Genetic and physical localization of the root-knot nematode resistance locus Mi in tomato

As part of a map-based cloning strategy designed to isolate the root-knot nematode resistance gene Mi, tomato F2 populations were analyzed in order to identify recombination points close to this economically important gene. A total of 21 089 F2 progeny plants were screened using morphological markers. An additional 1887 F2 were screened using PCR-based flanking markers. Fine-structure mapping of recombinants with newly developed AFLP markers, and RFLP markers derived from physically mapped cosmid subclones, localized Mi to a genomic region of about 550 kb. The low frequency of recombinants indicated that recombination was generally suppressed in these crosses and that crossovers were restricted to particular regions. To circumvent this problem, a population of Lycopersicon peruvianum, the species from which Mi was originally introgressed, that was segregating for resistance was developed. Screening of this population with PCR, RFLP and AFLP markers identified several plants with crossovers near Mi. Recombination frequency was approximately eight-fold higher in the Mi region of the L. peruvianum cross. However, even within the wild species cross, recombination sites were not uniformly distributed in the region. By combining data from the L. esculentum and L. peruvianum recombinant analyses, it was possible to localize Mi to a region of the genome spanning less than 65 kb. Received: 15 July 1997 / Accepted: 1 October 1997     

A heat shock following electroporation induces highly efficient transformation of Corynebacterium glutamicum with xenogeneic plasmid DNA

An improved method for the electrotransformation of wild-type Corynebacterium glutamicum (ATCC 13032) is described. The two crucial alterations to previously developed methods are: cultivation of cells used for electrotransformation at 18 °C instead of 30 °C, and application of a heat shock immediately following electrotransformation. Cells cultivated at sub optimal temperature have a 100-fold improved transformation efficiency (10⁸ cfu μg⁻¹) for syngeneic DNA (DNA isolated from the same species). A heat shock applied to these cells following electroporation improved the transformation efficiency for xenogeneic DNA (DNA isolated from a different species). In combination, low cultivation temperature and heat shock act synergistically and increased the transformation efficiency by four orders of magnitude to 2.5 × 10⁶ cfu μg⁻¹ xenogeneic DNA. The method was used to generate gene disruptions in C. glutamicum. Received: 26 March 1999 / Received revision: 9 June 1999 / Accepted: 11 June 1999     

The effect of sodium balance on sweat sodium secretion and plasma aldosterone concentration

The effect of manipulating sodium intake upon sweat sodium secretion was investigated during heat acclimation. Twenty-five male subjects were confined to an environmental chamber at a temperature of 25°C for 3 days, and then acclimated to heat by a further 5 days at 40°C. The subjects' daily sodium intake was controlled throughout as follows: high (HNa), 348.4 (0.8) mmol · day⁻¹, n = 7; moderate (MNa), 174.1 (0.6) mmol · day⁻¹, n = 9; or low (LNa), 66.3 mmol · day⁻¹, n = 9. Sodium losses were estimated from urinary, faecal and sweat collections using a whole-body washdown method. Plasma aldosterone concentration was also measured from venous blood sampled each morning. Measurements of body temperature and heart rate during the heat exposure phase indicated a degree of heat acclimation. During this heat phase there was a reduction (P < 0.01) in sweat sodium secretion for all three conditions which was greatest for the LNa condition, although this finding was not significant (P < 0.1). In the LNa condition, plasma aldosterone concentration increased (P < 0.05) prior to heat exposure, and the secretion of aldosterone was potentiated (P < 0.01) during the heat exposure in comparison with the MNa condition. In contrast, the HNa diet produced a fall (P < 0.05) in plasma aldosterone concentration prior to heat exposure and an attenuation of aldosterone secretion thereafter. These findings are inconsistent with the hypothesis that retention of sweat sodium is dependent upon a net body sodium deficit, but demonstrate that aldosterone secretion is potentiated under such conditions. Accepted: 22 May 1988     

The effect of 15 consecutive days of heat–exercise acclimation on heat shock protein 70

