Background: The Harderian gland (HG) of the terrapin, Pseudemys scripta, plays a prominent role in osmoregulation owing to the presence of "salt secreting cells" among the acinar cells of its glandular epithelium. Osmotic stress provokes different responses according to salinity. Seawater adaptation activates a major structural reorganization. The most striking change is shown by the type I glandular cells and "salt secreting cells." The latter increase in number and change from a unicellular form to multicellular complexes.
Methods: Terrapins were divided into eight groups for two experiments. For both experiments, one group was maintained in freshwater, whereas three groups were raised in seawater. For the first experiment, each group was administered with various doses of ovine prolactin on alternate days for 2 weeks. For the second experiment, each group received various doses of cortisol on alternate days for 2 weeks. In addition three freshwater and three seawater adapted terrapins, injected only with vehicle, were used as control for both experiments.
Results: Following prolactin treatment degenerative phenomena occurred in the salt cells of seawater-adapted HG, whereas inhibition of salt cell maturation was observed in freshwater-adapted HG. Although cortisol clearly maintained the number of the salt cells in seawater-adapted terrapin HG, it stimulated the salt cells in freshwater adapted terrapins.
Conclusions: These data strongly support the hypothesis that osmoregulatory activity of the Harderian gland of Pseudemys scripta is under hormonal factors which seem to interplay in reply to osmotic stresses.