Cold pressor test and plasma endothelin-1 concentration in primary open-angle and capsular glaucoma

The authors investigate cutaneous capillary blood flow using the cold pressor test and plasma endothelin-1 (ET-1) concentration in primary open-angle glaucoma (POAG) and capsular glaucoma (CG), and evaluate the connection between the two factors, which reflect vasoconstrictive mechanisms with a potential role in the pathogenesis of glaucoma.

The ET-1 concentration of venous blood plasma samples from 20 patients with POAG, 22 patients with CG, and 44 healthy volunteers was measured using a radioimmunoassay kit. On a separate occasion, the right hand was subjected to the cold pressor test (hand immersed in 4 degrees C water for 30 seconds, then in 30 degrees C water for 2 minutes), during which cutaneous capillary blood flow of the left middle finger was measured using a Periflux 4001 Master Laser Doppler Flowmeter (Perimed AB, Järfälla, Sweden).

In the CG group, baseline cutaneous capillary blood flow was significantly lower than either that of POAG (p = 0.001) or that of the healthy group (p = 0.046). In the CG group, time to maximal cold-induced flow reduction was significantly longer than in the POAG group (p = 0.028) or in the healthy group (p = 0.025). Also, recovery time was significantly longer in CG than in the healthy group (p = 0.008) and tended to be longer than in the POAG group. No statistically significant difference between the groups was found either in the frequency of increased vasospastic response (cold-induced flow reduction higher than 70% of the baseline value) or in ET-1 concentration. No correlation was seen between ET-1 concentration and the findings of the cold pressor test.

The results suggest that in CG, which is a systemic disease with vascular abnormalities, baseline cutaneous capillary perfusion and its response to cold and warmth are altered, without any alteration of plasma ET-1 level. The authors found that both plasma ET-1 level and the response to the cold pressor test are normal in patients with POAG. These findings suggest that regulation of cutaneous capillary perfusion and the concentration of plasma ET-1 are not related to each other in patients with glaucoma.