BOF: 2.11
A 56-year-old male who has
hypertension with evidence of end-organ damage has been started on captopril
for control of his hypertension. Shortly after this he develops a dry
irritating cough. Clinical examination of his chest is unremarkable and his
chest x-ray is clear. In this patient the dry cough is likely to be due to
inhibition of breakdown of:
a)
Bradykinin
b)
Histamine
c)
Serotonin
d)
Kallikrein
e)
Endothelin
Answer:
a)
Breakdown of bradykinin is
inhibited by ACE inhibitors and this is thought to be the reason why patients
develop a persistent dry cough.
The kinins are peptides, which
cause vasodilatation by relaxing vascular smooth muscle through the action of
NO (nitric oxide). They cause contraction of other visceral smooth muscle.
There are two types:
Bradykinin
Lysylbradykinin
They are formed from precursors;
high molecular weight kininogen and low molecular weight kininogen. The
conversion from kininogens to kinins is caused by proteases known as
kallikreins.
Bradykinin
and lysylbradykinin are inactivated by kininase I and kininase
II. Kininase II is the same enzyme as angiotensin II converting enzyme.
