Effects of cold and immobilization stress on noradrenaline turnover in brown adipose tissue of rat.

Abstract

Noradrenaline (NA) turnover of the interscapular brown adipose tissue (BAT) was determined in order to evaluate a role of sympathetic NA of this tissue in an enhanced nonshivering thermogenesis which had been previously evidenced in the repetitively stressed rats by immobilization (daily 3-h immobilization for 4 weeks) and the coldacclimated ones (5°C, 4 weeks). The disappearance rate of NA from the BAT following blockade of NA synthesis with a-methyl p-tyrosine was adopted for estimation of NA turnover of the tissue. Cold acclimation increased both fractional turnover rate (% /h) (k) and turnover rate (ngf (g BAT . h)). Repetitive immobilization stress also elevated turnover rate, but not k. In the warm non-stressed controls acute cold exposure to -5°C and acute immobilization stress elevated the turnover rate. The effect of cold exposure was significantly greater than that of immobilization stress for both indices of NA turnover. In the cold-acclimated rats acute cold exposure increased k as well as turnover rate, but not acute immobilization stress. In the repetitively immobilized rats both acute cold exposure and acute immobilization stress elevated k and turnover rate. These results indicate that immobilization enhances sympathetic activity of thermogenic tissue, BAT. The results also suggest that the extent of sympathetic participation is not necessarily the same between the cold-acclimated and the stressed rats.

Effects of Continuous and Intermittent Cold (SART) Stress on Sympathoadrenal System Activity in Rats

“…The brown fat is a major site of cold stress-induced nonshivering thermogenesis (44 ), and increased sympathetic activity is a major factor regulating thermogenesis in this tissue (45 ). Furthermore, cold exposure increases NA turnover of brown fat (46,47). In the present study, TH activity in brown fat was elevated significantly only after 5 days of continuously cold stress, but not by SART stress.…”

Repeated Immobilization Stress Increases Uncoupling Protein 1 Expression and Activity in Wistar Rats.

“…Regulation of UCP1 thermogenic function is mediated by tonic release of NE from the sympathetic nerve terminals that innervate BAT [4]. Immobilization increases sympathetic activity in BAT, as estimated by NE turnover rate [32]. In the present study, acute immobilization increased UCP1 function irrespective of repeated immobilization exposure.…”

“…We previously demonstrated that the BAT NE turnover rate was significantly higher in repeatedly immobilized rats than in naive rats when both groups were exposed to acute immobilization [32]. Glucocorticoids possess a powerful inhibitory effect on UCP1 function by attenuating SNS activity [33][34][35] and by directly suppressing UCP1 gene expression [17,20].…”

The Browning of White Adipose Tissue: Some Burning Issues

“…A negative stress for a rodent would be to be suspended by a hindlimb (Yamashita et al, 1995) or the tail (Lew et al, 2009), immobilized (Gao et al, 2003;Harris et al, 2006;Murazumi et al, 1987), or exposed to foot shock (McGregor et al, 1994) or social defeat (Lkhagvasuren et al, 2011). In all these cases, there are indications that at least the nerves to brown fat are activated; the sympathetic nerves to white adipose tissue are also most likely activated, and browning may thus be induced.…”