Baroreflex gain and time of pressure decay at different body temperatures in the tegu lizard, Salvator merianae

Abstract

Ectotherms may experience large body temperature (Tb) variations. Higher Tb have been reported to increase baroreflex sensitivity in ectotherm tetrapods. At lower Tb, pulse interval (PI) increases and diastolic pressure decays for longer, possibly resulting in lower end-diastolic pressures and mean arterial pressures (Pm). Additionally, compensatory baroreflex-related heart rate modulation (i.e. the cardiac branch of the baroreflex response) is delayed due to increased PI. Thus, low Tb is potentially detrimental, leading to cardiovascular malfunctioning. This raises the question on how Pm is regulated in such an adverse condition. We investigated the baroreflex compensations that enables tegu lizards, Salvator merianae, to maintain blood pressure homeostasis in a wide Tb range. Lizards had their femoral artery cannulated and pressure signals recorded at 15°C, 25°C and 35°C. We used the sequence method to analyse the heart rate baroreflex-related corrections to spontaneous pressure fluctuations at each temperature. Vascular adjustments (i.e. the peripheral branch) were assessed by calculating the time constant for arterial pressure decay (τ)—resultant from the action of both vascular resistance and compliance—by fitting the diastolic pressure descent to the two-element Windkessel equation. We observed that at lower Tb, lizards increased baroreflex gain at the operating point (Gop) and τ, indicating that the diastolic pressure decays at a slower rate. Gop normalized to Pm and PI, as well as the ratio τ/PI, did not change, indicating that both baroreflex gain and rate of pressure decay are adjusted according to PI lengthening. Consequently, pressure parameters and the oscillatory power fraction (an index of wasted cardiac energy) were unaltered by Tb, indicating that both Gop and τ modulation are crucial for cardiovascular homeostasis.

Anguimorpha as a model group for studying the comparative heart morphology among Lepidosauria: Evolutionary window on the ventricular septation

“…Blood pressure in tegu is approx. 50/37 mmHg (mean arterial pressure 5.66 kPa; Filogonio et al, 2020). The blood pressure is going hand in hand with high seasonal variability in metabolism as well as with ontogenetic shift and life‐histories not only in large tegu species (Piercy et al, 2015; Toledo et al, 2008) but also in the whole Teiidae family as it was observed in genus Ameiva (Morgan, 1988).…”

“…As a second outgroup to anguimorphs was chosen Salvator merianae (Teiidae) because this species occupies a similar ecological niche as varanids (Cechin et al, 2011) and tegus are also known for their seasonal endothermy linked to the reproduction (Tattersall et al, 2016). However, the heart morphology deviates from genus Varanus (Hanemaaijer et al, 2019; Jensen et al, 2014) and also the physiology is different from varanids, particularly when comparing blood pressure, which is almost double in favor of Varanidae (12 kPa, mammalian‐like) than of Teiidae (5.66 kPa, typical lizard; Filogonio et al, 2020; Millard & Johansen, 1974; Thompson & Withers, 1997). Moreover, there is no such high oxygen consumption level in Teiidae as in varanids and helodermatids (Albuquerque & Garland Jr, 2020), although the species in the group Teiidae are described mostly as active foragers similarly to varanids.…”

A comparison of four common mathematical models to assess baroreflex sensitivity

“…The baroreflex is a negative feedback system responsible for maintaining cardiovascular homeostasis by continuous buffering of rapid arterial pressure fluctuations through well‐orchestrated heart rate ( f H ) and vascular responses (Filogonio et al, 2020, 2021; Ogoh et al, 2003; Sandblom & Axelsson, 2005). This mechanism has been experimentally observed in all vertebrate groups and is essential in providing adequate tissue perfusion (Bagshaw, 1985; Kaufmann et al, 2020; Raven et al, 2019; Van Vliet & West, 1994).…”