Fig. 2. (A,B) Uptakes (relative to control tissues) of tracer amounts of putative paracellular probes in everted sleeves of intestine were not significantly self-inhibited (100 mmol l^–1 of the probes themselves) or inhibited by D-glucose (100 mmol l^–1). In pigeons (A), probe uptake normalized to control (100 mmol l^–1 mannitol) was not significantly different from 100% in pigeons except that lactulose was significantly inhibited by itself. Significant inhibition of L-rhamnose (<100% of uptake for control treatment) was noted in rats (B) when 100 mmol l^–1 D-glucose was present in solution. Asterisks indicate significantly less than 100% (P<0.02). Values are means ± s.e.m. (N=5–7 sleeves/treatment). (C,D) Raw uptakes (µl mg^–1 min^–1) of tracer amounts of D-glucose and putative paracellular probes in the presence of unlabeled mannitol (control), the probe itself or D-glucose in pigeons (C) and rats (D). There was no significant difference in D-glucose uptake between rats and pigeons (F_1,8=0.62; P=0.45).