Biomedical subjects

W W Burggren

Publications and source records attributed to W W Burggren.

At least 19 recordsLinked to original sources

PubMed2003

Heart rate responses to cooling in emu hatchlings.

Among fluctuations of instantaneous heart rate (IHR) in newly hatched chicks, heart rate (HR) oscillation with a mean frequency of 0.7 Hz has been designated as Type II HR variability characterized by low frequency (LF) oscillation [Comp. Biochem. Physiol. Part A 124 (1999) 461]. In response to exposure to lowered ambient temperature (Ta), chick hatchlings raised their HR baseline accompanied with the production or augmentation of Type II HR oscillation, indicating that LF oscillation is a phenomenon relating to thermoregulation [J. Therm. Biol. 26 (2001) 281]. In emu hatchlings that are precocial like chickens, Type II HR oscillation also occurred, but less frequently in comparison with chick hatchlings [Comp. Biochem. Physiol. Part A 131 (2002) 787]. This present experiment was conducted to elucidate how IHR of emu hatchlings responds to changes in Ta. Six hatchlings were measured for IHR and skin temperature (Ts) during a 3-h period when they were exposed to controlled Ta (ca. 35 degrees C), lowered Ta (ca. 15-30 degrees C) and again the controlled Ta for individual 1-h periods. In response to all the cooling and re-warming procedures, HR baseline changed depending upon the intensity of the Ta differences; i.e. large differences of Ta produced large changes in HR. HR fluctuations tended to augment during cooling with a few exceptions, but LF oscillation was not produced. Thus, LF oscillation, which was scarce even at the controlled Ta, could not be used as a thermoregulatory indicator in emus.

Animals↗

PubMed2002

Cardiac rhythms in prenatal and perinatal emu embryos.

Emu eggs weigh approximately 600 g and have an incubation duration (ID) of approximately 50 days. The egg mass is approximately 10-fold heavier than the chicken egg and the ID is approximately 2.5-fold longer. Daily changes in mean heart rate (MHR) of emu embryos were previously determined, but further measurement was needed to investigate the species-specific behavior of cardiac rhythm for comparison with other species. In the present study, we continuously measured the electrocardiogram of emu embryos while maintaining adequate gas exchange through the eggshell and determined instantaneous heart rate (IHR) during the last 2-7 days of incubation until hatching or death. The MHR over 1-min intervals was calculated from IHR data in order to present continuous developmental patterns of heart rate (HR) in a single graph and 24-h recordings of HR in a single panel, showing the HR trend over a prolonged period. However, neither circadian nor ultradian rhythms of HR were shown in these figures or by power spectrum analysis. The IHR distinctively fluctuated and the fluctuations were mainly comprised of three patterns of irregular HR accelerations in embryos that hatched. Respiratory sinus arrhythmia also occurred in perinatal embryos. During the final stages of the perinatal period, short-term, repeated, large accelerations of IHR appeared, which signaled imminent hatching and has been reported for chick embryos. IHR fluctuations in embryos that failed to hatch tended to become inactive towards death.

Animals↗

PubMed2002

Cardiac rhythms in developing emu hatchlings.

Six emu hatchlings were non-invasively measured for electrocardiogram (ECG) from their chest wall using flexible electrodes, and the instantaneous heart rate (IHR) was determined from ECG throughout the first week of post-hatching life. Although the baseline heart rate (HR) was low, approximately 100-200 beats per min (bpm), compared with chick hatchlings, the IHR fluctuated markedly. The fluctuation of IHR comprised HR variability and irregularities that were designated as types I, II and III in chick hatchlings and additional large accelerations distinctive of emu hatchlings. Type I was HR oscillation with a mean frequency of 0.37 Hz (range 0.2-0.7 Hz), i.e. respiratory sinus arrhythmia (RSA). From RSA, breathing frequency in emu hatchlings was estimated to be approximately half of that in chickens. Type II HR oscillation was also found in the emu; the frequency ranged from approximately 0.04 to 0.1 with a mean of 0.06 Hz, and the magnitude tended to be large compared with that of chickens. In addition to type III HRI, which was designated in chickens, large, irregular HR accelerations were characteristic of emu hatchlings. From IHR data, developmental patterns of mean heart rate (MHR) were constructed and plotted on a single graph to inspect the diurnal rhythm of MHR by visual inspection and power spectrum analysis. A circadian rhythm was not clear in the emu hatchlings, in contrast to chick hatchlings, which showed a dominant diurnal rhythm.

