Water and Electrolyte Content of Normal and Hypertensive Arteries in Dogs.

• Water and electrolytes are important constituents of the blood vessel wall since they affect the chemical environment of vascular smooth muscle and connective tissue as well as the mechanical properties of the wall itself. For example, in hypertension the water and electrolyte contents of blood vessels have been found to be altered. 1 " 3 While the dog is frequently utilized in cardiovascular research, quantitative information regarding normal distribution of water and electrolyte contents along the canine arterial tree is meager and few studies have involved more than one or two sites. 4 " 12 The primary objective of this investigation was to establish values for the normal water and electrolyte contents along the main arterial tree in dogs and to determine how the normal electrolyte pattern was altered in renal hypertension. Methods Mongrel dogs for this study were selected on the basis of size (over 12 kg), apparent good health, and middle age. All were sacrificed under anesthesia (1:1 mixture of 5.5 diallylbarbituric acid and pentobarbital 25 mg/kg) so that portions of the arterial tree could be obtained for analysis. The following sites were analyzed: ascending aorta, 0.5 cm distal to valves; descending aorta, proximal to the first intercostals; aorta, 2 cm above the diaphragm; aorta, proximal to the bifurcation; femoral artery; popliteal artery; caro-tid artery; lingual artery; main pulmonary artery; and mesenteric arteries of 0.5 to 1 mm diameter. Approximately 30 minutes were required for the complete dissection. The order in which segments were removed was varied from experiment-to-experiment. Whole arterial segments including adventitia, but no loose connective tissue, were quickly dissected , lightly blotted of adhering blood and placed in tared stoppered tubes. The fresh samples were weighed, oven-dried for 24 hours at 96°C, and reweighed. The weight difference was taken as the total water. The solids were extracted with ethyl ether, and weighed to determine the fat free solids. Electrolytes were extracted for three days using 0.75 normal HNO:t. This extraction technique yielded at least 99% recovery when known quantities of electrolyte were added to tissue samples. The sodium and potassium in the extract were analyzed with a flame photometer as described by Raymond. 13 Chloride from the same extract was determined in duplicate using a Cotlove chloride titrator. Serum electrolytes were analyzed using the same techniques. Serum solid matter was estimated from the measurement of the specific gravity using a drop technique into copper …