Analysis of morphological relationship between micro- and macromorphology of Mortierella species using a flow-through chamber coupled with image analysis

Using a flow-through chamber coupled with image analysis, the morphological parameters of 11 Mortierella species were quantified, and the relationship between micro- and macromorphology was investigated. On potato-dextrose-agar plates, 5 species formed rose petal-like colonies, 3 formed large round colonies, and 3 formed donut-like colonies. By observing micromorphology in a flow-through chamber, fungi were divided into 3 groups, classified according to morphological parameters: (i) a group with a high branch formation rate (q(b): tip/microm/h) and a low tip extension rate (q(tip): microm/tip/h); (ii) a group with a low branch formation rate and a high tip extension rate; and (iii) a group intermediate between the former and the latter groups. In suspension culture, group (i) fungi formed a hyphal bundle with a pulpy pellet-like morphology and a pellet core. In contrast, group (ii) fungi showed an aggregation of hyphae without the pellet core. In a narrow-specific hyphal growth rate (mu(l)) range (0.35-0.45 h(-1)), a higher branch formation rate led to increased hyphal branching, resulting in the formation of a hyphal bundle with a pulpy pellet-like morphology and a pellet core. When the branch formation rate was lower than 2 x 10(-3) tips/microm/h, the mycelia formed less branched but longer hypha. Our study surmises that a micromorphology consisting of a high hyphal growth rate (0.4 h(-1)), low tip extension rate (20 tips/microm/h), and high branch formation rate (8 x 10(-3) tips/microm/h) forms the suitable macromorphology for arachidonic acid production.     

Effect of operating parameters on specific production rate of a cloned-gene product and performance of recombinant fermentation process

A two-stage continuous system in combination with a temperature-sensitive expression system were used as model systems to maximize the productivity of a cloned gene and minimize the problem associated with the plasmid instability for a high-expression recombinant. In order to optimize the two-stage fermentation process, the effects of such operational variables as temperature and dilution rate on productivity of cloned gene were studied using the model systems and a recombinant, Escherichia coli K12 DeltaH1 Deltatrp/pPLc23trp A1. When the expression of cloned gene is induced by raising the operating temperature above 38 degrees C, a significant decrease in the colony-forming-units (CFU) of the plasmid-harboring cell was observed, and the decrease was related to the product concentration. In order to describe this phenomenon, a new kinetic parameter related to the metabolic stress (metabolic stress factor) was introduced. It is defined as the ratio of the rate of change of pheno-type from colony-forming to non-colony-forming cells to the product accumulation per unit cell mass. At a fixed temperature of 40 degrees C, the varying dilution rate D in the range of 0.35-0.90 h(-1) did not affect the metabolic stress factor significantly. At a fixed dilution rate of D = 0.35 h(-1), this factor remained practically constant up to 41 degrees C but increased rapidly beyond 41 degrees C. The effects of temperature and dilution rate in the second stage on the specific production rate were also studied while maintaining the apparent specific growth rate (mu(2) (app)) of the second stage constant at or near mu(2) (app) = 0.26 h(-1). Under a constant dilution rate, D(2) = 0.35 h(-1), the maximum specific production rate obtained was about q(p, max) = 38 units TrpA/mg cell/h at 41 degrees C. At a constant temperature, T(2) = 40 degrees C, specific production rate increased with decreasing dilution rate with in the dilution rate range of D(2) = 0.35-0.90 h(-1). Based on the results of our study, the optimal operating conditions found were dilution rate D(2) = 0.35 h(-1) and operating temperature T(2) = 41 degrees C at the apparent specific growth rate of 0.26 h(-1). Under the optimal operating conditions, about threefold increase in productivity was achieved compared to the best batch culture result. In addition, the fermentation period could be extended for more than 100 h.     

Siderophore iron transport followed by electron paramagnetic resonance spectroscopy

Siderophore iron transport was followed in Ustilago sphaerogena using isotope transport assays coupled with EPR spectroscopy. EPR spectroscopy was used as a quantitative tool to follow the rate of reduction of siderophore iron(III) to iron(II) in the cell suspension by following the disappearance of the signal at g = 4.3. This rate was compared with the rate of iron transport, measured by the disappearance of radioactively labeled iron from the medium. The transport of three iron chelates was examined: the ferric siderophores ferrichrome and ferichrome A, and iron(III) chelated to excess citrate. For the transport of ferrichrome, an iron(III) ionophore, the rate of reduction of iron(III) to iron(II) was significantly lower than the rate of uptake of isotope from the medium supernatant, which is consistent with the established mechanism of uptake of the entire complex followed by intracellular reduction to remove the iron from the ligand. However, the rate of reduction of ferrichrome A, a non-ionophore, was identical with the rate of transport of iron into the cell. Iron(III) citrate was reduced at a rate slightly lower than the rate of transport. These data suggest that reduction of iron(III) is involved in the transport of iron from ferichrome A and possibly from iron(III) citrate.     

