Circadian rhythms in blood pressure in free-ranging three-toed sloths (Bradypus variegatus)

Abstract

Blood pressure (BP) profiles were monitored in nine free-ranging sloths (Bradypus variegatus) by coupling one common carotid artery to a BP telemetry transmitter. Animals moved freely in an isolated and temperature-controlled room (24ºC) with 12/12-h artificial light-dark cycles and behaviors were observed during resting, eating and moving. Systolic (SBP) and diastolic (DBP) blood pressures were sampled for 1 min every 15 min for 24 h. BP rhythm over 24 h was analyzed by the cosinor method and the mesor, amplitude, acrophase and percent rhythm were calculated. A total of 764 measurements were made in the light cycle and 721 in the dark cycle. Twenty-four-hour values (mean ± SD) were obtained for SBP (121 ± 22 mmHg), DBP (86 ± 17 mmHg), mean BP (MBP, 98 ± 18 mmHg) and heart rate (73 ± 16 bpm). The SBP, DBP and MBP were significantly higher (unpaired Student t-test) during the light period (125 ± 21, 88 ± 15 and 100 ± 17 mmHg, respectively) than during the dark period (120 ± 21, 85 ± 17 and 97 ± 17 mmHg, respectively) and the acrophase occurred between 16:00 and 17:45 h. This circadian variation is similar to that observed in cats, dogs and marmosets. The BP decreased during "behavioral sleep" (MBP down from 110 ± 19 to 90 ± 19 mmHg at 21:00 to 8:00 h). Both feeding and moving induced an increase in MBP (96 ± 17 to 119 ± 17 mmHg at 17:00 h and 97 ± 19 to 105 ± 12 mmHg at 15:00 h, respectively). The results show that conscious sloths present biphasic circadian fluctuations in BP levels, which are higher during the light period and are mainly synchronized with feeding.

Observation of brown-throated three-toed sloths: mating behaviour and the simultaneous nurturing of two young

“…This species is distributed in many subtropical and tropical countries in South and Central America (Wetzel 1985). B. variegatus can be active both during hours of daylight and nocturnally (Sunquist and Montgomery 1973;Duarte et al 2003Duarte et al , 2004. However, there is a circadian rhythm in the blood pressure of this species suggesting it is more active during the light period (Duarte et al 2003).…”

“…However, there is a circadian rhythm in the blood pressure of this species suggesting it is more active during the light period (Duarte et al 2003). In general, it dedicates 91% of its time to resting, 7% to feeding and 2% undertaking locomotion (Duarte et al 2003).…”

“…B. variegatus can be active both during hours of daylight and nocturnally (Sunquist and Montgomery 1973;Duarte et al 2003Duarte et al , 2004. However, there is a circadian rhythm in the blood pressure of this species suggesting it is more active during the light period (Duarte et al 2003). In general, it dedicates 91% of its time to resting, 7% to feeding and 2% undertaking locomotion (Duarte et al 2003).…”

Plastic oscillators and fixed rhythms: Changes in the phase of clock-gene rhythms in the PVN are not reflected in the phase of the melatonin rhythm of grass rats

“…Since PER 1 and 2 appear to have redundant roles in circadian regulation (for example see (Maywood et al, 2014), these results serve to extend previous observations of phase differences in extra-SCN oscillators between grass rats and nocturnal rodents (Ramanathan et al, 2010b) to a hypothalamic nucleus with connections to autonomic neurons (Swanson and Kuypers, 1980, Swanson and Sawchenko, 1980, Swanson et al, 1980,Teclemariam-Mesbah et al, 1999) and to pre-autonomic brain sites (Stern, 2001, Kalsbeek et al, 2011). Species differences in the phase of the PVN oscillator may be responsible for the divergent phases of diurnal and nocturnal mammalian species with respect to rhythms that are controlled by autonomic outputs (Scheer et al, 1999, Scheer et al, 2001, Duarte et al, 2003, Scheer et al, 2003) Thus, these observations support the hypothesis that the emergence of a diurnal profile in mammals depends, at least in part, upon a reversal of the phase of extra-SCN oscillators from that typical of nocturnal species with respect to the phase of the oscillator of the SCN (Ramanathan et al, 2010a, Ramanathan et al, 2010b) and the light-dark cycle.…”

Circadian Variations in Blood Pressure, Heart Rate, and HR-BP Cross-Correlation Coefficient during Progression of Diabetes Mellitus in Rat

“…The diurnal variation in blood pressure rhythm has been demonstrated in man [1–3] and various mammalian species [4–6]. Some variations in the circadian blood pressure patterns have been attributed to endocrine influences [7, 8] while others are thought to be of neural origin [9]. Blood pressure and heart rate are thought to vary in different ways, with diurnal changes in weather, time of day, and temperature.…”