23:T534,In awake rats with indwelling catheters, the development of pulmonary hypertension after feeding Crotalaria spectabilis seeds is followed. Hypoxemia is excluded as a factor. Other hemodynamic changes are found before hypertension. After 7 days, pulmonary artery pressure (Ppa) is normal, 17.17 +/- 0.30 (SE) mmHg and from 14 days significantly increased (P < 0.01). Oxygen consumption (Vo2) is significantly increased by day 7 (control 22.72 +/- 2.13 ml . min-1 . kg-1; Crotalaria 42.47 +/- 2.95; P < 0.001). and cardiac index (CI) is significantly above normal after 7, 14, and 21 days (control 350 +/- 31 ml . min-1 . kg-1; 7 days Crotalaria 476 +/- 28; P < 0.02); pulmonary vascular resistance (PVR) increases to six times normal at day 33 (control 0.033 +/- 0.003 U/kg; 33 days Crotalaria 0.194 +/- 0.020; P < 0.001). The pulmonary arteries of these same rats were studied by quantitative morphometric techniques. The first change, muscle in smaller and more peripheral arteries than normal, is detected when Vo2 and CI are increased. Increased medial thickness of arteries < 200 micrometer diameter follows with Ppa rises. Even later, the larger arteries increase their media as the number of peripheral arteries falls and right ventricular hypertrophy becomes apparent, and hypertension and increased PVR are well established.24:T4c6,To study the influence of age and sex on the hemodynamic and structural response of the pulmonary vascular bed to chronic hypobaric hypoxia, "infant" Sprague-Dawley rats from 8 days old and "adult" rats from 9 wk old, each group including both sexes, were exposed to half atmospheric pressure for 1 mo and then allowed to recover in room air for up to 3 mo. During hypoxic exposure, pulmonary artery hypertension (Ppa) developed in all groups. The level of Ppa was similar in both male and female infant and in male adult rats but was significantly lower (P < 0.01) in the female adult rats. After recovery in room air, only partial regression of Ppa had occurred in all groups (P < 0.001). In male and female adult rats, recovery values were similar but infant rats had more residual Ppa than adults (P < 0.001). The structural changes that developed during hypoxia, especially the abnormal presence of muscle in small and peripheral intra-acinar arteries, were more severe in male adult rats compared with female adults (P < 0.01) and in infants of both sexes compared with male adults (P < 0.01). After recovery, residual structural changes were present in all rat groups but were most severe in the infants (P < 0.01).25:T6e3,

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