1. Myographic and histological techniques were used to study the mechanical and morphological properties of oesophageal and mesenteric veins from rabbits subjected to 0, 4, 14 and 90 days of partial portal vein stenosis.

2. The stenosis caused an immediate increase in portal pressure from 10.5 mmHg (1.4 kPa) to 20.5 mmHg (2.7 kPa); the pressure returned to the control level by 90 days.

3. The lumen diameter of oesophageal veins was increased by 76% after 4 days and by 147% after 90 days, while that of the mesenteric veins was unchanged. The media thickness in both veins increased rapidly, reaching a maximum at 14 days (82%, oesophageal; 56%, mesenteric) and thereafter decreasing.

4. The contractility of oesophageal veins was transiently decreased (at 4 days), while that of the mesenteric veins was transiently increased (at 14 days).

5. In further experiments, sclerosing of the oesophagus, which is believed to restrict flow without reducing pressure, restricted the increase in lumen diameter of oesophageal veins caudal to the sclerosing site, but did not affect the media thickness.

6. The results suggest that, in oesophageal and mesenteric veins, portal pressure is a primary determinant of media thickness but not of lumen diameter.

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