Effect of interleukin-1a, IL-1b and IL-1 receptor antibody on the proliferation and steroidogenesis of regenerating rat adrenal cortex

Several data suggest that the endocrine and immune systems are closely interconnected, therefore, we investigated the effect of interleukin-l on adrenocortical regeneration. The study was performed on adult rats subjected to left adrenal enucleation combined with contralateral adrenalectomy. The animals were given purified human recombinant IL-1alpha (5 mu g/kg), IL-1beta (5 mu g/kg) anti-human IL-1 receptor antibody (10 mu g/kg) and combination of interleukins and antibodies. The cell proliferation measured by bromodeoxyuridine incorporation and plasma corticosterone determined by a RIA kit were evaluated six days after operation. The mean cell growth ratio expressed as number of BrdU-positive cells per 1,000 cells was 11.86 +/- 0.45 in the control group. IL-lb significantly stimulated the proliferation ratio (15.30 +/- 0.88; p < 0.01) and this effect could be prevented by addition of IL-1rAb. The antibody caused also a well-marked inhibition of cell growth ratio (8.23 +/- 0.67; p < 0.01). The plasma corticosterone concentration was higher in IL-lb-treated animals than in the control group, 107.79 +/- 2.82 vs. 61.08 +/- 2.0 ng/ml, respectively, p < 0.01. On the other hand, IL-1rAb decreased corticosterone secretion (31.53 +/- 2.58 ng/ml, p < 0.01) and reversed the stimulatory effect of of IL-lb. In contrast, IL-la seemed to have no influence on adrenocortical regeneration. In conclusion, this study supported the thesis of close interconnection between immune and endocrine systems and revealed that IL-lb could act as a growth-promoting factor on regenerating adrenal cortex in the rat.