Variability and Impact of Self-Selected Interset Rest Periods During Experienced Strength Training

We investigated the variability of strength trained athletes' self-selected rest periods between sets of heavy squat training. Sixteen strength-trained male athletes (M_age = 23, SD = 3 years) completed two squat training sessions 48 hours apart. Each training session consisted of five sets of 5RM squats, interspersed with self-selected interset rest periods. A Gymaware linear optical encoder collected kinetic data for each squat and temporal data for each interset rest period. The participants' subjective ratings of the experience were taken before (Readiness to Lift [RTL]) and after (Rating of Perceived Effort [RPE]) each set. Mean total rest time and mean power output differed significantly between sessions. For both sessions, interset rest period increased, and power output decreased between Sets 3, 4, and 5 (95% CI range [-101, -17]) compared with Set 1. In both sessions, RPE increased significantly in Set 3 compared with Set 1 (95% CI range = [0.68, 2.19]), while RTL decreased significantly from Set 3 (95% CI range [-2.99, -0.58]) compared to Set 1. Interset rest period and power output demonstrated fair reliability between sessions (mean intraclass correlation coefficient = 0.55), while RPE and RTL demonstrated good and excellent reliability, respectively (mean intraclass correlation coefficient = 0.63 and 0.80). In conclusion, highly trained strength athletes demonstrated a significant difference in their between session power output and total rest time when using self-selected interset rest periods, despite stability in their subjective ratings of fatigue and effort. Interset rest periods can be self-selected reliably to complete strength training in heavy squat protocol; however, power output may decline during the set.

How many squat-stand manoeuvres to assess dynamic cerebral autoregulation?

Purpose

Squat–stand manoeuvres (SSMs) have been used to induce blood pressure (BP) changes for the reliable assessment of dynamic cerebral autoregulation. However, they are physically demanding and thus multiple manoeuvres can be challenging for older subjects. This study aimed to determine the minimum number of SSMs required to obtain satisfactory coherence, thus minimising the subjects’ workload.

Method

20 subjects performed SSMs at a frequency of 0.05 Hz. End-tidal CO₂, cerebral blood flow velocity, heart rate, continuous BP and the depth of the squat were measured. 11 subjects returned for a repeat visit. The time points at which subjects had performed 3, 6, 9, 12 and 15 SSMs were determined. Transfer function analysis was performed on files altered to the required length to obtain estimates of coherence and the autoregulation index (ARI).

Results

After three SSMs, coherence (0.05 Hz) was 0.93 ± 0.05, and peaked at 0.95 ± 0.02 after 12 manoeuvres. ARI decreased consecutively with more manoeuvres. ARI was comparable across the two visits (p = 0.92), but coherence was significantly enhanced during the second visit (p < 0.01). The intra-subject coefficients of variation (CoV) for ARI remained comparable as the number of manoeuvres varied.

Conclusions

This analysis can aid those designing SSM protocols, especially where participants are unable to tolerate a standard 5-min protocol or when a shorter protocol is needed to accommodate additional tests. We emphasise that fewer manoeuvres should only be used in exceptional circumstances, and where possible a full set of manoeuvres should be performed. Furthermore, these results need replicating at 0.10 Hz to ensure their applicability to different protocols.

Comparison of patient (POEM), observer (EASI, SASSAD, TIS) and corneometry measures of emollient effectiveness in children with eczema: findings from the COMET feasibility trial

BACKGROUND

Eczema affects around 20% of children, but multiple different outcome measures have hampered research into the effectiveness of different treatments.

OBJECTIVES

To compare the change in scores and correlations within and between five measures of eczema severity: Patient-Orientated Eczema Measure (POEM), Eczema Area and Severity Index (EASI), Six Area, Six Sign Atopic Dermatitis (SASSAD), Three Item Severity (TIS) and skin hydration (corneometry).

METHODS

Data from a feasibility trial that randomized young children with eczema to one of four emollients were used. Participants were followed for 3 months (84 days). Descriptive statistics (by emollient over time) and Spearman's correlation coefficients comparing scores at each time point and absolute change (between adjacent time points) for each outcome measure were calculated.

