Einfluß der Temperatur auf die RNA-Synthese von Escherichia coli CRT 266 (dna Bts) nach Infektion mit dem Bakteriophagen T3

Infection of the temperature-sensitive E. coli CRT 266 (dna B^ts) with T3-phages at the temperature of 30°C and 35°C, respectively, induced T3-specific RNA synthesis with a maximum rate at 7 min (30°C) and 4.5 min (35°C) afte infection. At temperatures above 40°C no T3-induced RNA synthesis could be observed. Infection of E. coli CR 34–45 (dna B⁺) with T3 phages at 30°C, 35°C and at temperatures above 40°C, however, produced T3-specific RNA synthesis. The maximum of T3-induced RNA synthesis could be observed between 7 min and 3 min depending on the temperature during infection. The inability to form T3-specific RNA after infection of E. coli CRT 266 at nonpermissive temperatures may be a cause for the absence of the formation of T3 phages and lysis of the host cells.     

Growth hormone and prolactin responses during partial and whole body warm‐water immersions

Aim: To elucidate the role of core and skin thermoreceptors in the release of growth hormone (GH) and prolactin (PRL), a sequence of two experiments using whole‐body (head‐out) and partial (one forearm) hot water immersions was performed. Methods: Experiment 1: Nine healthy men were exposed to head‐out and partial water immersions (25 min, 38–39 °C). Results: Head‐out immersion increased the core temperature (38.0 ± 0.1 vs. 36.7 ± 0.1 °C, P < 0.001) and plasma concentration of the hormones (GH, 16.1 ± 4.5 vs. 1.2 ± 0.4 ng mL^?1, P < 0.01; PRL, 9.1 ± 1.0 vs. 6.4 ± 0.4 ng mL^?1, P < 0.05). During the partial immersion the core temperature was slightly elevated (36.8 ± 0.1 vs. 36.6 ± 0.1, P < 0.001), the concentration of GH increased (4.8 ± 1.7 vs. 0.6 ± 0.3, P < 0.05), while plasma PRL decreased (7.6 ± 0.8, 6.0 ± 0.6, 5.2 ± 0.6, P < 0.01). Experiment 2: Seven volunteers immersed one forearm once in 39 °C and once in 38 °C water. The measurements were performed in 5‐min intervals. The GH concentration increased gradually from the beginning of the immersions (min 10; 39 °C: 1.9 ± 1.0 vs. 0.6 ± 0.3 ng mL^?1, P < 0.01; 38 °C: 0.19 ± 0.03 vs. 0.14 ± 0.03, P < 0.05) and peaked after their completion (39 °C: +10 min, 3.7 ± 2.0, P < 0.001; 38 °C: +15 min, 0.86 ± 0.61, P < 0.01). The core temperature was unchanged until min 15 of the 39 °C bath. Thereafter, it increased about 0.15 °C above the baseline (P < 0.01). Immersion in 38 °C water did not induce core temperature changes. Conclusions: Peripheral thermoreceptors are involved in GH release when the body is exposed to elevated environmental temperature while a substantial elevation of core temperature is a precondition of PRL release.     

Genomics of <Emphasis Type="Italic">Salmonella</Emphasis> phage ΦStp1: candidate bacteriophage for biocontrol

Multidrug-resistant Salmonella causing Salmonellosis is a food-borne pathogen and hence a public health hazard. Alternatives to antibiotics, such as phages, are possible solutions to this increasing drug resistance. In this context, several Salmonella phages were isolated and characterized. This paper describes the physiochemical and whole genome characterization of one such bacteriophage, ΦStp1, which efficiently infects serovars Salmonella Enteritidis and Salmonella Typhimurium. Morphological observations by transmission electron microscopy and phylogenetic analysis using terminase gene classified ΦStp1 to family Siphoviridae, closely resembling ‘T5 like phage’ morpho-types. With a maximum adsorption time of 50 min, ΦStp1 latent period was 30 min with 37 phages/cell burst size. ΦStp1 draft genome sequenced by shotgun method comprised 112,149 bp in 3 contigs with 37.99% GC content, 168 predicted ORFs, and 15 tRNAs. Genes involved in host shut down, DNA replication, regulation, nucleotide metabolism, lysis, and morphogenesis were also noted. The study not only provided an insight into the characteristics of phage genome, but also information about proteins encoded by bacteriophages, therefore contributing to understanding phage diversity. Sequence analysis also proved the absence of virulence and lysogeny-related genes, which only went to confirm ΦStp1 as a promising therapeutic agent against Salmonella infections.     