The purpose of this study was to investigate the alterations in serum heat shock protein (Hsp) 70 levels during a 15-consecutive-day intermittent heat–exercise protocol in a 29-year-old male ultra marathon runner. Heat acclimation, for the purpose of physical activities in elevated ambient temperatures, has numerous physiological benefits including mechanisms such as improved cardiac output, increased plasma volume and a decreased core temperature (T _c). In addition to the central adaptations, the role of Hsp during heat acclimation has received an increasing amount of attention. The acclimation protocol applied was designed to correspond with the athlete’s tapering period for the 2007 Marathon Des Sables. The subject (VO₂max = 50.7 ml·kg⁻¹·min⁻¹, peak power output [PPO] = 376 W) cycled daily for 90 min at a workload corresponding to 50% of VO₂max in a temperature-controlled room (average WBGT = 31.9 ± 0.9°C). Venous blood was sampled before and after each session for measurement of serum osmolality and serum Hsp70. In addition, T _c, heart rate (HR) and power output (PO) was measured throughout the 90 min to ensure that heat acclimation was achieved during the 15-day period. The results show that the subject was successfully heat acclimated as seen by the lowered HR at rest and during exercise, decreased resting and exercising T _c and an increased PO. The heat exercise resulted in an initial increase in Hsp70 concentrations, known as thermotolerance, and the increase in Hsp70 after exercise was inversely correlated to the resting values of Hsp70 (Spearman’s rank correlation = −0.81, p < 0.01). Furthermore, the 15-day heat–exercise protocol also increased the basal levels of Hsp70, a response different from that of thermotolerance. This is, as far as we are aware, the first report showing Hsp70 levels during consecutive days of intermittent heat exposure giving rise to heat acclimation. In conclusion, a relatively longer heat acclimation protocol is suggested to obtain maximum benefit of heat acclimation inclusive of both cellular and systemic adaptations.     

Recombination in paired and individual kernels of Zea mays L.

Kernels of Zea mays L. occur in pairs in adjacent rows. Fifty-six paired kernels from were selected from each of 24 ears. The resulting 1334 plants, 662 pairs and 10 individual survivors, were classified and expected frequencies of different categories of pairs determined. Analysis by chi-square disclosed no significant deviation from overall random distribution of crossovers and non-crossovers in paired plants. Accordingly, crossing-over is not related to the ontogeny of spikelets in pairs from a single protuberance on the young ear. Substances affecting crossingover in maize have been postulated. Any such substances thus appear to be formed late in development.Variation in recombination was observed among the small samples from the different ears. Six ears with presumptive high recombination and six with presumptive low recombination were chosen for further study, and 244 more kernels planted from each ear. The resulting data were pooled with that previously obtained to produce two equivalent-sized populations with presumptive high and low recombination frequencies for comparison. An eight-fold increase in double crossovers in the high recombination population was associated with a significant increase in single crossovers for the ws ₃–lg ₁ interval, region 1, and a highly significant increase in single crossovers for region 2. Coefficients of coincidence were determined for the two populations and diselosed that interference was greater in the low recombination population in addition to the reduced occrroence of single crossovers.Scientific Article No. A 1830, Contribution No. 4632 of the Maryland Agricultural Experiment Station, Department of Botany, based in part on a thesis presented by Susan R. Bard to the Faculty of the Graduate School of the University of Maryland in partial fulfillment of the requirements for the Degree of Master of Science.     

