PRSA-derived acceleration/deceleration (AC, DC) indices were quantified within 6-h blocks to assess circadian variation.

RESULTS

There were between-group differences for variables TS, DC and AC (P<0·0005, η(2) = 0·54-0·65), attributable solely to differences between healthy young and COPD subjects. Only HR (P<0·0005) and DC index (P = 0·008) showed circadian variation. A significant interaction 'trend' effect for HR (F(9,87) = 2·52, P = 0·015, η(2) = 0·21) reflected the strong influence of COPD on HR circadian variation (afternoon and night values being different to those in healthy subjects).

CONCLUSIONS

As expected, heart rate dynamics were substantially diminished in older (healthy and COPD) groups compared with healthy young controls. Patients with COPD showed similar heart rate dynamics compared with age-matched controls, both before and after hypoxia correction. However, there was a suggestion of diminished DC in COPD compared with age-matched controls (P = 0·059) that was absent following oxygen therapy. TS, DC and AC indices were altered by similar degrees in older subjects, apparently indicating equivalent tonic dysfunction of sympathetic/parasympathetic systems with ageing.

PhD by publication: a prospective as well as retrospective award? Some subversive thoughts

Although the discipline of nurse education within the UK has been part of the higher education sector since the 1950s, relatively few nurse academics currently hold a doctorate. This has implications at a national, local and personal level, and can be partly accounted for by the particular demographic and work issues faced by nurse academics, together with issues about the nature of the traditional PhD itself as a suitable and relevant qualification in the discipline of nurse education. As an alternative, we suggest a route to a PhD that takes advantage of the regulations already in place in many Higher Education Institutions (HEIs) for a 'staff doctorate' by publication and which has been set up to accredit academic staff who have a corpus of published papers. In addition to this retrospective PhD by publication we also suggest that that the prospective route to a PhD by publication be promoted, based on established programmes in Europe and Australia. We argue that both routes address many of the issues and difficulties faced by nurse academics, their HEIs and the discipline generally and are relevant to other countries in the developed world as well as the UK. Promotion of these routes will give individual tutors and lecturers the opportunity for academic, professional and personal development within their own organisation and at the same time enable HEIs within the developed world to increase their overall performance in the next Research Excellence Framework (or equivalent depending on their country), thus enhancing the standing and reputation of nursing as an academic discipline.

Totally implantable venous access devices - 20 years' experience of implantation in cystic fibrosis patients

INTRODUCTION

Totally implantable venous access devices (TIVADs) are widely used to provide long-term, central venous access for antibiotic delivery in cystic fibrosis patients. However, few studies have demonstrated long-term follow-up with large cohorts.

PATIENTS AND METHODS

This is a retrospective review of TIVADs implanted in cystic fibrosis patients by vascular surgeons at a tertiary referral centre, using an open venous cut-down technique, from March 1986 to July 2006. The cephalic vein was preferentially chosen for line placement, in the deltopectoral groove, under fluoroscopic control. TIVAD performance (life-span or survival) and complications were evaluated. Data were extracted by review of a local database (data collated prospectively since 1986), with supplementation from electronic patient records and medical notes.

RESULTS

In total 165 TIVADs in 109 patients (34 males, 75 females) were reviewed. Median survival was 1441 days (range, 6-4440 days). Cumulative patency was 146,072 catheter-days. No immediate intrathoracic complications (pneumothorax, haemothorax, nerve injury) occurred. There were 3 early and 82 late complications, namely: occlusion (33 TIVADs; median age 510 days), infection (23 TIVADs; median 376 days), leakage (16; median 283 days), pain or discomfort (6), venous thrombosis (5), extravasation/skin necrosis (1), vegetation in right atrium (1). Overall incidence of complications was 0.58 per 1000 catheter-days.

CONCLUSIONS

This study concurs with others that TIVADs are safe and effective, with a favourable life-span in cystic fibrosis patients if well looked after in a specialist centre. Complications of infection, leakage and occlusion do occur. Using an open, venous cut-down technique with fluoroscopic control avoids any immediate intrathoracic complications.

