AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 3 651-R657, Copyright © 1995 by American Physiological Society
Water intake and activity of hypothalamoneurohypophysial system during osmotic and sodium stimulation in rats
M. Kadekaro, J. Harris, S. Freeman, M. L. Terrell, E. Koehler and J. Y. Summy-Long
Division of Neurosurgery, University of Texas Medical Branch, Galveston 77555.
Intrajugular infusion (200 microliters/min for 10 min) of 0.85 M NaCl or
1.7 M mannitol in conscious adult male Sprague-Dawley rats increased plasma
osmolality similarly and had an additive effect when combined. Plasma Na+
concentration, however, increased with infusion of 0.85 M NaCl, decreased
with 1.7 M mannitol, and was not significantly altered by the combined
solution. Irrespective of changes in plasma Na+ concentration, plasma
vasopressin and oxytocin concentrations were elevated to a similar degree
after independent infusion of 0.85 M NaCl or 1.7 M mannitol. With the
combined infusion, the change in plasma vasopressin was additive but the
change in oxytocin tended to be greater. Accordingly, glucose utilization
increased throughout the hypothalamoneurohypophysial system after infusion
of 0.85 M NaCl and 1.7 M mannitol. With the combined infusion, however, the
change in glucose utilization in the paraventricular nucleus was additive
but a synergistic effect occurred in the supraoptic nucleus and neural
lobe. Drinking responses were similar in all groups receiving hypertonic
solutions, with no additive effect after the combined stimulus. Although
our results do not completely rule out the participation of cerebrospinal
fluid sodium receptors, it is more likely that osmoreceptors regulate the
activity of the hypothalamoneurohypophysial system and drinking behavior.
Unlike the magnocellular system, however, drinking behavior seems to be
negatively influenced by a stress component of the osmotic stimulation.
