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Nonreproducibility in scientific investigations has been explained by inadequately reporting methodology, honest error, and even misconduct. We hypothesized that, within the field of animal physiology, the most parsimonious explanation for nonreproducibility is inadequate reporting of key methodological details. We further hypothesized that implementation of relatively recently released reporting guidelines has positively impacted journal article quality, as measured by completeness of the methodology descriptions. We analyzed 84 research articles published in five primarily organismal animal physiology journals in 2008–2010 (generally before current guidelines) and 2018–2020. Compliance for reporting 34 variables referring to biology, experiments, and data collection was assessed. Reporting compliance was just ∼61% in 2008–2010, rising only slightly to 67.5% for 2018–2020. Only 21% of the reported variables showed significant differences across the period from 2008–2020. We conclude that, despite attempts by societies and journals to promote greater reporting compliance, such efforts have so far been relatively unsuccessful in the field of animal physiology.

Planarians are widely used animal models for studies in regeneration, developmental biology, neurobiology, and behavior. However, surprisingly little is known about other aspects of their basic biology, even though such information might help validate these flatworms as a general animal model. We hypothesized that planaria, although dependent on simple diffusion of O2across the integument for O2uptake, would nonetheless show changes in oxygen consumption (V̇o2) associated with reproductive mode (sexual or asexual), feeding (specific dynamic action; SDA), temperature (Q10values), and photoperiod typical of those responses of more complex invertebrates. In the current experiments, routine V̇o2was measured over the range of 13-28°C in Schmidtea mediterranea and Girardia dorotocephala. At the long-term maintenance temperature of 18°C, routine V̇o2was ~13 µL O2·g−1·h−1in the two asexual strains, but approximately twice as high (27 µL O2·g−1·h−1) in the sexual strain of S. mediterranea, suggesting a metabolic cost for sexual reproduction. Metabolic temperature sensitivity, measured by Q10, was about one to three for all three groups. All three groups showed a large (~2- to 3-fold) increase in V̇o2within a day following feeding, suggesting a large SDA effect. Starvation, causing “degrowth” in some planaria, resulted in a loss of one-third of body mass in sexual S. mediterranea but no body mass loss in either asexual strains. Collectively, these data indicate that, while being a relatively simple flatworm with no dedicated respiratory or circulatory system, their metabolic physiological responses are quite similar to those shown by more complex invertebrates and vertebrates, contributing to their validation as an animal model.

The physiological transition to aerial breathing in larval air-breathing fishes is poorly understood. We investigated gill ventilation frequency ( fG), heart rate ( fH), and air breathing frequency ( fAB) as a function of development, activity, hypoxia, and temperature in embryos/larvae from day (D) 2.5 to D30 posthatch of the tropical gar, Atractosteus tropicus, an obligate air breather. Gill ventilation at 28°C began at approximately D2, peaking at ∼75 beats/min on D5, before declining to ∼55 beats/min at D30. Heart beat began ∼36–48 h postfertilization and ∼1 day before hatching. fHpeaked between D3 and D10 at ∼140 beats/min, remaining at this level through D30. Air breathing started very early at D2.5 to D3.5 at 1–2 breaths/h, increasing to ∼30 breaths/h at D15 and D30. Forced activity at all stages resulted in a rapid but brief increase in both fGand fH, (but not fAB), indicating that even in these early larval stages, reflex control existed over both ventilation and circulation prior to its increasing importance in older fishes. Acute progressive hypoxia increased fGin D2.5–D10 larvae, but decreased fGin older larvae (≥D15), possibly to prevent branchial O2loss into surrounding water. Temperature sensitivity of fGand fHmeasured at 20°C, 25°C, 28°C and 38°C was largely independent of development, with a Q10between 20°C and 38°C of ∼2.4 and ∼1.5 for fGand fH, respectively. The rapid onset of air breathing, coupled with both respiratory and cardiovascular reflexes as early as D2.5, indicates that larval A. tropicus develops “in the fast lane.”

ANG II alters the short-term blood pressure buffering capacity of the baroreflex in many adult animals. In embryonic chickens, high plasma ANG II levels contribute to baseline mean arterial pressure (MAP, kPa) without changing heart rate (ƒH, beats/min). We hypothesized, on the basis of these features, that an ANG II-induced reduction in baroreflex sensitivity is present in embryonic chickens as in adults. We examined baroreflex function in day 19 embryonic chickens ( Gallus gallus domesticus) after chronic depletion of endogenous ANG II via angiotensin-converting enzyme (ACE) inhibition with captopril (5 mg/kg) from days 5–18 of incubation. The correlation between MAP and ƒHwas assessed using increasing doses of sodium nitroprusside, a vasodilator, and phenylephrine, a vasoconstrictor. We used two analytical methods to evaluate baroreflex function: a conventional “static” method, in which maximal MAP and ƒHresponses were examined, and a “dynamic” method that assessed beat-to-beat changes during the response to pharmacological manipulation. Captopril-treated embryos were hypotensive by 19% with baroreflex slopes ∼40% steeper and normalized gains ∼50% higher than controls, and differences across treatments were similar using either analytical method. Furthermore, reintroduction of ANG II via infusion raised MAP back to control levels and decreased the baroreflex gain in captopril-treated embryos. Therefore, during typical chicken development, ANG II dampens the baroreflex regulatory capacity and chicken embryos can be used as a natural model of elevated ANG II for studying developmental cardiovascular function. This study is the first to demonstrate that reduction of embryonic ANG II alters normal baroreflex function.

