Vasomotor response to thermal stimulation of the scrotal skin in rats

In 27 anesthetized rats arterial blood pressure and electrical activity of dorsal horn neurones were recorded during thermal stimulation of the scrotal skin. In 19 of these animals blood pressure increased during scrotal skin warming, showing a distinct threshold at about 37.5 degrees C in 16 rats. This effect was reproducible during the whole experiment although quantitative changes of the response occurred. In most experiments a transient response was seen at the beginning of the vasomotor reaction. The mean increase of blood pressure to a superthreshold warming step, derived from 11 experiments in which more than 3 temperatures were tested and in which the blood pressure was above 100 mm Hg, was 25 +/- 14 mm Hg. The observed threshold of the vasomotor response corresponds well with the threshold of activity increase in warm sensitive dorsal horn neurones to scrotal skin warming. It is suggested that the blood pressure reaction is mediated by scrotal skin warm receptors, which supports the notion that some organ specificity exists in thermoreceptors of the scrotal skin.