Neurodegenerative actions of interleukin-1 in the rat brain are mediated through increases in seizure activity

The cytokine interleukin-1 (IL-1) is an established and important mediator of diverse forms of neuronal injury in experimental animals. However, its mechanisms of action remain largely unknown. We have reported previously that IL-1 markedly enhances excitotoxic injury induced in the rat by striatal administration of the excitotoxin alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), leading to widespread neuronal loss throughout the ipsilateral cortex. Here we tested the hypothesis that IL-1 causes this injury through induction and/or enhancement of seizure activity in the rat. Consistently with this hypothesis, intrastriatal injection of AMPA or AMPA with IL-1 in the rat brain increased c-Fos expression in regions similar to those in which c-Fos has been reported previously in response to seizures. A significant increase in cortical neuronal activity (number of c-Fos positive cells) was observed in response to AMPA with IL-1 compared with AMPA (8 hr after injection). Increased seizure duration [3,522 +/- 660 sec (SEM) vs. 1,415 +/- 301 sec; P < 0.001] and cell death volume (140 +/- 20 mm3 vs. 52 +/- 6 mm3; P < 0.001) were seen in response to coinfusion of AMPA with IL-1 vs. AMPA alone. In addition, the anticonvulsant diazepam (intraperitoneal) significantly reduced cell death (P < 0.001) and seizure duration (P < 0.001) induced by AMPA with IL-1, and a significant correlation was found between seizure duration and cell death volume. These findings support our hypothesis that IL-1 enhances excitotoxic injury by enhancement of seizures, which may be of relevance to IL-1 actions in other forms of neuronal injury, including cerebral ischemia.

The Diana community nursing team and paediatric palliative care

This article describes the work of the Diana community nursing teams, a new nurse-led service funded by the Department of Health (DoH) to commemorate the life and work of Diana, Princess of Wales. It identifies paediatric palliative care as an emerging specialty within children's nursing and discusses how children and young people with life-limiting/threatening conditions and their families may benefit from this new service. It is anticipated that the Diana teams will work with existing services such as children's hospitals, outreach services, children's hospices, social services and education and voluntary agencies. A key element of this service will be the ability of Diana team members to work across professional and organizational boundaries to provide a seamless care service and promote the concept of 'joined-up working' (Hyman, 1998). Education in this specialty, preferably multidisciplinary education, is needed so that healthcare professionals in this field can share knowledge, skills and research findings and deliver up-to-date care based on clinical effectiveness.

A selective Pt-CdS photodiode to monitor erythemal flux

The design and potential benefit of a solar ultraviolet (UV) radiometer reporting a maximum instantaneous flux of erythemally weighted heterogeneous energy is considered. The proposed device is electronically peak detecting; the user would ideally 'point and paint' the sun to find a localized maximum. A projected exposure time can be calculated from an instantaneous reading of erythemally weighted flux for a given minimal erythemal dose (MED) specified by the user. This calculation, though not necessarily providing a true exposure time, may be useful and informative in that it serves as a more 'recognizable' measure of erythemal flux and introduces a custom scale for each individual via their MED. Erythemal flux is calculated as the weighted integral sum [symbol: see text]j(lambda,t) epsilon(lambda) d lambda, where j (lambda, t) is the instantaneous angular integrated spectral irradiance accepted by human skin. This instrument proposal uses a single interference filter over a Pt-CdS photodiode; the interference filter is offered as a nominal design transmittance. The simulated response of the selective photodiode has a near-linear relation to the effective irradiance. Test inputs for evaluation purposes and to elucidate a transducer response are constructed from a spline interpolation of the World Radiation Center (WRC) spectrum and classic transmittance models. Our desired erythemal flux is offered in interconvertible UV Indexes (UVIs) as a function of zenith angle and atmosphere, characterized by elevation, ozone path, and turbidity.

A comparison of the effects of capsaicin with inhibitory nerve stimulation in the rat anococcygeus muscle in vitro

Capsaicin was used to test whether centrifugal activation of sensory fibres in the rat anococcygeus muscle can contribute to non-adrenergic non-cholinergic (NANC) relaxation of the muscle. In a solution containing 0.5 mM Ca2+ and in the presence of carbachol (10 microM) capsaicin evoked a fast concentration-dependent relaxation of the muscle that was usually followed by a smaller, slower, relaxant response. The fast relaxant response was reduced when extracellular Ca2+ was raised to 2.5 mM, desensitized after a single application of capsaicin and was blocked by tetrodotoxin (1 microM) or ruthenium red (10 microM). The fast response was greatly reduced by haemoglobin, by cold storage of the muscles or by N-monomethyl-L-arginine (100 microM) in the absence but not in the presence of L-arginine (100 microM). It is concluded that centrifugal activation of sensory fibres evokes a nitric oxide-mediated relaxation of the anococcygeus muscles that probably contributes to electrically evoked NANC relaxation.

