Effect of papaya latex extract on gravid and non-gravid rat uterine preparations in vitro

Abstract

In search of uterotonic principles, papaya ( Carica papaya, Caricaceae) latex extract (PLE) was tested on rat uterine preparations in vitro at various stages of the estrous cycle and gestation periods. Rat uterine contractile activity was remarkably increased by different doses of PLE in proestrus and estrus stages compared to metestrus and diestrus stages of the estrous cycles. The maximum contractile activity of the uterus was observed at the later stages of pregnancy which correspond with the peak level of estrogen in the plasma. A direct dose-dependent spasmodic action with increased frequency and amplitude was observed with PLE in all non-gravid uterine preparations. Pretreatment of the tissue with phenoxybenzamine (PB) non-competitively blocked the effect of PLE. Blocking of the 5-HT receptors with methysergide partially blocked the excitatory response to PLE. Pretreating the tissue with Indomethacin, a cyclo-oxygenase inhibitor, had no effect on the response to PLE. The release of PLE induced mast cell degranulation and subsequent release of heparin, biogenic amines or prostaglandins (PGs) was ruled out by pretreating the tissue with sodium cromoglycate, a mast cell stabilizer. Pure papain induced uterine contractions were not sustained for a longer period and at higher concentrations the receptor proteins were affected by the enzymatic action of papain. From this study it is evident that the crude papaya latex contain a uterotonic principle which might be a combination of enzymes, alkaloids and other substances which can evoke sustained contraction of the uterus acting mainly on the alpha adrenergic receptor population of the uterus at different stages.