Cloning and characterization of the rpoH gene of Rhodobacter capsulatus

By using an oligonucleotide mixture corresponding to a region highly conserved among alternative sigma factors we identified a new σ factor gene (rpoH) from Rhodobacter capsulatus. This gene encodes a protein of 34 kDa with strong similarity to the RpoH (σ ³²) factors from other bacterial species. It was not possible to inactivate the R. capsulatusrpoH gene by introducing a resistance cassette, implying that it is essential for growth. The 5′ ends of the mRNAs were mapped to two sequences with similarity to an rpoH- and an rpoD-dependent promoter, respectively. The amounts of both these mRNAs increased after heat shock, but were unaffected by a decrease in oxygen tension. Western analysis using a σ factor-specific antibody revealed the accumulation of a protein of about 34 kDa after heat shock, and an increase in the amounts of a protein with the same size after reduction of oxygen tension in R. capsulatus cultures. Received: 16 March 1998 / Accepted: 28 July 1998     

The effect of hyperbaric oxygen preconditioning on heat shock protein 72 expression following in vitro stress in human monocytes

Hyperbaric oxygen (HBO) is thought to confer protection to cells via a cellular response to free radicals. This process may involve increased expression of heat shock proteins, in particular the highly inducible heat shock protein 72 (Hsp72). Healthy male volunteers (n = 16) were subjected to HBO for 1 h at 2.8 ATA. Inducible Hsp72 expression was measured by flow cytometry pre-, post- and 4 h-post HBO. Peripheral blood mononuclear cells (PBMC) were isolated from whole blood via density centrifugation pre-, post- and 4 h post-HBO. PBMC were then subjected to an in vitro heat shock at 40°C or hypoxia at 37°C (5% O₂) with a control at 37°C. Cells were then analysed for Hsp72 expression by flow cytometry. Monocytes showed no significant changes in Hsp72 expression following HBO. No detectable Hsp72 was seen in lymphocytes or neutrophils. Following in vitro hypoxic exposure, a significant increase in Hsp72 expression was observed in monocytes isolated immediately post- (p = 0.006) and 4 h post-HBO (p = 0.010) in comparison to control values. HBO does not induce Hsp72 expression in PBMC. The reported benefits of HBO in terms of pre-conditioning are not due to inducement of Hsp72 expression in circulating blood cells, but may involve an enhancement of the stress response.     

Ovarian and Uterine Ultrasonography in <Emphasis Type="Italic">Aotus azarai infulatus</Emphasis>

We evaluated the uterus and ovaries of owl monkeys (Aotus azarai infulatus) via gynecological ultrasound examination. We evaluated the subjects in 2 different time periods. The first period (P1) was characterized by the absence of mating, with daily examinations, during 4 mo (n = 10). At the end of P1, we paired the subjects for 30 d, but without ultrasonographic evaluation. The second period (P2) was characterized by the presence of mating, with examinations once a week, during 7 consecutive months (n = 9). We evaluated the uterus and ovaries in sagittal and transverse scans, using a 5–12 MHz linear array probe. The uterine volume (UV) was directly proportional to the number of previous parturitions. The right ovary volume (RtOV) is greater than the left (LtOV) in P1 and P2. There is a positive correlation (p < 0.05) between the females’ mass, RtOV (r = 0.28) and LtOV (r = 0.16).     

Serum level of soluble Hsp70 is associated with vascular calcification

It has been previously reported that serum levels of 70-kDa heat shock protein (Hsp70) are elevated in peripheral artery disease. The aim of the present study was to examine whether increased serum Hsp70 levels are related to the extent of arterial calcification and standard laboratory parameters of patients with peripheral artery disease, as well as to markers of inflammation (C-reactive protein), atherosclerosis (homocysteine), and calcification (fetuin-a). One hundred eighty chronic atherosclerotic patients with significant carotid stenosis and/or lower extremity vascular disease were enrolled in this cross-sectional study. Systemic atherosclerosis and calcification was assessed by ultrasound (carotid intima–media thickness (IMT), presence of calcification at the abdominal aorta, carotid and femoral bifurcations, and aortic and mitral cardiac valves). Standard serum markers of inflammation, diabetes, renal function, ankle-brachial indexes, and traditional risk factors for atherosclerosis were noted. Serum Hsp70 levels were measured with enzyme-linked immunosorbent assay. Standard laboratory parameters (clinical chemistry), C-reactive protein (CRP), and homocysteine levels were determined by an autoanalyzer using the manufacturer’s kits. Fetuin-a levels were measured by radial immunodiffusion. Patients’ median age was 64 (57–71) years, 69% were men, and 34.5% had diabetes. Serum heat shock protein 70 levels were significantly higher in patients with more severe arterial calcification (p < 0.02) and showed significant positive correlations with serum bilirubin (r = 0.23, p = 0.002) and homocysteine levels (r = 0.18, p = 0.02). Serum Hsp70 did not correlate with body mass index, IMT, CRP, or fetuin-a levels in this cohort. Logistic regression analysis confirmed the association between sHsp70 and calcification score (OR, 2.189; CI, 1.156–4.144, p = 0.016) and this correlation remained significant (OR, 2.264; CI, 1.021–5.020, p = 0.044) after the adjustment for age, sex, eGFR, smoking, CRP, and homocysteine levels. Our data show that serum Hsp70 levels correlate with the severity of atherosclerosis in patients with carotid artery disease and chronic lower limb ischemia. These data support a putative role for plasma Hsp70 in the development of arterial calcification. Nevertheless, further studies are required to investigate the usefulness of circulating Hsp70 level as a marker of atherosclerotic calcification.     

