“…Reduced first-pass effects after vaginal application of estrogens (Rigg et al, 1978) and propranolol (Patel et al, 1983) have been reported. Recently, comparative studies on the peptidase activity against enkephalins, substance P, insulin, and proinsulin in the absorptive mucous membranes in the rabbit have demonstrated that the supernatants of homogenates of the vaginal, nasal, buccal, rectal, and ileal mucous membranes exhibit similar proteolytic activity (Lee, 1988;Lee and Yamamoto, 1990).…”