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Aim: In this study, we quantified acute changes in the intracellular and extracellular fluid compartments during upright neutral‐ and cold‐water immersion. We hypothesized that, during short‐term cold immersion, fluid shifts would be wholly restricted to the extracellular space. Methods: Seven males were immersed 30 days apart: control (33.3 ° SD 0.6 °C); and cold (18.1 ° SD 0.3 °C). Posture was controlled for 4 h prior to a 60‐min seated immersion. Results: Significant reductions in terminal oesophageal (36.9 ° ± 0.1 °–36.3 ° ± 0.1 °C) and mean skin temperatures (30.3 ° ± 0.3 °–23.0 ° ± 0.3 °C) were observed during the cold, but not the control immersion. Both immersions elicited a reduction in intracellular fluid [20.17 ± 6.02 mL kg^?1 (control) vs. 22.72 ± 9.90 mL kg^?1], while total body water (TBW) remained stable. However, significant plasma volume (PV) divergence was apparent between the trials at 60 min [12.5 ± 1.0% (control) vs. 6.1 ± 3.1%; P < 0.05], along with a significant haemodilution in the control state (P < 0.05). Plasma atrial natriuretic peptide concentration increased from 18.0 ± 1.6 to 58.7 ± 15.1 ng L^?1 (P < 0.05) during cold immersion, consistent with its role in PV regulation. We observed that, regardless of the direction of the PV change, both upright immersions elicited reductions in intracellular fluid. Conclusion: These observations have two implications. First, one cannot assume that PV changes reflect those of the entire extracellular compartment. Second, since immersion also increases interstitial fluid pressure, fluid leaving the interstitium must have been rapidly replaced by intracellular water.     

Absolute quantification and NMR visibility of glycogen in the isolated,perfused rat heart using 13C NMR spectroscopy

NMR spectroscopy, possibly, does not detect 100% of large molecules such as glycogen (mol. wt = 10⁷–10⁹). Using both NMR and chemical quantification methods, we have, therefore, determined the NMR visibility of cardiac glycogen (defined as the ratio of the NMR value to the chemical value, expressed as a percentage) in the isolated, perfused heart. Rats (n = 7) were pretreated for 60 min with 0.2mg/kg isoproterenol (s.c.) to deplete their endogenous myocardial glycogen stores (mainly ¹²C). The hearts were then aerobically perfused (65 cm H₂O, at 37 °C) in a double-walled chamber (the annulus contained a standard), for 70 min with Krebs buffer plus 3.5 mM [¹³C]1-glucose and 5 mM sodium acetate (natural abundance). From 70 to 175 min the sole substrate was natural abundance acetate (5 mM). ¹³C NMR spectra for glycogen quantification were acquired in two different ways; by applying 896, 90° pulses at 0.33 s intervals with ¹H decoupling (‘fast’, practical spectra) and by applying 896, 90° pulses at 5 s intervals (‘slow’, impractical spectra). Hearts were then removed from the magnet, freeze-clamped ( −196 °C) and analysed chemically. Cardiac glycogen, quantified from the ‘fast’ spectra (using conversion factors) and the ‘slow’ spectra was 16.8 ± 1.1 and 16.1 ± 1.8 (mean ± SEM) μmol glucosyl units/heart, respectively. After correction of the chemical value for the residual [¹²C]glycogen (determined from ¹H NMR spectra of the extracted glycogen after hydrolysis), the NMR-visibilities were calculated to be 101 ± 6 and 109 ± 7%, for the ‘fast’ and ‘slow’ spectra, respectively. We conclude that, despite its size, cardiac glycogen is 100% visible in NMR spectra of isolated rat hearts.     

