Abstract
1. The effects, on the systemic and pulmonary circulation, of localized heating of the anterior hypothalamus, at different environmental temperatures, have been studied in the unanaesthetized ox.2. In a cool environment (15 degrees C), heating the hypothalamus elicited panting which was associated with increases in cardiac output, heart rate, pulmonary arterial pressure and central blood volume, and decreases in systemic total peripheral resistance, and the percentage of red cells in mixed venous blood.3. In a hot environment (40 degrees C), the cardiovascular responses were of smaller magnitude than in the cool environment. It was suggested that the smaller responses in the hot environment were probably related to a higher level of blood flow through the skin before the hypothalamus was heated.4. The cardiovascular responses to localized heating of the anterior hypothalamus were similar to those which occur during hyperthermia. However, there were also differences between the effects of the two procedures and it was concluded that hyperthermia involves the stimulation of other receptors in addition to those in the anterior hypothalamus.