Inhibition of angiotensin-converting enzyme activity by a partially purified fraction of Gynura procumbens in spontaneously hypertensive rats.
OBJECTIVE
To investigate the hypotensive and angiotensin-converting enzyme (ACE) inhibitory activities of a partially purified fraction (FA-I) of the leaves of Gynura procumbens and to qualitatively analyse the putative compounds present in the fraction.


METHODS
The hypotensive effect of FA-I was tested in both spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) by an intravenous administration of 0-10 mg/kg of the FA-I. Administration of captopril (20 microg/kg) served as the control. In vitro 0.0-2.0 mg/ml FA-I was added to a mixture of ACE and hippuryl-L-histidyl-L-leucine and assayed by a modification of the colourimetric method of Hurst and Lovell-Smith. All blood pressure measurements were monitored by the Macintosh MacLab set-up. ACE activity was measured by an in vitro assay in which the enzymatic cleavage of hippuryl-L-histidyl-L-leucine to form histidyl-leucine and hippurate was determined colourimetrically by a cyanuric chloride/dioxane reagent.


RESULTS
The FA-I produced a marked dose-dependent reduction in mean arterial pressure (MAP) in SHR and WKY rats, with an ED(50) of 1.09 and 1.05 mg/kg, respectively (p < 0.01). Furthermore, FA-I at 10 mg/kg strongly inhibited the angiotensin I-induced rise in MAP (p < 0.01). This response was comparable to that of captopril at 20 microg/kg. In the in vitro assay, ACE activity was inhibited with an IC(50) of 0.8 mg/ml. The qualitative phytochemical analysis of FA-I indicated the presence of glycoconjugates and peptides.


CONCLUSIONS
These results suggest that the hypotensive effect of G. procumbens may be due, in part, to the glycoconjugated or peptidal substances found in FA-I that exhibit an inhibitory effect on ACE.
Hoe
See-Ziau
SZ
Department of Physiology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
Kamaruddin
Mohd Yusof
MY
Lam
Sau-Kuen
SK
D000806:Angiotensin-Converting Enzyme Inhibitors / Q000494:pharmacology*; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D019659:Asteraceae / Q000737:chemistry*; D002216:Captopril / Q000494:pharmacology; D006973:Hypertension / Q000188:drug therapy*; D008517:Phytotherapy / Q000379:methods*; D010936:Plant Extracts / Q000494:pharmacology*; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY
D000806:Angiotensin-Converting Enzyme Inhibitors; D000959:Antihypertensive Agents; D010936:Plant Extracts; D002216:Captopril