RESULTS

In total, 197 children, mean ± SD age 21·7 ± 12·8 months, were randomized. POEM and TIS appeared to capture a range of eczema severity at baseline, but only POEM had close approximation to normal distribution. Mean POEM, EASI, SASSAD and TIS scores improved month by month, with POEM showing the greatest sensitivity (effect size 0·42). Correlations within POEM, EASI, SASSAD and TIS were moderate to good, decreasing over time. Correlations between measures were strongest for EASI, SASSAD and TIS. By contrast, corneometry scores were more variable, correlated less well over time and were poorly correlated with the other measures.

CONCLUSIONS

Except for corneometry, all measures appear to change in relation to emollient use over time and correlate well with themselves. POEM demonstrated the greatest range of scores at baseline and change in eczema severity over the first 28 days.

Development of PK- and PBPK-based modeling tools for derivation of biomonitoring guidance values

There are numerous programs ongoing to analyze environmental exposure of humans to xenobiotic chemicals via biomonitoring measurements (e.g.: EU ESBIO, COPHES; US CDC NHANES; Canadian Health Measures Survey). The goal of these projects is to determine relative trends in exposure to chemicals, across time and subpopulations. Due to the lack of data, there is often little information correlating biomarker concentrations with exposure levels and durations. As a result, it can be difficult to utilize biomonitoring data to evaluate if exposures adhere to or exceed hazard/exposure criteria such as the Derived No-Effect Level values under the EU REACH program, or Reference Dose/Concentration values of the US EPA. A tiered approach of simple, arithmetic pharmacokinetic (PK) models, as well as more standardized mean-value, physiologically-based (PBPK) models, have therefore been developed to estimate exposures from biomonitoring results. Both model types utilize a user-friendly Excel spreadsheet interface. QSPR estimations of chemical-specific parameters have been included, as well as accommodation of variations in urine production. Validation of each model's structure by simulations of published datasets and the impact of assumptions of major model parameters will be presented.

Structure of the restriction-modification controller protein C.Esp1396I

The controller protein of the Esp1396I restriction-modification (R-M) system binds differentially to three distinct operator sequences upstream of the methyltransferase (M) and endonuclease (R) genes to regulate the timing of gene expression. The crystal structure of a complex of the protein with two adjacent operator DNA sequences has been reported; however, the structure of the free protein has not yet been determined. Here, the crystal structure of the free protein is reported, with seven dimers in the asymmetric unit. Two of the 14 monomers show an alternative conformation to the major conformer in which the side chains of residues 43-46 in the loop region flanking the DNA-recognition helix are displaced by up to 10 A. It is proposed that the adoption of these two conformational states may play a role in DNA-sequence promiscuity. The two alternative conformations are also found in the R35A mutant structure, which is otherwise identical to the native protein. Comparison of the free and bound protein structures shows a 1.4 A displacement of the recognition helices when the dimer is bound to its DNA target.

Development and evaluation of a one-step real-time reverse transcription polymerase chain reaction assay for the detection of salmonid alphaviruses in serum and tissues

We designed 4 primer pairs to amplify conserved regions of the E1 or nsP4 genes of salmonid alphavirus (SAV) and evaluated their performance in optimized 1-step SYBR green real-time RT-PCR (RRT-PCR) assays. A single primer pair, amplifying a 227 bp segment of E1 was then chosen for further study. This RRT-PCR was shown to be highly repeatable and reproducible over a wide range of RNA dilutions, with a linear relationship between cycle threshold (Ct) value and RNA concentration over a 10(7) dilution range. The limit of detection was calculated to be < or = 1.5 TCID50 ml(-1). When applied to sera previously screened by virus isolation for SAV viraemia, the RRT-PCR correctly identified all 13 culture-positive samples, as well as finding an additional 28 sera positive. Relative semi-quantitation of sera showed a very highly significant relationship between copy number and TCID50 (p < 0.001, R2 = 0.9563). Following experimental infection of salmon, heart samples were consistently positive until 21 d post infection (dpi), with (weak) positive signals still detectable in 50% of fish 70 dpi.

