1. Analytical subcellular fractionation techniques have been applied to endoscopic human rectal biopsies to study the localization of enteroglucagon, somatostatin, vasoactive intestinal peptide and the properties of the principal subcellular organelles.

2. The peptide hormones, detected by radioimmunoassay, showed particulate localizations with single peaks in the density gradients for enteroglucagon (modal density 1.25) and somatostatin (modal density 1.23). Vasoactive intestinal peptide showed a less discrete localization but demonstrated a major peak (modal density, 1.17) with a small subsidiary peak (modal density 1.24).

3. The following organelles, characterized by their marker enzymes, were located in the density gradients; plasma membrane (5′-nucleotidase), mitochondria (malate dehydrogenase), peroxisomes (catalase), lysosomes (β-N-acetyl-d-glucosaminidase), endoplasmic reticulum (neutral α-d-glucosidase) and cytosol (lactate dehydrogenase).

4. This technique can be used to investigate disease of the human rectum at a subcellular level.

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