Morphogenic Effect of Exogenous Glucocorticoid Hormones in the Girardia tigrina Planarian ( Turbellaria , Tricladida ).

We have studied the effect of two glucocorticoid hormones: hydrocortisone and its synthetic analogue methylprednisolone on the regeneration activity of head and tail blastema of the Girardia tigrina planarian. The regeneration activity was studied in head and tail blastema formed after resection by means of lifetime computer morphometry and immunohistochemical labeling of neoblasts. The search for orthologous proteins-glucocorticoid receptors (hydrocortisone) was performed using the SmedGD database of the Schmidtea mediterranea planarian. The results indicate that both hormones influence the recovery rate of the regenerating head and tail blastema. The worms with regenerating tail blastema have less sensitivity to the hormones' treatment compared to the ones with regenerating head blastema. Hydrocortisone at a high concentration (10 -3 M) suppressed the regeneration rate, while stimulating it at lower concentrations (10 -4 -10 -6 M). The same concentrations of methylprednisolone inhibited the regeneration of head blastema, but did not affect the tail blastema regeneration. The two hormones acted differently: while hydrocortisone stimulated the proliferation of neoblasts in the periwound region, methylprednisolone reduced the mitotic activity, mainly on the tail zone furthest from the wound surface. We suggest that exogenous glucocorticoids can influence endogenous mechanisms of hormone-dependent regeneration.