Age-related differences in intestinal arteriolar responses to venous pressure elevation in the rat

We previously reported differences in intestinal arteriolar responses of adult and suckling rats to three stressors (hemorrhage, hypoxia, and hypothermia) that decreased intestinal blood flow. The small, premucosal arterioles of adult rats dilated in response to all three stressors, whereas the premucosal arterioles of suckling rats constricted or remained unchanged. One explanation for this difference might be absence of myogenic responsiveness in the premucosal arterioles of the immature rat.

We used in vitro videomicroscopy to observe the intestinal arteriolar responses to venous pressure elevation (a myogenic stimulus) in adult (8- to 12-week-old) and suckling (8- to 12-day-old) Sprague-Dawley rats. We increased portal venous pressure by 25 and 50% above the baseline pressure.

Arterioles in the rats displayed the expected "myogenic" response to venous pressure elevation (diameters decreased 12-29% when venous pressure was increased by 50%). In contrast to adult rats, arterioles in the suckling rats failed to constrict in response to increases in venous pressure (diameters increased 14-21% in response to a 50% increase in venous pressure).

These results suggest that the myogenic constrictor mechanisms for control of the microcirculation appear to be either nonfunctional or suppressed in the intestinal microcirculation of suckling rats.