EFFECTS OF PROLACTIN AND CORTISOL ON THE HARDERIAN-GLAND OF THE TERRAPIN, PSEUDEMYS-SCRIPTA, ADAPTED TO DIFFERENT SALINITIES

Background: The Harderian gland (HG) of the terrapin, Pseudemys script a, plays a prominent role in osmoregulation owing to the presence of ' 'salt secreting cells'' among the acinar cells of its glandular epithe lium. Osmotic stress provokes different responses according to salinit y, Seawater adaptation activates a major structural reorganization. Th e most striking change is shown by the type I glandular cells and ''sa lt secreting cells.'' The latter increase in number and change from a unicellular form to multicellular complexes. Methods: Terrapins were d ivided into eight groups for two experiments, For both experiments, on e group was maintained in freshwater, whereas three groups were raised in seawater, For the first experiment, each group was administered wi th 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 c ontrol for both experiments. Results: Following prolactin treatment de generative phenomena occurred in the salt cells of seawater-adapted HG , whereas inhibition of salt cell maturation was observed in freshwate r-adapted HG, Although cortisol clearly maintained the number of the s alt cells in seawater-adapted terrapin HG, it stimulated the salt cell s in freshwater adapted terrapins, Conclusions: These data strongly su pport the hypothesis that osmoregulatory activity of the Harderian gla nd of Pseudemys scripta is under hormonal factors which seem to interp lay in reply to osmotic stresses. (C) 1996 Wiley-Liss, Inc.