Effects of drugs interfering with the metabolism of octopamine on blood pressure of rats

1. p-Octopamine injected in lateral ventricle of conscious spontaneously hypertensive rats d decreased systolic blood pressure (SBP). 2. Precursors of octopamine—tyrosine, tyramine and phenylethanolamine (PEA)—had the same effect. The administration of pargyline, a MAO inhibitor, which increased brain octopamine, resulted in a reduction of systolic blood pressure; and this decrease was greater after administration of octopamine precursors and PEA. 3. Similarly, drugs known to inhibit activity of phenylethanolamine N-methyl-transferase (PNMT) and to increase brain octopamine level such as SKF 64139 and DCMB decreased SBP. 4. p-Octopamine hypotension was not antagonized by piperoxan, yohimbine and prazosin, a relatively selective antagonist of post-synaptic α adrenoceptors. 5. These results suggest that octopamine may be involved in central blood pressure regulation, and the receptors sensitive to octapamine appeared to be distinct from those receptive to the catecholamines.