Hypothalamic temperature and osmoregulation in the Pekin duck

Abstract

The temperature of the anterior and middle hypothalamus of conscious Pekin ducks was altered with chronically implanted thermodes. Both urine formation and salt secretion by the supraorbital glands were influenced by hypothalamic cooling. When osmotic diuresis was induced by continuous intravenous infusion of 1.2 ml·min⁻¹ of 293 mosm·kg⁻¹ mannitol in H₂O solution, hypothalamic cooling increased urine flow rate at reduced urine osmolality and unchanged osmolal excretion rate. The degree of this cold induced diuresis increased with cooling intensity. Additional ADH administration by continuous infusion at a supramaximal dose abolished the diuretic effect of hypothalamic cooling. When water diuresis was induced by intragastric continuous infusion of 1.2 ml·min⁻¹ of distilled water, hypothalamic cooling enhanced the diuresis, but hypothalamic warming had equivocal effects. The diuretic effects of hypothalamic cooling suggest an inhibition of endogeneous ADH release by lowering hypothalamic temperature. When the salt glands of salt adapted ducks were stimulated by continuous intravenous infusion of 0.2 ml·min⁻¹ of 800 mosm·kg⁻¹ NaCl in H₂O solution, hypothalamic cooling reduced the salt gland secretion rate to an extent depending on cooling intensity. It is concluded that the activities of those integrative and/or efferent hypothalamic neurons, which mediate the hormonal control of renal water absorption and the nervous control of salt secretion by the supraorbital gland, depend on their own temperature.