The effect of long‐chain monoenes on prostaglandin E 2 synthesis by rat skin

In order to ascertain whether the dermal lesions observed in male rats fed rapeseed oils are due to impaired prostaglandin biosynthesis, endogenous levels of prostaglandin E 2 (PGE 2 ) in skin and the capacity of this tissue to synthesize PGE 2 from arachidonic acid was investigated. Male Sprague‐Dawley rats were fed from weaning for 8 weeks either a standard rat diet (chow) or semisynthetic diets containing 20% by weight of the following fat sources: corn oil; commercial lard; commercial lard to which was added 5.4% free erucic acid; rendered pig fat; or the following rapeseed oils: Brassica napus var. Zephyr; B. campestris var. Span; B. campestris var. Arlo (15%) and var. Echo (85%) designated HEAR (high erucic acid rapeseed). The long‐chain monoene content (18∶1, 20∶1, and 22∶1) of the diets fed ranged from 30 to 71 mole % and that of skin from 27 to 74 mole %. A significant (P<0.01) correlation was found between the level of 18∶2n−6 in the diet and the endogenous PGE 2 levels in skin and the capacity of this tissue to synthesize PGE 2 . No relationship was found between these two PGE 2 parameters and the level of erucic acid in the diet. The rate of turnover of PGE 2 appeared to be lower in rats fed rapeseed oil as evidenced by the relatively high endogenous PGE 2 levels when these oils were fed (96 to 105 μg/g). On the other hand, the lowest capacity for PGE 2 synthesis was found with skin from rats fed Zephyr rapeseed oil, rats which also had the most severe incidence of hair loss and dermal lesions. Significant (P<0.01) negative correlations were observed between the level of monoenes and specifically the level of oleic (18∶1n−9) acid in the diets and PGE 2 synthesis capacity of skin, possibly confirming the known inhibitory effect of 18∶1n−9 on the prostaglandin synthesizing enzyme system.