The grazing response of cattle to pasture contaminated with rabbit faeces and the implications for the transmission of paratuberculosis

Transmission of Mycobacterium avium subspecies paratuberculosis, the organism responsible for paratuberculosis (or Johne's disease) in ruminants, occurs through the faecal-oral route. As M. a. paratuberculosis has been isolated from rabbit faeces, cattle grazing rabbit faecal contaminated pasture may thus be at risk.A herd of 57 beef cattle was monitored on a farm in Perthshire, throughout the 1999 'grazing year', to investigate whether the cattle avoided rabbit faecal contaminated pasture and thus the potential for disease transmission. Grazing was measured every two days over eight rotations by sward heights on 40 marked treatment plots (0.5 m x 0.5 m) to which 0, 10, 50 and 250 rabbit faecal pellets were added. Cattle were also monitored by an active transponder system which enabled individual animals contacting two plots per field rotation (one control and one contaminated) to be recorded. During the monitored grazing year, grazing pressure was low with a net mean sward offtake of 18% of sward height per rotation. There were no significant differences between rabbit faecal treatments (0, 10, 50 and 250 pellets) with respect to the height or proportion of sward removed, or between the numbers of contacts made by cattle on contaminated and uncontaminated plots. Over 90% of all the cattle contacted contaminated plots, indicating that the potential for disease transmission was widespread among the herd. To our knowledge, this is the first reported instance of a lack of avoidance by grazing cattle towards swards contaminated with faeces, and implies that the potential for transmission of paratuberculosis from rabbit contaminated pasture is high.

Needle fixation, the drug user's perspective: a qualitative study

AIMS

Changing drug users' injecting behaviour is central to the project of drug services. Information about the idea of "needle fixation" is fragmentary and of uncertain relevance to contemporary injecting drug users. The aim of the study is to describe injecting drug users' ideas about needle fixation.

PARTICIPANTS AND DESIGN

Twenty-four participants, some of whom identified themselves as needle fixated, were recruited from four drugs agencies in south Wales. Participants took part in semi-structured interviews, recorded, transcribed and qualitatively analysed using Atlas/ti software.

FINDINGS

Participants describe a range of behaviours and experiences which fit with previous ideas of needle fixation, including ritualization, substitution of other drugs, injection of water and associations with deliberate-self-harm and sex. Participants describe high levels of needle aversion and add detail to previous partial descriptions of needle fixation.

CONCLUSIONS

Issues conveniently considered together as needle fixation are current among injecting drug users and may be relevant to the inability of some drug users to change from injecting drug use.

Cardiac-specific overexpression of calsequestrin results in left ventricular hypertrophy, depressed force-frequency relation and pulsus alternans in vivo

Cardiac-specific overexpression of calsequestrin has been shown to result in significant decreases in contractile parameters and intracellular Ca(2+)transients in vitro. Therefore, the purpose of the present study was to determine the effects of calsequestrin overexpression on basal cardiac function and the force-frequency relation in vivo. Calsequestrin overexpression mice (CSQ-OE, n=20) and their isogenic controls (WT) were studied with an integrative approach using transthoracic echocardiography, stress-shortening relations, and invasive hemodynamics in intact closed-chest mice. M-mode echocardiography indicated that calsequestrin overexpression resulted in concentric hypertrophy (+52%) and an increase in LV ejection phase indices. However, mean end-systolic stress-shortening coordinates revealed that at matched end-systolic wall-stress, fractional shortening was depressed in CSQ-OE mice. This was confirmed by depressed indices of LV isovolumic contraction and relaxation in CSQ-OE v. WT mice. Furthermore, overexpression of calsequestrin resulted in a downward and leftward shift of the biphasic force-frequency relation; thus, the critical heart (HR(crit)) was significantly lower in calsequestrin-overexpression mice (264+/-15 bpm) than in wild-type controls (365+/-21 bpm). Surprisingly, calsequestrin overexpression was associated with the induction of pulsus alternans in every animal (at an average heart rate of 428+/-26 bpm), whereas none of the wild-type controls displayed this phenomenon. We conclude that: (i) although increased levels of calsequestrin result in decreased myocardial contractility and a depressed force-frequency relation, LV wall stress is reduced and chamber function is normal, and (ii) an increase in SR Ca(2+)storage capacity induces pulsus alternans in the intact anesthetized mouse.