Acute and adaptive responses in humans to exercise in a warm, humid environment

 Acute and repeated exposure for 8–13 consecutive days to exercise in humid heat was studied. Twelve fit subjects exercised at 150 W [45% of maximum O₂ uptake (V.O₂,_max)] in ambient conditions of 35°C and 87% relative humidity which resulted in exhaustion after 45 min. Average core temperature reached 39.9 ± 0.1°C, mean skin temperature (T– _sk) was 37.9 ± 0.1°C and heart rate (HR) 152 ± 6 beats min^–1 at this stage. No effect of the increasing core temperature was seen on cardiac output and leg blood flow (LBF) during acute heat stress. LBF was 5.2 ± 0.3 l min^–1 at 10 min and 5.3 ± 0.4 l min^–1 at exhaustion (n = 6). After acclimation the subjects reached exhaustion after 52 min with a core temperature of 39.9 ± 0.1°C, T– _sk 37.7 ± 0.2°C, HR 146 ± 4 beats min^–1. Acclimation induced physiological adaptations, as shown by an increased resting plasma volume (3918 ± 168 to 4256 ± 270 ml), the lower exercise heart rate at exhaustion, a 26% increase in sweating rate, lower sweat sodium concentration and a 6% reduction in exercise V.O₂. Neither in acute exposure nor after acclimation did the rise of core temperature to near 40°C affect metabolism and substrate utilization. The physiological adaptations were similar to those induced by dry heat acclimation. However, in humid heat the effect of acclimation on performance was small due to physical limitations for evaporative heat loss. Received: 3 July 1996 / Received after revision: 26 September 1996 / Accepted: 7 January 1997     

The induction of mild hypothermia improves systolic function of the resuscitated porcine heart at no further sympathetic activation

Aim: Mild hypothermia (MH) after cardiac arrest attenuates hypoxic brain injury and improves survival. As MH increases contractility in normal hearts, we hypothesized that MH improves cardiovascular function after cardiac arrest. Methods: In 16 anaesthetized pigs (64 ± 2 kg), ventricular fibrillation was induced electrically for 5 min. At 10 min after resuscitation and return of spontaneous circulation (ROSC), pigs were assigned to normothermia (NT, 38 °C, n = 8) or MH (33 °C, n = 8, intravascular cooling). Results: At ROSC 6 h vs. baseline, heart rate (HR) was unchanged in NT, but decreased in MH. Cardiac output (CO, l min^?1) decreased in MH (3.5 ± 0.2 vs. 5.5 ± 0.4, P < 0.05) more than in NT (4.8 ± 0.4 vs. 5.7 ± 0.4, P = ns). Mixed venous oxygen saturation decreased in NT (56 ± 2 vs. 66 ± 3%, P < 0.05), but remained constant in MH (64 ± 2 vs. 65 ± 2%) due to a 35% decrease of whole body oxygen consumption. Left ventricular (LV) dP/dt_max (mmHg s^?1) decreased in NT (1163 ± 97 vs. 1665 ± 134, P < 0.05), but was preserved in MH (1602 ± 102 vs. 1603 ± 96), whereas LV relaxation was profoundly slowed during MH. Pressure–volume analysis confirmed improved LV systolic function during MH, but also demonstrated decreased LV end‐diastolic distensibility, which was further potentiated by right atrial pacing at baseline HR. MH did not increase plasma catecholamine levels. Spectral analysis of heart rate variability revealed reduced sympathetic activation during MH. Conclusion: The induction of MH after cardiac resuscitation improves systolic myocardial function without further sympathetic activation. A reduced metabolism during MH outweighs a decreased CO and thereby acts favourably on systemic oxygen supply/demand balance.     

Isolation,characterization, and efficacy of bacteriophages isolated against Citrobacter spp. an in vivo approach in a zebrafish model (Danio rerio)

Citrobacter infections are becoming an increasingly significant health problem in aquaculture in South-Eastern countries. The objective of this study was to isolate and evaluate the potential of lytic bacteriophages against Citrobacter infections. TEM analysis revealed that the isolated phages Citrophage MRM19 and Citrophage MRM57 were identified to be Siphovirus and Podovirus family of the order Caudovirales. The phage life-cycle studies showed that Citrophage MRM19 had an adsorption time of 18 ± 1 min and a latency period of 25 ± 3 min with burst size of 110 ± 20 phages/infected cell and Citrophage MRM57 had an adsorption time of 15 ± 1 min and a latency period of 25 ± 2 min with burst size of 50 ± 5 phages/infected cell. In vitro studies indicated that the bacterial load was reduced by 5 and 7 log units within 12 h by Citrophage MRM19 and Citrophage MRM57. The in vivo efficacy of the phages was studied using zebrafish (Danio rerio) as a model organism in low-scale tanks. The study unveiled that the use of phages increased the survival up to 17%, 23%, and 26% in the case of Citrophage MRM19, Citrophage MRM57, and phage cocktail treatment, respectively. Our study indicated that bacteriophages are suitable biocontrol agents against Citrobacter spp. especially in aquaculture industry.     

