Ultrastructural evidence for beta-endorphin-like immunoreactivity in the nervous system of the rat duodenum

Biological redundancy of endogenous GPCR ligands in the gut and the potential for endogenous functional selectivity

This review focuses on the existence and function of multiple endogenous agonists of the somatostatin and opioid receptors with an emphasis on their expression in the gastrointestinal tract. These agonists generally arise from the proteolytic cleavage of prepropeptides during peptide maturation or from degradation of peptides by extracellular or intracellular endopeptidases. In other examples, endogenous peptide agonists for the same G protein-coupled receptors can be products of distinct genes but contain high sequence homology. This apparent biological redundancy has recently been challenged by the realization that different ligands may engender distinct receptor conformations linked to different intracellular signaling profiles and, as such the existence of distinct ligands may underlie mechanisms to finely tune physiological responses. We propose that further characterization of signaling pathways activated by these endogenous ligands will provide invaluable insight into the mechanisms governing biased agonism. Moreover, these ligands may prove useful in the design of novel therapeutic tools to target distinct signaling pathways, thereby favoring desirable effects and limiting detrimental on-target effects. Finally we will discuss the limitations of this area of research and we will highlight the difficulties that need to be addressed when examining endogenous bias in tissues and in animals.

The effect of ethanol on the biosynthesis and regulation of opioid peptides

Alcoholism and alcohol abuse are serious health problems. Alcohol is known to influence the activity of a number of biological systems, for example the hormonal and neuronal systems. One of the biological systems whose activity is greatly influenced by alcohol is the endogenous opiate system. Alcohol modifies the function of both opiate receptors and opioid peptides. In fact it has been proposed that many of the effects of ethanol are mediated by its effects on the endogenous opiate system. This review will present results from various laboratories on the effects of acute and chronic ethanol treatments on various species, and on the release, biosynthesis and post-translational processing of the endorphins, enkephalins and dynorphins, the three known families of endogenous opioid peptides. Furthermore, the effect of acute and chronic ethanol consumption on the beta-endorphin system in man, and the possible implications of the functional activity of the endogenous opiate system for the genetic predisposition to alcoholism will be discussed.

beta-Endorphin is contained within presumptive receptosomes and lysosomes of the myenteric plexus of the rat

Using the microdissection technique combined with the pre-embedding immunostaining method, beta-endorphin immunoreactivity (beta-END-IR) was noted within ring-shaped elements lying singly or in groups in nerve processes of the duodenal myenteric plexus of the rat. The beta-END-IR was noted as a strongly electron-dense precipitate rim on the inner surface of these elements. The membrane of the ring-shaped element as well as the beta-END precipitate rim were strikingly often unilaterally interrupted at the same site. Some of the ring-shaped beta-END-positive elements were noted within large osmiophilic bodies. The beta-END immunoreactive ring structure was 60-300 nm in diameter and possessed an empty electron-lucent space as well as a thin electron-dense membrane. The osmiophilic bodies were pleormorph, had a mean diameter of 250 nm and revealed thick electron-opaque membranes. Their inner spaces were homogenously filled with electron-dense materials. These findings might indicate that the beta-END-IR-containing ring-shaped elements represent receptosomes and that the pleomorph osmiophilic bodies are identical to lysosomes.