Effects of in vitro immunosuppression of interleukin-6 on the proliferation of rat hypophyseal cells

Interleukins -ILs- are proteins involved in the immune system and have been related to the endocrine regulation of the hypothalamic-hypophyseal-adrenal axis as well as to the secretion of ACTH, prolactin, GH and, possibly, LH. IL synthesis has been reported in the hypophysis and the action of these compounds is therefore believed to occur through paracrine mechanisms. IL-6 has been implicated as a regulatory factor involved in pituitary cellular proliferation. However it is not determined whether the IL-6 proliferative effects are paracrine effects. The aim of the present work was to address these questions. Accordingly, we performed an in vitro study on rat hypophyseal cells, neutralising the possible paracrine effect of IL-6 by immunosuppressing the protein by treatment with diluted (1:10) polyclonal antibody against IL-6 -Ab-IL-6- over 1, 3, 6 12 or 24 hours and later determining the degree of proliferation, determining the PCNA. In the control dishes, the percentages of PCNA-immunoreactive cells ranged from 43% to 50%, with no significant differences in the different time periods assayed. Immunosuppression of IL-6 induced significant decreases in the percentages of PCNA-immunoreactive cells (p<0.01 after 3, 6 and 12 hours). The results of the present study suggest a dual role for IL-6 in the modulation of hypophyseal cells; i.e., stimulating proliferation and inhibiting cellular apoptosis in the rat hypophysis.