Animals↗

PubMed2001

Growth and metabolism of larval zebrafish: effects of swim training.

Larval zebrafish (Danio rerio) of three different age classes ('yolk-sac' larvae, 96 h; 'swim-up' larvae, 9 days old; and 'free-swimming' larvae, 21 days old) were trained for 2, 6 and 11 days, respectively, to swim at 0 body lengths per second (BL s(-1)), 2 BL s(-1) and 5 BL s(-1). Survival was significantly diminished in larvae trained at 5 BL s(-1) compared to controls (0 BL s(-1)). Although training produced no significant differences in mass and length, the youngest larvae absorbed their yolk at a faster rate during training. Routine oxygen consumption ((MO(2)r)) and mass-specific routine oxygen consumption ((MO(2)r,m)) were not significantly affected by chronic training in the yolk-sac larvae and swim-up larvae. However, trained free-swimming larvae had a significantly higher (MO(2)r) (after 11 days of training) and (MO(2)r,m) (after 8 and 11 days of training) compared to control larvae. Trained free-swimming larvae consumed significantly less oxygen during swimming compared to control larvae, as measured by closed-system respirometry. Trained yolk-sac larvae exposed to increasing hypoxia levels were more effective O(2) regulators. Additionally, training enhanced survival during exposure to extreme hypoxia in all age groups. Thus, physiological acclimation to chronic swimming occurs in the earliest stages of life in the zebrafish.

Adaptation, Physiological↗

PubMed2000

Physiological variability in neonatal armadillo quadruplets: within- and between-litter differences.

The role of genetics on neonatal physiological variability was examined in the nine-banded armadillo (Dasypus novemcinctus). Since armadillos give birth to only monozygous quadruplets, the genetic variation within litters is essentially zero. Quadruplets born in captivity were isolated and weighed within 8 h of birth. Oxygen consumption (V.(O2)) was measured in resting neonates by flow-through respirometry, heart rate obtained from an electrocardiogram and ventilation was measured by impedance techniques. Following the measurements, neonates were returned to the mother. Measurements were repeated at 4 and 8 days after birth. Mean heart rate significantly increased from 132 beats min(-1) on the day of birth to 169 beats min(-1) on day 8. Mean ventilation rate significantly decreased from 81 breaths min(-1) on the day of birth to 54 breaths min(-1) on day 8. During this same developmental period, mean mass significantly increased from 100 g to 129 g, and mean mass-specific oxygen consumption significantly decreased from 32.2 ml O(2)kg(-1)min(-1) to 28.6 ml O(2)kg(-1) min(-1). For all variables measured, within-litter variability was always significantly less than between-litter variability, confirming a 'sibling effect' that we attribute to the genetic components determining physiological characters.

Aging↗

PubMed2000

Developmental changes in in vivo cardiac performance in the moth Manduca sexta.

