Baroreflex regulation affects ventilation in the Cururu toad Rhinella schneideri

Abstract

Anurans regulate short-term oscillations in blood pressure through changes in heart rate ( f H ), vascular resistance and lymphatic f H . Lung ventilation in anurans is linked to blood volume homeostasis by facilitating lymph return to the cardiovascular system. We hypothesized that the arterial baroreflex modulates pulmonary ventilation in the cururu toad Rhinella schneideri, and that this relationship is temperature dependent. Pharmacologically induced hypotension (sodium nitroprusside) and hypertension (phenylephrine) increased ventilation (25°C: 248.7±25.7 ml kg −1 min; 35°C: 351.5± 50.2 ml kg) and decreased ventilation (25°C: 9.0± 6.6 ml kg , respectively; negative values indicate an inverse relationship between blood pressure and ventilation (or breathing frequency), i.e. as blood pressure increases, ventilation decreases, and vice versa], while temperature had no effect on these sensitivities. Hyperoxia (30%; 25°C) diminished ventilation, but did not abolish the ventilatory response to hypotension, indicating a response independent of peripheral chemoreceptors. Although there are previous data showing increased f H baroreflex sensitivity from 15 to 30°C in this species, further increases in temperature (35°C) diminished f H baroreflex gain (40.5±5.62 versus 21.6±4.64% kPa −1 ). Therefore, besides an involvement of pulmonary ventilation in matching O 2 delivery to demand at higher temperatures in anurans, it also plays a role in blood pressure regulation, independent of temperature, possibly owing to an interaction between baroreflex and respiratory areas in the brain, as previously suggested for mammals.

Temperature and dehydration effects on metabolism, water uptake, and the partitioning between respiratory and cutaneous evaporative water loss in a terrestrial toad

“…As a result, while the relative contribution of EWL Resp increased from 2.4% to 8.1%, from 15°C to 35°C, the relative contribution of EWL Skin fell from 97.5% to 91.8%. These changes probably reflect the 3.5-fold elevation of R. diptycha oxygen uptake rate within the same temperature interval, which implies an increased rate of lung ventilation (see Kruhøffer et al, 1987;Branco et al, 1993;Bícego-Nahas et al, 2001;Zena et al, 2016). Thus, the temperature-induced increase in EWL Resp , relative to EWL Skin , in R. diptycha can be attributed to a concurrent temperature-induced increment in metabolism and lung ventilation (see also Mautz, 1982;Hillman et al, 2009).…”

“…However, lung ventilation in anurans can vary considerably among species (Hutchison et al, 1968), under different circumstances (Whitford, 1973) and in response to environmental factors (Boutilier, 1992). For example, lung ventilation is known to be affected by temperature (Kruhøffer et al, 1987;Branco et al, 1993;Bícego-Nahas et al, 2001;Zena et al, 2016) and dehydration (Boutilier et al, 1979). However, the interactive effects of both of these factors on the partitioning of total evaporation (EWL Total ) between EWL Resp and EWL Skin remains uncertain.…”

Analysis of the respiratory component of heart rate variability in the Cururu toad Rhinella schneideri

“…Such results are in agreement with relatively low heart rates in our toads (~17 beats.min −1 ) and probably reflect minimal discomfort associated with both cannulae and electrodes, in addition to a long recovery time from surgical procedures (7 days). Higher heart rates have been reported in earlier studies for the same species (~29 bpm; 18 , 24 ), in which maintenance of an intra-arterial catheter and short recovery time ( e . g .…”

“…Cardiorespiratory-coupling originates from reciprocal interaction between cardiovascular and respiratory systems in vertebrates 1 , 2 , 18 , 25 . Simultaneous recordings of f H , pulmocutaneous blood flow ( ) and ventilation in anuran amphibians have shown concurrent rises in f H and within each lung inflation cycle followed by a decrease in both parameters as the cycle ends 13 , 26 .…”

“…Measurements of the cyclic variations of f H in a beat-to-beat basis using power spectral analysis in order to establish the autonomic balance and the relationship between respiratory and cardiovascular system has never been reported for a terrestrial amphibian. Both sympathetic and parasympathetic nervous systems influence f H and in anuran amphibians 3 , 17 , 18 . The extent to which the balance between vagal and sympathetic nervous systems accounts for augmented f H and within each lung inflation cycle of adult amphibians is not completely understood 3 , 19 .…”