Low-temperature T4-like coliphages vB_EcoM-VR5, vB_EcoM-VR7 and vB_EcoM-VR20

Bacteriophages vB_EcoM-VR5, vB_EcoM-VR7 and vB_EcoM-VR20, showing an unusual low-temperature plating profile and producing constantly growing plaques, were isolated from aquatic environments of Lithuania. Although vB_EcoM-VR5, vB_EcoM-VR7 and vB_EcoM-VR20 resembled phage T4 both in their genome size and in their major structural protein (gp23) pattern, physiological properties of all three phages tested differed significantly from those of T4. With an optimum temperature for plating around 24°C and a high efficiency of plating in the range 7–30°C, bacteriophages vB_EcoM-VR7 and vB_EcoM-VR20 failed to plate at 37°C, whereas phage vB_EcoM-VR5 could not be plated at 40°C. Sequence analysis of diagnostic g23 PCR products revealed that g23 of vB_EcoM-VR5, vB_EcoM-VR7 and vB_EcoM-VR20 differed from the corresponding T4 g23 DNA sequence by 21, 21 and 20%, respectively.     

Micro‐Focus X‐Ray Tomography Study of the Microstructure and Morphometry of the Eggshell of Ostriches (Struthio Camerus)

In ostrich husbandry, economic losses have mainly been attributed to low hatchability of eggs, which has mostly been attributed to the structure of the eggshell. The main aim of this study was to investigate the morphology and the morphometry of the ostrich eggshell using micro‐focus X‐ray computer tomography and scanning electron microscopy. The mean weight and volume of the eggs were 1,312 ± 56SE g and 1,333 ± 44SE cm³, respectively. The mean thickness and the mean surface area of the eggshell was 1.83 ± 0.10SE mm and 619 ± 15SE cm² respectively and the mean total number of pores in the shell was 40,596 ± 1832SE. No significant correlations were found between the thickness of the shell and the weight of the eggs, the volume of the egg and the thickness of the shell, the diameter of the pores and the number of pores, the volume of the pores and the number of pores or the surface area of the pores and the number of pores. The mean diameters of the pores on the blunt (air cell) ? (0.02 ± 0.04SE mm) and the sharp (0.26 ± 0.36SE mm) parts of the eggshell were significantly different (P = 0.0001) while the mean volumes and the surface areas of the pores in these parts were not significantly different (P = 0.203 and P = 0.089, respectively). The sizes of the pores differed in different parts of the eggshell, which consisted mainly of tightly arranged mammillary cones that that fused to the palisade columns. The external surface of the ostrich eggshell was covered by a cuticle. Anat Rec, 299:1015–1026, 2016. © 2016 Wiley Periodicals, Inc.     

Molecular and physiological analysis of three Pseudomonas aeruginosa phages belonging to the “N4-like viruses”

We present a detailed analysis of the genome architecture, structural proteome and infection-related properties of three Pseudomonas phages, designated LUZ7, LIT1 and PEV2. These podoviruses encapsulate 72.5 to 74.9 kb genomes and lyse their host after 25 min aerobic infection. PEV2 can successfully infect under anaerobic conditions, but its latent period is tripled, the lysis proceeds far slower and the burst size decreases significantly. While the overall genome structure of these phages resembles the well-studied coliphage N4, these Pseudomonas phages encode a cluster of tail genes which displays significant similarity to a Pseudomonasaeruginosa (cryptic) prophage region. Using ESI-MS/MS, these tail proteins were shown to be part of the phage particle, as well as ten other proteins including a giant 370 kDa virion RNA polymerase. These phages are the first described representatives of a novel kind of obligatory lytic P. aeruginosa-infecting phages, belonging to the widespread “N4-like viruses” genus.     