While an extensive literature on cardiovascular development exists for insects, almost all studies focus on in vitro preparations, and very few report on more than a single developmental stage. The present study examines in vivo cardiac performance in the intact, unanesthetized larvae, pupae and adults of the tobacco hornworm Manduca sexta. For all three stages, electrode pairs of fine steel wire were inserted subcuticularly at two dorsal abdominal locations. Impedance signals produced by contraction of the dorsal abdominal vessel (tube heart) were amplified and recorded. In addition to providing heart rate, a comparison of the relative timing of the signal from each electrode pair allowed the calculation of the propagation velocity and direction of heart contraction. Experimental treatments of intact animals included exposure to hypoxia and hyperoxia (21 %, 15 %, 10 %, 5 %, 0 % and 100 % O(2)), to hypercapnia (0 %, 4 %, 8 %, 16 %, 20 % and 24 % CO(2)), to temperature variation (10, 20 and 30 degrees C) and to 2 min periods of forced activity. The pattern of contraction of the dorsal abdominal vessel of M. sexta changed substantially with developmental stage. Larvae showed a relatively simple, invariably posterior-to-anterior pattern (mean rate 34.8+/-1.16 beats min(-)(1)). The heart rate pattern in pupal M. sexta displayed great variability in rate, amplitude and direction. Periods of regular heart beats (21.5+/-1.09 beats min(-)(1)) were frequently and irregularly interrupted by periods of cardiac arrests ranging from a few seconds to over 20 min. Adults showed a highly stereotypic but complex pattern, with periods of 'fast forward' (FF; rate 47.6+/-2.6 beats min(-)(1)), 'slow forward' (SL; 32.8+/-3.0 beats min(-)(1)) and 'reversed' (R; 32.2+/-2.4 beats min(-)(1)) beating. The contraction propagation velocity in larvae and pupae averaged 5. 52+/-0.36 and 2.03+/-0.11 cm s(-)(1), respectively. The SF, R and FF phases of the adults had average propagation velocities of 5.52+/-0. 51, 5.05+/-0.52 and 5.43+/-0.37 cm s(-)(1), respectively. Heart rate and contraction propagation velocity were remarkably resistant to ambient hypoxia and hypercapnia at all developmental stages, decreasing significantly only at 0 % O(2) or 24 % CO(2). As expected, the heart rates of all three developmental stages increased significantly with increasing temperature, with heart rate Q(10) values for larvae, pupae and adults of 2.33, 3.14 and 1.61, respectively, between 10 and 20 degrees C. Corresponding Q(10) values for these stages between 20 and 30 degrees C were 2.22, 2.03 and 2.29. Larval heart rates showed no significant response to forced activity induced by prodding. In contrast, adult heart rate increased nearly fivefold from 50.1 beats min(-)(1) during rest to 223.5 beats min(-)(1) after 1 min of prodding. The activity-induced tachycardia in adults ceased within 10-12 min. Patterns of cardiac contraction in larval, pupal and adult M. sexta were as dissimilar as their morphological appearances and revealed a gradation from simple to complex. These developmentally based distinctive cardiac patterns are undoubtedly related to developmental differences in both morphology and life-style. Larvae are anatomically 'homogeneous' compared with other stages, with no distinct head, thorax and abdominal region (or wings) that might require selective perfusion or drainage. The far more complex pattern of heart activity seen in pupae probably relates to the dramatic changes in internal morphology during this stage. Simultaneous degradation and synthesis of tissues throughout the body may expose the heart to numerous peptides or neurohormones that affect cardiac activity. In adult moths, the complex and repetitive pattern of cardiac activity is reflected in the previously described complexity of hemolymph movement, together with thermoregulatory capabilities in this species that depend on well-regulated hemolymph movements between the thorax, wings and abdomen.

Animals↗

PubMed2000

Interruption of cardiac output does not affect short-term growth and metabolic rate in day 3 and 4 chick embryos.

The heart beat of vertebrate embryos has been assumed to begin when convective bulk transport by blood takes over from transport by simple diffusion. To test this hypothesis, we measured eye growth, cervical flexure and rates of oxygen consumption ( V(O2)) in day 3-4 chick embryos denied cardiac output by ligation of the outflow tract and compared them with those of embryos with an intact cardiovascular system. Eye diameter, used as the index for embryonic growth, increased at a rate of approximately 4.5-5 % h(-)(1) during the observation period. There was no significant difference (P>0.1) in the rate of increase in eye diameter between control (egg opened), sham-ligated (ligature present but not tied) and ligated embryos. Similarly, the normal progression of cervical flexure was not significantly altered by ligation (P>0.1). V(O2) (ml O(2 )g(-)(1 )h(-)(1)) at 38 degrees C, measured by closed respirometry, was not significantly different (P>0.1) on day 3 in sham-ligated (14.5+/-1.9 ml O(2 )g(-)(1 )h(-)(1)) and ligated 17.6+/-1.8 ml O(2 )g(-)(1 )h(-)(1)) embryos. Similarly, on day 4, V(O2) in sham-ligated and ligated embryos was statistically the same (sham-ligated 10. 5+/-2.9 ml O(2 )g(-)(1 )h(-)(1); ligated 9.7+/-2.9 ml O(2 )g(-)(1 )h(-)(1)). Expressed as a linear function of body mass (M), V(O2) in sham-ligated embryos was described by the equation V(O2)=-0.48M+24.06 (r(2)=0.36, N=18, P<0.01), while V(O2) in ligated embryos was described by the equation V(O2)=-0.53M+23.32 (r(2)=0.38, N=16, P<0.01). The regression line describing the relationship between body mass and V(O2) for pooled sham-ligated and ligated embryos (the two populations being statistically identical) was V(O2)=-0.47M+23.24. The slope of this regression line, which was significantly different from zero (r(2)=0.30, N=34, P<0.01), was similar to slopes calculated from previous studies over the same range of body mass.Collectively, these data indicate that growth and V(O2) are not dependent upon cardiac output and the convective blood flow it generates. Thus, early chick embryos join those of the zebrafish, clawed frog and axolotl in developing a heart beat and blood flow hours or days before required for convective oxygen and nutrient transport. We speculate that angiogenesis is the most likely role for the early development of a heart beat in vertebrate embryos.

