High Altitude Rats Research Articles

Calcium augments hypoxic vasoconstriction in lungs from high-altitude rats.

Isolated lungs from high-altitude rats compared with those from low-altitude rats have blunted hypoxic pressor responses. Because calcium is essential for the hypoxic pressor response and has been shown to be altered in the pulmonary arterial smooth muscle during high-altitude exposure, we wondered whether altered calcium metabolism might account for the blunted response. We attempted to unmask differences between high- and low-altitude rat lungs by altering extracellular calcium. The addition of calcium to the blood perfusate augmented the hypoxic pressure response of high-altitude lungs and depressed that of low-altitude lungs. Calcium addition did not affect pressor responses to angiotensin II, but slowed vasodilation after both angiotensin injection and removal of the hypoxic stimulus. The maximal KCl-induced contraction was blunted in rings of main pulmonary artery from high-altitude rats, but augmented in their aortic rings. Submaximally constricted (40 mM KCl) pulmonary arteries from low- but not high-altitude rats further constricted with calcium addition. Aortic rings exhibited an inverse behavior. Thus, calcium addition augmented the blunted vasopressor response in high-altitude rats lungs, possibly by an effect on lung arteries. The aorta and main pulmonary artery differ in calcium handling.

Blunted hypoxic vasoconstriction in lungs from short-term high-altitude rats

Blunted hypoxic vasoconstriction in lungs from short-term high-altitude rats

Chronic propranolol treatment blunts right ventricular hypertrophy in rats at high altitude.

Chronic beta-receptor blockade has been reported to inhibit right ventricular hypertrophy in rats at high altitude. If so, we wanted to determine whether beta-receptor blockade or some other drug action were involved and whether the heart, the lung vessels, or blood alterations were affected. In rats, chronic treatment with DL-propranolol (2 mg/kg ip once daily) reduced right ventricular hypertrophy and polycythemia of chronic high altitude. D-Propranolol and metoprolol did not reduce hypoxia-induced right ventricular hypertrophy or polycythemia. In isolated lungs from low-altitude rats treated chronically with DL-propranolol or with D-propranolol the pressor response to acute hypoxia was blunted. Chronic DL-propranolol blunted the acute hypoxic pressor response and angiotensin II induced vasoconstriction in lungs from high-altitude rats. Two effects of DL-propranolol treatment were seen: 1) blockade of beta 2-adrenergic receptors, which reduced the right ventricular hypertrophy of high altitude through reduction of hematocrit; and 2) a non-beta-effect, which reduced vascular responsiveness to acute hypoxia in the isolated lung preparation.

Myocardial electrolytes in hypobaric hypoxia.

Male, white rats (Holtzmann) were exposed to 7,200 m in a barometric chamber for six hours a day for three weeks. Control rats were kept at a sea level altitude of 200 m in Peoria, Illinois. At the end of the exposure period the rats were guillotined and their hearts removed. Approximately equal size strips were cut out of the right ventricles (RV), septa (S) and left ventricles (LV) and weighed on a Mettler balance. All heart pieces were dried overnight in a 40°C oven and reweighed following cooling. They were digested in concentrated nitric acid, diluted with distilled water; and sodium, potassium, calcium and magnesium were determined by atomic absorption spectrophotometry. RV and S muscle from the high altitude rats (HA) had a significantly higher water content. RV muscle from HA rats contained significantly more Na+, K+ and Ca++ and less Mg++ than sea level controls (SL). LV muscle from HA animals contained significantly less Na+ than SL controls. Within the HA hearts, the RV contained significantly more Na+, K+ and Ca++ and significantly less Mg++ than the S or LV. Evidence indicates that chronic high altitude exposure results in significant alterations in electrolyte distribution throughout the heart.