Studies on the carbohydrate metabolism of sheep. XIV. The adrenal response to psychological stress

The effect of change in environment on plasma cortisol and blood glucose levels in sheep has been studied in the following situations: movement from grazing paddock to small enclosed yards, movement from grazing paddock to indoor animal quarters, and short periods of transport. Consistent large increases in plasma cortisol values were recorded in previously grazing animals, but the degree of elevation during road transport was usually less in "trained" animals housed indoors. Previous undernourishment or fasting increased the changes in plasma cortisol level in response to stress. Individual variation in plasma cortisol response between animals was considerable. Pronounced, but variable, increases in blood glucose occurred in all experiments except those in which exercise (walking) was associated with the brief stressful situation created by moving animals from the paddock into an enclosed yard. It is concluded that movement to an unfamiliar environment is an emotionally stressful situation, but that there are important differences in the quantitative adrenal cortical response between the grazing animal and experimental animals housed indoors and already subjected to a series of novel environmental changes. It is further suggested that exercise during a short period of stress may modify or prevent the normal hyperglycaemic response to adrenaline release. These experiments provide further support for the conclusion that the elevated plasma cortisol levels observed in the "stress syndrome" of pregnancy toxaemia are primarily a response to physical or emotional stress, rather than to the nutritional stress of fasting or severe undernutrition.