Wavelength dependence of skin cancer induction by ultraviolet irradiation of albino hairless mice

Information on the variation in carcinogenicity with wavelength is crucial in risk assessments for skin cancers induced by UV radiation. Until recently the wavelength (lambda) dependencies of other detrimental UV effects, such as sunburn, have been used as substitutes. Direct information on the lambda dependency can only be obtained from animal experiments. To this end we accumulated a large data set on skin tumors induced by chronic UV exposure of albino SKH:HR1 mice (14 different broadband UV sources and about 1100 mice); the data come from the Photobiology Unit of the former Skin and Cancer Hospital in Philadelphia and from the Department of Dermatology of the University of Utrecht. The lambda dependency was extracted from this data set (a statistically satisfactory description with chi 2 = 13.4, df = 7) and represented by the Skin Cancer Utrecht-Philadelphia action spectrum, i.e., a set of factors to weight the exposures at different wavelengths according to their respective effectiveness (inversely proportional to the daily exposure required for a median tumor induction time of 300 days). The fits obtained with other already available action spectra proved to be poor (chi 2 > 60, df = 11). The maximum effectiveness was found at 293 nm, and above 340 nm the effectiveness showed a shoulder at about 10(-4) of the maximum. A sensitivity analysis of the final solution for the lambda dependency showed a large margin of uncertainty above 340 nm and an information gap below 280 nm. The large variation in tumor responses in the present data set can be transformed to a coherent, common dose-response relationship by proper spectral weighting with this single action spectrum.

All the observed universe has contributed to life

This paper presents evidence that virtually all electrons and nuclei of the atoms that are or have been part of living matter on Earth came from almost all stars in our and nearby galaxies and even from all other galaxies in the Universe that have produced observed high-energy gamma rays. However, a standard 70 kg human is always making about 7 3He, 600 40Ca, and 3000 14N nuclei every second by radioactive decay of 3H, 40K, and 14C, respectively.

Breath-by-breath measurement of oxygen consumption and FIO2-FEO2 with increased oxygen demand

Continuous on-line breath-by-breath measurement of pulmonary gas exchange was used to monitor the increase in oxygen uptake (VO2) and carbon dioxide excretion (VCO2) induced by the oxidative phosphorylation uncoupling agent 2, 4-dinitrophenol (DNP) in 10 dogs. With incremental doses of DNP totaling 5 mg/kg, the continuously monitored VO2 increased within 2-3 min after the first injection of the drug. VCO2 showed a similar response 4-6 min after the first injection. Temperature increase due to the pharmacological oxidative phosphorylation uncoupling required 20-30 min for a discernible change at this dose. This study also demonstrated a modified and compromised response to the drug in dogs where oxygen delivery was limited by mechanical ventilation.

Fibre types in Limulus telson muscles: morphology and histochemistry

Using a variety of techniques, we have demonstrated the presence of at least two fibre types in Limulus median telson levator muscle. By light and electron microscopy, large (2,156 microns 2 mean cross-sectional area) fibres have A-bands of 4.1 microns, one-half I bands of 2.15 microns and Z lines less than or equal to 0.5 microns in width. Few mitochondria are found in these fibres, which comprise 54% of those present in a given microscope field and which occupy 82% of the total cross-sectional area. Small fibres (484 microns 2 mean cross-sectional area) have A bands of 6.3 microns, one-half I bands of 3.1 microns and Z lines between 0.5 and 1.0 microns in width and are rich in mitochondria. Although small fibres comprise nearly one-half (46%) of the fibres in a field, they occupy only 18% of the total cross-sectional area. Histochemical staining for alkaline-stable myofibrillar ATPase activity and mitochondrial reduced beta-nicotinamide adenine nucleotide (beta-NADH) tetrazolium reductase activity confirms the presence of two fibre types. The large fibres react positively for the myofibrillar ATPase activity and negatively for the mitochondrial enzyme activity. The reverse is seen with the small fibres. Some fibres of intermediate size, having intermediate staining characteristics, were also observed. Native gel electrophoresis of both myofibrillar and purified myosin preparations supports the observed differences in myofibrillar ATPase activity in that two myosin isozymes are resolved on pyrophosphate gels. Although the thick filaments isolated from unstimulated small fibres are longer (greater than 6.0 microns) than those isolated from unstimulated large fibres (4.26 microns), all have a similar appearance with respect to the arrangement of myosin heads on their surfaces, and similar diameters. The implications of the observed heterogeneity of fibre types is discussed with reference to previously reported phenomena in Limulus telson muscle, including changes in length of thick filaments on fibre stimulation and the shape of the length-tension curve obtained from fibre bundles.

