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Crossley JL, Smith B, Tull M, Elsey RM, Wang T, Crossley DA. Hypoxic incubation at 50% of atmospheric levels shifts the cardiovascular response to acute hypoxia in American alligators, Alligator mississippiensis. J Comp Physiol B 2023; 193:545-556. [PMID: 37615772 DOI: 10.1007/s00360-023-01510-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Revised: 08/06/2023] [Accepted: 08/07/2023] [Indexed: 08/25/2023]
Abstract
We designed a series of studies to investigate whether hypoxia (10% O2) from 20% of incubation to hatching, or from 20 to 50% of incubation, affects cardiovascular function when juvenile American alligators reached an age of 4-5 years compared to juveniles that were incubated in 21% O2. At this age, we measured blood flows in all the major arteries as well as heart rate, blood pressure, and blood gases in animals in normoxia and acute hypoxia (10% O2 and 5% O2). In all three groups, exposure to acute hypoxia of 10% O2 caused a decrease in blood O2 concentration and an increase in heart rate in 4-5-year-old animals, with limited effects on blood flow in the major outflow vessels of the heart. In response to more acute hypoxia (5% O2), where blood O2 concentration decreased even further, we measured increased heart rate and blood flow in the right aorta, subclavian artery, carotid artery, and pulmonary artery; however, blood flow in the left aorta either decreased or did not change. Embryonic exposure to hypoxia increased the threshold for eliciting an increase in heart rate indicative of a decrease in sensitivity. Alligators that had been incubated in hypoxia also had higher arterial PCO2 values in normoxia, suggesting a reduction in ventilation relative to metabolism.
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Affiliation(s)
- Janna L Crossley
- Department of Surgery, Center for Organogenesis and Trauma, University of Texas Southwestern, Dallas, TX, 75390, USA
- Department of Biological Sciences, University of North Texas, 1155 Union Circle, Denton, TX, 76203, USA
| | - Brandt Smith
- Department of Biological Sciences, University of North Texas, 1155 Union Circle, Denton, TX, 76203, USA
| | - Melissa Tull
- Department of Biological Sciences, University of North Texas, 1155 Union Circle, Denton, TX, 76203, USA
| | - Ruth M Elsey
- Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, Grand Chenier, LA, 70643, USA
| | - Tobias Wang
- Department of Biology, Zoophysiology, Aarhus University, Aarhus C, Denmark
| | - Dane A Crossley
- Department of Biological Sciences, University of North Texas, 1155 Union Circle, Denton, TX, 76203, USA.
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Smith B, Crossley JL, Conner J, Elsey RM, Wang T, Crossley DA. Exposure to hypoxia during embryonic development affects blood flow patterns and heart rate in juvenile American alligators during digestion. Comp Biochem Physiol A Mol Integr Physiol 2023; 282:111440. [PMID: 37169243 DOI: 10.1016/j.cbpa.2023.111440] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Revised: 05/08/2023] [Accepted: 05/08/2023] [Indexed: 05/13/2023]
Abstract
The developmental environment can alter an organism's phenotype through epigenetic mechanisms. We incubated eggs from American alligators in 10% O2 (hypoxia) to investigate the functional plasticity of blood flow patterns in response to feeding later in life. Digestion is associated with marked elevations of metabolism, and we therefore used the feeding-induced stimulation of tissue O2 demand to determine whether there are lasting effects of developmental hypoxia on the cardiovascular response to digestion later in life. In all animals studied, digestion elicited tachycardia and an elevation of blood flow in the right aorta, left aorta, and the pulmonary artery, whereas flows in the carotid and subclavian artery did not change. We found that heart rate and systemic blood flow remained elevated for a longer time period in juvenile alligators that had been incubated in hypoxia; we also found that the pulmonary blood flow was elevated at 24, 36, and 48 h. Collectively, our findings demonstrate that exposure to hypoxia during incubation has lasting effects on the hemodynamics of juvenile alligators 4 years after hatching.
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Affiliation(s)
- Brandt Smith
- University of North Texas, Department of Biological Sciences, 1155 Union Circle, Denton, TX 76203, USA
| | - Janna L Crossley
- University of North Texas, Department of Biological Sciences, 1155 Union Circle, Denton, TX 76203, USA; Department of Surgery, Center for Organogenesis and Trauma, University of Texas Southwestern, TX 75390, USA
| | - Justin Conner
- University of North Texas, Department of Biological Sciences, 1155 Union Circle, Denton, TX 76203, USA
| | - Ruth M Elsey
- Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, Grand Chenier, LA 70643, USA
| | - Tobias Wang
- Department of Biology- Zoophysiology, Aarhus University, Aarhus C, Denmark
| | - Dane A Crossley
- University of North Texas, Department of Biological Sciences, 1155 Union Circle, Denton, TX 76203, USA.
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Starck JM, Wyneken J. Comparative and Functional Anatomy of the Ectothermic Sauropsid Heart. Vet Clin North Am Exot Anim Pract 2022; 25:337-366. [PMID: 35422257 DOI: 10.1016/j.cvex.2022.01.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The heart development, form, and functional specializations of chelonians, squamates, crocodilians, and birds characterize how diverse structure and specializations arise from similar foundations. This review aims to summarize the morphologic diversity of sauropsid hearts and present it in an integrative functional and phylogenetic context. Besides the detailed morphologic descriptions, the integrative view of function, evolution, and development will aid understanding of the surprising diversity of sauropsid hearts. This integrated perspective is a foundation that strengthens appreciation that the sauropsid hearts are the outcome of biological evolution; disease often is linked to arising mismatch between adaptations and modern environments.