The effect of divalent metal cations on the inhibition of human coagulation factor Xa by plasma proteinase inhibitors

The inactivation of human coagulation factor Xa by the plasma proteinase inhibitors alpha 1-antitrypsin, antithrombin III and alpha 2-macroglobulin in purified systems was found to be accelerated by the divalent cations Ca2+, Mn2+ and Mg2+. The rate constant for the inhibition of factor Xa by antithrombin III rose from 2.62 X 10(4) M-1 X min-1 in the absence of divalent cations to a maximum of 6.40 X 10(4) M-1 X min-1 at 5 mM Ca2+, 8.10 X 10(4) M-1 X min-1 at 5 mM Mn2+, with a slight decrease in rate at higher cation concentrations. Mg2+ caused a gradual rise in rate constant to 5.65 X 10(4) M-1 X min-1 at 20 mM. The rate constant for the inhibition of factor Xa by alpha 1-antitrypsin in the absence of divalent cations was 5.80 X 10(3) M-1 X min-1. Ca2+ increased the rate to 1.50 X 10(4) M-1 X min-1 at 5 mM and Mn2+ to 2.40 X 10(4) M-1 X min-1 at 6 mM. The rate constant for these cations again decreased at higher concentrations. Mg2+ caused a gradual rise in rate constant to 1.08 X 10(4) M-1 X min-1 at 10 mM. The rate constant for the factor Xa-alpha 2-macroglobulin reaction was raised from 6.70 X 10(3) M-1 X min-1 in the absence of divalent cations to a maximum of 4.15 X 10(4) M-1 X min-1 at 4 mM Ca2+, with a decrease to 3.05 X 10(4) M-1 at 10 mM. These increases in reaction rate were correlated to the binding of divalent cations to factor Xa by studying changes in the intrinsic fluorescence and dimerization of factor Xa. The changes in fluorescence suggested a conformational change in factor Xa which may be responsible for the increased rate of reaction, whilst the decrease in rate constant at higher concentrations of Ca2+ and Mn2+ may be due to factor Xa dimerization.     

Hydrogen sulfide production from elemental sulfur by Desulfovibrio desulfuricans in an anaerobic bioreactor

Feasibility of elemental sulfur reduction by Desulfovibrio desulfuricans in anaerobic conditions in a stirred reactor was studied. Hydrogen was used as energy source, whereas the carbonated species were bicarbonate and yeast extract. Attention was paid to reactor engineering aspects, biofilm formation on the sulfur surface, hydrogen sulfide formation rate and kinetics limitations of the sulfur reduction. D. desulfuricans formed stable biofilms on the sulfur surface. It was found that active sulfur surface availability limits the reaction rate. The reaction rate was first order with respect to sulfur and hydrogen velocity had no effect in the reaction rate for the range 8.2 x 10(-2) to 4.1 x 10(-1) Nm(3) m(-2) min(-1). At a superficial gas velocity (u(G)) = 3.1 x 10(-2) Nm(3) m(-2) min(-1), H(2)S(g) production rate decreased due to a deficient H(2)S stripping. A maximum H(2)S(g) production rate of 2.1 g H(2)S L(-1) d(-1) was achieved during 5 days with an initial sulfur density of 4.7% (w/v).     

Effects of Biofeedback Training on Voluntary Heart Rate Control During Dynamic Exercise

The aims of this study were to (1) compare the effect of biofeedback with that of verbal instructions on the control of heart rate during exercise on a treadmill, (2) test the possible effect of workload on this control, and (3) examine the effect of workload on baseline heart rate at rest and during exercise. The study involved 35 participants who were randomly assigned to each of 4 experimental conditions generated by combining the 2 independent variables: training strategy for heart rate control (heart rate biofeedback or verbal control instructions) and work level (30 or 50% of maximal heart rate). By the end of 5 experimental sessions, participants trained with heart rate biofeedback showed a greater attenuation of the increase in heart rate produced by exercise than participants trained with verbal control instructions. The workload did not influence the voluntary control of heart rate, nor did it affect resting baseline heart rate, but it did affect exercise baseline heart rate.     