Narrow-band UV radiation and induction of dermal elastosis and skin cancer

A narrow-band UV light source with emission peaks at 292, 300, 307, 317, and 336 nm was developed and used to irradiate whole cages of hairless mice. The purpose was to obtain experimental information on the action spectrum for photocarcinogenesis and dermal elastosis. Groups of 20 mice were irradiated with 500 J/m2 daily, 5 times per week during one year. The total dose was 130 kJ/m2. All mice irradiated with 292 nm and 300 nm developed squamous cell carcinomas. None in the other groups developed malignant skin tumors. Elastosis was estimated quantitatively. The elastic fibers covered 3% of a representative microscopic section of dermis in the control group. In the groups irradiated with peaks at 336 nm, 317 nm, 307 nm, 300 nm, and 292 nm the corresponding percentages were 6%, 13%, 28%, 32%, and 36%, respectively. The shorter the wavelengths the more pronounced was a subepidermal zone replacing the elastotic tissue to the deeper dermis. This zone stained corresponding to a content of glycosaminoglycans (GAG), sulphated GAG, hyaluronic acid, mature collagen, and new reticulin.

Toxicity of 8-methoxypsoralen, 5-methoxypsoralen, 3-carbethoxypsoralen, or 5-methylisopsoralen with ultraviolet radiation in the hairless (HRA/Skh) mouse

An experimental design to simulate PUVA therapy (oral 8-methoxypsoralen followed by uv radiation) has been tested in a 13-week subchronic study to determine the relative toxicities of 8-methoxypsoralen (8-MOP), 5-methoxypsoralen (5-MOP), 5-methylisopsoralen (5-MIP), and 3-carbethoxypsoralen (3-CEP) in inbred hairless mice (HRA/Skh). Drug was administered by 1-hr pulse feedings three times a week after mice were fasted overnight; individually housed animals were then exposed to uv radiation (320-400 nm; less than 2% output less than 320 nm). 8-MOP or 5-MOP administered orally (at doses of approximately 240 or 480 mg/m2 body surface area per week) followed one-half hour later with uv radiation of 2 J/cm2 for 13 weeks were found to cause skin toxicity including inflammation, hyperplasia, ulceration, and cellular atypia. Dose-related toxicity was not seen in other organ systems. Corresponding levels of 5-MIP or 3-CEP with uv radiation did not produce skin toxicity. These studies show that the psoralens with two potential DNA-binding sites (8-MOP and 5-MOP) were more toxic than psoralens with only one photoreactive site (5-MIP and 3-CEP).

Ocular effects of treatment with various psoralen derivatives and ultraviolet-A (UVA) radiation in HRA/Skh hairless mice

Hairless (HRA/Skh) mice were administered one of four dietary concentrations (50, 100, 625 or 1250 ppm) of 8-methoxypsoralen (8-MOP) or 5-methoxypsoralen (5-MOP), or molar equivalent concentrations of 5-methylisopsoralen (5-MIP) or 3-carbethoxypsoralen (3-CPS) by 'pulse feeding' technique, 3 days per week for 13 weeks. For the final 11 weeks psoralen derivative administration was followed by exposure to 0.2 or 48 J/cm2 of unfiltered ultraviolet-A (UVA) radiant energy from FR74T12PUVA lamps. At 0 and 13 weeks eyes were dilated with 0.2% atropine solution and were examined using a binocular indirect ophthalmoscope with a +20.0 D condensing lens. The lids, cornea, anterior chamber and the lens were evaluated for pathological changes. Ocular damage consisting of dense central corneal opacification was seen at significant levels in animals given 8-MOP or 5-MOP and exposed to UVA. In addition, opacities in the area of the posterior lens were seen in all experimental groups and appeared to be related to drug treatment, independent of light exposure, and therefore appeared not to be related to drug-light interaction. Some corneal and lenticular opacification was seen at non-significant levels in all experimental and control groups.

