Functional changes in the microcirculation of alloxan-induced diabetic rats.

1. The constrictor response of microvessels to norepinephrine and tyramine, and the dilator response to acetylcholine and papaverine was equivalent in normal and alloxan-induced diabetic rats. 2. Acetylcholine and phentolamine were equally effective as antagonists of the vasoconstrictor action of norepinephrine in both groups of animals. 3. The minimum effective doses of histamine and PAF-acether to produce maximum dilation of microvessels, or to antagonize the response to norepinephrine in normal rats had to be increased 20-fold to evoke equivalent effects in diabetic animals.