Intestinal secretion of mucin in chronically reserpine-treated rats.

Intestinal glycoprotein synthesis and secretion were measured in vivo and in vitro in rats treated for 7 days with reserpine. Goblet cell mucin was measured by radioimmunoassay. Reserpine-treated rats contained 1.4 times more mucin in intestinal tissue than control rats (P less than 0.05) and incorporated [1-14C]glucosamine in vivo at 1.52 times the rate of controls (P less than 0.01). Intestinal slices incubated for 90 min in vivo incorporated 1.4 times more [14C]glucosamine (P less than 0.001) and 3.0 times more [3H]threonine (P less than 0.01) into protein of reserpine-treated tissue than controls. The extra 14C was localized to mucin and to smaller components that had affinity for Concanavalin-A-Sepharose, did not bind to mucin antibody, and were therefore nonmucin glycopeptides. In vitro secretion of mucin was three times greater for reserpine-treated tissue than for control tissue (P less than 0.0001). There was an impairment in the mucin secretory response of reserpine-treated tissue to the addition of cholera toxin. Thus, chronic reserpine treatment results primarily in a generalized increase in the rate of intestinal glycoprotein synthesis, subsequent accumulation in tissues, and an increased (but not fully proportional) secretion of mucin. We speculate that in cystic fibrosis a similar sequence of glycoprotein abnormalities may be responsible for the gradual obliteration of exocrine gland ducts with viscous mucus.