Regulation of intestinal goblet cell secretion. I. Role of parasympathetic stimulation

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Abstract
The in vivo effects of the parasympathomimetic drug pilocarpine on rat intestinal goblet cells were analyzed by autoradiography, light microscopy (LM) and EM. Pilocarpine accelerated the release of mucus by compound exocytosis from crypt (but not surface) goblet cells throughout the small and large intestine. Pilocarpine-induced mucus secretion was blocked by atropine alone in ileum and colon, total inhibition in proximal small intestine required a combination of atropine and tubocurarine. The sensitivity of morphological-autoradiographic methods for detection of goblet cell secretion was compared with that of a biochemical detection method, separation of labeled high-MW glycoproteins by Sepharose 4B gel filtration of luminal washings. Even when secretion of labeled mucus by compound exocytosis was demonstrated by LM, EM and autoradiography gel filtration assay of luminal washings from pilocarpine-injected rats did not reveal an increase in labeled high-MW glucoproteins. Autoradiographs of mucosal tissue after luminal washing showed that newly secreted, labeled mucus was retained in the crypts and was unavailable to the biochemical assay. Direct observation of exocytosis in individual goblet cells apparently provided a qualitative but sensitive assay for short-term acceleration of intestinal mucus secretion.