Diabetes affects blood pressure and heart rate responses during acute hypothermia

Many diabetics are cold-intolerant and experience dramatic changes in normal systemic function during hypothermia. Little is known of the cardiovascular adjustments in diabetics exposed to an acute cold stress. In an effort to identify the alterations in mean arterial blood pressure (MAP) and heart rate (HR) in the diabetic during environmental cooling (10 ± 2 °C), we compared the in vivo MAP and HR responses of urethane-anaesthetized (1.5 g kg^?1), streptozotocin-diabetic (STZ, 65 mg kg^?1, n = 12) and control (CON, n = 10) rats during acute hypothermia. MAP was measured directly via an indwelling carotid artery cannula and HR was calculated from the peak systolic pressure waves. Overall, the STZ rats were more cold-intolerant than CON as evidenced by the greater rate of decline in colonic temperature (T_c) from 36 to 28 °C (STZ, 0.16 °C min^?1 vs. CON, 0.06 °C min^?1; P < 0.05). Prior to cooling, HR was significantly lower (P < 0.05) in STZ (282 ± 9 beats min^?1) than in CON rats (399 ± 24 beats min^?1); however, during the acute hypothermic period, HR displayed a similar rate of decline in both groups. With respect to MAP, both groups demonstrated similar pre-experimental pressor responses (CON, 81.7 ± 5.4 vs. STZ, 83.2 ± 5.1 mmHg, P > 0.05). During progressive hypothermia, MAP gradually increased (P < 0.05) in the CON group from baseline (T_c = 36 °C) and reached peak values (118.4 ± 2.5 mmHg) at T_c = 30 °C, while the STZ group failed to exhibit any cold pressor response. At the conclusion of the experiment (T_c = 28 °C), the STZ group pressor response to hypothermia was not different from baseline (T_c = 36 °C, 83.2 ± 5.1 vs. T_c = 28 °C, 77.4 ± 3.4 mmHg; P > 0.05). The absence of any pressor response in the diabetic group during progressive hypothermia reflects the poor overall vasoconstrictive capacity to cooling and could partially explain the rapid decline of core temperature in this group.     

Expression and activity of the glutamate transporter EAAT2 in cardiac hypertrophy: implications for ischaemia reperfusion injury

The expression and activity of the glutamate transporter, excitatory amino acid transporter 2 (EAAT2), in cardiac hypertrophy were investigated with respect to glutamate’s potential as a cardioprotective agent. Sarcolemmal vesicles (SV) isolated from hypertrophic hearts of male spontaneously hypertensive rats (SHR) or normotrophic hearts from age-matched male Wistar Kyoto rats (WKY) were used to measure the relative level of EAAT2 expression by Western blotting and the initial rate of 0–0.3 mM l-[¹⁴C]glutamate uptake. The effects of 20-min global normothermic ischaemia ±0.5 mM glutamate on cardiac function were measured in isolated working SHR/WKY hearts. In a separate series of hearts, glutamate, lactate and ATP levels were measured. Both the level of EAAT2 expression and the V _max for sodium-dependent l-[¹⁴C]glutamate uptake were significantly greater in SHR SV compared to WKY SV. The reperfusion cardiac output (CO) of SHR hearts was significantly worse than that of the WKY hearts (24.3±2.2 ml/min vs 39.8±3.3 ml/min, n=7/9±SE, p<0.01). The addition of 0.5 mM l-glutamate improved the SHR reperfusion CO to 45.2±5 ml/min, (n=6±SE, p<0.01) but had no effect on WKYs (46.2±3.8 ml/min, n=6±SE). SHR with 0.5 mM l-glutamate had higher glutamate levels at the start of ischaemia, plus higher glutamate and ATP levels at the end of ischaemia compared to any other group. These results suggest that increased glutamate transporter expression and activity in the SHR hearts helped facilitate glutamate entry into the SHR cardiomyocytes leading to improved myocardial metabolism during ischaemia and better functional recovery on reperfusion.     

