AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 1 236-R247, Copyright © 1995 by American Physiological Society
Gut-brain signaling of water absorption inhibits vasopressin in rats
A. J. Baertschi and R. A. Pence
Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville 22908.
The mechanism for inhibition of vasopressin (AVP) by gastric water infusion
was examined in 24- or 48-h dehydrated conscious rats (n = 136 rats, 255
experiments; mean AVP baseline = 6.3 pg/ml). Gastric water infusions of 1
(n = 8), 2.5 (n = 19), and 4 ml (n = 10) caused a volume-dependent
inhibition of plasma AVP by -0.31, -1.77*, and -3.02* pg/ml, with decreases
of systemic osmolality of -1.06, -1.52, and -4.26* mosmol/kgH2O (* =
significant vs. isotonic, Duncan's test). Gastric isotonic infusions (1-4
ml) had no effect or slightly increased AVP. Systemic infusions of 1.25 (n
= 6), 2.1 (n = 10), and 6.3 ml (n = 8) inhibited AVP by -0.48, -1.07, and
-2.51 pg/ml, with decreases in systemic osmolality of -1.61, -2.77*, and
-7.21* mosmol/kgH2O. Systemic isotonic infusions (2.1 and 6.3 ml) slightly
inhibited AVP by -0.71 and -0.85 pg/ml. Individual changes in AVP by
gastric infusion of 2.5 ml of water did not correlate with changes in
systemic osmolality, mean arterial pressure, or heart rate but highly
correlated with preinfusion AVP (r = 0.74, P < 0.0001, n = 28).
Pretreatment with systemic atropine methyl bromate (0.7 mg/rat), which
abolishes the AVP secretion to gastric hypertonic saline, did not affect
the AVP response to gastric water infusion (n = 9). Combination of 2.5 ml
of gastric water and systemic hypertonic saline prevented the decrease in
systemic osmolality and still significantly inhibited plasma AVP. Maximal
inhibition of AVP by gastric water was reduced by 62.6% after lesion of the
common hepatic vagal branch (n = 5) relative to shams with identical
abdominal surgery (n = 6) and by 62.7 and 72.5% after right (n = 11) and
left (n = 8) cervical vagotomy relative to 12 shams (P < 0.05). The
results show that 1) gastric water absorption is signaled mainly by
splanchnic osmosensors, 2) water signaling is atropine insensitive, and 3)
the major water-signaling pathway projects through the common hepatic vagal
branch and cervical vagal nerves.
