Effects of TRH and TRH-like peptide pGLU-HIS-GLY-NH(2) on adrenocortical cell proliferation in rats.

The effects of three peptides-colon mitosis inhibitor (CMI), its amide, and thyroliberin (TRH)-on the adrenocortical cell proliferation were studied. As an index of cell proliferation, the incorporation of bromodeoxyuridine (BrDU) into adrenocortical cell nuclei was used. It was found that: Twelve hours after the injection, only CMI-amide significantly increased the total number of BrDU-immunopositive cell nuclei per equatorial section of the adrenal cortex. This mitogenic effect was observed separately for the entire section, zona glomerulosa, and zona fasciculata. TRH stimulated the cell proliferation of the adrenal cortex 24 h after the injection. Its mitogenic effect was observed for entire section and zona glomerulosa. These findings suggest that these two related peptides, TRH and CMI-amide, should be considered as growth factors for the adrenal cortex.