Animals↗

PubMed2000

Continuous measurements of instantaneous heart rate and its fluctuations before and after hatching in chickens.

There has been considerable interest in heart rate (fh) fluctuations in relation to cardiovascular control systems and foetal conditions during pregnancy in mammals. Prominent fluctuations in fh also occur in avian embryos, which are an important experimental model for studying developmental physiology. The present study determined the instantaneous fh of seven chick embryos continuously from the last stage of prenatal development (day 18), throughout the pipping (perinatal) period (days 19-21) until hatching and, subsequently, of newly hatched chicks (up to day 2). The distinctive patterns of instantaneous fh fluctuations took the form of specific changes within a broad mean fh baseline. Cyclic oscillations (ultradian rhythm) occurred until an early stage of the perinatal period, when the fh baseline started rising. Subsequently, the baseline dropped and respiratory arrhythmia began to appear concomitant with external pipping. During the final stage of external pipping, when the fh baseline rose again prior to hatching, three unique patterns of instantaneous fh fluctuations were evident: relatively long-lasting cyclic small accelerations, irregular intermittent large accelerations and short-term repeated large accelerations. Furthermore, repeated alternate occurrences of the latter two types of acceleration formed an additional oscillating pattern with a period of 10-15 min. During the early period after hatching, when the fh baseline reached its maximum, instantaneous fh changed relatively slowly accompanied by transient rapid decelerations, probably due to augmented vagal tone. Subsequently, the mean fh baseline dropped to its minimum, and a circadian rhythm and three types of previously reported fh fluctuations (types I-III) appeared. Developmental patterns of mean fh and the appearance of distinctive patterns of instantaneous fluctuations in fh and circadian rhythms were not influenced by an ultimate failure of hatching after a normal development. The demonstration of complex, repeatable patterns of fh fluctuation that change during development suggests that the avian embryo model should be useful in studying the phenomenon of fh fluctuation and its underlying causes.

Animals↗

PubMed1999

Heart rate responses to altered ambient oxygen in early (days 3-9) chick embryos in the intact egg.

Normal heart rate (HR), and the HR responses to hypoxia and hyperoxia during early heart development in chick embyros have not been studied in detail, particularly in undisturbed embryos within the intact egg. HR was measured in day 3-9 chick embryos at 38 degrees C using relatively noninvasive impedance cardiography. Embryos were exposed to air (control) and to hypoxic (10% O2) or hyperoxic (100% O2) gas for a 2-h or 4-h period, during which HR was continually monitored. Control (normoxic) HR increased from about 150 beats per min (bpm) on day 3 to about 240 bpm on days 7-9. HR in very early embryos showed a variety of moderate responses to hypoxia (all survived), but as development progressed beyond day 6, hypoxic exposure induced a profound bradycardia that frequently terminated in death before the end of the measurement period. In contrast to the marked developmental changes in hypoxic sensitivity, HR showed little response to hyperoxia throughout development, suggesting no "hypoxic drive" to HR. We speculate that hypoxia has little effect early in development because of the embryo's small absolute O2 demand, but as the embryo grows, hypoxia represents a progressively more severe perturbation. Although general trends were identified, there was considerable variation in both HR and HR responses to ambient O2 changes between individuals of the same developmental stage.

Animals↗

PubMed1999

O2 consumption and heart rate in developing zebrafish (Danio rerio): influence of temperature and ambient O2.

