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The autonomic control of upright posture tachycardia in the arboreal lizard Iguana iguana
Author(s) -
Troiano Natalia Miriã,
Armelin Vinicius Araújo,
Braga Victor Hugo da Silva,
Abe Augusto Shinya,
Rantin Francisco Tadeu,
Florindo Luiz Henrique
Publication year - 2018
Publication title -
journal of experimental zoology part a: ecological and integrative physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.834
H-Index - 11
eISSN - 2471-5646
pISSN - 2471-5638
DOI - 10.1002/jez.2213
Subject(s) - iguana , tachycardia , ectotherm , medicine , heart rate , cardiology , blood pressure , anesthesia , biology , endocrinology , ecology
In terrestrial environments, upright spatial orientation can dramatically influence animals’ hemodynamics. Generally, large and elongated species are particularly sensitive to such influence due to the greater extent of their vascular beds being verticalized, favoring the establishment of blood columns in their bodies along with caudal blood pooling, and thus jeopardizing blood circulation through a cascade effect of reductions in venous return, cardiac filling, stroke volume, cardiac output, and arterial blood pressure. This hypotension triggers an orthostatic‐(baroreflex)‐tachycardia to normalize arterial pressure, and despite the extensive observation of this heart rate ( f H ) adjustment in experiments on orthostasis, little is known about its mediation and importance in ectothermic vertebrates. In addition, most of the knowledge on this subject comes from studies on snakes. Thus, our objective was to expand the knowledge on this issue by investigating it in an arboreal lizard ( Iguana iguana ). To do so, we analyzed f H , cardiac autonomic tones, and f H variability in horizontalized and tilted iguanas (0°, 30°. and 60°) before and after muscarinic blockade with atropine and double autonomic blockade with atropine and propranolol. The results revealed that I. Iguana exhibits significant orthostatic‐tachycardia only at 60 o inclinations—a condition that is primarily elicited by a withdrawal of vagal drive. Also, as in humans, increases in low‐frequency f H oscillations and decreases in high‐frequency f H oscillations were observed along with orthostatic‐tachycardia, suggesting that the mediation of this f H adjustment may be evolutionarily conserved in vertebrates.