Activation of autonomic nervous system during exposure of rats to restraint and water immersion stress. II. Comparison with restraint stress.

To determine whether initial sympatho-adrenal stimulation during stress was responsible for inducing a parasympathetic stimulation, the autonomic nervous activities were estimated in rats subjected to either restraint stress or restraint and water immersion stress. The parasympathetic and sympatho-adrenal activities were estimated functionally by measuring responses of gastric motility and heart rate, and also chemically by measuring catecholamine content in urine and tissues such as the heart and adrenals. Restraint and water immersion produced a definite parasympathetic predominance in contrast to the case of restraint alone. But both kinds of stress developed an increase in the sympatho-adrenal activity, and the extent of their increase was almost the same when evaluated on the basis of urinary catecholamine content. These findings indicate that initial sympatho-adrenal stimulation is not directly associated with parasympathetic stimulation. A marked fall in body temperature during stress was assumed to participate somewhere in the induction of parasympathetic stimulation.