NEW CARDIOTONIC FROM Bufo paracnemis PAROTOID SECRETION

ARNAUD-BATISTA, F.J.; FONTELES, M.C.; SANTOS, C.F.; REFOSCO. R.M.; OLIVEIRA, R.G.; COSTA, P.P.C.; CARDI, B.A.; CARVALHO, K.M.; NASCIMENTO, N.R.F.

Superior Institute of Biomedicine, State University of Ceara.

Digitalis glycosides are widely used to treat cardiac failure but a narrow therapeutic index limits its use. A new cardiotonic was isolated from Bufo paracnemis by HPLC using the following protocol. 1g of the venom was dissolved in 80% ethanol (V/V), centrifuged at 10.000g during 30 min and the supernatant was eluted with HPLC-grade water using a linear gradient of 0-40% acetonitrile on a C18 column. The peak 3 (P3) was then lyophilized and diluted in 5% DMSO in saline (V/V) for pharmacological experiments. The cardiotonic activity was evaluated in the isolated guinea-pig heart perfused and on the electrically driven guinea-pig left atrium. P3 (10, 100 and 1000 mg.ml-1) induced an increase in force by 23.5 ± 8.3 %; 50 ± 14.7% and 279.2 ± 35.7 % in the perfused heart. The addition of P3 up to 100  mg.ml-1 to electrically stimulated left atria with submaximal pulses (5 ms, 2.5 Hz) induced a maximal increase in force of 769.5 ± 126 % (CE50 = 128.9 [ 59.5-279.6] mg.ml-1) compared with 408.3 ± 72.2 % (CE50 =  0.14 [ 0.09-0.22] mg.ml-1) achieved with digoxin. We also evaluated the effects of P3 on selected electrocardiographic parameters on the rat EKG.  For this purpose, male Wistar-Kyoto rats (300-350g) were anesthetized and infused with (300 mg.Kg-1.min-1)  P3 or digoxine and EKG acquired by subcutaneous platinum electrodes. The infusion of digoxine induced classical signs of intoxication: bradycardia (311±10 bpm vs. 258±7.7 bpm before arrhythmias), increase in PR segment duration (13.4 ±3.4 ms control vs. 33.4 ± 6.7 ms, before severe arrhythmia initiated), J-point depression (since 1st minute of infusion). Other findings include, T depression, second-grade atrio-ventricular block (AVB) under 4-5 min infusion and cardiac arrest (at 6-7 min) leading animals to death. On the other hand, the infusion of P3 during 20 minutes was devoided of EKG alterations. This results supports that P3 is a promising cardiotonic agent with larger safety index than digitals.

KEY WORDS: Cardiac failure, pharmacological therapy

SUPPORT: FUNCAP, CNPqCorrespondence to: Nilberto R. F. do Nascimento, Instituto Superior de Biomedicina, UECE, Fortaleza, Ceará, (85) 3101-9836, E-mail: nilberto@uece.br.