The rate of removal of pyrimidine dimers in quiescent cultures of normal human and xeroderma pigmentosum cells

The rate of removal of pyrimidine dimers from DNA of UV (254 nm)-irradiated (1 J/m2) normal and xeroderma pigmentosum (XP) cells maintained in culture as nondividing populations was determined. Several normal and XP strains from complementation groups A, C and D were studied. The excision rates and survival ability of nondividing cells were examined to determine if an abnormal sensitivity was associated with a decreased rate of dimer excision. The results show that all normal strains studied excise pyrimidine dimers at the same rate, with the rate curve characterized by two components. All 'excision-deficient' XP strains excise dimers at a slower-than-normal rate, with the rate curves also characterized by two components. The rate constants for the first components of all of the XP strains (group A, C and D) are the same, one tenth of the normal rate constant, except for XP8LO (group A). XP8LO has a first-component rate constant similar to that of normal strains and a second component rate constant similar to that of other group A strains (XP12BE, XP25RO). Thus, the slower rate of dimer excision in XP8LO is due to a defect in the mechanism responsible for the second component of the excision-rate curve. In general, an abnormal sensitivity of nondividing cells to UV is associated with a reduced dimer-excision rate. A notable exception to this is the group C strain XP1BE which has an initial repair rate similar to that of group A XP12BE but is considerably more resistant when survival is measured.     

Discrete residues in the c(2)b domain of synaptotagmin I independently specify endocytic rate and synaptic vesicle size

It has been demonstrated that synapses lacking functional synaptotagmin I (Syt I) have a decreased rate of synaptic vesicle endocytosis. Beyond this, the function of Syt I during endocytosis remains undefined. Here, we demonstrate that a decreased rate of endocytosis in syt(null) mutants correlates with a stimulus-dependent perturbation of membrane internalization, assayed ultrastructurally. We then separate the mechanisms that control endocytic rate and vesicle size by mapping these processes to discrete residues in the Syt I C(2)B domain. Mutation of a poly-lysine motif alters vesicle size but not endocytic rate, whereas the mutation of calcium-coordinating aspartate residues (syt-D3,4N) alters endocytic rate but not vesicle size. Finally, slowed endocytic rate in the syt-D3,4N animals, but not syt(null) animals, can be rescued by elevating extracellular calcium concentration, supporting the conclusion that calcium coordination within the C(2)B domain contributes to the control of endocytic rate.     

Centrifugation and addition of glycerol at 22 degres C instead of 4 degrees C improve post-thaw motility and fertility of stallion spermatozoa

The aims of this study were to evaluate the effects of cooling rate to 4 degrees C and temperature at the time of centrifugation/glycerol-addition (freezing extender: INRA82 + 2% egg yolk + 2.5% glycerol) on postcentrifugation recovery rate, post-thaw motility and per-cycle fertility. When centrifugation/glycerol-addition was performed at 4 degrees C (14 ejaculates), a moderate cooling rate (37 degrees C to 4 degrees C in I h) resulted in higher post-thaw motility (45%) than when using a slow cooling rate (37 degrees C to 4 degrees C in 4 h) (39%; P<0.05). When centrifugation/glycerol-addition was performed at 22 degrees C (37 degrees C to 22 degrees C in 10 min) (10 ejaculates), post-thaw motility was lower when spermatozoa were frozen directly from 22 degrees C (23%) than when spermatozoa were cooled to 4 degrees C (22 degrees C to 4 degrees C in 1 h) before freezing (47%; P<0.0001). When centrifugation/glycerol-addition was performed at 22 degrees C (before cooling at a moderate rate), as opposed to 4 degrees C (after cooling at a moderate rate), a significant improvement of 1) recovery of spermatozoa after centrifugation (P<0,0001), 2) post-thaw motility of spermatozoa at thawing (40% vs 36% (n < or = 291 ejaculates/group), P<0.0001) and 3) per-cycle fertility (56% vs 42% (n > or = 190 cycles/group), P<0.01) was observed. In conclusion, centrifugation/glycerol-addition at 22 degrees C followed by cooling to 4 degrees C at a moderate rate results in an improvement of post-thaw motility, spermatozoa recovery rate and per cycle fertility.     

