Assessment of heart function: After the animals were killed by cervical dislocation, the chest was quickly opened and a stainless steel cannula (with an external diameter of 0.6 mm for day 1 or 4 and 0.8 mm for day 7) was inserted into the aorta. The heart was rapidly excised and perfused in the Langendorff mode under constant pressure, corresponding to the mean arterial pressure for the given developmental stage, ie, 17,27 and 35 cm H2O on days 1,4 and 7, respectively. The hearts were perfused by a Tyrode’s solution containing (in mmol/L): NaCl 145.0, KCl 5.9, CaCl2 1.25, MgCl2 1.2, glucose 11.0, mannitol 1.1 and HEPES 5.0; pH was adjusted to 7.4 by TRIS. The solution was saturated with 100% O2 and temperature was maintained at 37°C. The hearts were electrically stimulated at a rate of 200 beats/min with silver electrodes attached to the base of the heart. The stimulation was performed with pulses of alternating polarity, with 1 ms duration and voltage set at 50% above the threshold level.The resting force was gradually increased by means of a micromanipulator to the level at which the developed force of contraction (DF) was approximately 80% of the maximum force reached at optimum preload. The contractile function of the isolated heart was measured with an isometric force transducer connected by means of a glass fibre, two-arm titanium lever and silk suture (0.7 metric) to the apex of the heart. DF (g) and its first derivative [+dF/dtmax, g/s] were evaluated automatically from the force signal by an online computer . For measuring the inotropic response of isolated hearts to Ca2+ the hearts were initially perfused with Tyrode’s solution with Ca2+ concentration of 1.25 mol/L. After stabilization, the Ca2+ concentration was decreased to 0.6 mmol/L and thereafter again gradually increased up to 10 mmol/L. The highest effect of each concentration was evaluated and expressed per heart weight analysis and as a percentage of the maximum response. Very cheap drugs at your disposal – buy celexa antidepressant to get best deals at best pharmacy.