Thermoregulatory responses to intra-abdominal heating of sheep.

When electrical heat sources were implanted in the abdominal cavities of sheep and heated to dissipate 20 to 22 watts of additional endogenous heat in the animal, a rapid increase in respiratory frequency and respiratory water loss occurred 3 to 5 minutes after the initiation of heating. The response was accompanied by a marked decline of the temperature of the hypothalamus, with an increase of less than 1.0 degrees C in skin temperature over the location of the heaters in the abdomen. When the same skin area was heated externally in the absence of internal heating, no significant response was seen. The results support the concept of the existence of thermoreceptors, located in deep tissues or veins, which play a role in the regulation of body temperature.