Opioids in neural and nonneural tissues

Developmental changes in the inhibition of cultured rat uterine cell proliferation by opioid peptides

Opioid peptides are negative regulators of cell proliferation in several organs including the uterus. In the present study, the ontogeny of the direct inhibitory action of opioid peptides on the proliferation of cultured rat uterine cells was investigated. Uteri of 7, 14, 21, 28, 35 and 60-day-old rats were removed in a sterile way. Tissue blocks were dispersed by limited digestions with trypsin and collagenase. Cells were cultured in enriched Dulbecco's modified Eagle's medium (DMEM). Treatments were present during the entire culture period. Cell densities of the monolayers were determined by counting the cells following trypsinization and trypan blue exclusion. Rat uterine mixed cell cultures grew to confluence within 10 days. The average population doubling time gradually increased with the age of animals. Epidermal growth factor (EGF) increased cell densities of cultures from all age groups. The oestradiol (E2)-responsiveness appeared at 21 days of age. The effect of [D-Met2-Pro5]-enkephalinamide (ENK) was biphasic. ENK and [Met5]-enkephalin (OGF) decreased cell densities of both unstimulated and EGF-stimulated cultures from 7-day-old rats to the same extent. ENK failed to act in 14-day-old animals. From 21 days of age on, the E2- or EGF-stimulated proliferation was inhibited only by ENK and DAMGO, while 30 nm DPDPE, Dynorhin-A, OGF, [Leu5]-enkephalin, beta-endorphin, and morphiceptin were ineffective. The half-inhibitory concentration of ENK was 0.3 nm. The effects of ENK were prevented by concomitant treatment with naloxone. Our novel data demonstrate two different phases of the inhibitory action of opioid peptides on rat uterine cell proliferation during ontogeny with an insensitive interval in between.

Kappa1-opioid binding sites are the dominant opioid binding sites in surgical specimens of human pheochromocytomas and in a human pheochromocytoma (KAT45) cell line

The adrenal medulla produces opioids which exert paracrine effects on adrenal cortical and chromaffin cells and on adrenal splanchnic nerves, via specific binding sites. The opioid binding sites in the adrenals are detectable mainly in the medullary part of it and differ in type between species. Thus, the bovine adrenal medulla contains mostly kappa-opioid binding sites and fewer delta- and mu-opioid binding sites while primate adrenals contain mainly delta sites and few kappa-opioid binding sites. Most chromaffin cell tumors, the pheochromocytomas, produce opioids which suppress catecholamine production by the tumor. The aim of the present work was to identify the types of opioid binding sites in human pheochromocytomas. For this purpose, we characterized the opioid binding sites on crude membrane fractions prepared from 14 surgically excised pheohromocytomas and on whole KAT45 cells, a recently characterized human pheochromocytoma cell line. Our data showed that human pheohromocytomas are heterogeneous, as expected, with regard to the production of catecholamines and the distribution and profile of their opioid binding sites. Indeed, only one out of the 14 pheochromocytomas expressed exclusively delta and mu opioid sites, while in the remaining 13 tumors kappa-type binding sites were dominant. The KAT45 cell line possessed a significant number of kappa1 binding sites, fewer kappa2-opioid binding sites and kappa3-opioid binding sites, and minimal binding capacity for delta- and mu-opioid receptor agonists sites. More specifically, the kappa1 sites/cell were approximately 18,000, the kappa2 4500/cell and the kappa3 sites 2000/cell. Our findings for the surgical specimens and the cell line combined with previously published pharmacological data obtained from KAT45 cells suggest that kappa sites appear to be the most prevalent opioid binding sites in pheochromocytomas. Finally, in normal bovine adrenals the profile of opioid binding sites differs in adrenaline and noradrenaline producing chromaffin cells. To test the hypothesis that the type of catecholamine produced by a pheochromocytoma depends on its cell of origin, we compared our binding data with the catecholamine content of each pheochromocytoma examined. We found no correlation between the type of the predominant catecholamine produced and the opioid binding profile of each tumor suggesting that this hypothesis may not be valid.