Effect of indoor lighting on normal skin

A small but measurable component of some indoor lighting is ultraviolet radiation (UVR); whether it is sufficient to modify the indoor worker's risk for chronic skin changes is not directly answerable with available technology. A first approach to this question involves a) estimating a range of annual background solar exposure for indoor workers currently at risk; b) determining whether, and at what levels, UVR exposure is a part of specified indoor lighting; and c) calculating the increment in risk implied by a and b. This algorithm predicts that some lighting conditions that meet NIOSH recommended standards would still result in significant increases in the risk of cumulative UVR damage, including skin cancer. More information concerning actual exposure conditions, the relation of spectral effectiveness for luminosity and UVR production, and dose-time reciprocity are required to improve our predictions of long-term cutaneous effects of indoor lighting.

Skin-tumour promoting activity of methyl ethyl ketone peroxide—a potent lipid-peroxidizing agent

The tumour-promoting activity of methyl ethyl ketone peroxide (MEKP) was tested on the skin of hairless mice using a two-stage initiation-promotion protocol. When ultraviolet radiation in the UVB region (280-320 nm) was used as tumour initiator, MEKP showed weak promoting activity. The promotional activity of MEKP was potentiated by diethyl maleate, which is known to deplete intracellular glutathione, suggesting that lipid peroxidation may be important in the tumour promotion.

Separation of aerobic glycolysis from oxidative metabolism and contractility in rat anococcygeus muscle

The relationship of aerobic glycolysis (JLac) and O2 utilization (JO2) to contractility and the activity of the Na+-K+ pump was investigated in rat anococcygeus smooth muscle. Removal of extracellular potassium concentration ([K+]o) caused an initial increase followed by a decrease in JLac below the resting rate. Restoration of [K+]o caused JLac to increase, and this response, but not the initial one observed in zero [K+]o, was prevented by ouabain. These changes in JLac were not related to contractility, since a similar response was observed in both phentolamine-treated and chemically denervated muscles that exhibited minimal force and no significant changes in JO2. Tension development of innervated muscles incubated in K+-free medium was related to changes in JO2. A logarithmic relationship between JLac and [K+]o suggested that changes in JLac resulted from effects on glucose transport or utilization secondary to changes in the membrane potential. In stimulated muscles JLac and JO2 were both positively correlated with isometric force and were not affected by ouabain. Separation of JLac from JO2 and force production under some conditions supports the hypothesis that a functional compartmentalization of metabolic pathways exists in anococcygeus muscle.

Different biologic effectiveness of blacklight fluorescent lamps available for therapy with psoralens plus ultraviolet A

In 1976 we reported a change in spectral distribution of "blacklight" fluorescent lamps. It was not possible to determine the spectral composition of these lamps by any codes or packaging materials. Phototherapy booths utilizing standard BL-HO lamps will accept lamps of at least two spectral distributions; both types are commercially available. This study was conducted to determine the biologic efficacy of these two lamp types that we refer to as BL-O and BL-N. The BL-O spectrum had a peak emission at approximately 350 nm with 98% of the energy between 320 and 400 nm. The BL-N spectrum had its peak emission at 365 nm with a range from 340 to 400 nm. The BL-O spectrum was at least 2.5 to 4 times as effective as BL-N in causing minimally perceptible phototoxicity in albino hairless mice given oral doses of 8 mg/kg of 8-methoxypsoralen. Food and Drug Administration (FDA)-approved specifications imply that the BL-O spectrum is to be used for psoralens and ultraviolet A (PUVA) phototherapy. If lamps with the BL-N spectrum are replaced by lamps with the BL-O spectrum, the metered dose must be reduced to no more than one-fourth of the previous dose or the patient may suffer serious phototoxic reactions.

An animal model to determine sunscreen protectiveness against both vascular injury and epidermal cell damage

Sunscreen preparations can reduce the erythemogenic ( sunburning ) effects of solar ultraviolet radiation (UVR). Less is known about the ability of sunscreens to protect against other forms of UVR-induced damage. This study was designed to yield data on epidermal cell damage at UVR doses sufficient to provoke vascular changes (edema and erythema) in hairless mice, and to determine the comparative effectiveness of a commercial sunscreen in protecting against these two criteria of injury. The sunscreen (Piz Buin 12 Sun Protection Cream) was used at full concentration and at three serial dilutions. The dorsa of 144 hairless mice were treated with one of six sunscreen or vehicle preparations and subsequently irradiated with one of six exposures to an appropriately filtered xenon arc solar simulator. Vascular responses were determined by observing the animals for alterations in the gross appearance of the treated and irradiated sites (edema and erythema). Epidermal cell damage was assessed by determining the sunburn cell ( SBC ) indices in the epidermis removed 24 hours after irradiation. Both the vascular responses and SBC indices indicated that the sunscreen provided concentration-dependent protection against radiation damage. Furthermore, SBC indices provided a relatively continuous variable for quantification of sunscreen effectiveness.