Monitoring of morphological development of the arachidonic-acid-producing filamentous microorganism Mortierella alpina

Morphological parameters, such as hyphal growth rate, tip formation rate, tip extension rate and branch formation rate, of Mortierella alpina have been measured using a flow-through chamber under 25 different combinations of carbon and nitrogen concentrations. Morphological parameters were influenced not by C/N ratio but by carbon concentration in the medium. Specific rates of hyphal growth and tip formation both remained constant at a low carbon concentration of 5 g/l. Tip extension rate from one tip was 60 microm tip(-1) h(-1) at a carbon concentration below 15 g/l, and the branching formation rate was independent of carbon concentration. Tip extension rate was a function of specific hyphal growth rate, which in turn was linearly proportional to the specific tip formation rate, demonstrating that tip extension rate was exponentially proportional to the specific tip formation rate. Branch formation rate per hyphal element remained unchanged even at tip extension rates lower than 60 microm tip(-1) h(-1) and at specific hyphal growth rates lower than 0.83 h(-1), but decreased drastically at higher rates of tip extension and hyphal growth.     

Relationships among fertility, scrotal circumference, seminal quality, and libido in Santa Gertrudis bulls

Forty Santa Gertrudis bulls were used to examine relationships among scrotal circumference, seminal quality, libido, and fertility [assessed as the percent pregnant of estrous females (PE rate) and the percent pregnant of females mated (PM rate)]. These bulls were selected from 220 two year old bulls to represent variations in scrotal circumference and seminal quality. Each of the 40 bulls were exposed to 100 cyclic Santa Gertrudis heifers for a 4-day (96 hr) breeding period. The number of estrous females available to each bull varied from 12 to 27. A breeding soundness examination (BSE) was conducted on each bull approximately 45 days prior to the 4-day breeding period and immediately after the 4-day breeding period. The three components of the BSE scroe (scrotal circumference, spermatozoal abnormalities and spermatozoal motility) were not significantly correlated with PE rate or PM rate at either evaluation. There was no significant correlation between PM rate and scrotal circumference; however, each of the 4 bulls having a scrotal circumference less than 30 cm had a PM rate below 31%. Relationships between seminal quality and PM rate were unclear and differed between the two evaluations. There was a trend for bulls having poor seminal quality at the first evaluation to improve by the second evaluation. Consequently, fluctuations in seminal quality between evaluations is one possible explanation for low correlations between seminal parameters and PM rate. Libido (number mated/number in estrus x 100) was positively correlated (r = 0.44) with PE rate. Using a stepwise regression procedure, the independent variables accounting for the most variation in PE rate (dependent variable) included libido, secondary spermatozoal abnormalities, and BSE score (r(2) = 0.44). Results of this study indicate that current methods of fertility evaluation did not accurately predict the fertility of individual Santa Gertrudis bulls as measured by PE rate and PM rate during a 4 day breeding period.     

The modulatory effects of noradrenaline on vagal control of heart rate in the dogfish,Squalus acanthias

The possible interactions between inhibitory vagal control of the heart and circulating levels of catecholamines in dogfish (Squalus acanthias) were studied using an in situ preparation of the heart, which retained intact its innervation from centrally cut vagus nerves. The response to peripheral vagal stimulation typically consisted of an initial cardiac arrest, followed by an escape beat, leading to renewed beating at a mean heart rate lower than the prestimulation rate (partial recovery). Cessation of vagal stimulation led to a transient increase in heart rate, above the prestimulation rate. This whole response was completely abolished by 10(-4) M atropine (a muscarinic cholinergic antagonist). The degree of vagal inhibition was evaluated in terms of both the initial, maximal cardiac interval and the mean heart rate during partial recovery, both expressed as a percentage of the prestimulation heart rate. The mean prestimulation heart rate of this preparation (36+/-4 beats min(-1)) was not affected by noradrenaline but was significantly reduced by 10(-4) M nadolol (a beta-adrenergic receptor antagonist), suggesting the existence of a resting adrenergic tone arising from endogenous catecholamines. The degree of vagal inhibition of heart rate varied with the rate of stimulation and was increased by the presence of 10(-8) M noradrenaline (the normal in vivo level in routinely active fish), while 10(-7) M noradrenaline (the in vivo level measured in disturbed or deeply hypoxic fish) reduced the cardiac response to vagal stimulation. In the presence of 10(-7) M noradrenaline, 10(-4) M nadolol further reduced the vagal response, while 10(-4) M nadolol + 10(-4) M phentolamine had no effect, indicating a complex interaction between adrenoreceptors, possibly involving presynaptic modulation of vagal inhibition.     

