The study shows that thymosin‑alpha‑1, a peptide from the thymus, can boost the release of the stress hormone corticosterone from rat adrenal cells, but only when another hormone (ACTH) is present. It doesn’t raise hormone levels on its own, suggesting it works together with the body’s own stress signals.

Products derived from the activated immune system have been reported to modulate neuroendocrine function. In addition, a direct connection between neuroendocrine and immune responses to stress has recently been proposed. We now provide evidence that heterogeneous lymphokine-containing supernatants from mitogen-stimulated rat spleen cells can stimulate both basal and corticotropin-induced corticosterone secretion from rat adrenal cells in an in vitro perifusion system. Moreover, thymosin alpha 1, a 28-amino acid residue peptide found both in thymus and lymphocyte-derived supernatants was also able to synergistically stimulate corticotropin-stimulated corticosterone release, without affecting basal corticosterone output in this same in vitro adrenal cell perifusion system. These results reinforce the suggestion about the existence of bidirectional interactions between the immune and neuroendocrine systems. They also indicate that this communication may occur directly at the adrenal gland level, a major effector site of the body's response to stress.