EFFECTS OF A SYNTHETIC RAT ADRENOMEDULLIN ON REGIONAL HEMODYNAMICS INRATS

The effects of rat adrenomedullin, a novel vasorelaxant peptide, on sy stemic and regional hemodynamics were examined in conscious Sprague Da wley (SD) rats and spontaneously hypertensive rats (SHR). The intraven ous infusion of adrenomedullin at rates of 1.67 and 5 mu g/kg per min decreased the mean arterial pressure in a dose-dependent fashion in bo th types of rats. Adrenomedullin at a rate of 5 mu g/kg per min increa sed the heart rate and cardiac output. As a result, the total peripher al resistance significantly decreased. With regards to the regional he modynamics, adrenomedullin significantly increased the flow rates in t he lungs, heart, spleen, kidneys, adrenal glands and small intestine o f SHR. The flow rates in the brain and skin did not change and the flo w rates in the skeletal muscle and testis were decreased. These region al hemodynamic changes were also observed in SD rats and there was no qualitative difference in the regional responses to adrenomedullin bet ween SHR and SD rats. Thus, adrenomedullin predominantly increased the flow rates in organs in which adrenomedullin gene was highly expresse d. It therefore seems that adrenomedullin may act as a local vasodilat ory hormone rather than as a circulatory hormone.