Haemodynamic effects of NO-synthase inhibitors, NG-monomethyl-L-arginine, NG-nitro-L-arginine and NG-nitro-L-arginine methyl ester, and NO-donor, glyceryl trinitrate, in conscious SHRSP and WKY.

1. The experiments were carried out by an ordinary and a microsphere method in order to clarify the effects of three nitric oxide-synthase inhibitors and -donor on the circulating system between SHRSP and WKY. 2. Intravenous administration of each compound possessing the nitric acid-synthase inhibiting action markedly elevated the systolic blood pressure both in SHRSP and WKY, but more prominently in the former. 3. The hypotensive and tachycardic responses to glyceryl trinitrate were more enhanced after treatment with NG-nitro-L-arginine and NG-nitro-L-arginine methyl ester but not with NG-monomethyl-L-arginine compared with the non-treated one. 4. All peripheral organs except the brain decreased their regional blood flow after administration of NG-nitro-L-arginine, indicating a crucial involvement of nitric oxide in the peripheral circulation. 5. It was suggested that the nitric oxide system worked more sensitively and actively in SHRSP than in WKY in order to maintain the peripheral blood flow and systemic blood pressure.