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  • 1
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    Pulmonary blood flow regulation in an aquatic snake (1989)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1989-07-21
    Description: Regulation of pulmonary blood flow was studied during voluntary diving in the aquatic file snake, Acrochordus granulatus. Measurements of pressure and blood flow in pulmonary and systemic vessels indicate that blood flow completely bypasses the lung for significant periods during prolonged and quiescent submergence (greater than 30 minutes). When the lung is ventilated, pulmonary blood flow increases to 36 milliliters per minute per kilogram of body mass (measured in the anterior pulmonary artery), and the cardiac output largely bypasses the systemic circulation. These reciprocating patterns of preferential blood flow reflect inverse relations between flow and vascular resistance, with the result that systemic and pulmonary arterial pressures remain virtually constant throughout repetitive dive cycles. Neuropharmacological studies of freely diving snakes and isolated, perfused lung preparations show that pulmonary blood flow is regulated by an interplay of adrenergic vasodilatation and cholinergic vasoconstriction within the densely innervated lung vasculature. The patterns of blood circulation shown by diving Acrochordus reflect an unusual lability of intracardiac shunts.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lillywhite, H B -- Donald, J A -- HL 33821/HL/NHLBI NIH HHS/ -- New York, N.Y. -- Science. 1989 Jul 21;245(4915):293-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Zoology, University of Florida, Gainesville 32611.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2749262" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Blood Flow Velocity ; Blood Pressure ; Cardiac Output ; Diving ; Heart Rate ; Pulmonary Artery/*physiology ; *Pulmonary Circulation ; Snakes/*physiology ; Vascular Resistance
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Adaptive strategies: behavioral energetics (1984)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1984-05-11
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lillywhite, H B -- New York, N.Y. -- Science. 1984 May 11;224(4649):596.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17838352" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    Lipid barrier to water exchange in reptile epidermis (1980)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1980-03-07
    Description: Extraction of lipids from the shed epidermis of the terrestrial snake Elaphe obsoleta obsoleta increases cutaneous water loss in vitro as much as 15-fold. Partial denaturation of epidermal keratin without lipid extraction increases cutaneous water loss only twofold. Histological observations and thin-layer and gas-liquid chromatography of the lipid extracts indicate a complex mixture of polar and neutral lipids predominantly in the mesos layer of the cornified epidermis. Comparative measurements of cutaneous water loss in other species of snakes and a lizard show that permeabilities differ naturally but are essentially identical after lipid extraction. These findings establish the importance of lipids in the permeability barrier of reptilian skin and suggest that keratin or scale morphology are of nominal importance in limiting water exchange.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Roberts, J B -- Lillywhite, H B -- New York, N.Y. -- Science. 1980 Mar 7;207(4435):1077-9.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17759840" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Sea snakes anticipate tropical cyclone (2010)
    Springer
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    Publication Date: 2010-07-03
    Print ISSN: 0025-3162
    Electronic ISSN: 1432-1793
    Topics: Biology
    Published by Springer
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  • 5
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    Adaptive Strategies: Behavioral Energetics. (1984)
    American Association for the Advancement of Science
    Details
    Publication Date: 1984-05-11
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science
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  • 6
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    Cardiovascular responses of semi-arboreal snakes to chronic, intermittent hypergravity (1996)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Cardiovascular functions were studied in semi-arboreal rat snakes (Elaphe obsoleta) following long-term, intermittent exposure to +1.5 Gz (head-to-tail acceleration) on a centrifuge. Snakes were held in a nearly straight position within horizontal plastic tubes during periods of centrifugation. Centrifugal acceleration, therefore, subjected snakes to a linear force gradient with the maximal force being experienced at the tail. Compared to non-centrifuged controls, Gz-acclimated snakes showed greater increases of heart rate during head-up tilt or acceleration, greater sensitivity of arterial pressure to circulating catecholamines, higher blood levels of corticosterone, and higher blood ratios of prostaglandin F 2 alpha/prostaglandin E2. Cardiovascular tolerance to increased gravity during graded Gz acceleration was measured as the maximum (caudal) acceleration force at which carotid arterial blood flow became null. When such tolerances were adjusted for effects of body size and other continuous variables incorporated into an analysis of covariance, the difference between the adjusted mean values of control and acclimated snakes (2.37 and 2.84 Gz, respectively) corresponded closely to the 0.5 G difference between the acclimation G (1.5) and Earth gravity (1.0). As in other vertebrates, cardiovascular tolerance to Gz stress tended to be increased by acclimation, short body length, high arterial pressure, and comparatively large blood volume. Voluntary body movements were important for promoting carotid blood flow at the higher levels of Gz stress.
    Keywords: Life Sciences (General)
    Type: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology (ISSN 0174-1578); Volume 166; 241-53
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  • 7
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    Tolerance of snakes to hypergravity (1996)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Sensitivity of carotid blood flow to increased gravitational force acting in the head-to-tail direction(+Gz) was studied in diverse species of snakes hypothesized to show adaptive variation of response. Tolerance to increased gravity was measured red as the maximum graded acceleration force at which carotid blood flow ceased and was shown to vary according to gravitational adaptation of species defined by their ecology and behavior. Multiple regression analysis showed that gravitational habitat, but not body length, had a significant effect on Gz tolerance. At the extremes, carotid blood flow decreased in response to increasing G force and approached zero near +1 Gz in aquatic and ground-dwelling species, whereas in climbing species carotid flow was maintained at forces in excess of +2 Gz. Tolerant (arboreal) species were able to withstand hypergravic forces of +2 to +3 Gz for periods up to 1 h without cessation of carotid blood flow or loss of body movement and tongue flicking. Data suggest that the relatively tight skin characteristic of tolerant species provides a natural antigravity suit and is of prime importance in counteracting Gz stress on blood circulation.
