Histological Changes in the Skin of Rana pipiens Produced by Either KCl Loading or Fasting

The present study was performed to determine if either potassium loading or fasting results in histological changes in the skin. Rana pipiens were loaded with KCl and skin biopsies obtained (Group I). These biopsies were compared with biopsies from NaCl loaded frogs (Group II). In blind studies of microscopic sections, 13 of 17 biopsies of a mixture of I and II were correctly diagnosed by one observer and similarly, 14 of 17 of Group I and II were correctly diagnosed by a second observer (P = 0.0245 and 0.0063, respectively). The characteristics used to distinguish skins from KCl treated frogs versus controls treatment included: (i) an abundance of large euchromatin cells on or near the surface; (ii) changes in the basal cell layer with elongation and rotation of the nuclei; (iii) lighter cells in the spinosal layers; and (iv) sometimes the skin became thicker. The water-soluble nondialyzable material of the frog skin was extracted, and we found that it increased by 4.4 times following KCl loading (P < 0.05). However, the protein fraction was not increased by loading the frog for 3 days with NaHCO₃. We conclude that potassium loading results in characteristic histological changes in the skin and that this is probably related to the ability of the skin to excrete potassium. In addition, a comparison of biopsies of skin from fed frogs with samples from frogs fasted for 40 to 49 days showed a change in the thickness of the skin. Skins of fed frogs averaged 57.0 ± 1.4 μ thick compared with fasted, 39.9 ± 2.7 μ (P < 0.001).