Normal aerobic metabolic rates persist in the early chicken embryo after elimination of cardiac output, but the dependence of tissue growth and differentiation on blood flow is unknown in these early stages. We partially ligated (25–50% occlusion) the ventricular outflow tract of Hamburger-Hamilton stage (HH) 16–18 embryos, producing a wide range of cardiac output. For the next ∼48 h (to HH 24), we measured heart rate (HR), stroke volume (SV), and cardiac output (CO), as well as these growth indicators: eye diameter, chorioallantoic vessel density, and body mass. Acutely, HR declined with partial ligation (from 108 to 98 beats/min). Paradoxically, SV and CO decreased sharply in most embryos but increased in others, collectively producing the desired large variation (up to 25-fold) in CO and permitting assessment of tissue growth over a very large range of blood perfusion. Eye diameter doubled (from 0.6 to 1.2 mm) with development from HH 16 to HH 24, but within a developmental cohort there was no significant correlation between eye diameter and CO over a 25-fold range of CO. Similarly, chorioallantoic membrane vessel index was independent of CO over the CO range at all stages. Finally, body mass increase during development was not significantly affected by partial conal truncal ligation. Collectively, these data suggest that normal eye and vessel growth and body mass accumulation occur independent of their rate of blood perfusion, supporting the hypothesis of prosynchronotropy—that the heart begins to beat and generate blood flow in advance of the actual need for convective blood flow to tissues.

Renewed interest in the use of the embryonic chicken as a model of perinatal cardiovascular regulation has inspired new questions about the control mechanisms that respond to acute perturbations, such as hypoxia. The objectives of this study were to determine the cardiovascular responses, the regulatory mechanisms involved in those cardiovascular responses, and whether those mechanisms involved the central nervous system (CNS) of embryonic chickens. Heart rate (fH) and blood pressure were measured in chicken embryos of different incubation ages during exposure to different levels of hypoxia (15, 10, and 5% O2). At all levels of hypoxia and at all developmental ages, a depression of fHand arterial pressure was observed, with the exception of day 20 embryos in 15 and 10% O2. The intensity of the embryonic fHand blood pressure responses were directly related to the level of hypoxia used. Muscarinic and α-adrenergic receptor stimulation limited the hypoxic hypotension on days 15– 19 and 15– 21, respectively, as indicated after blockade with atropine and phentolamine. During the final 3 days of incubation, the intensity of the hypoxic hypotension was magnified due to α-vasodilation caused by β-adrenergic and muscarinic receptor stimulation. In 19- to 21-day-old embryos, the fHresponse to hypoxia was limited by α-adrenergic receptor stimulation as indicated by the accentuated bradycardia after blockade with phentolamine. Furthermore, on day 21, atropine limited the hypoxic bradycardia, indicating that muscarinic receptors also play a role in the fHresponse at this age. In addition, the muscarinic actions on the heart and the adrenergic effects on the vasculature appeared to occur through a hypoxic-induced direct release from chromaffin tissue and autonomic nerve terminals. Thus, in embryonic chickens, the only cardiovascular response to hypoxia that involves the CNS was the cholinergic regulation of arterial pressure after day 15 of incubation. Therefore, although embryonic chickens and fetal sheep, the standard models of perinatal cardiovascular physiology, respond to hypoxia with a similar redistribution of cardiac output, the underlying mechanisms differ between these species.

Cardiovascular responses (blood pressure, heart rate, stroke volume, cardiac output, and peripheral vascular resistance) to acute hypoxia (Po2 = 70 mmHg) in developing larvae of Xenopus laevis from Nieuwkoop-Faber (NF) stage 45 and up to newly metamorphosed froglets were investigated. The results revealed two distinct response patterns to acute hypoxia in "early" (NF stages 45-48 and 49-51) and "late" (NF stages 52-53, 54-57, and 58-62) larval Xenopus. The early larvae responded to acute hypoxia with a significantly decreased stroke volume, cardiac output, and blood pressure. Peripheral resistance increased, whereas no change in heart rate occurred. In late larvae, stroke volume and blood pressure increased during acute hypoxia, but an offsetting bradycardia prevented major changes in cardiac output. We conclude that, up to stage 51 of development, hypoxia exerts a direct inhibitory effect on the heart and smooth muscle of the blood vessels, with no Frank-Starling relationship apparent. Older larvae show evidence of both intrinsic and extrinsic regulation of the cardiovascular system in response to acute hypoxia, suggesting that there is a specific point in larval development when cardiovascular regulation during hypoxia is expressed.

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.

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.

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.

