Interleukin-1 beta, but not IL-1 alpha, stimulates cell proliferation in the adrenal cortex.

Endocrine and immune systems are closely interconnected, so the effect of interleukin-1 on adrenal cortex proliferation in vivo was investigated. Interleukin-1 alpha (IL-1 alpha) and IL-1 beta (0.1, 1 and 10 micrograms/kg) were given twice daily alone or in combination with interleukin-1 receptor-antibody (IL-1rAb) to adult male Wistar rats. The cell proliferation ratio was measured by 5-bromo-2'-deoxyuridine (BrdU) incorporation. BrdU-positive cells were counted in entire equatorial sections of the gland, and, in addition, separately for each adrenocortical zone. IL-1 beta (1 and 10 micrograms/kg) enhanced cell growth in the adrenal cortex. This was due to the stimulation of cell proliferation in the zona glomerulosa and fasciculata. IL-1rAb exerted an opposite effect, and reversed the stimulatory influence of IL-1 beta. IL-1 alpha did not evoke any significant changes in the proliferation ratio of the adrenocortical cells. The results indicate a close interconnection between the immune and endocrine systems with IL-1 beta providing a growth-promoting stimulus to adrenocortical cells.