Leucine-enkephalin and methionine-enkephalin produce opposing effects on plasma corticosterone levels in ether-stressed mice.

The inhibitory effects of intracerebroventricular administration of saline on the plasma corticosterone response to ether stress in mice was reduced by Met-enkephalin and enhanced by Leu-enkephalin. When administered simultaneously the effects of the two peptides opposed each other. Met and Leu-enkephalin may subserve different physiological functions in the response of the hypothalamus-pituitary-adrenal system to stress.