AJP - Regulatory, Integrative and Comparative Physiology, Vol 266, Issue 6 1752-R1758, Copyright © 1994 by American Physiological Society
Loss of osmotic thirst in multiple system atrophy: association with sinoaortic baroreceptor deafferentation
M. Bevilacqua, G. Norbiato, V. Righini, T. Vago, L. Castelli, F. Carella and T. Caraceni
Servizio di Endocrinologia, Luigi Sacco Hospital, Vialba, Italy.
We evaluated plasma osmolality (pOsm), thirst, and vasopressin response to
hypertonic saline infusion in 14 patients with multiple system atrophy
(MSA). This disease is characterized by the degeneration of noradrenergic
neurons in the central nervous system and severe orthostatic hypotension.
Seven patients were also characterized by the lack of vasopressin response
to hypotension (group B) and seven by a preserved response (group A). In
group A pOsm rose from 290 +/- 2 to 312 +/- 6 mosmol/kgH2O, vasopressin
from 0.9 +/- 0.3 to 5.7 +/- 0.5 pmol/l, and thirst from 1.1 +/- 0.1 to 8.7
+/- 1.1 cm on the visual analog scale. After saline, patients drank 1,215
+/- 150 ml of water (no different from healthy controls). In group B
patients' pOsm rose from 296 +/- 3 to 325 +/- 6 mosmol/kgH2O and
vasopressin from 1.2 +/- 0.1 to 19.6 +/- 0.4 pmol/l (P < 0.01 vs. group
A and controls). Group B patients had no thirst during saline and drank
little after the challenge (175 +/- 50 ml; P < 0.01 vs. group A and
control). Forced drinking decreased vasopressin in patients before changes
in pOsm, showing that inhibitory afferents from oropharyngeal mucosa were
intact. In MSA patients with altered afferent control of vasopressin there
is a dissociation between the osmotic control of thirst and the osmotic
control of vasopressin.
