Lack of Histamine Involvement in Parathyroid Hormone Hypotensive Action

Abstract

Promethazine and cimetidine blocked the hypotensive actions of 2-pyridylethylamine, an H₁ agonist and dimaprit, an H₂ agonist, respectively, but not that of bovine parathyroid hormone fragment [bPTH-(1-34)]. Rats were treated repeatedly with the histamine releaser, compound 48/80, until the releaser could no longer produce a decrease in blood pressure. The hypotensive action of bPTH-(1-34) could still be seen. Rats with histamine partially depleted with one injection of compound 48/80 were injected with cimetidine and pyrilamine, an H₁antagonist, which together blocked the hypotensive action of subsequent injections of compound 48/80, but not that of bPTH-(1-34). These data suggest that the vasodilatory action of bPTH-(1-34) does not involve the release or action of histamine.