Impairment of the ocular circulation induced by
diabetes mellitus has not been fully defined, but is thought to be related to hemodynamic changes in the ocular circulation. The purpose of the present study is to investigate the functional and morphological changes occurring in the ciliary artery wall of rabbits with
alloxan-induced
diabetes mellitus. A single intravenous bolus injection of
alloxan (100 mg/kg) was given to each of 26 10-week-old rabbits and 16
sham-injected control rabbits. Twenty weeks later, control rabbits and diabetic rabbits were sacrificed, and their ciliary arteries were mounted in a myograph system. The responses of these arteries to high K+
solution (K-
Krebs solution),
phenylephrine and
carbachol were investigated using isometric tension recording.
L-NAME (
NG-nitro-l-arginine methyl ester; 100 microM) and
indomethacin (1 microM) were also used to test the mechanism causing the
carbachol induced relaxation. The arteries were also examined morphologically. The maximum tensions induced by K-
Krebs solution in this tissue were not significantly different: 17.2+/-0.8 mN (n=16) in the control rabbits and 17.6+/-0.8 mN (n=23) in the diabetic rabbits (P=0.36).
Phenylephrine caused dose-dependent contraction with EC50 values of 1.3+/-0.4 microM (n=6) in the control and 5.1+/-2.3 microM (n=6) in the diabetic rabbits, but there was no significant difference between the two (P=0.36).
Carbachol induced dose-dependent relaxations in segments precontracted with K-
Krebs solution. These relaxations were significantly reduced in the diabetic rabbits. The maximum relaxation induced by
carbachol was 77.0+/-2.4% (10 microM) and 66.4+/-2.5% (100 microM) in the control and diabetic rabbits, respectively. These values were significantly different (P=0.0076). The IC(50) value for
carbachol was 396.3+/-58.4 nM (n=16) in the control, and 443.6+/-141.1 nM (n=23) in the diabetic rabbit (P=0.87). Application of a 100 microM
nitric oxide synthase inhibitor,
L-NAME, significantly inhibited the amplitude of relaxations evoked by
carbachol (P=0.0066). However, these relaxations were not inhibited by pretreatment with 1 microM
indomethacin (P=0.60). Histologically, the frequency of invaginations was less in the diabetic arterioles with a flattening of the lamina in the diabetic rabbits than in the controls. The cytoplasm of endothelial cells contained large vacuoles, indicating weak adhesion to the lamina. Some endothelial cells even showed vacuolar degeneration due to breakdown of the cell membranes. However, the smooth muscle cells were well preserved in the diabetic rabbit. These results suggest that the mechanism of impairment of ocular circulation induced by
diabetes mellitus is mainly the reduction of
NO synthase due to endothelial cell dysfunction. Furthermore, the characteristics of rabbits with
alloxan-induced
diabetes mellitus probably make them a useful model for investigating ocular complications induced by diabetic mellitus.