Central arterial hemodynamics (blood pressure and velocity) as a function of ontogeny and season were determined in larval Rana catesbeiana (body mass 0.3-8.7 g, 20-22 degrees C). Ventricular systolic pressure increased from 1.8 mmHg at stage (St) II to 11.9 mmHg at St XIII, while ventricular diastolic pressures usually were less than 1.0 mmHg. In early stages (up to St V-VII) of fall/winter larvae, the pressure waveform in the conus arteriosus was often biphasic. The first peak was due to weak ventricular contraction (sometimes inadequate to eject blood into the arterial tree), and a stronger second peak resulted from conal contraction. In these young fall/winter larvae, the conus--not the ventricle--was the major circulatory pump. Older larvae (greater than St X) showed "adultlike" central hemodynamics, with the ventricle ejecting blood through the conus into the central arterial circulation. Systolic blood pressure was considerably higher in young spring/summer (April-June) larvae, and the ventricle rather than the conus was the main circulatory pump at all stages, in contrast to fall/winter larvae. Thus both season and development have profound influences on the central hemodynamics of bullfrog larvae.

In the conscious, undisturbed toad, Bufo marinus, pulmonary arterial blood flow increased during periods of lung ventilation and decreased in intervening periods of pulmonary apnea. In unidirectionally ventilated, anesthetized toads, lung inflation produced by increasing the outflow resistance to pulmonary gas flow to 3 cmH2O caused a significant increase in pulmonary arterial blood flow and a significant decrease in cutaneous arterial blood flow. Changes in flow were associated with reciprocal changes in calculated vascular resistance. Mean pulmocutaneous pressure and cardiac frequency did not change significantly. Thus lung inflation (in the absence of changes in the composition of intrapulmonary gases) increased the proportion of total pulmocutaneous flow routed to the lungs and decreased the proportion directed to the skin. Unidirectional ventilation with air + 5% CO2 at constant lung volume produced a significant decrease in pulmonary arterial blood flow, an increase in calculated pulmonary arterial flow resistance, and a small increase in the flow to the cutaneous artery. Concomitant mild hypoxia potentiated the effects of pulmonary hypercapnia, although hypoxia alone was less effective than hypercapnia alone in decreasing pulmonary flow. Pulmonary arterial blood flow was decreased by infusion of acetylcholine into the pulmocutaneous artery, but epinephrine had no effect on either the pulmonary or cutaneous artery at doses below those that produced systemic effects. Atropine blocked all changes in pulmonary arterial blood flow. This and other evidence suggest that calculated arterial resistance changes are due to reflex changes in the tone of vascular smooth muscle. Intrapulmonary CO2-sensitive mechanoreceptors possess appropriate response characteristics to mediate the afferent limb of the reflex.

Heart rate (fH) at 20-23 degrees C was recorded in six different developmental stages of the bullfrog, Rana catesbeiana (n = 104, body mass 40 mg to 90 g), at rest after normoxic acclimation, during acute changes in O2 availability, and after brief but intense activity. The effects of cholinergic blockade and combined cholinergic and beta-adrenergic blockade on the response to this experimental protocol were also assessed. Mild tonic vagal inhibition of fH was evident during larval development but disappeared after metamorphosis. There was no tonic sympathetic stimulation of fH at rest in any developmental stage. Intense activity produced a tachycardia in all developmental stages but newly hatched larvae. In adults, tachycardia during activity resulted from beta-adrenergic stimulation but in larvae may have resulted from the direct effects of increased venous return stretching the cardiac pacemaker. Neither acute hypoxia or hyperoxia affected fH in any developmental stage, with the single exception of a severe depression of fH occurring at a PO2 of 30 Torr in newly hatched larvae. These results indicate that, although the heart of the newly hatched larvae is essentially devoid of regulation, cholinergic and beta-adrenergic mechanisms for reflex regulation of fH appear early in larval development. These mechanisms, although most fully expressed in the adult bullfrog, are essentially intact before metamorphosis of the larva.

The interaction between lung and gill ventilation was investigated in unanesthetized Rana catesbeiana larvae (stage XVII-XIX) in hypoxic (PO2 = 80 +/- 1 Torr), normoxic (PO2 = 142 +/- 1 Torr), and hyperoxic (PO2 = 580 +/- 23 Torr) water. Lung inflation with N2, air, or O2 initially reduced the frequency (fG) and buccal pressure amplitude (PBC) of the following gill ventilation cycles. However, 65 s after lung inflation fG was significantly greater for N2 inflation than for air inflation, whereas fG after O2 inflation was significantly lower. In further experiments, the effects of lung inflation and gaseous PO2 on gill ventilation were dissociated. Flow of N2, air, or O2 was established through the lungs of tadpoles in hypoxic water. Flow of N2 produced a significant rise in fG and flow of O2 a significant fall compared with airflow. Regardless of the PO2 of the gas, subsequent lung inflation produced by occlusion of the outflow cannula caused a fall in fG and PBC from the preestablished flow value. We conclude that lung inflation per se and the resulting increase in PO2 both contribute to the suppression of gill ventilation following spontaneous air breathing, which serves to limit O2 loss of the gills in aquatic hypoxia.