Heterogeneity of immunoreactive dynorphin B-like material in human, rat, rabbit and guinea-pig heart

Intracrine Endorphinergic Systems in Modulation of Myocardial Differentiation

A wide variety of peptides not only interact with the cell surface, but govern complex signaling from inside the cell. This has been referred to as an "intracrine" action, and the orchestrating molecules as "intracrines". Here, we review the intracrine action of dynorphin B, a bioactive end-product of the prodynorphin gene, on nuclear opioid receptors and nuclear protein kinase C signaling to stimulate the transcription of a gene program of cardiogenesis. The ability of intracrine dynorphin B to prime the transcription of its own coding gene in isolated nuclei is discussed as a feed-forward loop of gene expression amplification and synchronization. We describe the role of hyaluronan mixed esters of butyric and retinoic acids as synthetic intracrines, controlling prodynorphin gene expression, cardiogenesis, and cardiac repair. We also discuss the increase in prodynorphin gene transcription and intracellular dynorphin B afforded by electromagnetic fields in stem cells, as a mechanism of cardiogenic signaling and enhancement in the yield of stem cell-derived cardiomyocytes. We underline the possibility of using the diffusive features of physical energies to modulate intracrinergic systems without the needs of viral vector-mediated gene transfer technologies, and prompt the exploration of this hypothesis in the near future.

Relative contribution of endogenous opioids to myocardial ischemic tolerance1

BACKGROUND

Opioid preconditioning by exogenous opioids experimentally protects the myocardium against ischemia/reflow injury. Additionally, endogenous opioid peptides released during ischemia also enhance ischemic tolerance. Promiscuous opioid receptor agonists conceal the differential contribution of the mu, delta, and kappa opioid subtypes. This study compared the impact of selective delta and kappa opioid receptor antagonists on postischemic functional and metabolic recovery. Also measured were changing levels of peptides dynorphin B and met-enkephalin during ischemia/reflow injury.

MATERIALS AND METHODS

Using the rabbit Langendorff model, the functional recovery of control hearts (following 2 h of global ischemia) was compared to hearts pretreated with delta antagonist NTB (1 microM) or kappa antagonist, nor-BNI (1 microM). Measures included percentage of return of isovolumetric developed pressure (LVDP), myocardial oxygen consumption (MVO(2)) and coronary flow (CF). In additional studies, untreated hearts were harvested at baseline, following ischemia, or following 5 or 45 min of reflow. Tissue concentrations of met-enkephalin and dynorphin B were measured by RIA.

RESULTS

After 45 min of reflow, hearts pretreated with either NTB or nor-BNI showed impaired functional recovery by a decrease in LVDP (P < 0.05); however, MVO(2) or CF were unaffected. RIA data shows that baseline levels of both peptides are similar and increase significantly during ischemia, but reflow dynorphin levels drop far below baseline, while met-enkephalin returns to baseline.

CONCLUSION

Antagonism of both delta and kappa opioid receptor subtypes equally contributes to impaired left ventricular function, independent of altered perfusion or metabolic rate. Endogenous kappa-receptor agonists may contribute primarily during ischemia or early reflow, since low late reflow dynorphin content did not correlate with altered functional recovery.

Cardiac opioids

Opioid peptides have long been considered as neuropeptides or neurotransmitters. The more recent discovery of these same peptides in non-neuronal tissue suggests that the peptides may have autocrine, paracrine, or endocrine functions as well. The opioid peptides, enkephalins, dynorphins, and endorphins, have been found in isolated cardiac myocytes and heart tissue. This review will cover the recent literature on opioid peptides in respect to cardiac distribution, biochemistry, and function.

Characterization of beta-endorphin- and alpha-MSH-related peptides in rat heart

POMC-derived peptides and mRNA have been identified in heart tissue, although POMC processing has not been fully characterized. In the present study, we found that beta-lipotropin and ACTH were localized in rat heart, although they were almost entirely converted to beta-endorphin- and alpha-MSH-related peptides. Ion exchange HPLC analysis revealed that beta-endorphin(1-31) was further processed to alpha-N-acetyl-beta-endorphin(1-31), which comprised 35.9 +/- 0.1% of total immunoreactivity, and smaller amounts of beta-endorphin(1-27), beta-endorphin(1-26), and their alpha-N-acetylated derivates. The predominant alpha-MSH immunoreactive peptides coeluted with alpha-MSH and N,O-diacetyl-alpha-MSH by reverse-phase HPLC, although small amounts of ACTH(1-13)-NH2 were also present. Thus, multiple forms of beta-endorphin and alpha-MSH are localized in rat heart. beta-Endorphin(1-31) is a minor constituent, however, indicating that nonopioid beta-endorphin peptides predominate.

Prodynorphin mRNA expression in adult cultured rat ventricular cardiac myocytes

Prodynorphin mRNA was synthesized both in rat atrial and ventricular tissue, as well as in adult cultured rat ventricular cardiac myocytes. In the cultured cells, the content of prodynorphin mRNA did not differ from that detected in the original ventricle, indicating that the myocardial cell is an important source for prodynorphin mRNA in the rat ventricular tissue. This study demonstrated the presence of immunoreactive dynorphin B-like material in the cultured cardiomyocytes. Gel permeation chromatography analysis of this material revealed the presence of forms with an apparently higher molecular weight than authentic dynorphin B.

Immunoreactive dynorphin A-like material in extracted human hypothalamic-hypophysial plasma

Immunoreactive dynorphin A-like material (ir-dyn A) in human plasma was measured by a validated radioimmunoassay. In peripheral plasma extracts mean concentrations between 20 and 40 fmol/ml were determined in volunteers and in patients with pituitary adenomas. In this latter group superimposable levels were detected three days before and during transsphenoidal microsurgery. Interestingly, ir-dyn A levels evaluated in extracts of hypothalamic-hypophysial plasma obtained during surgery, just after tumor removal, were 4-5 times higher than in peripheral plasma. Reverse-phase high performance liquid chromatography (rp-HPLC) of extracts of peripheral plasma samples revealed two immunoreactive peaks. The major form had the same retention time of dyn A-(1-32); whereas a second, more lipophilic, peak eluted later and was not further characterized. In contrast, rp-HPLC analysis of extracts of plasma collected from the suprapituitary region displayed only one peak eluting in the position of synthetic dyn A-(1-17). The presence of dyn-related peptides in hypothalamic-hypophysial plasma supports the hypothesis that they may play a part in the regulation of hypothalamic and/or pituitary functions in humans.

The distribution of neuropeptide Y and dynorphin immunoreactivity in the brain and pituitary gland of the platyfish, Xiphophorus maculatus, from birth to sexual maturity

Immunoreactive neuropeptide Y and dynorphin have been localized in the brain and pituitary gland of the platyfish, Xiphophorus maculatus, at different ages and stages of development from birth to sexual maturity. Immunoreactive neuropeptide Y was found in perikarya and tracts of the nucleus olfactoretinalis, telencephalon, ventral tegmentum and in the neurohypophysis and in the three regions of the adenohypophysis. Immunoreactive dynorphin was found in nerve tracts in the olfactory bulb and in cells of the pars intermedia and the rostral pars distalis of the pituitary gland.