Effects of isoprenaline on functional capillary density in the subendocardial and subepicardial layer of the rat myocardium

Abstract

The functional capillary density in subepicardial and subendocardial layers of rat heart was measured during rest and during isoprenaline-induced (5.0 microgram X kg-1 X min-1, i.v. over 3 minutes) cardiac stimulation. For determination of the number of perfused capillaries, a fluorescent dye (thioflavine S) was infused into the left atrium; 1, 3, 5 and 10 sec, respectively, after starting dye application, hearts were excised and rapidly cooled down to -50 degrees C. In histological sections capillaries which had been perfused during the dye infusion could be identified and counted. An increase in the number of stained vessels was found in both layers of the myocardium when the time of dye exposure was prolonged. Under these conditions the rise was much smaller in isoprenaline-treated animals, this effect being most marked in the subendocardial layer (3560 +/- 199 cap./mm2, control group; 2190 +/- 30 cap./mm2, isoprenaline-treated group; dye exposure 10 sec). Isoprenaline - at the dose used - induced an increase in total blood flow (3.7 +/- 0.6 ml X min-1 X g-1, control group; 6.8 +/- 0.7 ml X min-1 X g-1, isoprenaline-treated group), however, with a relatively less pronounced increase in the subendocardial blood flow (subendocardial/subepicardial flows: 1.08 +/- 0.13, control group; 0.66 +/- 0.01, isoprenaline-treated group). These results favour the view that isoprenaline-induced relative reduction in the subendocardial blood flow is due to disturbance of perfusion pressure and extravascular compression rather than to exhaustion of the myocardial capillary reserve.

Perfusion Pressure and Transmural Flow Distribution in the Left Ventricles of Isolated Rat Hearts

“…However, it needs the histological technique used here for precise evaluation of the myocardial layers in these small hearts. Using usual dissection technique after intravenous injection of coloured microspheres into six rats a subendo/ subepicardial quotient of only 1.08 f 0.13 has been found (Vetterlein & Schmidt 1980). A comparison of the cardiac function between four groups of paced hearts after 30 min perfusion with 30, 50, 80 and 120 cmHzO, respectively, revealed an increase in left ventricular pressure amplitude, coronary flow, myocardial oxygen consumption and transmural flow quotient with the perfusion pressure ( Fig.…”

“…However, it needs the histological technique used here for precise evaluation of the myocardial layers in these small hearts. Using usual dissection technique after intravenous injection of coloured microspheres into six rats a subendo/ subepicardial quotient of only 1.08 f 0.13 has been found (Vetterlein & Schmidt 1980).…”

Density of plasma-perfused capillaries in the rat heart during carbocromene-induced vasodilation

“…For calculation of the coronary flow rate the same method was applied as described earlier (35). Non-radioactive microspheres with a diameter of 8.8 _ 0.9 ~tm (3M Comp.)…”

“…As described in a preceding study, fluorescent dyes were added to the blood stream for different periods of time, and the filling of the capillary network with the plasma label was determined by rapidly freezing the heart and counting the stained vessels in histological sections (35,38). In order to assure rapid freezing of the organ, all experiments were performed on rats.…”

A modified regionally ischemic porcine heart preparation with eligible residual blood flows

“…In the septum the subepicardial layer was identical with the right ventricular subendocardial layer. The 48 samples of each experiment each weighing about 200 mg were dissolved in 6m KOH at a temperature of 37~ (11) and centrifuged at 6000 x g to assure that the microspheres were distributed in the pellet (12). The upper part of the supernatant was washed twice with an isotonic saline solution.…”