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α‐Methyldopa induces a naltrexone‐insensitive antinociception and hypomotility in rats
Author(s) -
Giersberge Paul L.M.,
Duinkerken Elizabeth,
Sweep C.G.J. Fred,
Wiegant Victor M.,
Ree Jan M.,
Jong Wybren
Publication year - 1990
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1990.tb12951.x
Subject(s) - naltrexone , methyldopa , clonidine , pharmacology , endogenous opioid , opioid , alpha (finance) , medicine , chemistry , endocrinology , blood pressure , receptor , construct validity , nursing , patient satisfaction
1 This study served to investigate whether endogenous opioid peptides play a role in the putative antinociceptive and the sedative actions of α‐methyldopa. 2 In conscious normotensive rats, α‐methyldopa induced hypotension, starting around 1 h and reaching a maximum 3–4 h after administration. Pretreatment with naltrexone resulted in an inhibition of α‐methyldopa‐induced hypotension. 3 α‐Methyldopa dose‐dependently increased hot plate latency which became evident after a 4 h lag period and reaching a maximum effect at 6 h. The antinociceptive effect of α‐methyldopa was not affected by naltrexone. 4 In a small open field, α‐methyldopa dose‐dependently suppressed locomotion and sniffing behaviour. These effects of α‐methyldopa were apparent 1 h after administration and were naltrexone‐insensitive. 5 No changes in the level of β‐endorphin‐like immunoreactivity in plasma and cerebrospinal fluid were observed after administration of α‐methyldopa. 6 The results indicate that endogenous opioid peptides are involved in the hypotensive action of α‐methyldopa but not in α‐methyldopa‐induced hypomotility and antinociception.