AJP - Heart and Circulatory Physiology, Vol 246, Issue 2 197-H206, Copyright © 1984 by American Physiological Society
Heart cyclic nucleotide responses to sustained aortic constriction in neonatal and adult rats
R. T. Dowell, J. L. Haithcoat, H. M. Thirkill and W. K. Palmer
The present studies examined adenosine and guanosine 3',5'-cyclic
monophosphate (cAMP and cGMP) levels in left ventricular tissue of neonatal
and adult rats subjected to 3-10 days of abdominal aortic constriction.
Left ventricular cAMP levels were elevated after 3 days of pressure
overloading in neonatal rats (2,274 +/- 430 pmol/g; mean +/- SE) compared
with composite control values (1,280 +/- 124) obtained from sham-operated
neonates, sham-operated adults, and aortic-constricted adult groups. cAMP
levels declined progressively until, at 10 days after aortic constriction,
values were lower (681 +/- 25 pmol/g) than control (1,621 +/- 107). Left
ventricular cGMP level was higher in sham-operated neonatal (38 +/- 3
pmol/g) than in sham-operated adult rats (17 +/- 1) at 3 and 10 days
postsurgery, but pressure overloading exerted no effect on cGMP
measurements. Adenylate cyclase activity in left ventricular tissue
homogenate was higher in 3-day sham-operated neonatal (58 +/- 3 pmol X mg
protein-1 X min-1) compared with sham-operated adult (10 +/- 1) rats as the
result of augmented nonmuscle cell activity. Elevated cAMP values in 3-day,
pressure-overloaded neonates occurred despite lower adenylate cyclase
activity (44 +/- 2), via degradative modulation (cAMP phosphodiesterase).
Guanylate cyclase activity in left ventricular tissue was consistent with
prevailing cGMP levels and was not influenced by aortic constriction. The
present experiments show that neonatal cardiac enlargement is associated
with biphasic alterations in cAMP level which are modulated, at least in
part, via degradative reactions.