Identification by 16S rRNA gene analyses of a potential novel mycobacterial species as an etiological agent of canine leproid granuloma syndrome

PCR amplifications of the 16S rRNA gene were performed on 46 specimens obtained from 43 dogs with canine leproid granuloma syndrome to help determine its etiology. Sequence capture PCR was applied to 37 paraffin-embedded specimens from 37 dogs, and nested PCR was attempted on DNA from 9 fresh tissue specimens derived from 3 of the 37 aforementioned dogs and from an additional 6 dogs. Molecular analyses of the paraffin-embedded tissues and fresh tissue specimen analyses were performed at separate institutions. PCR products with identical sequences over a 350-bp region encompassing variable regions 2 and 3 of the 16S rRNA gene were obtained from 4 of 37 paraffin-embedded specimens and from all 9 specimens of fresh tissue originating from 12 of the 43 dogs. Identical sequences were determined from amplicons obtained from paraffin-embedded and fresh specimens from one dog. The consensus DNA sequence, amplified from paraffin-embedded tissue and represented by GenBank accession no. AF144747, shared highest nucleotide identity (99.4% over 519 bp) with mycobacterial strain IWGMT 90413 but did not correspond exactly to any EMBL or GenBank database sequence. With a probe derived from the V2 region of the novel canine sequence, reverse cross blot hybridization identified an additional four paraffin-embedded specimens containing the same novel sequence. In total, molecular methodologies identified the proposed novel mycobacterial sequence in 16 of 43 dogs with canine leproid granuloma syndrome, indicating that the species represented by this sequence may be the principal etiological agent of canine leproid granuloma syndrome.

Influence of sarcoplasmic reticulum calcium loading on mechanical and relaxation restitution

Mechanical and relaxation restitution represent the restoration of contractile force and relaxation, respectively, in premature beats having progressively longer extrasystolic intervals (ESI); these phenomena are related to intracellular activator Ca(2+) by poorly defined mechanisms. We tested the hypothesis that the level of phospholamban [which modulates the affinity of the sarcoplasmic reticulum (SR) Ca(2+)-ATPase for Ca(2+), and thus the SR Ca(2+) load] may be an important determinant of both mechanical and relaxation restitution. Five mice with ablation of the phospholamban (PLB) gene (PLBKO), eight isogenic wild-type controls (129SvJ), eleven mice with PLB overexpression (PLBOE), and nine isogenic wild-type (FVB/N) controls were anesthetized and instrumented with a 1.4-Fr Millar catheter in the left ventricle and a 1-Fr pacemaker in the right atrium. At a cycle length of 200 ms, extrastimuli with increasing ESI were introduced, and the peak rates of left ventricular isovolumic contraction (+/-dP/dt(max)) were normalized and fit to monoexponential equations. In a subset, the protocols were repeated after ryanodine (4 ng/g) was administered to deplete SR Ca(2+) stores. The time constant of mechanical restitution in PLBKO was significantly shorter [6.3 +/- 1.2 (SE) vs. 47.7 +/- 7.6 ms] and began earlier (50 +/- 10 vs. 70 +/- 19 ms) than in 129SvJ. In contrast, the time constant of mechnical restitution was significantly longer (80.3 +/- 7.6 vs. 54.1 +/- 9.2 ms) in PLBOE than in FVB/N. The time constant of relaxation restitution was less in PLBKO than in 129SvJ (26.2 +/- 9.9 vs. 44.6 +/- 3.3, P < 0.05) but was similar in PLBOE and FVB/N (21.1 +/- 6.3 vs. 20.5 +/- 5.7 ms). Intravenous ryanodine decreased significantly the time constants of mechanical restitution in PLBOE, 129SvJ, and FVB/N but was lethal in PLBKO. In contrast, ryanodine increased the time constant of relaxation restitution. Thus 1) the phospholamban level is a critical determinant of mechanical restitution and (to a lesser extent) relaxation restitution in these transgenic models, and 2) ryanodine differentially affects mechanical and relaxation restitution. Furthermore, our data suggest a dissociation of processes within the SR that govern contraction and relaxation.

