In an earlier communication1 it was pointed out that, in the cat, after inducing secretory activity in the thyroid gland, either by stimulation of the cervical sympathetic nerves or by injection of small doses of epinephrin, there can be demonstrated an increased effectiveness of epinephin as a pressor agent. In other words, thyroid secretion renders more excitable those sympathetic structures acted on by epinephrin in raising arterial pressure. It was further shown that this effect is manifest only after a latent period, which may vary from about forty to sixty minutes, and that it is of considerable duration, having been observed for as long as seven hours.
A number of investigators, notably Asher and von Rodt,2 Ossokin3 and Oswald4 maintain that thyroid secretion increases the responsiveness of vagus terminations to electrical stimulation. If this be true, thyroid secretion must be regarded as having a sensitizing effect on both true sympathetic