Measurement of heat production in dog submandibular gland

In dog submandibular glands, we measured changes in metabolic heat production during a secretory period which was induced by electrical stimulation of the chorda tympani. When measured with fine thermocouples, the temperature of both the gland itself and venous blood from the gland increased by 0.1-0.7 degrees C at the maximum. The blood flow was about 0.3 g.min-1.g-1 wet weight of gland at a resting period and increased to 1-3 g.min-1.g-1 at the maximum of secretory response. The resting heat production in vitro, measured by a microcalorimeter, was 3.3 mW.g-1 at 27 degrees C and 7.8 mW-g-1 at 37 degrees C. The specific heat of the blood and the salivary gland, measured by a microcalorimeter, were 3.97 and 3.91 J.g-1, degrees C-1, respectively. The change in conductive heat loss, measured by a thermopile under stimulated conditions, ranged from 4 to 6 mW.g-1 at the maximum. Metabolic heat production during secretion in vivo (37 degrees C) was estimated from temperature changes in the glandular tissue and blood, blood flow, specific heat and resting heat production. Values obtained were in the range from 15 to 80 mW.g-1 at the maximum. Heat production increased rapidly within the first 20 sec to reach a maximum and then declined with time, but slow heat production continued. On the basis of the present results together with those from former studies on ionic transport in the salivary gland, we discussed the relation of heat production to transport of substances during secretory processes.