[Mechanisms of cold-induced pulmonary hypertension in rats].

The objectives of the present study are to directly measure the pulmonary and systemic arterial pressures in unanesthetized, and unrestrained rats during exposure to cold and to assess pulmonary vascular responsiveness to administration of the alpha-and beta-adrenergic receptor antagonists phenoxybenzamine (1mg/kg, i.v.) and propranolol (20 micrograms/kg, i.v.), during exposure to cold. Furthermore, the rats underwent long-term exposure to cold, and pulmonary arterial pressure, systemic arterial pressure, heart rate, arterial blood gases and colonic temperature were measured. A special hand-made catheter filled with heparinized saline was inserted into the pulmonary artery via the right jugular vein, the right atrium and the right ventricle. Mean pulmonary arterial pressure was elevated during cold exposure for 2 hours. Arterial blood oxygen tension slightly decreased and carbon dioxide tension slightly rose under these conditions. The increase in cold-induced pulmonary arterial pressure was significantly lower after the administration of propranolol, but there was no change after the administration of phenoxybenzamine. However, after administrating the alpha-adrenergic blocking agent a resultant increase in heart rate and fall in systemic arterial pressure during cold exposure prevented our evaluation of the pulmonary circulatory changes. These results show that beta-adrenergic responsiveness of pulmonary vascular smooth muscle may have a role in the maintenance of cold-induced pulmonary hypertension.