Increased splenic capacity in response to transdermal application of nitroglycerine in the dog

This study was conducted to determine if application of transdermal 2% nitroglycerine ointment (TDNG) to dogs anesthetized with alpha chloralose would produce splenic dilatation by relaxation of venous smooth muscle. Sonomicrometer crystals were applied to the spleen in each of 15 dogs, and a pressure-measuring catheter was inserted into a splenic vein. The sonomicrometer crystals permitted measurement of splenic dimension, which is known to correlate with splenic volume. Ten dogs were given 2.5 cm TDNG/10 kg, and 5 dogs (vehicle controls) were given only petrolatum, both applied to the inner surface of the auricular pinna. Splenic dimension in all dogs receiving TDNG increased significantly (P < .05) by 7.0 +/- 4.8%, whereas splenic dimension in dogs receiving petrolatum did not increase. Splenic venous pressures did not change significantly in either group. Spleens began to dilate 482 +/- 652 seconds after application of TDNG and achieved maximal dilatation at 861 +/- 632 seconds. Splenic dilatation occurred in the absence of elevation of splenic venous pressure, indicating that the dilatation probably resulted from relaxation of splenic smooth muscle. TDNG was absorbed transdermally and produced splenic dilatation in health dogs anesthetized with alpha chloralose. If the spleen is a sentinel for peripheral veins, then TDNG may increase venous capacity, retaining blood from the lungs and thereby functioning to reduce pulmonary congestion and edema in dogs with left-sided heart failure.