Impact of centrally applied biogenic amines upon the energy balance of fowl.
The impact of intraventricular injections of 100 microng of the biogenic amines, norepinephrine or dopamine, upon the energy balance of white leghorn hens Gallus domesticus was examined. Both drugs reduce metabolic heat production (about 35% at 9 and 20 degrees C, and about 15% at 35 degrees C) by inhibiting shivering or by reducing activity or both. Also the drugs inhibit the opposing thermal response, evaporative heat loss (about 3% at 9 and 20 degrees C, and about 20% at 35 degrees C) by reducing respiration rate. The relative balance of inhibiting these opposing responses by the drugs results in hypothermia at 9 and 20 degrees C, and hyperthermia or no change in body temperature at 35 degrees C. Both drugs usually caused an initial vasodilation of the feet and comb at all temperatures tested but did not persist long enough to have much of an impact on body temperature. It was concluded that differing ambient temperatures do not alter the action of the biogenic amines upon the modes of physical thermoregulation in chickens even though the direction of body temperature change is reversed at different ambient temperatures.