Body mass, length, oxygen consumption (MO2) and heart rate (fH) were measured in "embryos" (prior to hatching), "larvae" (days 10-20), "juveniles" (days 30-70 in 10-day intervals), and "adults" (day 100) of the zebrafish Danio rerio. Fish were chronically reared at either 25, 28, or 31 degreesC and then acutely exposed to hypoxia at different developmental stages. We hypothesized that at any given rearing and measurement temperature, D. rerio would maintain MO2 at lower ambient PO2 [i.e., have a lower critical partial pressure (Pcrit)] as development progressed and that at any given developmental stage individuals reared and measured at higher temperatures would show a more pronounced hypoxic bradycardia. MO2 in normoxic fish at 28 degreesC peaked at approximately 40 micromol. g-1. h-1 at day 10, thereafter falling to 4-5 micromol. g-1. h-1 at day 100. The Q10 for MO2 was 4-5 in embryos, falling to 2-3 from day 10 to day 60 and rising again to 4-5 at day 100. Pcrit at 28 degreesC was approximately 80 mmHg in embryos but decreased sharply to 20 mmHg at 100 days, supporting the hypothesis that more mature fish would be better able to oxygen regulate to lower ambient PO2 levels. Pcrit increased sharply with measurement temperature. Heart rate (fH) at 28 degreesC increased from about 125 beats/min in embryos to a peak of approximately 175 beats/min at days 10-30 and then fell to approximately 130 beats/min by day 100. Unlike for MO2, the Q10 for fH was more constant at 1.2-2.5 throughout development. Hypoxic exposure at any temperature had no effect on fH until approximately day 30, after which time a hypoxic bradycardia was evident. As evident for MO2, the bradycardia in older larvae was more profound at higher temperatures. On the assumption that bradycardia is indicative of hypoxic stress, the increasing prevalence of a hypoxic bradycardia in older, warmer individuals supports the hypothesis that increasing hypoxic susceptibility with development would be exacerbated by increasing temperature. Collectively, these data indicate that the ability to regulate MO2 and fH in response to the compounding demands of increased temperature and/or decreased oxygen availability first develops after approximately 20 days in D. rerio and, thereafter, the ability to maintain MO2 in the face of ambient hypoxia progressively builds through to adulthood. Additionally, the temperature responses of metabolism and heart rate differ substantially at different phases of development, suggesting a loose coupling between the respiratory and cardiovascular systems, at least early in development.

Aging↗

PubMed1998

Cardio-respiratory ontogeny during chronic carbon monoxide exposure in the clawed frog Xenopus laevis.

The present study investigates the ontogeny of cardio-respiratory physiology in Xenopus laevis where O2 transport is obstructed. Animals were raised from eggs (NF stage 1) to metamorphic climax (NF stage 63), while maintained either in air or in chronic 2 kPa CO, which functionally ablates O2 transport by hemoglobin (Hb). Whole-animal rate of oxygen consumption (.MO2), whole-body lactate concentration, individual mass, heart rate (fh) and stroke volume (Vs) were measured. Additionally, cardiac output (.Q) and the ratio of the rate of oxygen consumption to the total rate at which oxygen is transported in the blood (.MO2/.QO2) were calculated to determine limitations imparted when O2 transport is impaired. Our data on early development suggest that the onset of convective blood flow occurs prior to the absolute need for convection to supplement diffusive transport. Values for .MO2, whole-body lactate concentration, mass and fh did not differ significantly between controls and CO-exposed animals. However, CO-exposed animals showed a significant (P<0.05) increase in Vs, .MO2/.QO2 and .Q compared with controls. These results indicate that limiting blood O2 transport is not deleterious to metabolism and development as a whole and that convective oxygen transport via Hb is not essential for normal cardiovascular or respiratory function during larval development.

Animals↗

PubMed1996

Disruption of hemoglobin oxygen transport does not impact oxygen-dependent physiological processes in developing embryos of zebra fish (Danio rerio).

