title: Winter metabolic depression does not change arterial baroreflex control of heart rate in the tegu lizard Salvator merianae.
abstract: Baroreflex regulation of blood pressure is important for maintaining appropriate tissue perfusion. Although temperature affects heart rate (fH) reflex regulation in some reptiles and toads, no data are available on the influence of temperature-independent metabolic states on baroreflex. The South American tegu lizard Salvator merianae exhibits a clear seasonal cycle of activity decreasing fH along with winter metabolic downregulation, independent of body temperature. Through pharmacological interventions (phenylephrine and sodium nitroprusside), the baroreflex control of fH was studied at ∼ 25 °C in spring-summer- and winter-acclimated tegus. In winter lizards, resting and minimum fH were lower than in spring-summer animals (respectively, 13.3 ± 0.82 versus 10.3 ± 0.81 and 11.2 ± 0.65 versus 7.97 ± 0.88 beats min(-1)), while no acclimation differences occurred in resting blood pressure (5.14 ± 0.38 versus 5.06 ± 0.56 kPa), baroreflex gain (94.3 ± 10.7 versus 138.7 ± 30.3% kPa(-1)) or rate-pressure product (an index of myocardial activity). Vagal tone exceeded the sympathetic tone of fH, especially in the winter group. Therefore, despite the lower fH, winter acclimation does not diminish the fH baroreflex responses or rate-pressure product, possibly because of increased stroke volume that may arise because of heart hypertrophy. Independent of acclimation, fH responded more to hypotension than to hypertension. This should imply that tegus, which have no pressure separation within the single heart ventricle, must have other protection mechanisms against pulmonary hypertension or oedema, presumably through lymphatic drainage and/or vagal vasoconstriction of pulmonary artery. Such a predominant fH reflex response to hypotension, previously observed in anurans, crocodilians and mammals, may be a common feature of tetrapods.
authors.affiliation: Department of Animal Morphology and Physiology, College of Agricultural and Veterinarian Sciences, São Paulo State University, Jaboticabal, São Paulo 14884-900, Brazil National Institute of Science and Technology - Comparative Physiology (INCT - Fisiologia Comparada), 14884-900, Jaboticabal, São Paulo, Brazil.
authors.forename: Lucas A
authors.initials: LA
authors.lastname: Zena
authors.affiliation: Department of Animal Morphology and Physiology, College of Agricultural and Veterinarian Sciences, São Paulo State University, Jaboticabal, São Paulo 14884-900, Brazil National Institute of Science and Technology - Comparative Physiology (INCT - Fisiologia Comparada), 14884-900, Jaboticabal, São Paulo, Brazil.
authors.forename: Valter
authors.initials: V
authors.lastname: Dantonio
authors.affiliation: Department of Animal Morphology and Physiology, College of Agricultural and Veterinarian Sciences, São Paulo State University, Jaboticabal, São Paulo 14884-900, Brazil National Institute of Science and Technology - Comparative Physiology (INCT - Fisiologia Comparada), 14884-900, Jaboticabal, São Paulo, Brazil.
authors.forename: Luciane H
authors.initials: LH
authors.lastname: Gargaglioni
authors.affiliation: National Institute of Science and Technology - Comparative Physiology (INCT - Fisiologia Comparada), 14884-900, Jaboticabal, São Paulo, Brazil Department of Zoology, Institute of Bioscience, São Paulo State University, Rio Claro, São Paulo 13506-900, Brazil.
authors.forename: Denis V
authors.initials: DV
authors.lastname: Andrade
authors.affiliation: National Institute of Science and Technology - Comparative Physiology (INCT - Fisiologia Comparada), 14884-900, Jaboticabal, São Paulo, Brazil Department of Zoology, Institute of Bioscience, São Paulo State University, Rio Claro, São Paulo 13506-900, Brazil.
authors.forename: Augusto S
authors.initials: AS
authors.lastname: Abe
authors.affiliation: Department of Animal Morphology and Physiology, College of Agricultural and Veterinarian Sciences, São Paulo State University, Jaboticabal, São Paulo 14884-900, Brazil National Institute of Science and Technology - Comparative Physiology (INCT - Fisiologia Comparada), 14884-900, Jaboticabal, São Paulo, Brazil keniacb@yahoo.com.br keniacb@fcav.unesp.br.
authors.forename: Kênia C
authors.initials: KC
authors.lastname: Bícego
mesh_terms: D000064:Acclimatization; D000818:Animals; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D008116:Lizards / Q000378:metabolism / Q000502:physiology*; D008297:Male; D009599:Nitroprusside / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D012621:Seasons; D013696:Temperature
chemical_list: D009599:Nitroprusside; D010656:Phenylephrine
keywords: Adrenergic receptors; Baroreceptor; Blood pressure; Cholinergic tone; Hibernation; Seasonal changes