Control of Cardiorespiration during Shivering Thermogenesis in the Pigeon

Abstract

Shivering thermogenesis is the most important source of extra heat production in resting birds to maintain deep body temperature at a constant level under cold conditions. The main heat by shivering is produced by the large breast muscle whose mass amounts to 15–25% of avian’s body weight. The frequency of electrical activity recorded in the pectoral muscle is about 200 Hz and seems to be independent of the intensity of tremor (Hohtola 1982). The cold tremor in pigeons is obviously due to contractions of white, fast-twitch glycolytic muscle fiber types (George, 1984). Hohtola (1982) had previously demonstrated a close correlation between the integrated EMG during shivering and the oxygen consumption in pigeons. No increase of blood lactate acid was found during violent shivering which resulted in up to five times of basic metabolism in birds and mammals (cf. Bligh, 1983). In contrast to severe physical work no oxygen debt has been observed during shivering. The increase of oxygen consumption with increasing intensity of cold tremor refers to a precise cooperation between temperature regulation and the cardiorespiratory system. How this interaction of the autonomic feedback control systems may function, shall be described in this paper.