Embryonic hemoglobin circulated by the developing heart in the early vertebrate embryo is widely assumed (without substantiation) to perform the same vital role of O2 carriage that it does in fetuses and adults. In order to challenge this assumption, we measured highly O2-dependent physiological variables like O2 consumption, cardiac performance, and initial swim bladder filling in the presence and absence of functional hemoglobin in the embryos and early larvae of the zebra fish, Danio ( = Brachydanio) rerio. Functional ablation of hemoglobin by carbon monoxide or phenylhydrazine did not reduce whole-animal O2 consumption, which was approximately 85 to 90 mumol.g-1.h-1. Similarly, no differences in heart variables like ventricular pressure development or heart rate, which increased from 135 to 175 bpm between stages 36h and 96h (indicating developmental stages 36 and 96 hours after fertilization, respectively), were observed in these experiments. Initial opening of the swim bladder was not influenced in the presence of CO-occupied hemoglobin but was significantly impaired when the embryonic hemoglobin was chemically modified by incubation with phenylhydrazine. That aerobic processes continue without hemoglobin O2 transport indicates the adequacy in the embryo of simple O2 diffusion alone even in developmental stages with extensive convective blood circulation generated by the heart.

Animals↗

PubMed1995

Fixed patterns of bradycardia during late embryonic development in domestic fowl with C locus mutations.

A predictable late embryonic bradycardia (relative to normal White Leghorn chickens) has been documented in chicken strains with C locus mutations. The basis of the bradycardia remains unknown but clearly is related to a mutation at the C locus, which contains the structural gene for tyrosinase. When compared with the heart rate of normal White Leghorns (approximately 295-305 beats/min from day 8 to day 20 of incubation), ca/ca and other C locus mutants showed a 10-12% reduction in heart rate during the last 4 days of incubation. Embryonic mortality occurred in both mutant and normal strains at an equivalent rate (approximately 23%); a significant bradycardia (when compared with surviving embryos of the same strain) developed on the day before death in White Leghorn but not mutant strains. The bradycardia did not affect embryonic oxygen consumption (approximately 0.2 ml O2.egg-1.min-1 at day 14 and 0.4 ml O2.egg-1.min-1 at day 20), which showed only minor differences between strains that can be attributed to differences in embryonic mass on days 16-20.

Animals↗

PubMed1995

Blood pressures and heart rate during larval development in the anuran amphibian Xenopus laevis.

Heart rate and blood pressure were measured in lightly anesthetized developing Xenopus laevis from hatching (body mass approximately 3 mg) to the end of metamorphosis (< or = 1 g). Blood pressures in the conus arteriosus, truncus arteriosus, and ventricle were measured by a servo-null micropressure system. Heart rate was determined from blood pressure recordings, and cardiac cycles were videotaped through a dissecting microscope. Heart rate varied from 50 to 150 beats/min and showed a negative correlation with body mass, with a slope less than predicted from allometric equations based on adult vertebrates. Mean truncus pressures showed a positive correlation with body mass, increasing from 4 mmHg in a 25-mg larva to 9 mmHg in a 1-g larva. The pressure waveform during ventricular systole was similar in all developmental stages examined, whereas those in conus and truncus varied with development. Conus pressures differed distinctly from truncus pressure during diastole in all larvae examined, suggesting the existence of functional valves between conus and truncus as early as stage 46 of the Nieuwkoop-Faber larval staging system. Although the developmental patterns of heart rate and blood pressure in X. laevis showed significant correlation with body mass, body mass explained less than one-half of the variation in these variables. Therefore developmental factors other than body mass, such as changes in heart mass and the addition of new resistance vessels, may influence heart rate and blood pressure during development in X. laevis.

Animals↗

PubMed1995

Cardiac output and peripheral resistance during larval development in the anuran amphibian Xenopus laevis.

Stroke volume (SV) and cardiac output (CO) were measured in anesthetized larvae of Xenopus laevis from hatching (3 mg) to the end of metamorphosis (approximately 1 g). CO and SV were calculated from videotaped images of the intact beating heart. SV increased from 2.4 x 10(-3) microliters at 3 mg body mass to 7.6 microliters at 1 g. CO increased from 0.25 microliter/min at 3 mg to 623 microliters/min at 1 g. With use of CO, along with arterial pressures from another study [P.-C. L. Hou and W. W. Burggren. Am. J. Physiol. 269 (Regulatory Integrative Comp. Physiol. 38): R1120-R1125, 1995], peripheral resistance and cardiac work were also calculated. Resistance decreased rapidly from 701 peripheral resistance units (PRU, mmHg.s.mm-3) at 3 mg body mass to 79 PRU at 20 mg and gradually declined toward 0.9 PRU at 1 g. Cardiac work increased from 0.06 dyn.mm at 3 mg body mass to 1.27 dyn.mm at 20 mg and then climbed sharply to 717 dyn.mm at 1 g. The general pattern of change in hemodynamic variables (except heart rate) during larval development is similar in Xenopus laevis and chick embryos, suggesting a common pattern for hemodynamic development in vertebrate embryos/larvae.