Cocaine alters heart rate dynamics in conscious ferrets.

This study was designed to test the hypothesis that cocaine intoxication induces distinctive alterations in sinus rhythm heart rate dynamics. Time-series and spectral analysis techniques were used to examine the effects of lethal doses of cocaine on heart rate variability in conscious, restrained ferrets. In all animals (n = 5), cocaine administration resulted in a marked decrease in sinus rhythm heart rate variability prior to sudden death. Heart rate variability (coefficient of variation of heart rate) just prior to death (0.018 +/- 0.005) was significantly (p less than 0.02) decreased compared to that at baseline prior to cocaine administration (0.061 +/- 0.022). There was also a significant (p less than 0.02) decrease in total spectral power prior to death compared to baseline. Transient low-frequency (0.04-0.10 Hz) oscillations in heart rate were also noted in three of the five animals following cocaine administration. There were, however, no significant changes in mean heart rate in response to cocaine. Alterations in heart rate dynamics were not seen in three saline-treated controls. Lethal effects of cocaine included ventricular arrhythmias (n = 2) and seizures (n = 3). One animal developed transient ST segment elevations that were consistent with coronary vasospasm. In conclusion, lethal doses of cocaine in the conscious ferret induce characteristic alterations in heart rate dynamics. These abnormalities (loss of heart rate variability and the appearance of low-frequency heart rate oscillations) are similar to those reported previously in certain patients at high risk of sudden cardiac death due to organic heart disease.     

The effect of the dilution rate on CHO cell physiology and recombinant interferon-gamma production in glucose-limited chemostat culture

The physiology of a recombinant Chinese hamster ovary cell line in glucose-limited chemostat culture was studied over a range of dilution rates (D = 0.008 to 0.20 h(-1)). The specific growth rate (mu) deviated from D at low dilution rates due to an increased specific death rate. Extrapolation of these data suggested a minimum specific growth rate of 0.011 h(-1) (mu(max) = 0.025 h(-1)) The metabolism at each steady state was characterized by determining the metabolic quotients for glucose, lactate, ammonia, amino acids, and interferon-gamma (IFN-gamma). The specific rate of glucose uptake increased linearly with mu, and the saturation constant for glucose (K(s)) was calculated to be 59.6 muM. There was a linear increase in the rate of lactate production with a higher yield of lactate from glucose at high growth rates. The decline in the rate of production of lactate, alanine, and serine at low growth rate was consistent with the limitation of the glycolytic pathway by glucose. The specific rate of IFN-gamma production increased with mu in a manner indicative of a growth-related product. Despite changes in the IFN-gamma production rate and cell physiology, the pattern of IFN-gamma glycosylation was similar at all except the lowest growth rates where there was increased production of nonglycosylated IFN-gamma. (c) 1993 John Wiley & Sons, Inc.     

Rewarming rates and thermogenesis in hibernating echidnas.

We measured body temperatures (T(b)) in 14 free-ranging echidnas (Tachyglossus aculeatus) using implanted data-loggers. An average of 1020+/-744 days of T(b) data was recorded from each animal. The average maximum T(b) was 35.3+/-0.7 degrees C (n=14), and the lowest T(b) was 4.7 degrees C. Detailed analysis of rewarming events from four echidnas showed rewarming time to be dependent on initial T(b) (rewarming time in hours=15.6-0.41T(initial), n=31) with an average rewarming rate of 1.9+/-0.4 degrees C h(-1). Based on an hourly sampling rate, the peak rewarming rate was found to be 7.2+/-0.8 degrees C h(-1) (n=12), which was measured at a mean T(b) of 26.2+/-2.4 degrees C. This rate of heating was calculated to be equivalent to a peak oxygen consumption rate of 1.4+/-0.2 ml O2 g h(-1), approximately 9 times the basal metabolic rate. We found that a plot of rate of change of T(b) against T(b) for the entire data set from an individual echidna provided a useful summary and analytical tool.     

