Pituitary, adrenal and thyroid influences on osmoregulation in the euryhaline elasmobranch, dasyatis sabina

Abstract

1. Experiments were undertaken to examine the role of various endocrine glands in regulating plasma solute concentrations in the euryhaline elasmobranch, Dasyatis sabina, exposed to various environmental dilutions. 2. Hypophysectomy (with the exception of the ventral lobe of the proximal pars distalis) resulted in a depression of plasma osmolarity; this reduction was due primarily to lowered urea levels. 3. Removal of the rostral lobe of the pars distalis in Dasyatis caused a significant increase in plasma osmolarity, urea and sodium concentrations. Treatment of rostral lobectomized stingrays with mammalian prolactin reversed the effects of this operation, reducing blood urea and sodium levels. Pituitary prolactin activity (measured using the Gillichthys xanthophore assay) increased approximately 100-fold within 24 hr after stingrays were transferred from sea water to 33% sea water, lending further support to the hypothesis that a prolactin-like hormone functions in osmoregulation. 4. Mammalian ACTH had no apparent effect on plasma solute levels in rostral lobectomized animals. ACTH did, however, reverse the effects of prolactin in rostral lobectomized animals when these hormones were given simultaneously. 5. Plasma osmolarity was significantly reduced by interrenalectomy. 6. Thyroidectomy resulted in an elevation of plasma urea levels; replacement therapy with thyroxine reversed the effects of thyroidectomy. 7. These data indicate that pituitary (particularly a prolactin-like hormone), interrenal and thyroid hormones are involved in the osmotic adaptation of this euryhaline elasmobranch to dilute environments.