Further evidence that BAT thermogenesis modulates cardiac rate in infant rats

Abstract

Previous research in infant rats suggested that brown adipose tissue (BAT), by providing warm blood to the heart during moderate cold exposure, protects cardiac rate. This protective role for BAT thermogenesis was examined further in the present study. In experiment 1, 1-wk-old rats in a warm environment were pretreated with saline or chlorisondamine (a ganglionic blocker), and then BAT thermogenesis was stimulated by injection with the β3-agonist CL-316243. In experiment 2, pups were pretreated with chlorisondamine and injected with CL-316243, and after BAT thermogenesis was stimulated the interscapular region of the pups was cooled externally with a thermode. In both experiments, cardiac rate, oxygen consumption, and physiological temperatures were monitored. Activation of BAT thermogenesis substantially increased cardiac rate in saline- and chlorisondamine-treated pups, and focal cooling of the interscapular region was sufficient to lower cardiac rate. The results of these studies support the hypothesis that BAT thermogenesis contributes directly to the modulation of cardiac rate.

Effect of prenatal cocaine on early postnatal thermoregulation and ultrasonic vocalization production

“…Although BAT is located throughout the body, the large interscapular depot of BAT, which is responsible for the delivery of warm blood to the heart and the consequent modulation of cardiac rate (Blumberg et al, 1997; Sokoloff et al, 1998), is of particular importance, as the heart acts as a pumping mechanism to distribute the heat generated by BAT throughout the body via the circulatory system. Our lack of group differences in T IS−Back (our measure of BAT thermogenesis) fit with the lack of effect on cardiac rate or R-R Intervals shown here.…”

“…Isolated rat pups produce heat primarily through brown adipose tissue (BAT) thermogenesis (Smith, 1964; Alberts, 1978), supported by modulation of cardiorespiratory responses (Blumberg et al, 1997). Brown adipose tissue thermogenesis is immediately apparent at birth in rats (Blumberg et al, 1997; Sokoloff et al, 1998), and its disruption may play a role in the development of obesity and diabetes (Cinti, 2006, 2005; Cypess et al, 2009). …”

“…Prenatal cocaine likely alters thermally induced vocalizations through its impact on central serotonin (Ray et al, 2011) and norepinephrine (Madden et al, 2013), metabolism and cardiac rate (Blumberg et al, 1997; Sokoloff et al, 1998), and the developing stress response systems (Yee et al, 2011); all of which independently alter thermoregulation and vocalizations. Additionally, maternal cocaine use has been strongly associated with malnourishment of the mother and fetus, as well as placental vasoconstriction, which further complicates nourishment delivery to the fetus, potentially altering long-term adipose tissue volume and function (Mostyn and Symonds, 2009).…”

Thermoregulatory and Cardiac Responses of Infant Spontaneously Hypertensive and Wistar-Kyoto Rats to Cold Exposure

“…[7][8][9] Specifically, heat produced by brown adipose tissue (BAT) during moderate cold exposure helps to warm cardiac muscle and by doing so contributes to the maintenance of cardiac rate. In contrast, pronounced bradycardia is produced by either extreme air temperatures that overwhelm the ability of BAT to deliver warm blood to cardiac muscle or ganglionic blockade that prevents the activation of BAT thermogenesis in response to the cold.…”

“…The ECG analog signal was digitized at a rate of 1000 samples per second, and interbeat intervals (IBI) were determined continuously online with a customized software program with a peak threshold detector (this method provides results identical to direct measurement of intervals between successive R waves). 9 IBI data were acquired by the computer at a rate of 30 samples per minute.…”