Type I and II metabotropic glutamate receptor agonists and antagonists evoke cardiovascular effects after intrathecal administration in conscious rats

• Published in: British journal of pharmacology 1999-10, Vol.128 (3), p.823-829
• Main Authors: Li, Xiao C, Beart, Philip M, Monn, James A, Jones, Nicole M, Widdop, Robert E
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Blood Pressure - drug effects; Central nervous system; Central neurotransmission. Neuromudulation. Pathways and receptors; conscious rat; Excitatory Amino Acid Agonists - administration & dosage; Excitatory Amino Acid Agonists - pharmacology; Excitatory Amino Acid Antagonists - administration & dosage; Excitatory Amino Acid Antagonists - pharmacology; Fundamental and applied biological sciences. Psychology; Heart; Heart Rate - drug effects; Injections, Spinal; intrathecal; Male; Metabotropic glutamate receptors; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate - drug effects; spinal cord; Vertebrates: cardiovascular system; Vertebrates: nervous system and sense organs
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1038/sj.bjp.0702850

In the present study, the role of metabotropic glutamate receptors (mGluRs) in central cardiovascular regulation in conscious rats was examined. To this end, agonists and antagonists for type I and II mGluRs were administered intrathecally, and the temporal changes in blood pressure and heart rate were recorded. L‐glutamate (1 μmol) and the prototypical mGluR agonist (1S,3R)‐ACPD (0.1 and 0.3 μmol) both increased mean arterial pressure (MAP) and heart rate (HR), implicating functional mGluRs in the spinal cord. The type I mGluR agonist DHPG (0.01–0.1 μmol) evoked increases in MAP (max=25±5 mmHg) and HR (max=88±23 beats min−1). The duration of action, but not the maximum effects, were dose‐related and ranged from approximately 10 min to 90 min for MAP and HR, respectively. The type I/II mGluR agonist CCG‐1 (0.1 and 0.3 μmol) caused smaller, variable increases in MAP and HR of intermediate duration (5–20 min), whereas the type II MGluR agonist APDC (0.1 and 1.0 μmol) caused marked, but transient (3–5 min), pressor and tachycardic responses. The highest doses of DHPG and CCG‐1, but not APDC, also evoked behavioural responses similar to a spontaneous nociceptive behavioural effect reported previously. The type I and II mGluR antagonists (AIDA and LY307452, respectively) were also given approximately 5 min before the administration of the respective type I and II mGluR agonists (DHPG and APDC). Both compounds caused pressor and tachycardic responses, with the effect of AIDA, but not LY307452, returning to control levels before mGluR agonist administration. AIDA significantly attenuated the overall cardiovascular effects of DHPG, while LY307452 significantly attenuated the overall cardiovascular effects of APDC. These results indicate that functional type I and II mGluRs exist in the spinal cord, and that their activation evokes prolonged cardiovascular effects. British Journal of Pharmacology (1999) 128, 823–829; doi:10.1038/sj.bjp.0702850