The mus308 locus of Drosophila melanogaster is implicated in the bypass of ENU-induced O-alkylpyrimidine adducts

The mus308 locus of D. melanogaster was originally characterized by virtue of a mutant phenotype that resulted in specific hypersensitivity to cross-linking agents. However, the gene product has also been implicated in the repair of lesions other than cross-links. The gene was recently sequenced, and it encodes a protein with motifs characteristic of both DNA polymerases and helicases. We present mutability studies, using the recessive lethal (RL) test, which show that N-ethyl-N-nitrosourea (ENU) induces hypermutability in mus308-deficient conditions, although only in early broods. Further studies elucidated the role of MUS308 in repair processes by characterizing the spectrum of molecular mutations induced by in vivo ENU in postmeiotic germ cells, in mus308 conditions. These revealed that, in comparison to repair-proficient conditions, there is an increase in the frequency of GC → AT and AT → GC transitions, and AT → TA transversions. Moreover, frameshift mutations, which have not previously been reported to form part of the ENU spectrum, were also found. These results indicate that MUS308 is needed to process ENU-induced lesions, and support the hypothesis that the mus308 gene plays a role in post-replication bypass of O-alkylpyrimidines, probably mediated by recombination, which serves to increase the time available for error-free repair of these persistent and highly mutagenic lesions. Received: 22 March 1999 / Accepted: 17 November 1999     

The time-profile of the PBMC HSP70 response to in vitro heat shock appears temperature-dependent

Summary. Heat shock proteins (HSPs) are synthesised by cells subsequent to a stress exposure and are known to confer protection to the cell in response to a second challenge. HSP induction and decay are correlated to thermotolerance and may therefore be used as a biomarker of thermal history. The current study tested the temperature-dependent nature of the heat shock response and characterised its time profile of induction. Whole blood from 6 healthy males (Age: 26 ± (SD) 2 yrs; Body mass 74.2 ± 3.8 kgs; VO_2max: 49.1 ± 4.0 ml·kg⁻¹·min⁻¹) were isolated and exposed to in vitro heat shock (HS) at 37, 38, 39, 40, and 41 °C for a period of 90 min. After HS the temperature was returned to 37 °C and intracellular HSP70 was quantified from the leukocytes at 0, 2, 4, and 6 h after heat treatment. The concentration of HSP70 was not different between temperatures (P > 0.05), but the time-profile of HSP70 synthesis appeared temperature-dependent. At control (37 °C) and lower temperatures (38–39 °C) the mean HSP70 concentration increased up to 4 h post HS (P < 0.05) and then returned towards baseline values by 6 h post HS. With in vitro hyperthermic conditions (40–41 °C), the time-profile was characterised by a sharp rise in HSP70 levels immediately after treatment (P < 0.05 for 40 °C at 0 h), followed by a progressive decline over time. The results suggest a temperature-dependent time-profile of HSP70 synthesis. In addition, the temperature at which HSP70 is inducted might be lower than 37 °C.     

