Cardiovascular responses to locomotor activity and feeding in unrestrained three-toed sloths, Bradypus variegatus

Abstract

Heart rate (HR) and systolic (SBP), diastolic (DBP) and mean (MBP) blood pressure were recorded by biotelemetry in nine conscious unrestrained sloths for 1 min every 15 min over a 24-h period. The animals were allowed to freely move in an acoustically isolated and temperature-controlled (24 ± 1ºC) experimental room with light-dark cycle (12/12 h). Behavior was closely monitored through a unidirectional visor and classified as resting (sitting or suspended), feeding (chewing and swallowing embauba leaves, Cecropia adenops), or locomotor activity around the tree trunk or on the room floor. Locomotor activity caused statistically significant increases in SBP (+8%, from 121 ± 22 to 131 ± 18 mmHg), DBP (+7%, from 86 ± 17 to 92 ± 10 mmHg), MBP (+8%, from 97 ± 19 to 105 ± 12 mmHg), and HR (+14%, from 84 ± 15 to 96 ± 15 bpm) compared to resting values, indicating a possible major influence of the autonomic nervous system on the modulation of cardiac function during this behavior. During feeding, the increase in blood pressure was even higher (SBP +27%, from 119 ± 21 to 151 ± 21 mmHg; DBP +21%, from 85 ± 16 to 103 ± 15 mmHg; MBP +24%, from 96 ± 17 to 119 ± 17 mmHg), while HR remained at 14% (from 84 ± 15 to 96 ± 10 bpm) above resting values. The proportionally greater increase in blood pressure than in HR during feeding suggests an increase in peripheral vascular resistance as part of the overall response to this behavior.

Immobilization of Free-Ranging Hoffmann's Two-Toed and Brown-Throated Three-Toed Sloths Using Ketamine and Medetomidine: A Comparasion of Physiologic Parameters

“…The mean conscious heart rate of B. variegatus in our study (76.0611 BPM) was similar to that previously reported; 79.8622.3 and 84615 BPM (Duarte et al, 1982(Duarte et al, , 2004. In another study, wild C. didactylus anesthetized with KM had an initial mean heart rate of 61615 BPM with a moderate decrease to 46613 BPM (Vogel et al, 1998).…”

“…Alternatively, posture and its effect on heart rate and blood pressure have been previously studied in B. variegatus. Threetoed sloths (Bradypus tridactylus), tilted either from erect-to-supine or supine-toerect body position, showed a significant increase in blood pressure and heart rate, which returned to baseline values within 4 min (Duarte et al, 1982). In our study, sloths were maintained in ventral or dorsal recumbency during the entire procedure; therefore, no postural changes occurred that could have affected blood pressure.…”

“…This discrepancy may be explained by the different medetomidine dosages used in the two studies, 0.04 mg/kg compared to 0.02 mg/kg used in our study; or to species differences between C. didactylus and C. hoffmanni. Based on the normotensive blood pressures recorded in previous studies (Duarte et al, 2003;Johansen et al, 1966), hypertension was observed initially in many sloths after KM administration, especially in B. variegates. Overall, in our study, systolic blood pressure varied significantly between species, gender, and time.…”

“…In a previous study, systolic blood pressure in unanesthetized three-toed sloths ranged from 147-230 mm Hg (Johansen et al, 1966). However, a later study reported that mean systolic/diastolic arterial blood pressure in conscious, relaxed three-toed sloths was 129/86 mm Hg (Duarte et al, 1982). The causes of result differences between these two studies are not clear, but may have been due to monitoring equipment used, or to adaptation of the subjects to captivity and testing.…”

“…Additionally, circadian rhythms may also affect physiologic parameters such as blood pressure. In one study of B. variegatus, higher blood pressures (systolic, diastolic, and mean) were recorded during the light period and were associated with feeding and movement (Duarte et al, 2003). In a different study of B. variegatus, heart rate was slower during the light period and was directly associated with a decrease in motor activity (Silva, 1996).…”