Structure of Limulus and other invertebrate thick filaments

We have demonstrated remarkable similarity among the skeletal muscles of chelicerate arthropods with respect to the cross-bridge arrangement on the surface of their thick filaments. The latter, gently isolated from the muscles of three representative species (Limulus telson , tarantula leg and scorpion leg and tail) have been examined by electron microscopy and optical diffraction using both negatively stained and unidirectionally metal shadowed preparations. The filaments are highly periodic and produce clear and detailed diffraction patterns. The cross-bridge projections form integral surface helices, with an axial spacing of 14.5 nm between adjacent crowns and a major axial repeat every 43.5 nm. We have demonstrated previously that Limulus filaments are four-stranded and analysis of both electron micrographs and their transforms, as well as optical reconstructions of the arachnid filaments is consistent with their also having a four-start surface helix, which is right-handed in all cases. Of all those examined, thus far, only Limulus thick filaments have been demonstrated to change length under various conditions. Shortened Limulus filaments isolated from K+-stimulated fibers retain the 43.5 nm axial repeat periodicity and 14.5 nm axial spacing between crowns. In preliminary analysis of negatively stained and metal shadowed preparations, we see no systematic change with respect to screw or rotational symmetry in short as compared with long filaments. A few of the former have a very slightly increased diameter (3-4 nm) in the middle of each filament arm. This region often shows disorder on optical transforms. From our results we cannot rule out the possibility that disaggregation and reaggregation of thick filament proteins accompany the changes in length of Limulus thick filaments.

Modification of photocarcinogenesis by chemical agents

The evidence is long standing and compelling that chemical agents can modify the carcinogenic effects of light. Various types of chemical-light interaction are discussed, and events in chemical photocarcinogenesis, chemically enhanced photocarcinogenesis, and promotion of photocarcinogenesis are described. Specific examples of each type of process are given, and the importance of interaction of various wavelengths of UV radiation for these processes is stressed.

Simulated stratospheric ozone depletion and increased ultraviolet radiation: effects on photocarcinogenesis in hairless mice

Solar ultraviolet radiation at the surface of the earth is a recognized cause of skin cancer. Postulated anthropogenic reductions in the thickness of the ozone layer would lead to an increased amount of ultraviolet radiation and hence would be expected to increase the risk of skin carcinogenesis. This study uses hairless (Skh:HR) mice as an animal model to study this increased risk. The mice were exposed 5 days/week to graded doses of ultraviolet radiation from a xenon arc lamp attenuated by five different thicknesses of Schott glass filters (WG320) to simulate various ozone layer thicknesses. A Robertson-Berger sunburning ultraviolet meter was used as one of the forms of dosimetry. The results of the various exposure treatments are expressed as the percentage of animal with tumors (incidence) versus time after commencing irradiation and as cumulative tumor yield (average number of tumors per survivor) versus time. With any given filter, the time to 50% incidence is inversely related to daily dose in Robertson-Berger meter units. The time to 50% incidence for comparable Robertson-Berger meter doses through different filter thicknesses increases with increasing thickness. These results indicate that the effective dose for skin cancer induction may be estimated from the Robertson-Berger meter dose but that the Robertson-Berger meter response spectrum underestimates the photocarcinogenic effectiveness of the shorter wavelengths. The cumulative tumor yield data are also consistent with these conclusions. Alternate weighting of the source spectra with the acute-response action spectrum for mouse skin edema gave a better correlation between unit dose and time to a tumor response, independent of the source spectral distribution. This suggests that the mouse skin edema action spectrum, indistinguishable from a human skin erythema action spectrum for lambda greater than 295 nm, is similar in shape to the mouse skin photocarcinogenesis action spectrum for lambda greater than 295 nm.

