The chorioallantoic membrane in irritation testing.

The chorioallantoic membrane (CAM) of the chick embryo is a fusion membrane with a blood vessel complex. It was examined as a possible means of predicting the irritant potential of chemicals for the conjunctiva, as observed in the Draize eye test. Nine chemicals of known irritancy potential for the eye in vivo were selected from published data, and each was tested at four different concentrations. The treated CAMs were examined macroscopically at 4, 24 and 48 hr after treatment, and were then prepared for histological examination. A dose response was observed for each chemical. In only four of the nine chemicals could the response in the CAM be considered to predict the in vivo activity. In another two, the correlation was poor. Three chemicals, glycerine, polyethylene glycol and Tween 80, all reported to be harmless to the eye, were embryotoxic at more than one concentration. Histological changes were degeneration or necrosis at the treated site without the chemical features of heterophil (chicken neutrophil) infiltration or significant macrophage infiltration. It is concluded that the CAM is not a suitable tissue for predicting in vivo irritant potential of substances for the conjunctiva, and that it provides no more information than could be obtained from cell cultures.

The effect and mode of action of zinc pyrithione on cell growth. II. In vivo studies.

The effect of topical application of the anti-dandruff agent zinc pyrithione (ZnPTO) on epidermal DNA synthesis in normal and hexadecane-stimulated rat skin was investigated. Autoradiography was used to determine the percentage of epidermal cells labelled with [3H]thymidine (labelling index). ZnPTO at 1% in shampoo base caused a slight increase in the labelling index in normal skin, similar to the effect of the shampoo base alone. No effect of 1% ZnPTO as an aqueous dispersion was observed. ZnPTO at 1% in shampoo base did not reduce the large increase in labelling index produced by hexadecane, nor did shampoo base alone or 1% ZnPTO in water. The shampoo base with or without 1% ZnPTO had only a very slight effect on the histopathology of normal and hexadecane-treated skin, and 1% ZnPTO in water had no effect. It is concluded that the in vitro potential of ZnPTO to cause growth inhibition is not achieved in vivo, presumably because of low percutaneous absorption. This evidence does not support a cytostatic mode of action in clearing dandruff.