Cardiovascular effects of intraventricular injection of fmrfamide, met-enkephalin and their common analogues in the rat

Abstract

1. The molluscan neuropeptide, Phe-Met-Arg-Phe-NH 2 (FMRFamide), the mammalian opioid peptide met-enkephalin, and their common analogues, met-enkephalin-Arg 6-Phe 7 (YGGFMRF) and Tyr-Gly-Gly-Phe-Met-Arg-Phe-amide (YGGFMRFamide), were injected into the lateral ventricle of the rat; the cardiovascular effects were studied. 2. FMRFamide caused a rapid, transient elevation in blood pressure accompanied by a great increase in pulse pressure. These effects were followed by secondary increases in blood and pulse pressures. 3. Met-enkephalin produced an initial reduction in blood pressure which was followed by a gradual increase at the higher of two test doses (300 nmole). 4. Injection of YGGFMRF resulted in a gradual increase in blood pressure. This response resembled that to met-enkephalin. 5. The initial response to YGGFMRFamide was similar to that to FMRFamide: increases in both blood and pulse pressures after injection. However, the secondary effect of YGGFMRFamide, a prolonged reduction in blood pressure, was not produced by FMRFamide. These results suggest that the initial excitatory cardiovascular responses may be due to the presence of the C-terminal amide. 6. All of the cardiovascular effects of injecting these peptides into the lateral ventricle were abolished by pre-treatment with naloxone in a dose that, itself, produced no cardiovascular changes. In conclusion, these peptides seem to act via the naloxone sensitive opiate receptors in the rat brain.