Delayed recovery of β-glucuronidase activity driven by an Arabidopsis heat shock promoter in heat-stressed transgenic Nicotiana plumbaginifolia

 The expression of the Arabidopsis heat shock protein (HSP) 18.2 promoter-β-d-glucuronidase (GUS) chimera gene was investigated in transgenic Nicotiana plumbaginifolia plants during the recovery phase at normal temperatures (20–22  °C) after a heat shock (HS) treatment. GUS activity increased during the recovery phase after HS at 42  °C for 2 h, and maximal GUS activity was observed after 12 h at normal temperatures, at levels 50–100 times higher than the activity immediately after HS. After HS at 44  °C, little GUS activity was observed during the first 20–24 h at normal temperatures, but the activity increased gradually thereafter, to reach a maximum at 40–50 h. After HS at 45  °C, no GUS activity was observed throughout the experimental period. RT-PCR analysis showed that GUS mRNA remained for 10 h after a 2-h HS at 42  °C and for 40 h after a 2-h HS at 44  °C. These findings demonstrate that brief HS treatment, especially at a sublethal temperature, induces a long-term accumulation of HSP-GUS mRNA during the recovery phase. Received: 31 July 1998 / Revision received: 4 November 1998 / Accepted: 19 February 1999     

Homologous recombination and allele replacement in transformants of Fusarium fujikuroi

The ascomycete Fusarium fujikuroi could be transformed stably to hygromycin resistance only when the transforming plasmid contained a fragment of DNA from the fungus. The transformation frequencies were roughly independent of the sequence of the particular fungal DNA fragment used, of its size (1.8 or 6 kb), and of whether this DNA was present only once in the fungal genome or about forty times (the genes for ribosomal RNA). The plasmid was integrated into the fungal genome by homologous recombination in the eighteen transformants tested; ectopic integration was never observed. The carB gene of F. fujikuroi was cloned and shown to complement unpigmented mutants deficient in phytoene dehydrogenase. A mutant carB allele was prepared in vitro and used to transform wild-type protoplasts; the transformants contained a genomic duplication and were heterozygous for carB; the mutant allele replaced the original wild-type allele when this was spontaneously lost in the transformants. This loss was due to gene conversion in some cases and to recombination between repeated sequences in others. Received: 5 November 1999 / Accepted: 16 March 2000     

A meiosis-specific protein kinase, Ime2, is required for the correct timing of DNA replication and for spore formation in yeast meiosis

 In this report we study the regulation of premeiotic DNA synthesis in Saccharomyces cerevisiae. DNA replication was monitored by fluorescence-activated cell sorting analysis and by analyzing the pattern of expression of the DNA polymerase α-primase complex. Wild-type cells and cells lacking one of the two principal regulators of meiosis, Ime1 and Ime2, were compared. We show that premeiotic DNA synthesis does not occur in ime1Δ diploids, but does occur in ime2Δ diploids with an 8–9 h delay. At late meiotic times, ime2Δ diploids exhibit an additional round of DNA synthesis. Furthermore, we show that in wild-type cells the B-subunit of DNA polymerase α is phosphorylated during premeiotic DNA synthesis, a phenomenon that has previously been reported for the mitotic cell cycle. Moreover, the catalytic subunit and the B-subunit of DNA polymerase α are specifically degraded during spore formation. Phosphorylation of the B-subunit does not occur in ime1Δ diploids, but does occur in ime2Δ diploids with an 8–9 h delay. In addition, we show that Ime2 is not absolutely required for commitment to meiotic recombination, spindle formation and nuclear division, although it is required for spore formation. Received: 20 February 1996 / Accepted: 7 June 1996     

The Occurrence of Double Strand DNA Breaks is not the Sole Condition for Meiotic Crossing over in Drosophila Melanogaster

Analysis of the interchromosomal effects of In(2L+2R)Cy, In(3L+3R)LVMand their joint effect on the frequencies of single and double crossovers in the cv-v-fregion of the X chromosome as well as interference showed that both inversions, occurring separately, increased the frequency of single as well as double crossovers and the coefficient of coincidence. However, when the inversions occurred together the frequencies of single crossovers no longer increased, but the frequency of double crossovers, as well as the coefficient of coincidence did increase. These results indicate firstly that the interchromosomal effects influence some precondition of exchange, but that this precondition is not an occurrence of double strand DNA breaks. Thus, the occurrence of double strand DNA breaks is not the sole condition for crossing over in Drosophila melanogaster.     

