Relative irritancy of free fatty acids of different chain length

Free fatty acids of human skin surface lipids have previously been implicated in the pathogenesis of acne vulgaris because of their apparent irritant and comedogenic properties. Prior studies on the relative irritancy of free fatty acids revealed the saturated C8 to C14 fatty acids and a C18 dienoic unsaturated fatty acid (linoleic) to be most irritating. Saturated free fatty acids from C3 to C18, and unsaturated C18 free fatty acids were applied daily under occlusive patch tests to human skin until detectable erythema appeared. The most irritating fatty acids were C8 through C12. Of the unsaturated fatty acids tested, only linoleic acid produced irritation.

Cytochemical electron microscopic studies of the action of phorbol myristate acetate on platelets

Phorbol myristate acetate (PMA), the active principle of croton oil, is a potent platelet aggregating agent. A previous electron microscopic study indicated that PMA caused selective labilization of platelet granules. The present investigation has employed cytochemical procedures to clarify problems concerning the action of PMA on platelets. Results of this study confirm the suggestion that vacuoles in PMA-treated platelets derive primarily from granules, and demonstrate that the swollen vacuoles are continuous with channels of the open canalicular system (OCS) and surrounding plasma. Despite loss of the barrier separating vacuolated granules from the OCS, the contents of the organelles were not extruded from the PMA aggregated platelets. Stabilization of platelet surface membranes did not inhibit the action of PMA on platelet granules, and examination of replicas of freeze-fractured PMA platelets failed to reveal any specific injury produced by the agent. The findings have elucidated some of the effects of PMA on platelet structure, but have not solved the basic mechanism of drug action.

Ultrastructural features on the platelet response to phorbol myristate acetate

Phorbol myristate acetate (PMA) the active ingredient of croton oil, is a potent stimulus of irreversible platelet aggregation. The present study has examined the effects of PMA on platelet fine structure during aggregation and after incubation. PMA appears to act primarily on channels of the open canalicular system and intracellular granules. Small amounts of the agent cause dilatation of some open channels and conversion of granules to swollen vacuoles. Platelet discoid shape is not affected significantly by the changes in channels and vacuoles, and aggregation occurs without shape change. EDTA inhibits PMA-induced aggregation but does not prevent the conversion of platelet granules to vacuoles. In unstirred systems PMA causes similar changes in platelet fine structure and spontaneous aggregation. The drug appears to affect the permeability barrier separating granule contents from open channels, thereby leading to osmotic swelling of the storage organelles. PMA is the first agent observed to have a selective influence on the stability of platelet granules.