Lung angiotensin converting enzyme activity in chronically hypoxic rats.

Area of Science:

• Physiology
• Cardiovascular Research
• Respiratory Medicine

Background:

• Chronic hypoxia is known to reduce lung angiotensin converting enzyme (ACE) activity.
• The relationship between reduced ACE activity and the development of pulmonary hypertension in hypoxia is not fully understood.

Purpose of the Study:

• To investigate whether reduced lung ACE activity in chronic hypoxia is a cause or consequence of pulmonary hypertension.
• To differentiate the effects of hypoxia per se from the hemodynamic factors associated with pulmonary hypertension on lung ACE activity.

Main Methods:

• Rats were exposed to hypobaric hypoxia (380 mm Hg) for 2 to 24 days.
• Measurements included right ventricular mean systolic pressure (Prvs) and lung tissue ACE activity.
• Recovery groups were monitored for up to 153 days after 24 days of hypoxia.

Main Results:

• After 2 days of hypoxia, Prvs and ACE activity did not differ significantly from controls.
• 4 to 24 days of hypoxia led to increased Prvs and decreased lung ACE activity.
• During recovery, ACE activity and Prvs returned to normal levels by 15 and 56 days, respectively.

Conclusions:

• Reduced lung ACE activity in chronic hypoxia appears to be associated with the hemodynamic changes of pulmonary hypertension.
• The findings suggest that decreased ACE activity is a consequence, rather than a primary cause, of hypoxia-induced pulmonary hypertension.