Heart rate, blood pressure and baroreflex gain in three species of anurans from different environments

Abstract

Anurans from different environments vary with respect to lymph mobilization capacity which is linked to blood pressure/volume status. We hypothesized that anurans from different environments might also vary in their ability to regulate blood pressure and heart rate through the baroreflex. We altered mean arterial blood pressure (MAP) pharmacologically and measured changes in heart rate (HR) to determine baroreflex gain. Experiments were conducted at 20 °C with three species of anurans from terrestrial (cane toad, Rhinella marina), semi‐aquatic (North American bullfrog, Lithobates catesbeianus) and aquatic (African clawed frog, Xenopus laevis) environments. MAP was increased with phenylephrine (Phe; 20–200 μg/kg, i.v.) and decreased with sodium nitroprusside (SNP; 20–200 μg/kg, i.v.). Heart rate ranged from 27 ± 3 to 31 ± 2 beats min−1 (P>;0.05), but MAP was significantly higher in R. marina (5.3 ± 0.2 kPa) compared with X. laevis (3.6 ± 0.2 kPa) or L. catesbeianus (4.2 ± 0.2 kPa). The baroreflex gain (ΔHR/ΔMAP) ranged from was −6.5 ± 0.5 to −7.2 ± 0.8 beats min−1 kPa−1 but was not significantly different. These data indicate that baroreflex gain does not vary in three species representing a wide environmental range, but the more terrestrial species (cane toad) operates at a higher arterial blood pressure suggesting that baroreflex resetting has occurred in this species. Supported by NSF‐IOS 0843082 and HHMI.