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ALTERED BASAL RELEASE AND PRESSOR EFFECT OF L‐DOPA IN THE ROSTRAL VENTROLATERAL MEDULLA OF SPONTANEOUSLY HYPERTENSIVE RATS
Author(s) -
Yue JinLiang,
Miyamae Takeaki,
Ueda Hiroshi,
Misu Yoshimi
Publication year - 1995
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1111/j.1440-1681.1995.tb02964.x
Subject(s) - rostral ventrolateral medulla , medicine , endocrinology , postsynaptic potential , chemistry , aromatic l amino acid decarboxylase , glutamate receptor , tetrodotoxin , dopamine , medulla oblongata , central nervous system , receptor
Summary 1. Transmitter‐like L‐DOPA functions as a tonic to produce postsynaptic cardiopressor responses in the rostral ventrolateral medulla (RVLM) of rats. We attempted to clarify whether a transmitter‐like L‐DOPA system is altered in the RVLM of spontaneously hypertensive rats (SHR) to maintain the hypertension. 2. By microdialysis of left RVLM area, the basal L‐DOPA release was higher in SHR than in Wistar‐Kyoto (WKY) rats. This release was partially inhibited by tetrodotoxin (TTX, 1 μmol/L) to a similar degree in both strains. TTX‐sensitive L‐DOPA release was higher in SHR than in WKY. 3. L‐DOPA (10–600 ng) and L‐glutamate (10–300 ng) microinjected into left RVLM produced dose‐dependent hypertension and tachycardia. Pressor but not tachycardiac responses to L‐DOPA at lower doses were slightly greater in SHR than in WKY, whereas no difference to L‐glutamate was observed in either strain. 4. In RVLM regions, there was no difference of tyrosine hydroxylase activity in SHR or WKY; however, L‐aromatic amino acid decarboxylase activity was lower in SHR than in WKY. 5. Enhanced presynaptic neuronal L‐DOPA release, including a decrease in decarboxylation and sensitization of postsynaptic pressor sites to L‐DOPA in RVLM, may be involved in the maintenance of hypertension in SHR.