Isolated human chorionic vascular reactivity: technical considerations for fresh preparations

1. Sixty chorionic vascular rings from normal term placentas were immersed in an organ bath for isometric tension recording to study (A) the contractile response to 120 mM of potassium chloride (KCl) after adjustment and equilibration to 1-5 g of passive tension; and (B) the concentration-response curve to KCl after adjustment and equilibration to the optimal passive tension. 2. Adjustment to 4 g of passive tension elicited the maximal (P < 0.007) and the latest (P < 0.006) KCl-induced contraction among arterial rings. Venous rings showed the greatest contraction when adjusted to 3 g, but the differences were not significant except when compared to 1 g of passive tension (P < 0.03). 3. The EC50 for chorionic arteries and veins was 14.2 and 25.7 mM, respectively (P < 0.003). The maximal contraction was already obtained with 40 mM of KCl. 4. Our results suggest that (A) the optimal passive tension for fresh human chorionic arteries is 4 g; (B) chorionic venous reactivity is less influenced by the initial tension; and (C) the optimal concentration of KCl to be used as a contracting agent of these tissues is 40 mM.