Starvation reduces the heat shock protein responses in white sturgeon larvae

This study investigates the responses of white sturgeon larvae (Acipenser transmontanus) to starvation and thermal stress, through the measurement of nutritional status (i.e. growth performances) and cellular biomarkers: heat shock proteins (Hsp) 70 and 90. White sturgeon larvae (25 day post hatch; initial weight 179.0 ± 5.1 mg) were fed (20% body weight per day) or starved for 24, 48 or 72 hrs. Every 24 hrs, five larvae from each of the starved or fed treatment replicates were exposed to heat shock resulting from an increase in water temperature from 19°C to 26°C, at a rate of 1°C per 15 min, and maintained at 26°C for 4 hrs. No mortality was observed in this study. Starvation significantly (p < 0.05) decreased the body weight and body contents of energy, protein, and lipid of the experimental larvae, compared to the fed larvae. Heat shock induced the expressions of Hsp70 and Hsp90 in both the fed and starved group; however, starvation reduced the induction at all sampling points. The current study demonstrates that poor larval nutritional status, assessed by the aforementioned parameters, reduced heat shock responses to thermal stress, as measured by heat shock protein levels. Furthermore, Hsp70 and 90 are more sensitive to heat shock and starvation, respectively. This may be, in part, a result of the different functioning of the heat shock proteins in cellular stress response and warrants further study.     

Correlation between auditory sensitivity and vocalization in anabantoid fishes

Several anabantoid species produce broad-band sounds with high-pitched dominant frequencies (0.8–2.5 kHz), which contrast with generally low-frequency hearing abilities in (perciform) fishes. Utilizing a recently developed auditory brainstem response recording-technique, auditory sensitivities of the gouramis Trichopsis vittata, T. pumila, Colisa lalia, Macropodus opercularis and Trichogaster trichopterus were investigated and compared with the sound characteristics of the respective species. All five species exhibited enhanced sound-detecting abilities and perceived tone bursts up to 5 kHz, which qualifies this group as hearing specialists. All fishes possessed a high-frequency sensitivity maximum between 800 Hz and 1500 Hz. Lowest hearing thresholds were found in T. trichopterus (76 dB re 1 μPa at 800 Hz). Dominant frequencies of sounds correspond with the best hearing bandwidth in T. vittata (1–2 kHz) and C. lalia (0.8–1 kHz). In the smallest species, T. pumila, dominant frequencies of acoustic signals (1.5–2.5 kHz) do not match lowest thresholds, which were below 1.5 kHz. However, of all species studied, T. pumila had best hearing sensitivity at frequencies above 2 kHz. The association between high-pitched sounds and hearing may be caused by the suprabranchial air-breathing chamber, which, lying close to the hearing and sonic organs, enhances both sound perception and emission at its resonant frequency. Accepted: 26 November 1997     

Joint Molecule Resolution Requires the Redundant Activities of MUS-81 and XPF-1 during Caenorhabditis elegans Meiosis