P2X3 receptor gating near normal body temperature

P2X₃ purinoreceptors expressed in mammalian sensory neurons are involved in nociception, mechanosensory transduction, and temperature sensation. Homomeric P2X₃ receptors desensitize rapidly (<500 ms after activation by an agonist) and recover from desensitization very slowly (20–25 min at room temperature). They are susceptible to use-dependent inhibition by low nanomolar concentrations of ATP through developing the “high-affinity binding site” (HABS), which traps ATP molecules, thus keeping receptors in a desensitized state (Pratt et al., J Neurosci 25:7359–7365, 2005). Indeed, here we demonstrated directly that the desensitization of the receptor, after being activated by ATP, proceeds independently of the presence of agonist. We found that the temperature sensitivity of P2X₃ receptors is abnormal: development of desensitization does not depend on temperature within the range between 25 and 40°C, whereas the recovery from desensitization is greatly \accelerated with temperature increase (Q ₁₀ ∼10). The sensitivity of HABS to low nanomolar ATP near normal body temperature (35°C) is substantially lower than at 25°C (IC₅₀ is 3.2 ± 0.3 nM at 35°C and 0.79 ± 0.09 nM at 25°C). HABS itself is subjected to slow desensitization partially loosing its sensitivity to ATP: at 35°C the response completely recovers in 10 min in the presence of 3 nM ATP, making the receptor operational in the presence of up to 30 nM ATP. Unusual combination of temperature sensitivity/insensitivity of P2X₃ receptors may be related to their pivotal role in the processing of thermal sensitivity as revealed by recent knockout experiments.     

Interaction of bacteriophage 1P with the cell surface components of Rhizobium trifolii 24SM

Phage 1P is a BRADLEY C type with an octahedron head 52 nm in diameter and a short tail 10.2 nm long. The process of phage adsorption in to the host cells has been studied. At first, virions attached themselves to the host exopolysaccharide (EPS) capsule, with subsequent penetration through the capsular layer towards the cell wall. Isolated EPS preparation, composed mainly of mannose, galactose and glucose did not neutralize the phages. The rate of attachment of phage 1P to the mucoid strain R. trifolii 24SM and to its nonmucoid, morphologically rough mutants, 24AR and 24R, is the same. The cell wall of R. trifolii 24SM contains lipopolysaccharide (LPS) receptors, which bind phage particles irreversibly. Purified LPS showed a PhI₅₀ value of 0.05 μg ml^?1. One particle of phase 1P is neutralized by 5 × 10^?16 g of LPS.     

Fluid balance, thermal stress, and post exercise response in women's Islamic athletic clothing

This study examined heat stress, heart rate (HR), fluid balance, micro-environment temperature and humidity with Islamic athletic clothing (IC) compared to traditional soccer uniform (SC). Ratings of perceived exertion (RPE), session RPE (S-RPE), comfort, and cooling response were also examined. Female volunteers (N = 8) completed a treadmill [(V)\dot]\textO_2\textpeak \dot{V}{\text{O}}_{{2{\text{peak}}}} test and then, in a randomized, counter-balanced order, two intermittent running bouts (45 min total) in a hot environment (30.0°C WBGT) in IC and SC. Thereafter, participants sat for 40 min in the hot ambient environment. Repeated measures ANOVA revealed significantly greater micro-environment temperature (p = 0.02) (IC 33.3 ± 3.2°C, SC 32.0 ± 2.8°C) and humidity (p = 0.04) (IC 48.4 ± 8.1%, SC 42.9 ± 7.9%) in IC during the exercise trial but no difference in the 40-min recovery period for micro-environment temperature (p = 0.25) or humidity (p = 0.18). No significant difference (p > 0.05) was shown for core temperature (T _rec) (IC 38.3 ± 0.4°C, SC 38.2 ± 0.4°C), HR (IC l54 ± 28 beats min⁻¹, SC 151 ± 26 beats min⁻¹) or RPE (IC 4.7 ± 2.1, SC 3.8 ± 1.7) during the exercise trial or recovery period. Results from a paired t test revealed a significantly greater (p < 0.05) S-RPE (IC 5.8 ± 1.2, SC 4.3 ± 1.9), sweat loss (IC 1.4 ± 0.4 L h⁻¹, SC 1.2 ± 0.4 L h⁻¹) and greater discomfort during the exercise and recovery period for the IC. IC clothing appears to have no detrimental effects on heat storage or heat strain during exercise or recovery.     

