Thymic extracts and lymphokine-containing supernatant fluids stimulate the pituitary-adrenal axis, but not cerebral catecholamine or indoleamine metabolism.

Injection of thymosin fraction 5 (TF5) or the supernatant fluid from concanavalin A-stimulated rat spleen cells into mice significantly increased plasma concentrations of corticosterone at 1 or 3 h. However, measurement of the concentrations of the catecholamines, norepinephrine and dopamine, the indoleamine, serotonin, and their major metabolites, in prefrontal cortex, parietal cortex, nucleus accumbens, septum, caudate-putamen, hypothalamus, and brain stem did not indicate any statistically significant changes. Nor was there any alteration in splenic norepinephrine content. These data suggest that TF5 and lymphokines do not cause a generalized stress response, but rather a selective activation of the pituitary-adrenal axis, probably by causing release of adrenocorticophic hormone from the pituitary. There was no evidence that the corticotropin-releasing activity of TF5 was related to an effect on hypothalamic biogenic amines. These data are discussed in the light of previous results obtained with lymphokine-containing supernatant fluids.