Response of the Infantile Rat to Stress

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Abstract
The adrenal gland of the neonatal rat is responsive to stress. Three-min. exposure at 2 days of age to either heat or electric shock caused a significant increase in plasma corticosterone from a resting level of approximately 11 to 27 [mu]g/100 ml following heat stress and to 16 [mu]g/100 ml following shock. In the 9-day-old rat the corticosterone levels rose from a normal of approximately 6 to 14 [mu]g/100 ml following heat and to 13 [mu]g/100 ml following shock. The time required for maximum response was 30 min. in the 2-day-old and 60 min. in the 9-day-old rat. Corticosterone levels in the adrenal gland increased in the 9-day-old following either heat or electric shock; however, in the 2-day-old rat only heat was adequate to induce a significant increase in the concentration of corticosterone in the adrenal gland. The increased adrenal response was obtained, when present, in 5 min. in both the 2-day-old and the 9-day-old rat.