Animals↗

PubMed1994

Patterns of form and function in developing hearts: contributions from non-mammalian vertebrates.

Although most research on developmental cardiovascular physiology has focused on the bird embryo as a model for emulating developmental processes in mammals, there are increasingly compelling reasons to expand research to a variety of lower vertebrate systems. These reasons include circumventing inherent limitations of the avian embryo and identifying general vertebrate developmental patterns in the cardiovascular system. In this paper, we first review data from hemodynamic studies on amphibians and birds (and what little exists from fish and reptiles), to provide a background against which lower vertebrate development can be examined. We then describe non-mammalian, non-avian paradigms for studying developmental patterns of vertebrate hearts. Developmental spects of cardiovascular performance, especially heart rate, blood pressure and cardiac output and how they change with ontogeny, are described for several amphibians and a few reptiles, identifying, where possible, processes in common with birds and mammals. Finally, we indicate productive areas for future research with lower vertebrate cardiovascular systems, such as establishing "critical windows" for cardiovascular physiology during development, and determining the extent of developmental plasticity at the level of organ system physiology.

Animals↗

PubMed1993

Developmental changes in the acetylcholine influence on heart muscle of Rana catesbeiana: in situ and in vitro effects.

The influence of acetylcholine (ACh) on cardiac performance of larval (Taylor Kollros [TK] stages II-XVIII) and postmetamorphic (3-609 g) Rana catesbeiana was analyzed in situ (circulatory system intact) and in vitro (isolated heart or ventricular strip preparations). Topical application of ACh to the heart in situ resulted in a dose-dependent decrease in heart rate and in a slight decrease in systolic ventricular pressure in all developmental stages. Injection of acetylcholine into the ventricle lumen in situ caused a dose-dependent transient decrease in systolic ventricular pressure, with little heart rate effect. Intraventricular ACh injection also changed the hemodynamic coupling between ventricle and conus arteriosus, generating a biphasic pressure profile in the conus due to sequential contractions of the ventricle and of the conus. In situ the sensitivity of the ventricle to ACh decreased during larval development, with the lowest sensitivity in small postmetamorphic adults. ACh applied in vitro to cardiac muscle strips or small hearts produced a negative inotropic effect. The ACh dose necessary to induce a 50% reduction in muscle strip contraction force in vitro decreased substantially during larval development, indicating an increase in ACh sensitivity with development. The effects of ACh both in vitro and in situ were diminished or eliminated by topical application or injection of atropine, suggesting the presence of muscarinic cholinergic receptors. After preincubation with the acetylcholinesterase blocker eserine, injection of ACh into the conus arteriosus decreased systolic ventricular pressure with a delay of 4-10 seconds, probably representing the minimum blood circulation time.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1992

Development of blood pressure and cardiac reflexes in the frog Pseudis paradoxsus.

Systemic arterial blood pressure and heart rate (fH) were measured in unanesthetized, unrestrained larvae and adults of the paradoxical frog, Pseudis paradoxus from São Paulo State in Brazil. Four developmental groups were used, representing the complete transition from aquatic larvae to primarily air-breathing adults. fH (49-66 beats/min) was not significantly affected by development, whereas mean arterial blood pressure was strongly affected, being lowest in the stage 37-39 larvae (10 mmHg), intermediate in the stage 44-45 larvae (18 mmHg), and highest in the juveniles and adults (31 and 30 mmHg, respectively). Blood pressure was not significantly correlated with body mass, which was greatest in the youngest larvae and smallest in the juveniles. In the youngest larvae studied (stages 37-39), lung ventilation was infrequent, causing a slight decrease in arterial blood pressure but no change in heart rate. Lung ventilation was more frequent in stages 44-45 larvae and nearly continuous in juveniles and adults floating at the surface. Bradycardia during both forced and voluntary diving was observed in almost every advanced larva, juvenile, and adult but in only one of four young larvae. Developmentally related changes in blood pressure were not complete until metamorphosis, whereas diving bradycardia was present at an earlier stage.

Aging↗