ABSTRACT
Adrenomedullin is a fifty-two-amino acid polypeptide that was first discovered in pheochromocytoma cells, and later in the normal adrenal medullae, lungs, kidneys, and blood. In mammals, adrenomedullin has vasodepressive effects, mainly by decreasing peripheral vascular resistance. I investigated the effects of adrenomedullin in fish to see if this novel neuropeptide would have an effect in lower vertebrates, or if its actions were limited to the higher vertebrates. Bolus injections of adrenomedullin resulted in a reduction of heart rate and dorsal aortic pressure in the rainbow trout Oncorhynchus mykiss. However, adrenomedullin had no effect in the Atlantic cod, Gadus morhua. The effects of adrenomedullin in trout appear to be due to a direct action on the peripheral vasculature, as pre-treatment of celiac artery strips with tetrodotoxin had no effect on the ability of adrenomedullin to relax the strip.