AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 3 533-R538, Copyright © 1993 by American Physiological Society
Cardiovascular actions of ANF: contributions of renal, neurohumoral, and hemodynamic factors in sheep
C. J. Charles, E. A. Espiner and A. M. Richards
Department of Endocrinology, Christchurch Hospital, New Zealand.
Whereas the short-term effects of atrial natriuretic factor (ANF) are well
documented, less is known concerning the possible hypotensive action of
sustained low-dose ANF infusions. Accordingly, we have examined the
sequential renal, hormonal, and hemodynamic responses to 48-h low-dose ANF
infusions in eight normotensive conscious sheep and evaluated the effects
of these infusions on autonomic (baroreceptor), adrenocortical, and pressor
responsiveness to exogenous stimulation. Plasma ANF levels tended to rise
in response to ANF infusions, but the difference between ANF and control
day levels was not significantly different. Systolic arterial pressure
(SAP) was significantly lower after ANF infusion (P = 0.01) and was
associated with a reduction in calculated total peripheral resistance
(CTPR, P = 0.007). Mean arterial pressure also tended to be lower (P =
0.08) in response to ANF. No change was seen in urinary volume or sodium
excretion or in plasma angiotensin II (ANG II), aldosterone, or cortisol
levels. ANF significantly attenuated the pressor response to exogenous ANG
II (P = 0.01) but did not affect the adrenocortical responsiveness or
autonomic (baroreceptor) responsiveness to exogenous stimulation. This
study demonstrates that chronic low-dose infusions of ANF that barely
elevate plasma ANF levels induce significant cardiovascular effects,
including lowering of SAP associated with a fall in CTPR and attenuation of
pressor responsiveness to physiological increments in ANG II, thus
providing further support for the importance of ANF in blood pressure
homeostasis in normal sheep.