    Keywords: Life Sciences (General)
    Type: Physiological zoology (ISSN 0031-935X); Volume 69; 2; 293-303
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  • 8
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    Blood vessel adaptation to gravity in a semi-arboreal snake (1996)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The effects of vasoactive agonists on systemic blood vessels were examined with respect to anatomical location and gravity acclimation in the semi-arboreal snake, Elaphe Obsoleta. Major blood vessels were reactive to putative neurotransmitters, hormones or local factors in vessel specific patterns. Catecholamines, adenosine triphosphate, histamine and high potassium (80 mM) stimulated significantly greater tension per unit vessel mass in posterior than anterior arteries. Anterior vessels were significantly more sensitive to catecholamines than midbody and posterior vessels. Angiotensin II stimulated significantly greater tension in carotid artery than in midbody and posterior dorsal aorta. Arginine vasotocin strongly contracted the left and right aortic arches and anterior dorsal aorta. Veins were strongly contracted by catecholamines, high potassium and angiotensin II, but less so by adenosine triphosphate, arginine vasotocin and histamine. Precontracted vessel were relaxed by acetylcholine and sodium nitroprusside, but not by atrial natriuretic peptide or bradykinin. Chronic exposure of snakes to intermittent hypergravity stress ( + 1.5 Gz at tail) did not affect the majority of vessel responses. These data demonstrate that in vitro tension correlates with that catecholamines, as well as other agonists, are important in mediating vascular responses to gravitational stresses in snakes.
    Keywords: Life Sciences (General)
    Type: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology (ISSN 0174-1578); Volume 165; 7; 518-26
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  • 9
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    Contribution of the vertebral artery to cerebral circulation in the rat snake Elaphe obsoleta (1998)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Blood supplying the brain in vertebrates is carried primarily by the carotid vasculature. In most mammals, cerebral blood flow is supplemented by the vertebral arteries, which anastomose with the carotids at the base of the brain. In other tetrapods, cerebral blood is generally believed to be supplied exclusively by the carotid vasculature, and the vertebral arteries are usually described as disappearing into the dorsal musculature between the heart and head. There have been several reports of a vertebral artery connection with the cephalic vasculature in snakes. We measured regional blood flows using fluorescently labeled microspheres and demonstrated that the vertebral artery contributes a small but significant fraction of cerebral blood flow (approximately 13% of total) in the rat snake Elaphe obsoleta. Vascular casts of the anterior vessels revealed that the vertebral artery connection is indirect, through multiple anastomoses with the inferior spinal artery, which connects with the carotid vasculature near the base of the skull. Using digital subtraction angiography, fluoroscopy, and direct observations of flow in isolated vessels, we confirmed that blood in the inferior spinal artery flows craniad from a point anterior to the vertebral artery connections. Such collateral blood supply could potentially contribute to the maintenance of cerebral circulation during circumstances when craniad blood flow is compromised, e.g., during the gravitational stress of climbing.
    Keywords: Life Sciences (General)
    Type: Journal of morphology (ISSN 0362-2525); Volume 238; 1; 39-51
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  • 10
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    Cardiovascular Responses of Snakes to Gravitational Gradients (1998)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: Snakes are useful vertebrates for studies of gravitational adaptation, owing to their elongate body and behavioral diversification. Scansorial species have evolved specializations for regulating hemodynamics during exposure to gravitational stress, whereas, such adaptations are less well developed in aquatic and non-climbing species. We examined responses of the amphibious snake,\italicize (Nerodia rhombifera), to increments of Gz (head-to-tail) acceleration force on both a short- and long-arm centrifuge (1.5 vs. 3.7 m radius, from the hub to tail end of snake). We recorded heart rate, dorsal aortic pressure, and carotid arterial blood flow during stepwise 0.25 G increments of Gz force (referenced at the tail) in conscious animals. The Benz tolerance of a snake was determined as the Gz level at which carotid blood flow ceased and was found to be significantly greater at the short- than long-arm centrifuge radius (1.57 Gz vs. 2.0 Gz, respectively; P=0.016). A similar pattern of response was demonstrated in semi-arboreal rat snakes,\italicize{Elaphe obsoleta}, which are generally more tolerant of Gz force (2.6 Gz at 1.5m radius) than are water snakes. The tolerance differences of the two species reflected cardiovascular responses, which differed quantitatively but not qualitatively: heart rates increased while arterial pressure and blood flow decreased in response to increasing levels of Gz. Thus, in both species of snakes, a reduced gradient of Gz force (associated with greater centrifuge radius) significantly decreases the Gz level that can be tolerated.
    Keywords: Life Sciences (General)
    Type: Experimental Biology ''98; Apr 18, 1998 - Apr 22, 1998; San Francisco, CA; United States
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