Cardiovascular active substances from the straw mushroom, Volvariella volvacea

The straw mushroom Volvariella volvacea is one of the common edible mushrooms in Hong Kong and is widely cultivated in Southeast Asian countries. It has been reported to produce a hypotensive response in animals including humans. An aqueous extract of the mushroom (SME) was prepared and given through intravenous injections to normotensive rats. The blood pressure changes produced by SME alone or in the presence of various drugs were studied. The effects of SME on the kidney function of water‐loaded rats and on isolated tissue preparations of the tail artery and right atrium were examined. An i.v. injection of SME produced a hypotensive effect in rats with an ED50 of 25 mg dry weight/kg body weight. This hypotensive effect of SME was attenuated or blunted in the presence of hexamethonium, phentolamine, pyrilamine and cimetidine suggesting the involvement of the α‐adrenergic component of the autonomic system and/or histamineergic stimulation. SME did not increase urinary excretion nor sodium diuresis. It produced positive chronotropic and inotropic effects on isolated right atria and induced contraction of isolated tail artery strips. This latter contractile response was inhibited by antagonists of serotonin and α‐adrenoceptor, ketanserin and phentolamine respectively. Partial purification using dialysis and liquid chromatography revealed that the hypotensive active substances had molecular masses between 8000 and 12000 dalton. These substances were heat stable and resistant to trypsin digestion. In view of the similarity in blood pressure and cardiovascular response, SME might contain serotonin‐like substances.