Influence of transgenic overexpression of phospholamban on postextrasystolic potentiation

Twelve mice with PLB overexpression (PLBOE), and 11 isogenic FVB/N wild-type (WT) controls, were anesthetized and instrumented with a 1.4 F Millar catheter in the LV and a 1 F pacemaker in the right atrium. At a cycle length of 200 ms and a fixed extrastimulus of 120 ms, extrastimuli with increasing intervals (PESI) up to 1000 ms were introduced, and the peak rates of LV isovolumic contraction (+/- dP/dtmax) were normalized and fit to monoexponential equations. In a subset of animals, the protocols were repeated after ryanodine (4 ng/g) was given to deplete SR Ca2+ stores. The time constant and the plateau of the exponential curve fits were significantly greater in PLBOE than WT (107.8 +/- 7.0 v 75.2 +/- 5.5 ms and 1.39 +/- 0.03 v 1.08 +/- 0.02, both P < 0.05). At 200, 600 and 1000 ms, the normalized dP/dt was significantly greater in PLBOE than WT. After ryanodine, normalized dP/dt was significantly decreased in PLBOE, but unchanged in WT. The protein levels of the sodium-calcium exchanger normalized to calsequestrin were increased 3.7 +/- 0.3-fold in PLBOE compared to controls. In conclusion, the phospholamban level is a critical determinant of postextrasystolic potentiation in this transgenic model, and is differentially impaired by ryanodine at long diastolic intervals in PLBOE v controls. These differences may be due in part to changes in the protein level and resultant activity of the sodium calcium exchanger.

Modulation of force-frequency relation by phospholamban in genetically engineered mice

Phospholamban levels regulate cardiac sarcoplasmic reticulum Ca2+ pump activity and myocardial contractility. To determine whether and to what extent phospholamban modulates the force-frequency relation and ventricular relaxation in vivo, we studied transgenic mice overexpressing phospholamban (PLBOE), gene-targeted mice without phospholamban (PLBKO), and isogenic wild-type controls. Contractility was assessed by the peak rate of left ventricular (LV) isovolumic contraction (+dP/dtmax), and diastolic function was assessed by both the peak rate (-dP/dtmax) and the time constant (tau) of isovolumic LV relaxation, using a high-fidelity LV catheter. Incremental atrial pacing was used to generate heart rate vs. -dP/dtmax (force-frequency) relations. Biphasic force-frequency relations were produced in all animals, and the critical heart rate (HRcrit) was taken as the heart rate at which dP/dtmax was maximal. The average LV +dP/dtmax increased in both PLBKO and PLBOE compared with their isogenic controls (both P < 0.05). The HRcrit for LV +dP/dtmax was significantly higher in PLBKO (427 +/- 20 beats/min) compared with controls (360 +/- 18 beats/min), whereas the HRcrit in PLBOE (340 +/- 30 beats/min) was significantly lower compared with that in isogenic controls (440 +/- 25 beats/min). The intrinsic heart rates were significantly lower, and the HRcrit and the +/-dP/dtmax at HRcrit were significantly greater in FVB/N than in SvJ control mice. We conclude that 1) the level of phospholamban is a critical negative determinant of the force-frequency relation and myocardial contractility in vivo, and 2) contractile parameters may differ significantly between strains of normal mice.

Invasive hemodynamics and force-frequency relationships in open- versus closed-chest mice

We compared hemodynamics, ventricular function, and force-frequency relationships in six open-chest and six closed-chest anesthetized mice (FVB/N strain). Left ventricular (LV) pressure was measured with a 1.8- or 1.4-Fr Millar catheter placed via the right carotid artery and the LV apex in the closed- and open-chest state, respectively. Pacing was performed with electrodes placed either directly on atrial appendages (open chest) or with a 1-Fr bipolar catheter via the jugular vein (closed chest). Closed-chest animals had greater spontaneous heart rate (267 +/- 106 vs. 147 +/- 27 beats/min), LV systolic (81 +/- 14 vs. 48 +/- 9 mmHg) and diastolic pressures (11.2 +/- 4.8 vs. 5.6 +/- 2.4 mmHg), and maximal rise (+ dP/dtmax: 6,208 +/- 2,519 vs. 3,682 +/- 671 mmHg/s) and fall in pressure development (-dP/dtmax: -6,094 +/- 2,386 vs. -3,001 +/- 399 mmHg/s). LV systolic pressure (98 +/- 18 vs. 52 +/- 11 mmHg), + dP/dtmax (9,240 +/- 2,459 vs. 5,777 +/- 2,473 mmHg/s), and -dP/dtmax (-8,375 +/- 2,551 vs. -3,753 +/- 1,170 mmHg/s) were significantly higher when animals were matched at a heart rate of 420 beats/min in closed-chest vs. open-chest animals. Biphasic force-frequency relationships were seen in all animals, but the critical heart rate was greater in the closed- than open-chest animals (432 +/- 42 vs. 318 +/- 42 beats/min). We conclude that 1) there are significant differences between invasive indexes of systolic and diastolic function between the closed- and open-chest preparations, 2) there is a biphasic force-frequency relationship in the anesthetized mouse, and 3) dP/dtmax can be used to assess the cardiovascular phenotype.

