On the "Normalization" of active developed force of isolated helical strips of muscular and elastic arteries for variation in wall thickness.

Responses of helical strips of ventral tail (muscular) and anterior mesenteric (elastic) artery of rats of two different sizes to a fixed concentration of norepinephrine (NE, 6 X 10(-7)M) were plotted versus incremental levels of resting tension. In addition, complete NE cumulative dose-response curves (6 X 10(-10) to 6 X 10(-4)M) were obtained at the optimal resting tension of each strip. Thirteen measurements or calculations of strip dimensions were made on each vessel and active developed force was divided by each of the dimensions. Vessels from larger rats had thicker walls. The active versus resting tension curve for the muscular artery was steeper and thus determination of optimal resting tension is more critical in this artery. Among the measurements used, active developed force of the muscular artery strip was best "normalized" for variation in wall thickness when expressed as percentage or force per unit of total or tunica media cross-sectional area. Active developed force of the elastic artery strip was best "normalized" for variation in wall thickness when expressed as percentage or per unit of total volume. NE dose-response curves have substantially different appearances when responses are expressed in alternative ways. In conclusion, careful attention to these technical details is necessary in comparison of active developed force in arteries of different sizes. Different techniques may be needed for muscular and elastic arteries.