Age-related differences in intestinal microvascular responses to low-flow states in adult and suckling rats.

We used in vivo videomicroscopic techniques to compare the intestinal microvascular responses of 8- to 12-wk-old adult rats with those observed in 8- to 12-day-old suckling rats. Changes in intestinal microarteriolar diameters and blood flow were measured during hemorrhage (5 and 10 ml/kg), hypoxia (10% O2 breathing environment), and hypothermia (surface cooling to 34 degrees C and 31 degrees C). Intestinal blood flow (as measured by optical Doppler velocimetry) was decreased by a similar amount in both adult and suckling rats during all three periods of stress. Large arteriolar diameter changes were also similar in adult and suckling rats. In contrast, there were substantial differences in the responses of the small premucosal arterioles. These premucosal arterioles selectively dilated in adult rats, suggesting a redistribution of blood flow toward the mucosa during each of the three periods of stress. These same microvessels failed to dilate in the suckling rats during each of the three periods of stress, suggesting that the intestinal microvasculature in the immature rat lacks vasodilator mechanisms that are active in the adult rat. We propose that altered microvascular control could make the developing intestine prone to mucosal damage during periods of decreased perfusion.