The role of the cytoskeleton in left ventricular pressure overload hypertrophy and failure

To characterize alterations in gene expression which may occur during the development of compensated left ventricular pressure overload hypertrophy (CH) and the transition to decompensated congestive heart failure (DH), differential RNA display was used to compare mRNA transcripts from sham operated, 4-week, and 8-week thoracic aorta banded guinea-pigs. Of several regulated transcripts chosen for analysis, one was identified by nucleotide sequence homology as titin, a sarcomeric cytoskeletal protein. By differential display and comparative PCR, titin transcripts were increased in CH and then declined in DH. Comparative PCR of desmin and tubulin demonstrated increased mRNA levels for these cytoskeletal proteins in CH and DH. Western analysis showed associated increases in titin (DH) and desmin (CH and DH) protein expression but no increase in tubulin protein. Isolated Langendorff cardiac mechanics failed to reveal functional differences in either hypertrophy phenotype when microtubules were depolymerized (colchicine 10(-6)M). In summary, the major cytoskeletal proteins are differentially regulated in LV pressure overload hypertrophy and failure. Neither the level of beta-tubulin or its polymerization state appear to affect LV function in this model of cardiac hypertrophy.

In vivo echocardiographic detection of enhanced left ventricular function in gene-targeted mice with phospholamban deficiency

We evaluated the ability of M-mode and Doppler echocardiography to assess left ventricular (LV) function reliably and repeatedly in mice and tested whether these techniques could detect physiological alterations in phospholamban (PLB)-deficient mice. Anesthetized wild-type mice (n = 7) and mice deficient in PLB (n = 8) were studied with two-dimensional guided M-mode and Doppler echocardiography using a 9-MHz imaging and 5- to 7.5-MHz Doppler transducer. Data were acquired in the baseline state and after intraperitoneal isoproterenol administration (2.0 micrograms/g IP). Interobserver and intraobserver variability and reproducibility were excellent. PLB-deficient mice were associated with significant (P < .05) increases in several physiological parameters (mean +/- SD) compared with wild-type control mice: normalized mean velocity of circumferential shortening (7.7 +/- 2.1 versus 5.5 +/- 1.0 circ/sec), peak aortic velocity (105 +/- 13 versus 75 +/- 9.2 cm/s), mean aortic acceleration (57 +/- 16 versus 31 +/- 4 m/s2), and peak early-diastolic transmitral velocity (80.0 +/- 7.2 versus 66.9 +/- 7.7 cm/s). LV dimensions, shortening fractions, heart rates, late diastolic transmitral (A) velocities, and early to late (E/A) diastolic velocity ratios were similar in both groups. Isoproterenol administration resulted in significant increases in Doppler indices of ventricular function in control but not PLB-deficient mice. These findings indicate that assessment of LV function can be performed noninvasively in mice under varying physiological conditions and that PLB regulates basal LV function in vivo.

Myosin heavy chain regulation and myocyte contractile depression after LV hypertrophy in aortic-banded mice

Using an adult mouse aortic-banded model of pressure-overload hypertrophy and isolated cardiomyocyte mechanics studies, we examined the hypothesis that contractile depression is due to altered cardiac contractile proteins rather than changes in left ventricular (LV) geometry, loading, or the extracellular matrix. FVB mice were banded at the transverse aortic arch or sham operated and studied after 7 days. In nine animals the gradient across the aortic band averaged 47 +/- 4 mmHg. Compared with sham-operated controls, banded animals had increased LV weight-to-body weight ratio (2.8 +/- 0.1 and 3.5 +/- 0.1, respectively; P = 0.035). Left ventricles from additional age-matched groups of mice that underwent identical surgical procedures were examined for altered transcriptional control of myosin heavy chains (MHCs). beta-MHC protein content increased (15 +/- 2%) vs. shams (3.8 +/- 2%; P = 0.004). Dot blots of LV RNA showed a corresponding increase in beta-MHC transcripts in banded animals (15.8 +/- 2%) vs. controls (5.7 +/- 2%; P = 0.012). Contractile performance was assessed using enzymatically disaggregated isolated LV myocytes paced at 0.5 Hz. There was no difference in percentage myocyte shortening between banded (8.6 +/- 0.5%) and control (9.1 +/- 0.5%) animals. However, maximal velocity of contraction was depressed after aortic banding (129 +/- 11 vs. 233 +/- 28 microns/s; P = 0.007), as was velocity of relaxation (105 +/- 11 vs. 188 +/- 22 microns/s; P = 0.007). These results suggest that depressed myocyte contractility after induction of pressure-overload hypertrophy in aortic-banded mice may be, in part, a consequence of transcriptional upregulation of the beta-MHC.

