We have obtained evidence by autoradiography and immunocytochemistry that mature secretory granules of the pancreatic B-cell gain access to a lysosomal compartment (multigranular or crinophagic bodies) where the secretory granule content is degraded . Whereas the mature secretory granule content shows both insulin and C-peptide (proinsulin) immunoreactivities, in crinophagic bodies only insulin, but not C-peptide, immunoreactivity was detectable . The absence of C-peptide (proinsulin) immunoreactivity in multigranular bodies, i.e., in early morphological stages of lysosomal digestion, was compatible with the ready access and breakdown of C-peptide and/or proinsulin by lysosomal degrading enzymes, while the insulin crystallized in secretory granule cores remained relatively protected . However, in the final stage of lysosomal digestion, i .e., in residual bodies where the secretory granule core material is no longer present, insulin immunoreactivity became undetectable . Lysosomal digestion thus appears to be a normal pathway for insulin degradation in the pancreatic B-cell.The pancreatic B-cell shares with other polypeptide-secreting cells the ability to store its secretory products within cytoplasmic granules available for release by exocytosis (1, 2). However, the totality of insulin manufactured is not destined to be secreted, since it has been shown that the B-cell can degrade a significant portion of its own secretory product (3, 4). One commonly assumed mechanism of intracellular degradation ofinsulin by the B-cell is the fusion ofsecretory granules with primary lysosomes (5, 6), a mechanism called granulolysis or crinophagy and initially described in the mammotroph cells ofthe anterior pituitary (7) and pancreatic A-cells (8) . In the B-cell, morphological evidence for crinophagy consists of cytoplasmic organelles (secondary lysosomes) that present a very variable morphology but usually contain dense masses resembling a-secretory granule cores. The lysosomal nature of these structures (also called crinophagic or multigranular bodies) is evidenced by their content in marker lysosomal enzymes such as acid phosphatase or arylsulfatase (9), but whether the content ofthe granule core-like material is related to insulin polypeptides has not been ascertained. For this purpose, we have followed, by electron microscopic autoradiography, the labeling of the multigranular bodies in pulsechase experiment with tritiated leucine, and determined their 222 immunoreactive content using anti-insulin and anti-C-peptide antisera revealed by the protein A-gold method. MATERIALS AND METHODSRat islets of Langerhans in sections of pancreatic tissue or isolated by collagenase digestion (10) were studied throughout . The material examined originated from the tissue store of the laboratory . All blocks were from five untreated normal rats, the pancreas (or isolated islets) of which were fixed in 2 .5% glutaraldehyde alone or with a mixture of 1 .25% glutaraldehyde, I % paraformaldehyde, and 0 .02% trinitrocresol (11), then...

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Urocortin (Ucn) 2 is a new member of the corticotrophin-releasing hormone (CRH) neuropeptide family that is expressed in the central nervous system and peripheral tissues. However, the expression levels of Ucn 2 in various tissues of the rat remains unclear. Thus, the aim of the present study was to characterise the expression of Ucn 2 in the various tissues of the rat. Reverse transcriptase-polymerase chain reaction analysis demonstrated that Ucn 2 mRNA is expressed in the hypothalamus, pituitary, adrenal, stomach, skin, ovary, uterus and skeletal muscle. Histologically, Ucn 2 mRNA and Ucn 2-like immunoreactivity (LI) were demonstrated in both the anterior and intermediate lobes of the pituitary, but not detected in the posterior lobe. Furthermore, all Ucn 2-positive cells in the anterior and intermediate lobes were also positive for beta-endorphin. Ucn 2 mRNA was detected in the adrenal cortex and medulla although Ucn 2-LI was only found in the adrenal medulla. High-performance liquid chromatography analysis of hypothalamic, pituitary, and adrenal extracts showed that the main Ucn 2-LI peak occurred at the same molecular size as that of synthetic Ucn 2. These results suggest that Ucn 2 is synthesised in various tissues, including the anterior and intermediate lobes of the pituitary and the adrenal.

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