Validity of Vascular Prostaglandin Assay Methods

Abstract

This study directly compares the three major methods of prostaglandin as say for explanted blood vessels in an effort to determine whether reliable assays can be performed on small, localized areas. Under general anesthesia, canine femoral arteries and veins (n =16) were excised after measurement of in vivo dimensions. Each vessel was divided into three segments. Vessel segments were (1) incubated as whole rings ("biopsy" method), (2) incubated with the luminal surface covered by a plexiglass well (well method), or (3) perfused with a pulsa tile pump at physiologic pressure, temperature, and flow rate for two fifteen minute cycles with a balanced salt solution (perfusion method). Perfusion seg ments were also tested by the well and biopsy methods after thirty minutes of ex vivo perfusion. Assays of stable metabolites for prostacyclin (Pc) and throm boxane A₂ (Tx) were performed using commercially available radioimmuno assay techniques. Luminal perfusion was used as the "gold standard" for corre lation.

Mean values for Pc, Tx, and Pc/Tx ratio were compared for each method on both arteries and veins. In each case, the well method was statistically equiva lent to the perfusion method for the second fifteen-minute cycle, while the biop sy method was significantly different in several groups. Linear regression analysis revealed significant positive correlations between the well method and the per fusion method (r>0.74, P<0.01). The biopsy method did not correlate with the perfusion method in a significant manner (r 0.18 and 0.50, p<0.05).

Significant differences between the first and second perfusion cycle were seen in most cases. The wall method revealed trends toward decreased thromboxane production but no change in prostacyclin production for specimens after thirty minutes of perfusion.

Conclusions: (1) The well incubation method demonstrates a significant positive corre lation with luminal perfusion while allowing assay of small localized areas. (2) Luminal perfusion is a reproducible technique, but larger vessel areas and more complex appara tus are required. Significant variations in luminal prostaglandin synthesis occur with se quential perfusion cycles, and the mechanism for the decrease in prostacyclin/thromboxane synthetase level or differing mechanisms for prostacyclin and thromboxane synthesis. (3) The vessel biopsy method is not reliable for comparisons with luminal perfusion or as a means of measuring luminal prostaglandin production.