Desensitization by noradrenaline of responses to stimulation of pre- and postsynaptic adrenoceptors

1 The effect of exposing isolated preparations of rat aortic strip, rat atria and mouse vas deferens to perfusions of Krebs solution containing various concentrations of noradrenaline on their sensitivity to the drug has been determined.2 The responses evoked by stimulation of postsynaptic adrenoceptors in all the tissues and presynaptic alpha-adrenoceptors in the mouse vas deferens were diminished by the perfusion of noradrenaline through the organ bath for 30 min.3 The concentration of noradrenaline required to produce desensitization was higher in the mouse vas deferens than in the other tissues and more was required to desensitize the chronotropic responses than the inotropic responses in rat isolated atria.4 The inclusion of cocaine (10(-5) M) in the bathing solution to block uptake(1) increased the sensitivity of most tissues to noradrenaline. With the possible exception of the response to stimulation of presynaptic receptors in the mouse vas deferens, desensitization was somewhat increased in its presence.5 When uptake(2) was blocked by oestradiol (10(-5) M), it was not possible to desensitize the contractor responses of the aortic strip and vas deferens to exogenous noradrenaline, nor the inotropic response of the atria to the drug. However, oestradiol failed to block the desensitization of chronotropic responses and responses to stimulation of presynaptic receptors in the vas deferens.6 Blockade of monoamine oxidase (MAO) with iproniazid (7.2 x 10(-4) M) or with pargyline (5 x 10(-4) M) did not affect the desensitization process in the aortic strip.7 Blockade of catechol-O-methyltransferase (COMT) with U-0521 (5.3 x 10(-5) M) greatly increased desensitization in the aortic strip and desensitization of inotropic responses in the atria. It had no effect on desensitization of chronotropic responses. Its effect on responses in the mouse vas deferens was not determined.8 The perfusion of methoxamine at concentrations about 1000 times higher than those of noradrenaline also produced desensitization in the aortic strip.9 The desensitization of presynaptic receptors in the mouse vas deferens was shown to be specific and that of the responses to postsynaptic receptor stimulation to be non-specific.10 It is concluded that responses to adrenoceptor stimulation may be desensitized by accumulation of noradrenaline inside the cells bearing the receptors and that the desensitization is caused by noradrenaline itself not by a metabolite. Desensitization may also be caused without accumulation of noradrenaline in uptake(2) and for some receptors these may not be alternative mechanisms.

Drought and dependence in the Sahel

The relationship between human activity and environmental degradation has been documented in numerous studies. With regard to West Africa, E.P. Stebbing was already warning of ecological degradation due to overcultivation and overgrazing in the 1930s. Less well documented are the reasons why people who understand many of the requirements of ecologically sound farming and herding nonetheless mismanage natural resources to the point of disaster. An examination of the 1968-1973 drought in the Sahel zone of West Africa (formerly French West Africa) suggests that the lack of economic autonomy for Sahelian countries is a major cause not only of their economic stagnation and underdevelopment but equally of the degradation of their ecosystems. Specific policies, initiated during the colonial period and continued by independent governments, can be identified as reducing the ability of West African famers and herders to exploit their environment with an adequate safety margin. Largely as a result of the 1968-1973 drought, there has been asn upsurge of interest in the Sahel on the part of international and national aid agencies. However, it is very possible that the programs devised by these groups will promote neither economic autonomy nor ecological stability for the countries in that region. A development strategy based largely on self-reliance, on the other hand, could the more successful in protecting both the populations and the ecology of the Sahel.