Modulation of systolic and diastolic function by endothelin-1: relation to coronary flow

Different conclusions have been reached with regard to the effect of endothelin (ET-1) on cardiac contractility. We examined systolic and diastolic function in response to constant known concentrations of ET-1 with or without ET-1 induced reductions in coronary flow (CF). Rat hearts (n= 21) were buffer-perfused using constant coronary flow (cCF) or constant perfusion pressure (cPP). Left ventricular function was assessed isovolumically. Addition of ET-1 (10^-9 M) in the cCF group caused a gradual increase in PP from 61 ± 2 to 165±6mmHg (mean±SE) (P < 0.01). Within 10 min left ventricular systolic pressure (LVSP) increased from 111 ± 2 to a maximum of 134±4mmHg (P < 0.01) and [L\dP/dt] increased from 1640 ± 81 to a maximum of 2020 ± 92 mmHg s“¹ (P < 0.01). After 15 min left ventricular end diastolic pressure (LVEDP), a measure of diastolic stiffness (DS), also increased. With ET-1 (10 ⁸ M), similar haemodynamic alterations appeared more rapidly. In the cPP group, ET-1 (10”⁹ M) caused a sharp decrease in CF and LVSP fell from 115 ± 8 to 62±12 mmHg at 10 min (P < 0.001). Systolic function remained stable at a reduced level for 1 h. DS did not change. Thus, ET-1 possesses positive inotropic effects and increases diastolic stiffness. Both effects may be masked by vasoconstriction-induced ischaemia.     

Lack of contribution of P2X receptors to neurally mediated vasoconstriction in the rabbit kidney in vivo

Aim: The contribution of adenosine triphosphate (ATP) to the neural control of regional renal perfusion in vivo remains unknown. We therefore examined whether P2X receptors mediate renal vascular responses to electrical stimulation of the renal nerves (RNS) in pentobarbitone anaesthetized rabbits. Methods: Responses to RNS were tested before and during renal arterial infusion of α,β‐methylene ATP (α,β‐mATP, 7–56 μg kg⁻¹ min⁻¹) to desensitize P2X₁ receptors. RNS consisted of 3 min trains at graded frequencies and short trains of RNS (4–32 pulses). Results: Three‐minute trains of RNS reduced renal blood flow (RBF), cortical laser Doppler flux (CLDF), and medullary LDF (MLDF) by −90 ± 3%, −89 ± 3% and −31 ± 11%, respectively, at 4 Hz. MLDF was reduced less than CLDF or RBF. During short train RNS, RBF, CLDF and MLDF were reduced by −22 ± 2%, −15 ± 2% and −12 ± 2%, respectively, for 32 s at 1 Hz. CLDF and MLDF were reduced to a similar extent. Infusion of α,β‐mATP induced transient reductions in RBF, CLDF and MLDF, but within 5 min these variables had recovered to control levels. Vascular responses to RNS were not significantly altered by α,β‐mATP treatment. Conclusions: In the rabbit kidney in vivo, α,β‐mATP‐sensitive receptors mediate vasoconstriction and reduce perfusion in both cortical and medullary vascular beds. However, these receptors do not mediate neurally induced reductions in renal perfusion.     

Exercise-induced decreases in sarcoplasmic reticulum Ca2+–ATPase activity attenuated by high-resistance training

Muscle biopsies were performed on the vastus lateralis muscle prior to and during a high-resistance training (HRT) programme in order to examine the effects of hypertrophy on sarcoplasmic reticulum Ca²⁺ ATPase activity at rest and during exercise. In six male untrained volunteers (peak aerobic power, V˙O ₂ peak = 3.39 ± 0.13 L min^?1, mean ± SE), the resting Ca²⁺ ATPase activity (μmol min^?1 g wet wt^?1) at 0 (4.89 ± 0.20), 4 (5.62 ± 0.56), 7 (5.15 ± 0.41) and 12 (4.82 ± 0.11) weeks was unchanged by HRT. During cycle ergometer exercise, prior to training, Ca²⁺-ATPase was reduced (P < 0.05) by 14% during the initial 30 min at 58% VO ₂ peak and (P < 0.05) a further 19% during 30 min at 72% VO ₂ peak. Following 7 and 12 weeks of training, the decreases in SR Ca²⁺-ATPase were less pronounced (P < 0.05). These results indicate that muscle hypertrophy, although incapable of altering Ca²⁺-ATPase pump activity at rest, can attenuate the decrease observed in exercise by mechanism(s) as yet unknown.