The generation and resolution of joint molecule recombination intermediates is required to ensure bipolar chromosome segregation during meiosis. During wild type meiosis in Caenorhabditis elegans, SPO-11-generated double stranded breaks are resolved to generate a single crossover per bivalent and the remaining recombination intermediates are resolved as noncrossovers. We discovered that early recombination intermediates are limited by the C. elegans BLM ortholog, HIM-6, and in the absence of HIM-6 by the structure specific endonuclease MUS-81. In the absence of both MUS-81 and HIM-6, recombination intermediates persist, leading to chromosome breakage at diakinesis and inviable embryos. MUS-81 has an additional role in resolving late recombination intermediates in C. elegans. mus-81 mutants exhibited reduced crossover recombination frequencies suggesting that MUS-81 is required to generate a subset of meiotic crossovers. Similarly, the Mus81-related endonuclease XPF-1 is also required for a subset of meiotic crossovers. Although C. elegans gen-1 mutants have no detectable meiotic defect either alone or in combination with him-6, mus-81 or xpf-1 mutations, mus-81;xpf-1 double mutants are synthetic lethal. While mus-81;xpf-1 double mutants are proficient for the processing of early recombination intermediates, they exhibit defects in the post-pachytene chromosome reorganization and the asymmetric disassembly of the synaptonemal complex, presumably triggered by crossovers or crossover precursors. Consistent with a defect in resolving late recombination intermediates, mus-81; xpf-1 diakinetic bivalents are aberrant with fine DNA bridges visible between two distinct DAPI staining bodies. We were able to suppress the aberrant bivalent phenotype by microinjection of activated human GEN1 protein, which can cleave Holliday junctions, suggesting that the DNA bridges in mus-81; xpf-1 diakinetic oocytes are unresolved Holliday junctions. We propose that the MUS-81 and XPF-1 endonucleases act redundantly to process late recombination intermediates to form crossovers during C. elegans meiosis.     

The Impact of heat exposure and repeated exercise on circulating stress hormones

To determine if heat exposure alters the hormonal responses to moderate, repeated exercise, 11 healthy male subjects [age = 27.1 (3.0) years; maximal oxygen consumption, V˙O_2max = 47.6 (6.2) ml · kg · min⁻¹; mean (SD)] were assigned to four different experimental conditions according to a randomized-block design. While in a thermoneutral (23°C) or heated (40°C, 30% relative humidity) climatic chamber, subjects performed either cycle ergometer exercise (two 30-min bouts at ≈50% V˙O_2max, separated by a 45-min recovery interval, CEx and HEx conditions), or remained seated for 3 h (CS and HS conditions). Blood samples were analyzed for various exercise stress hormones [epinephrine (E), norepinephrine (NE), dopamine, cortisol and human growth hormone (hGH)]. Passive heating did not alter the concentrations of any of these hormones significantly. During both environmental conditions, exercise induced significant (P < 0.001) elevations in plasma E, NE and hGH levels. At 23°C during bout 1: E = 393 (199) pmol · l⁻¹ (CEx) vs 174 (85) pmol · l⁻¹ (CS), NE = 4593 (2640) pmol · l⁻¹ (CEx) vs 1548 (505) pmol · l⁻¹ (CS), and hGH = 274 (340) pmol · l⁻¹ (CEx)vs 64 (112) pmol · l⁻¹ (CS). At 40°C, bout 1: E = 596 (346) pmol · l⁻¹ (HEx) vs 323 (181) pmol · l⁻¹ (HS), NE = 7789 (5129) pmol · l⁻¹ (HEx) vs 1527 (605) pmol · l⁻¹ (HS), and hGH = 453 (494) pmol · l⁻¹ (HEx) vs 172 (355) pmol · l⁻¹ (HS). However, concentrations of plasma cortisol were increased only in response to exercise in the heat [HEx = 364 (168) nmol · l⁻¹ vs HS = 295 (114) nmol · l⁻¹). Compared to exercise at room temperature, plasma levels of E, NE and cortisol were all higher during exercise in the heat (P < 0.001 in all cases). The repetition of exercise did not significantly alter the pattern of change in cortisol or hGH levels in either environmental condition. However, repetition of exercise in the heat increased circulatory and psychological stress, with significantly (P < 0.001) higher plasma concentrations of E and NE. These results indicate a differential response of the various stress hormones to heat exposure and repeated moderate exercise. Accepted: 16 April 1997