Active wall tension — Length curve and morphology of isolated bovine retinal small arteries: Important feature for pharmacodynamic studies

Abstract

The active and passive wall tension—internal circumference (diameter) relations of isolated ring segments of bovine retinal small arteries (i.d. ca. 200 μm) were studied in vitro using an isometric myograph. The active tension of the vessels (when fully activated with 10 −5 m 5-HT and 10 −5 m PGF 2α in high K +-saline) reached a maximum (1·2 N m −1) at an internal circumference, L 0, where the passive tension (measured in Ca 2+-free solution) were 0·89 N m −1. Below and above L 0 the active tension fell linearly, the zero tension intercepts being 0·48 L 0 and 1·61 L 0. The passive wall tension rose exponentially as a function of the internal circumference (diameter) and was 43 times higher at 1·4 L 0 than at L 0. A small transient spontaneous contraction was observed after rapid stretch of the arteries. Papaverine and Ca 2+-free solution did not change the wall tension of vessels stretched to L 0, indicating absence of stable spontaneous myogenic tone in the vessels. Histological examination showed that the retinal artery media on average had three smooth muscle cell layers which in total were 12 μm thick. The media/lumen ratio was 7%. Smooth muscle cell volume was 1228 μm 3, constituting about 72% of the media volume. The active wall tension—internal circumference relation and morphology of bovine retinal small arteries is generally equal to that of arteries of similar size from other species, but active force generation of the retinal vascular smooth muscle cells is considerably lower.