Effect of parathyroid hormone on myocardial bloodflow and infarct size following coronary artery occlusion in the dog.

OBJECTIVE

To investigate the cardioprotective effect of both the amino terminal of bovine parathyroid hormone (bPTH-[1-34]) and human parathyroid hormone (hPTH-[1-84]) following coronary artery occlusion.

DESIGN

Animals were randomly assigned to one of three treatment groups following circumflex coronary artery occlusion.

ANIMALS

Experiments were performed using 19 mongrel dogs of either sex. As four animals died during experimentation, data are shown for 15 dogs (n = 5 for each treatment group).

INTERVENTIONS

Animals received saline, bPTH-(1-34) or hPTH-(1-84) following occlusion of the circumflex coronary artery. Peptides were given at 0.008 nmol/kg/min. All treatments were infused directly into the coronary circulation. Infusion rate was 1 mL/min for 10 mins at 30 min intervals until the end of the experiment (480 mins after onset of occlusion). Hemodynamic variables were monitored throughout the experiment. Radioactive microspheres were injected 10 mins before, and 30, 240 and 480 mins following, occlusion of the coronary vessel to determine regional myocardial blood-flows. At the end of the experiment, area at risk and infarct size were measured by simultaneous infusion of Evans blue dye and triphenyl tetrazolium chloride stain.

MAIN RESULTS

Neither bPTH-(1-34) nor hPTH-(1-84) significantly reduced area of risk or infarct size as a percentage of area at risk compared with controls. These results were corroborated by regional blood-flows measured using radioactive microspheres. There was no significant difference in hemodynamic variables among the groups except that left atrial pressure was consistently lower following treatment with hPTH-(1-84).

CONCLUSIONS

No evidence was found that either bPTH-(1-34) or hPTH-(1-84) salvaged ischemic myocardium in a canine model of myocardial infarction. Treatment with hPTH-(1-84) was associated with a reduction in left atrial pressure. This latter phenomenon may constitute a beneficial effect of this peptide on diastolic myocardial function.