AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 4 1089-R1097, Copyright © 1994 by American Physiological Society
Hypothalamic thermal stimulation modulates vasopressin release in hyperosmotically stimulated rabbits
R. Keil, R. Gerstberger and E. Simon
Max-Planck-Institut fur Physiologische und Klinische Forschung, WG Kerckhoff-Institut, Bad Nauheim, Germany.
Under thermoneutral conditions conscious rabbits received systemic
infusions of NaCl as hypertonic solution (90 mueq.min-1.kg body wt-1),
which raised their plasma osmolality from 283 to 312 mosmol/kgH2O. Rabbits
receiving isotonic saline served as controls. Hypertonic stimulation
induced a 60% reduction of both respiratory frequency and evaporative water
loss. Rectal temperature rose by 0.4 degrees C despite enhanced peripheral
vasodilation as indicated by increased ear skin temperature. Plasma
vasopressin (AVP), aldosterone (ALDO), and corticosterone (COR) were
significantly elevated from 6 to 16 pg/ml, 90 to 180 pg/ml, and 17 to 40
ng/ml, respectively. To elucidate the importance of central temperature for
AVP and adrenal corticosteroid release, hypothalamic thermal stimulations
(20 min) were superimposed during established iso- and hyperosmotic
steady-state conditions. Different from isosmotic controls, hyperosmotic
animals responded to hypothalamic cooling (37 degrees C) with a significant
decrease in plasma AVP from 16 to 13 pg/ml and to hypothalamic warming (41
degrees C) with a significant rise from 16 to 19 pg/ml. A weak temperature
effect on COR release was also disclosed, especially of hypothalamic
cooling, which significantly lowered plasma COR from 42 to 34 ng/ml. These
results provide evidence for positive local temperature coefficients of
hypothalamic control of AVP release and suggest a similar property also for
the control of COR release by the hypothalamo-adenohypophysial axis.