Mechanism of the cardiovascular response to systemic intravenous administration of leucine-enkephalin in the conscious dog

Leucine-enkephalin (Leu⁵-ENK) (35 μg/kg) increased heart rate and mean systemic arterial blood pressure following intravenous injection into chronically-instrumented, conscious dogs. Repeated injections at five-minute intervals were not associated with a diminished response. Naloxone (1 mg/kg) pre-treatment inhibited both heart rate and blood pressure increases. Prazosin (1 mg/kg) attenuated the increase in blood pressure but did not influence the heart rate response. Propranolol (1 mg/kg) attenuated the heart rate response but not the pressor response. Clonidine (30 μg/kg) attenuated the positive chronotropic effect of Leu⁵-ENK. Atropine (1 mg/kg) plus propranolol (1 mg/kg) blocked the heart rate response but the pressor effect was still present. The attenuation of the heart rate response by propranolol and the pressor response by prazosin suggests an adrenergic component to the enkephalin response; the reduction in the heart rate response by clonidine and atropine-propranolol indicates a role for cholinergic mechanisms in the chronotropic response. Hexamethonium (10 mg/kg) blocked the heart rate response and markedly inhibited the pressor response. Vagal interruption attenuated both heart rate and blood pressure responses. It is concluded that intravenous Leu⁵-ENK stimulates afferent pathways located in fibers which are contained in the vagosympathetic trunk to reflexly increase heart rate and blood pressure.     

Cycling efficiency and pedalling frequency in road cyclists

The purpose of this study was to determine the influence of pedalling rate on cycling efficiency in road cyclists. Seven competitive road cyclists participated in the study. Four separate experimental sessions were used to determine oxygen uptake (VO(2)) and carbon dioxide output (VCO(2)) at six exercise intensities that elicited a VO(2) equivalent to 54, 63, 73, 80, 87 and 93% of maximum VO(2) (VO(2max)). Exercise intensities were administered in random order, separated by rest periods of 3-5 min; four pedalling frequencies (60, 80, 100 and 120 rpm) were randomly tested per intensity. The oxygen cost of cycling was always lower when the exercise was performed at 60 rpm. At each exercise intensity, VO(2) showed a parabolic dependence on pedalling rate (r = 0.99-1, all P < 0.01) with a curvature that flattened as intensity increased. Likewise, the relationship between power output and gross efficiency (GE) was also best fitted to a parabola (r = 0.94-1, all P < 0.05). Regardless of pedalling rate, GE improved with increasing exercise intensity (P < 0.001). Conversely, GE worsened with pedalling rate (P < 0.001). Interestingly, the effect of pedalling cadence on GE decreased as a linear function of power output (r = 0.98, n = 6, P < 0.001). Similar delta efficiency (DE) values were obtained regardless of pedalling rate [21.5 (0.8), 22.3 (1.2), 22.6 (0.6) and 23.9 (1.0)%, for the 60, 80, 100 and 120 rpm, mean (SEM) respectively]. However, in contrast to GE, DE increased as a linear function of pedalling rate (r = 0.98, P < 0.05). The rate at which pulmonary ventilation increased was accentuated for the highest pedalling rate (P < 0.05), even after accounting for differences in exercise intensity and VO(2) (P < 0.05). Pedalling rate per se did not have any influence on heart rate which, in turn, increased linearly with VO(2). These results may help us to understand why competitive cyclists often pedal at cadences of 90-105 rpm to sustain a high power output during prolonged exercise.     

Changes in autonomic responding to stress after practice at controlling heart rate

Subjects in this experiment viewed a stressful film and then received one of five treatments: (a) practice at increasing heart rate without feedback, (b) practice at decreasing heart rate without feedback, (c) practice at increasing heart rate with feedback, (d) practice at decreasing heart rate with feedback, or (e) a control condition. Subjects then returned on the following day, practiced controlling heart rate again (or sat quietly, for subjects in the control condition), and then viewed the stressful film again. Heart-rate results indicated that subjects in both feedback groups manifested tonic decreases in heart rate from the first viewing of the film to the second, whereas subjects in both of the no-feedback groups manifested no changes in heart rate between viewings, and subjects in the control condition manifested increases in heart rate between viewings. However, all five groups of subjects displayed phasic increases in heart rate during specific stressors in the film during both viewings. The tonic changes in heart rate noted between viewings of the film for the feedback groups were not accompanied by parallel changes in electrodermal activity or respiration rate. Self-report ratings of subjects' beliefs about ability to control heart rate were significantly correlated with the tonic changes in heart rate that were noted between viewings of the stressful film.