E. Yegin et al., SERUM ANGIOTENSIN-CONVERTING ENZYME AND PLASMA ATRIAL-NATRIURETIC-PEPTIDE LEVELS IN HYPERTHYROID AND HYPOTHYROID RABBITS, Japanese Heart Journal, 38(2), 1997, pp. 273-279
Background. It is known that serum angiotensin-converting enzyme (ACE)
and plasma atrial natriuretic peptide (p-ANP) levels increase in hype
rthyroidism. However, the precise mechanism of the effects of thyroid
hormone on ANP release remains to be clarified. No study investigating
serum ACE together with p-ANP levels has been performed in experiment
al hyperthyroid and hypothyroid rabbits. The present study was designe
d in order to provide additional evidence of increased ANP production
and secretion in hyperthyroidism and to investigate the relationships
between ANP, ACE and thyroid hormones. Methods. Male New Zealand white
rabbits (2.3-3.4 kg) were used throughout the study. Hyperthyroidism
was induced by daily intraperitoneal administration of L-thyroxin (50
mu g/100 g). Hypothyroidism was induced by daily intraperitoneal injec
tion of propylthiouracil (2 mg/100 g body weight). Twelve days after t
he end of treatment, animals were sacrified under anesthesia and blood
samples were obtained from the aorta for serum ACE and thyroid hormon
e and p-ANP determinations. Results. Serum ACE, plasma renin activity
(PRA) and p-ANP were higher in hyperthyroid rabbits and lower in hypot
hyroid rabbits than in euthyroid rabbits. ANP concentration in atria w
as lower in hyperthyroid rabbits and higher in hypothyroid rabbits tha
n in euthyroid rabbits. p-ANP, PRA and serum ACE levels were positivel
y correlated with serum thyroxin levels. Inverse correlation was found
between serum thyroxin and ANP concentration in atria (a-ANP), and be
tween p-ANP and a-ANP. Conclusions. Our results indicate that not only
p-ANP but also serum ACE activity was markedly increased in experimen
tal hyperthyroid rabbits. It was thought that there were both direct a
nd indirect effects of thyroxin on the release of ANP.