Energy utilization by Limulus telson muscle at different sarcomere and A-band lengths

Phosphorylargnine utilization (delta PArg) was determined in isolated Limulus telson muscle during isometric and isovelocity contractions at long, intermediate, and short lengths when thick filaments were either long and staggered, long and aligned, or shortened. Muscles developed 30% of maximum force at a length of 0.5 Lo (Lo 7 micrometers sarcomere length) during isometric tetani of 5, 15, and 30 s; however, the rate of delta PArg was the same in both the 0.5 Lo and Lo groups. External force and delta PArg were both less during isometric tetani at lengths of 1.7 and 2.0 Lo compared with the values at Lo, as expected due to a reduction in thick-thin filament overlap. However, at lengths of 0.6 and 0.3 Lo delta PArg was the same as at Lo despite a decrease in external isometric tension. No significant delta PArg was measured when telson muscles shortened rapidly (0.8 Vmax) at long or short lengths indicating the thick filament shortening per se required little, if any, energy expenditure. The overall chemical efficiency of telson muscles for performing external work during slow isovelocity contractions was 31% in groups shortening equivalent distances (0.5 Lo) from starting lengths of 1.6 and 1.3 Lo and 15% in the group shortening from 1.1 Lo.

Chemical energetics of force development, force maintenance, and relaxation in mammalian smooth muscle

High-energy phosphate utilization (delta approximately P) associated with force development, force maintenance, and relaxation has been determined during single isometric tetani in the rabbit taenia coli. ATP resynthesis from glycolysis and respiration was stopped without deleterious effects on the muscle. At 18 degrees C and a muscle length of 95% l0, the resting rate of energy utilization is 1.8 +/- 0.2 nmol/g . s-1, or 0.85 +/- 0.2 mmol approximately P/mol of total creatine (Ct) . s-1, where Ct = 2.7 mumol/g wet wt. During the initial 25 s of stimulation when force is developed, the average rate of delta approximately P was -8.2 +/- 0.8 mmol/mol Ct . s-1, some four times greater than during the subsequent 35 s of force maintenance, when the rate was -2.0 +/- 0.6 mmol approximately P/mol Ct . s-1. The energy cost of force redevelopment (0 to 95% P0) after a quick release from the peak of a tetanus is very low compared with the initial force development. Therefore, the high rate of energy utilization during force development is not due only to internal work done against the series elasticity nor to any high rate of cross-bridge cycling inherently associated with force development. The high economy of force maintenance compared with other muscle types is undoubtedly due to a slower cross-bridge cycle time. The energy utilization during 45 s of relaxation was not statistically significant, and integral of Pdt/delta approximately P was higher during relaxation than during force maintenance in the stimulated muscle.

Lipid oxidation: biologic effects and antioxidants--a review

The detection and measurement of lipid oxidation in biological systems and some biologic effects of this oxidation are reviewed. The role of lipid oxidation in the process of photocarcinogenesis and the protective effect of antioxidants against this process also are discussed. The mechanism of such protection is unknown and studies directed at elucidating the mechanism of antioxidant effect in photocarcinogenesis and in some other pathological conditons believed to involve lipid oxidation are needed. In addition to this, epoxidation of lipids observed in monolayer studies requires further investigation, particularly in the presence of some other unsaturated molecules. The possible significance of such a study--particularly in the presence of polycyclic aromatic hydrocarbon carcinogens, where formation of epoxides is generally accepted as active intermediates--is also discussed. In addition, present knowledge on the role of lipid peroxides in the destruction of proteins and biomembranes, in chemically induced toxicity and in generation of singlet oxygen is presented.

Screening for the safety of chemicals

It will be obvious that the screening of chemicals is a multidisciplinary exercise involving toxicologists, chemists and occupational physicians. The variety of means available whereby chemicals are screened, indicate that no single test is adequate. While in vivo and in vitro test methods have an important role in screening, there must be knowledge of the chemical and physical properties of the chemical. Similarly, an awareness of the possibility of human exposure must exist. The occupational physician should play a coordinating role in this exercise which is, after all, designed to protect human health. No matter how useful the animal tests, the short term tests, the study of the shape of the molecule and so on, no real assessment of the situation can be made unless there is a careful examination of the proposed process in which it is intended to use the chemical, so that the possibility of human exposure and, hence, hazard can be assessed.

