AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 4 735-R741, Copyright © 1986 by American Physiological Society
Cardiovascular and endocrine responses to head-up tilt and vasopressin infusion in humans
P. Bie, N. H. Secher, A. Astrup and J. Warberg
The effects of passive tilt on arterial and central venous pressures (MAP
and CVP), heart rate (HR), arterial concentrations of vasopressin (AVP) and
aldosterone (ALDO), osmolality, and hematocrit were studied in eight
healthy young men. Tilting was performed at 30 degrees/min to 20 or 40
degrees and maintained for 45 min. The 20 degrees tilt did not change MAP
while CVP fell by 5.9 mmHg (P less than 0.01) and HR increased by 5
beats/min (51-56 beats/min, P less than 0.05). AVP and ALDO concentrations
were unchanged. At 40 degrees, MAP increased by 5.7 mmHg (86.0-91.7 mmHg, P
less than 0.01), CVP decreased by 7.4 mmHg (P less than 0.01), HR rose by 8
beats/min (55-63 beats/min, P less than 0.01), and pulse pressure fell by 6
mmHg (P less than 0.05). ALDO increased fivefold (P less than 0.05), but
AVP did not change. Infusions of AVP at 0.25 or 1.0 ng X min-1 X kg body
wt-1 elevated plasma AVP to 11 +/- 1 and 52 +/- 8 pg/ml. Only the larger
dose caused a small increase in MAP while CVP and HR remained unchanged;
however, washout of a subcutaneous depot of Xe was reduced greater than 60%
even by the lower dose. It is concluded that small-angle nonhypotensive
passive tilt does not affect AVP measurably despite substantial reductions
of CVP and a marked increase in ALDO. Elevations of AVP elicit marked
subcutaneous vasoconstriction also in the absence of changes in CVP, HR,
and MAP.
