Effects of rate of blood flow on fractional extraction and on uptake of infused noradrenaline by brown adipose tissue in vivo

Abstract

The rate of blood flow (Q) to interscapular brown adipose tissue (IBAT) and the arteriovenous difference in plasma noradrenaline (NA) across the tissue were measured in warm-acclimated (WA) or cold-acclimated (CA) rats during infusion of NA at doses of 1-12.5 ng min-1 g-0.74 (approximately 0.2-2.7 micrograms min-1 kg-1) and in the period of steady calorigenic response associated with steady concentration of NA in arterial plasma (ANA). ANA was linearly related to the dose of NA. Calorigenic response, percentage of cardiac output to IBAT, and Q per gram of IBAT were sigmoid functions of ANA and at their maxima were about 2.5 times greater in CA than in WA rats. The rate of uptake of NA by IBAT increased with ANA and Q, each of which had a major influence on rate, but the coefficient of extraction of NA by the tissue (ENAIBAT) declined. Measurements in rats given a dose of propranolol that partially inhibited the NA-induced increase in Q to IBAT indicated that the decline in ENAIBAT was attributable primarily to the increase in Q rather than to increasing saturation of uptake mechanisms. Diffusion-limited extraction of NA is the probable basis for the effect of Q on ENAIBAT. Possible implications of flow-dependent extraction of NA in studies involving measurements of the uptake of exogenous NA by tissues or organs are discussed.

Role of Adrenal Medulla in Morphine‐induced Hyperthermia Through Central Action

“…Morphine has been shown previously to increase catecholamine release from the adrenal medulla (Gunne, 1963;Anderson & Slotkin, 1975). These hormones have a non-shivering thermogenic function (Banet, Hensel & Liebermann, 1978) which is probably mediated by action on brown adipose tissue in the rat (Foster, Depocas & Frydman, 1980). Adrenal denervation also blocked the morphine-induced hyperthermia in the present study.…”

Uptake and Turnover Rate of Norepinephrine in Interscapular Brown Adipose Tissue of the Young Rat

“…The intensity of norepinephrine uptake by a tissue such as ISBAT is under several pa rameters among which are the concentration of the labelled transmitter in the blood, the blood flow through the tissue, the density of its sympathetic innervation, and the effi ciency of the transport system [7,9,30]. The concentration of radioactivity in the blood is taken into account in the first experiment, but this concentration does not seem to be involved in the effects of hypothyroidism, as we found nearly the same differences be tween the two experimental groups in both types of experiment.…”

“…In this respect, Foster et al [9] showed directly that the extraction of norepinephrine from the blood by the ISBAT changes according to the blood flow. The dose of labelled norepinephrine we injected into our animals, though very low (approximately 1.6 ng/'g body weight), could even modify by itself the blood flow through the tissue and its own uptake.…”

Enhanced Nonshivering Thermogenic Activity of the Heat‐Tolerant FOK Rata

“…However, if this is the case, it is surprising that the thermogenic indices in BAT are not larger in FOK as compared to other groups, because BAT is the major site of NST. In this context, it seems to be worth noting that the rate of blood flow through BAT is an important factor in the thermogenic activity of BAT 8 . Therefore, it is likely that the marked response to NA in the blood flow through BAT compensates for the small size and low in vitro thermogenic activity of BAT and contributes to the enhancement of NST, causing the high capacity of cold tolerance in the FOK rat.…”