Activation of autonomic nervous system during exposure of rats to restraint and water immersion stress. I. Activating pattern of autonomic nervous system.

Abstract

We studied the activity of one division of the autonomic nervous system, independently of the other, under restraint and water (25°) immersion. For such evaluation, heart rate, gastric motility and catecholamine content of tissues or urine were measured in rats of which the autonomic nervous activity was reduced by adrenal medullectomy (AMX), guanethidine (GNT), atropine (ATR), or their combinations. Heart rate in the controls was increased after restraint or immediately after water immersion and this change was blocked by AMX plus GNT. ATR accelerated the heart rate, but did not affect the extent of the stress-induced increase in the heart rate. With an increase in the duration of water immersion, a decrease in heart rate occurred closely linked with hypothermia in all animal groups, suggesting that heart rate was influenced by hypothermia more prominently than by the autonomic nervous controls. AMX plus GNT significantly shortened the occurrence time of increased gastric motility which was observed after water immersion, while ATR completely inhibited an increase in gastric motility. The determination of catecholamine content showed a stress-induced activation of sympatho-adrenal function and its blockade by the treatment with AMX plus GNT. It is finally suggested that the stress procedures used here may immediately enhance the sympatho-adrenal activity lasting for at least 3 hr and steadily raise the vagal activity reaching the plateau 2 hr later.