Growth hormone decreases phase II ventricular tachyarrhythmias during acute myocardial infarction in rats

Abstract

GH (growth hormone) administration during acute MI (myocardial infarction) ameliorates subsequent LV (left ventricular) dysfunction. In the present study, we examined the effects of such treatment on arrhythmogenesis. A total of 53 Wistar rats (218+/-17 g) were randomized into two groups receiving two intraperitoneal injections of either GH (2 international units/kg of body weight; n=26) or normal saline (n=27), given at 24 h and 30 min respectively, prior to MI, which was generated by left coronary artery ligation. A single-lead ECG was recorded for 24 h post-MI, using an implanted telemetry system. Episodes of VT (ventricular tachyarrhythmia) and VF (ventricular fibrillation) during the first hour (phase I) and the hours following (phase II) MI were analysed. Monophasic action potential was recorded from the lateral LV epicardium at baseline and 24 h post-MI, and APD90 (action duration at 90% of repolarization) was measured. Infarct size was calculated 24 h post-MI. Infarct size and phase I VT+VF did not differ significantly between groups, but phase II hourly duration of VT+VF episodes was 82.8+/-116.6 s/h in the control group and 18.3+/-41.2 s/h in the GH group (P=0.0027), resulting in a lower arrhythmic (P=0.016) and total (P=0.0018) mortality in GH-treated animals. Compared with baseline, APD90 was prolonged significantly 24 h post-MI in the control group, displaying an increased beat-to-beat variation, but remained unchanged in the GH group. We conclude that GH decreases phase II VTs during MI in the rat. This finding may have implications in cardiac repair strategies.

Attenuation of post-infarction remodeling in rats by sustained myocardial growth hormone administration

“…For alginate + GH, GH (S8648, Sigma Aldrich) was dissolved in normal-saline and was added dropwise into solution A, under constant magnetic stirring for 30 min, followed by the addition of solution B. The final alginate-hydrogel (concentrations: alginic acid 1% per weight; CaCl 2 4.2 mM; GDL 8.4 mM) was stored in 0.2 ml-aliquots; based on our previous work (Elaiopoulos et al, 2007;Hatzistergos et al, 2008), each alginate + GH aliquot contained 5 mg of GH.…”

Chronic skeletal muscle ischemia preserves coronary flow in the ischemic rat heart

“…Myocardial infarction was generated in vivo as previously described (1,9). In brief, animals were intubated and mechanically ventilated as outlined above.…”

Arrhythmogenesis after acute myocardial necrosis with and without preceding ischemia in rats

“…The main findings are as follows: (a) During the early stages, MI resulted in frequent, selfterminating episodes of polymorphic VT/VF; this response is characteristic of the rat coronary ligation model, as previously demonstrated by our group [15][16][17][18][19] and others [14]. By sharp contrast, coagulation necrosis immediately induced sustained VF in all animals, followed by a (lower) second peak, after approximately 1 h; during subsequent stages, the incidence of VT/VF decreased rapidly in this group.…”

“…MI was induced as described previously [16][17][18]; briefly, the left coronary artery was encircled approximately 4 mm from its origin, extending from the left atrial appendage to the pulmonary cone. The suture was threaded through a snare, which was released after 30 min to achieve reperfusion.…”