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Affiliation(s)
- J Matthias Starck
- Department of Biology, Ludwig-Maximilians-University Munich, Planegg-Martinsried D82152, Germany.
| | - Jeanette Wyneken
- Florida Atlantic University, FAU Marine Lab at Gumbo Limbo Environmental Complex, Boca Raton, FL 33431-0991, USA
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Conner JL, Crossley JL, Elsey R, Nelson D, Wang T, Crossley DA. Does the left aorta provide proton-rich blood to the gut when crocodilians digest a meal? ACTA ACUST UNITED AC 2019; 222:jeb.201079. [PMID: 30787137 DOI: 10.1242/jeb.201079] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Accepted: 02/15/2019] [Indexed: 11/20/2022]
Abstract
Reptiles have the capacity to differentially perfuse the systemic and pulmonary vascular circuits via autonomic regulation of the heart and the vascular trees. While this aptitude is widely recognized, the role of 'shunting' as a homeostatic mechanism to match convective transport with tissue demand remains unknown. In crocodilians, it has been hypothesized that a pulmonary vascular bypass of systemic venous blood - a right-to-left (R-L) shunt - serves to deliver CO2-rich blood with protons needed for gastric acid secretion during digestion. This hypothesis is partially based on the unique crocodilian vascular anatomy where a left aorta (LAo) arises from the right ventricle, and appears to preferentially supply the gastrointestinal system, whereas the right aorta emerges from the left ventricle. Recent theoretical considerations imply that a R-L shunt would have minuscule effects on P CO2 , but direct measurements of blood gases in both the right and left aortae or both the right and left atria in fed animals have not been conducted. For this reason, we measured blood parameters including P O2 , P CO2 , pHe and [HCO3 -] in the right and left aortae and atria following ingestion of a gavage-fed standardized meal (5% body mass). Blood samples were taken at 3, 6, 12, 24, 36 and 48 h into the digestive period to encompass the period of maximal gastric acid secretion. At no point did P CO2 or pH differ between the left and right aortae, whereas P O2 was significantly lower in the left aorta at several time points during digestion. Our findings do not support the hypothesis that a R-L shunt serves to deliver CO2 for the gastrointestinal system after feeding in crocodilians.
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Affiliation(s)
- Justin L Conner
- Department of Biological Sciences, University of North Texas, Denton, TX 76203, USA
| | - Janna L Crossley
- Department of Biological Sciences, University of North Texas, Denton, TX 76203, USA
| | - Ruth Elsey
- Department of Wildlife and Fisheries, Grand Chenier, LA 70603, USA
| | - Derek Nelson
- Department of Biological Sciences, University of North Texas, Denton, TX 76203, USA
| | - Tobias Wang
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark
| | - Dane A Crossley
- Department of Biological Sciences, University of North Texas, Denton, TX 76203, USA
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Young BA, Adams J, Segal S, Kondrashova T. Hemodynamics of tonic immobility in the American alligator (Alligator mississippiensis) identified through Doppler ultrasonography. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2018; 204:953-964. [PMID: 30259097 DOI: 10.1007/s00359-018-1293-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2018] [Revised: 09/11/2018] [Accepted: 09/21/2018] [Indexed: 11/28/2022]
Abstract
American alligators (Alligator mississippiensis) held inverted exhibit tonic immobility, combining unresponsiveness with flaccid paralysis. We hypothesize that inverting the alligator causes a gravitationally promoted increase in right aortic blood flowing through the foramen of Panizza, with a concurrent decrease in blood flow through the primary carotid, and thereby of cerebral perfusion. Inverting the alligator results in displacement of the liver, post-pulmonary septum, and the heart. EKG analysis revealed a significant decrease in heart rate following inversion; this decrease was maintained for approximately 45 s after inversion which is in general agreement with the total duration of tonic immobility in alligators (49 s). Doppler ultrasonography revealed that following inversion of the alligator, there was a reversal in direction of blood flow through the foramen of Panizza, and this blood flow had a significant increase in velocity (compared to the foraminal flow in the prone alligator). There was an associated significant decrease in the velocity of blood flow through the primary carotid artery once the alligator was held in the supine position. Tonic immobility in the alligator appears to be a form of vasovagal syncope which arises, in part, from the unique features of the crocodilian heart.
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Affiliation(s)
- Bruce A Young
- Department of Anatomy, Kirksville College of Osteopathic Medicine, A.T. Still University, Kirksville, MO, 63501, USA.
| | - James Adams
- Department of Anatomy, Kirksville College of Osteopathic Medicine, A.T. Still University, Kirksville, MO, 63501, USA
| | - Solomon Segal
- Department of Anatomy, Kirksville College of Osteopathic Medicine, A.T. Still University, Kirksville, MO, 63501, USA
| | - Tatyana Kondrashova
- Department of Family Medicine, Preventitive Medicine, and Community Health, Kirksville College of Osteopathic Medicine, A.T. Still University, Kirksville, MO, 63501, USA
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