The PC12 rat pheochromocytoma cell line expresses the prodynorphin gene and secretes the 8 kDa dynorphin product

Most adrenal chromaffin cells synthesize opioids derived from proenkephalin but not from prodynorphin. However, human pheochromocytomas and the PC12 rat pheochromocytoma cell line synthesize dynorphins. The aim of this study was to confirm the presence of the authentic prodynorphin transcript and its dynorphin product in PC12 cells. We have found that the sequence of a 458 bp cDNA fragment derived from RT-PCR amplification of total PC12 RNA was in complete accordance with the published sequence of the equivalent region of the prodynorphin gene. It encodes the potent endogenous kappa opioid agonists alpha-neo-endorphin, dynorphin A and dynorphin B. Furthermore, immunoaffinity-purified PC12 cell extracts were subjected to RP-HPLC. Most of its IR-dynorphin eluted on a peak exhibiting the retention time of similarly treated rat anterior pituitary. The expression of the prodynorphin gene in pheochromocytomas can be explained as either the result of (a) the process of dedifferentiation of chromaffin cells to pheochromocytoma which may thus cause the expression of a previously unexpressed prodynorphin or that (b) those pheochromocytomas expressing the prodynorphin gene derive from the few, centrally located chromaffin cells, which express this gene even under normal conditions.

PC12 cells as a model to study the effects of opioids on normal and tumoral adrenal chromaffin cells

Normal adrenal chromaffin cells produce delta opioid peptides while at the same time they have mainly kappa opioid receptors. This paper describes our date regarding the expression of the prodynorphin gene, the precursor of a family of endogenous kappa opioid ligands, in the PC12 rat pheochromocytoma cell line, and the effects of synthetic kappa opioid agonists and of Naloxone on various aspects of PC12 cell function including their secretion of catecholamines, proliferation and differentiation. This is the first part of a series of projects aimed at studying, (a) the conditions under which the prodynorphin gene is expressed in normal adrenomedullary cells, and (b) the physiological role of the endogenous kappa opioids in the physiology of the adrenal medulla.

Opioids inhibit dopamine secretion from PC12 rat pheochromocytoma cells in a naloxone-reversible manner

Opioids inhibit the release of catecholamines in the nervous system. Normal adrenal chromaffin cells produce delta opioids and they respond to them by suppressing the release of their catecholamines. Chromaffin cell tumors, the pheochromocytomas, produce mainly kappa opioids. The aim of this work was: (a) to test if pheochromocytomas retain the response of normal chromaffin cell catecholamines to delta opioids and to naloxone (a general opioid antagonist), and (b) to test if kappa opioids exert any specific effect on catecholamine release from these tumors. Since we have previously shown that, in common with human pheochromocytomas, the PC12 rat pheochromocytoma cells express the prodynorphin gene and secret its kappa opioid products, we used these cells to examine the effect of several opioid agonists and of naloxone on basal, nicotine-, and KCl-induced dopamine release. Dopamine is the main PC12 catecholamine. We have found that the specific kappa opioid agonist U-69593 inhibited the release of dopamine in a dose-dependent manner (IC50=0.5 x 10(-8)M). Under basal conditions the mean concentration of dopamine in the culture media was 11.25 +/- 0.57 ng/mg of total cellular protein (n=13). A 30 min exposure to U-69593 at 10(-6) M suppressed basal dopamine release to 58 +/- 2% (n=7) of controls. A 12 hr pre-incubation with U-69593 caused the same degree of suppression. The effect of the synthetic kappa opioid agonist dynorphin A was indistinguishable from that of U-69593. DADLE (a mu and delta synthetic opioid agonist) was significantly less effective in suppressing dopamine release (IC50=10(-7)M). The concentration of dopamine following exposure to 10-6 M of DADLE for 30 min was 74 +/- 5% of the controls (n=4). The mu opioid agonist DAGO was ineffective. The suppressive effect of all opioid agonists was blocked by naloxone suggesting that conventional opioid receptors were involved.

Role of opioid peptides in the regulation of DNA synthesis in immature rat uterus

The effects of a single dose of naloxone and of [D-Met2,Pro5]enkephalinamide on the DNA synthesis in the uterus of 7, 14 and 21-day-old rat were studied. After [D-Met2,Pro5]enkephalinamide treatment, an age-dependent decrease in in vitro [3H]thymidine incorporation into DNA was observed in all studied age groups. In the 21-day-old age group a reduced rate of DNA synthesis was detected for 12 h after [D-Met2,Pro5]enkephalinamide treatment followed by the return to control values at 24 h. The rate of inhibition was more marked in the younger age groups. The effect was also more pronounced in younger animals. Specific [3H]naloxone binding was detected both in membrane and nuclear fractions of uterine homogenates. While no age-related changes in binding affinities were found, the number of binding sites varied characteristically during development. Our data suggest the novel involvement of opioid peptides and their receptors in the regulation of uterine development.