Aging, environmental influences, and photocarcinogenesis

Repeated exposure of human skin to solar ultraviolet radiation (UVR) over a period of many years is responsible for the induction of most nonmelanoma skin cancers in man. The tumors are progressively more common in chronologically older people. Is this fact purely a function of adequate dose accumulation and development time, or is tumor expression influenced by "physiological age"? The answer to this question influences risk estimates of the results of atmosphere modification. Data from animal studies indicate that the tumor incidence is affected by dose-delivery factors and not just by the accumulated lifetime dose. In addition, young mice are more prone to tumor induction by a given UVR dose than are older animals. Because the quanlity and quantity of the stimulus (UVR) can be readily manipulated and accurately described, studies on photocarcinogenesis offer distinct possibilities for untangling some of the interactive variables in the aging process.

Enhancement of experimental photocarcinogenesis by topical retinoic acid

Topical application of retinoic acid (RA) solutions greatly enhanced the response of hairless mouse skin to a moderate dose of simulated sunlight. Tumors appeared much earlier, and in much greater numbers, in animals treated daily with 1 or 10 micrograms of RA in methanol immediately after 2 h exposure to a xenon arc filtered through 2 mm of Schott WG 320 glass (approximately equivalent in human erythema effectiveness to 5 min of mid-summer noon solar exposure in northern mid-latitudes), compared to mice treated with light and methanol only. The higher amount of RA, in combination with light, produced moderate epidermal hyperplasia and some scaling and transient erythema, but no gross ulceration or inflammation of skin. The lower amount of RA, though about equally effective in carcinogenesis, produced minimal epidermal hyperplasia compared to the ultraviolet radiation + methanol control.

Interaction of light and chemicals in carcinogenesis

Interactions between chemicals and UV light, as they may affect the carcinogenic process, are examined in terms of the three-component system: chemical, light, and biologic target. Various two-component interactions, in addition to unique three-component interactions, are considered. Available information is incomplete concerning such possibilities as promotion by noncarcinogenic light, the contribution of acute or chronic phototoxic events to chemical or physical carcinogenesis, and the relationship between either photochemical carcinogenesis or chemically enhanced photocarcinogenesis and demonstrable phototoxic activity. Interactions such as optical absorption by, or photochemical alteration of, chemicals are considered primarily as confounding variables in experimental situations. It is argued that realities of human exposure may reduce the complexity of these problems in practical safety or regulatory considerations.

Experimental ultraviolet photocarcinogenesis: wavelength interactions and time-dose relationships

Tumors were induced in the skin of SKH hairless mice by exposure to fluorescent FS sun lamps or to a long-arc xenon solar simulator. Tumores developed about equally well with varying amounts of UV-A radiation (lambda greater than 320 nm) given simultaneously. In contrast, incremental changes in the UV-B region (lambda less than 320 nm) led to substantial increases in carcinogenic effectiveness. A tumor-"initiating" dose of UV-B (4-10 wk of daily FS lamp exposures) was rendered less effective by subsequent exposures of the mice to UV-A (6 hr/day, F-40 T12BL lamps). The mechanism for this effect is not known. Most tumors induced by a short course (10 wk) of FS lamp exposure grew slowly or regressed, whereas mice exposed for a longer period (30 wk) developed more tumors, and many of those that appeared early grew aggressively. Effects of daily dose fractionation were less clear, and the subject requires further study. These and other variables are being tested in a program designed to yield useful information on the effects of changing spectrum, dose, and dose delivery rates on sunlight-induced cancer.

Chemical energetics of single isometric tetani in mammalian smooth muscle

A rabbit taenia coli preparation has been used to study the chemical energetics of smooth muscle contraction. Under the experimental conditions, the muscle had no spontaneous mechanical activity, but could be fully activated with the use of electrical field stimulation. ATP resynthesis from glycolysis and respiration was stopped with a procedure that involved treatment with metabolic inhibitors at 5 degrees C followed by rewarming to 18 degrees C. This procedure did not alter the high-energy phosphate contents of mechanical responses of the muscle. Use of this preparation to determine ATP and phosphorylcreatine changes during isometric tetani at 18 degrees C and a length of 86% LO showed that there was net ATP breakdown initially with no significant phosphorylcreatine splitting. This was followed by an increase in the rate of phosphorylcreatine splitting with net ATP synthesis. The average rate of total high-energy phosphate utilization was about 0.01 mumol/g.s for up to 60 s or about 150 times less than that of frog sartorius at the same temperature.