Catecholamines and cold thermogenesis in sheep

Abstract

Experiments were performed to assess the role of catecholamines in cold thermogenesis in warm- and cold-acclimated adult sheep. Urinary excretion of both noradrenaline and adrenaline increased in sheep exposed to cold. Propranolol (1 mg/kg) reduced cold thermogenesis in warm- and cold-acclimated sheep by 8% and 12% respectively. Noradrenaline and adrenaline infusions at 1 μg/kg min for 30 min had no significant effect on the rate of heat production of warm- or cold-acclimated sheep. Phenoxybenzamine (3.0 mg/kg) almost abolished cold thermogenesis in warm-acclimated sheep. Cold-acclimated animals treated with phenoxybenzamine were able to maintain homeothermy during severe cold stress. These findings support previous reports which suggest that catecholamines are involved in metabolic cold acclimation in the sheep, but indicate clearly that they have no direct thermogenic effect in cold-acclimated adults of this species.

Insulin secretion in sheep exposed to cold.

“…Since Leduc (1961) reported that cold exposure increased the urinary excretion of catecholamines in rats, this observation has been confirmed by numerous other workers. The increased excretion of catecholamines reported herein confirms the results reported in rats (LeBlanc & Nadeau, 1961; Leduc, 1961;Motelica, 1969;Shum, Johnson & Flattery, 1969;Smith & Dugal, 1964), in man (Arnett & Watts, 1960;Suzuki, Tonoue, Matsuzaki & Yamamoto, 1967), in sheep (Webster, Heitman, Hays & Olynyk, 1969) and in cattle (Alvarez & Johnson, 1970). There was also an increase in heart rate in the sheep exposed to cold.…”

Metabolic responses of the whole body, portal-drained viscera and hind quarter to acute cold exposure and feeding in sheep: Effects of nonselective and selective β-adrenoceptor blockade

“…The significant increase in whole-body oxygen consumption in response to cold is consistent with previous observations reported in the literature (Thompson et al 1975;Webster et al 1969). These authors showed that cold exposure caused at least a two-fold increase in metabolic activity, a change comparable with the response observed in the present study.…”

“…These authors showed that cold exposure caused at least a two-fold increase in metabolic activity, a change comparable with the response observed in the present study. In the present study, propranolol slightly, but not significantly, blocked the cold-induced increase in oxygen consumption, whereas in the study of Webster et al (1969), propranolol caused a significant decrease in heat production of sheep exposed to a severe cold stress (-30°C). The lack of significant change in response to the nonselective blocker in the present study could be explained in part by the less severe conditions used, i.e.…”

“…A portion of the increased metabolic activity in the cold could involve β-adrenoceptor processes (Webster 1969). Infusion of catecholamines (adrenaline and noradrenaline) and cold exposure cause an increase in heat production in sheep (Graham and Christopherson 1981).…”

“…Thus, there is not complete agreement in the literature with respect to the role of β-adrenoceptors in regulating the heat production response to feeding. An elevation in thermogenesis occurs in response to adrenaline and noradrenaline (Graham and Christopherson 1981;Miaron and Christopherson 1997) and may be blocked by β-adrenoceptor antagonists (Webster et al 1969;Miaron and Christopherson 1997) and, hence, constitutes a basis for β-adrenoceptor modulation of the energy requirement in sheep. A decrease in whole blood amino acid concentration has been reported during fasting (Ericksson et al 1988) and lower plasma levels are associated with trauma-and cold-related stressors (Souba and Dauglas 1983);Kelly 1987).…”