Co-localization of RNAs coding for phenylethanolamine N-methyltransferase and proenkephalin A in bovine and ovine adrenals

Intrafetal insulin-like growth factor-I infusion stimulates adrenal growth but not steroidogenesis in the sheep fetus during late gestation

We investigated the effects of an intrafetal infusion of IGF-I on adrenal growth and expression of the adrenal steroidogenic and catecholamine-synthetic enzyme mRNAs in the sheep fetus during late gestation. Fetal sheep were infused for 10 d with either IGF-I (26 microg/kg.h; n = 14) or saline (n = 10) between 120 and 130 d gestation, and adrenal glands were collected for morphological analysis and determination of the mRNA expression of steroidogenic and catecholamine-synthetic enzymes. Fetal body weight was not altered by IGF-I infusion; however, adrenal weight was significantly increased by 145% after IGF-I infusion. The density of cell nuclei within the fetal adrenal cortex (the zona glomerulosa and zona fasciculata), and within the adrenaline synthesizing zone of the adrenal medulla, was significantly less in the IGF-I-infused fetuses compared with the saline-infused group. Thus, based on cell-density measurements, there was a significant increase in cell size in the zona glomerulosa and zona fasciculata of the adrenal cortex and in the adrenaline-synthesizing zone of the adrenal medulla. There was no effect of IGF-I infusion on the adrenal mRNA expression of the steroidogenic or catecholamine-synthetic enzymes or on fetal plasma cortisol concentrations. In summary, infusion of IGF-I in late gestation resulted in a marked hypertrophy of the steroidogenic and adrenaline-containing cells of the fetal adrenal in the absence of changes in the mRNA levels of adrenal steroidogenic or catecholamine-synthetic enzymes or in fetal plasma cortisol concentrations. Thus, IGF-I infusion results in a dissociation of adrenal growth and function during late gestation.

Actions of hypoxia on catecholamine synthetic enzyme mRNA expression before and after development of adrenal innervation in the sheep fetus

We have investigated adrenal mRNA expression of the catecholamine synthetic enzymes tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) following acute hypoxia in fetal sheep before (< 105 days gestation, n = 20) and after (> 125 days gestation, n = 20) the development of adrenal innervation and following pretreatment with the nicotinic receptor anatgonist hexamethonium (n = 12). Total RNA was extracted from fetal adrenal glands collected at specific time points at 3-20 h after the onset of either hypoxia ( approximately 50% reduction in fetal arterial oxygen saturation (SO2) for 30 min), or normoxia. Before 105 days, there was a decrease in adrenal TH mRNA expression at 20 h after hypoxia and adrenal TH mRNA expression was directly related to the changes in arterial PO2 measured during normoxia and hypoxia. After 125 days, adrenal TH mRNA levels were suppressed for up to 12 h following hypoxia. In both age groups, adrenal PNMT mRNA expression increased at 3-5 h after hypoxia and was inversely related to the changes in fetal arterial PO2 during normoxia or hypoxia. After 125 days, the administration of hexamethonium (25 mg kg(-1), I.V.) reduced TH mRNA but not PNMT mRNA expression after normoxia. After hexamethonium pretreatment, there was no significant change in either adrenal TH or PNMT mRNA expression following hypoxia. We conclude that acute hypoxia differentially regulates adrenal TH and PNMT mRNA expression in the fetal sheep both before and after the development of adrenal innervation. After the development of adrenal innervation, however, the effect of acute hypoxia upon adrenal TH and PNMT mRNA expression is dependent upon neurogenic input acting via nicotinic receptors.

Glucocorticoids decrease phenylethanolamine N-methyltransferase mRNA expression in the immature foetal sheep adrenal

This study examined the impact of a chronic physiological elevation of plasma cortisol levels on adrenal catecholamine synthetic enzyme and proenkephalin A mRNA expression in foetal sheep. Cortisol (2.5-3. 0 mg.5 ml-1.24 h-1, n=9) or saline (0.9% saline, n=6) was infused into foetal sheep for 7 days between 109 days and 116 days gestation. Foetal plasma cortisol concentrations were higher (P<0.0005) in the cortisol infused foetuses when compared with the saline infused group (43.07+/-4.13 nmol.l-1 vs 1.67+/-0.10 nmol.l-1). There were no differences, however, in the plasma ACTH levels between the two groups. Using Northern blot analysis, adrenal phenylethanolamine N-methyltransferase (PNMT) mRNA expression was found to be reduced (P<0.005) fivefold in the cortisol infused foetuses when compared with the controls, as was the relative area of the adrenal medulla which stained positively with anti-PNMT (28.1+/-2.5% vs 44.8+/-4.8%, P<0.007). No effect of cortisol infusion was observed on adrenal tyrosine hydroxylase mRNA and protein expression or proenkephalin A mRNA expression. We conclude that before birth, adrenaline synthesis may be suppressed by a novel direct, or indirect, inhibitory effect of glucocorticoids on PNMT mRNA expression.

The new chromogranin-like protein NESP55 is preferentially localized in adrenaline-synthesizing cells of the bovine and rat adrenal medulla

The protein NESP55, a new member of the chromogranin family, is present in large dense-core secretory granules of neuroendocrine tissues. We investigated its cellular distribution in adrenal medulla with immunohistochemistry and in situ hybridization. A preferential co-localization of NESP55 with phenylethanolamine-N-methyltransferase in the adrenergic cell population was found by immunolabelling of consecutive sections. Noradrenergic cells also contained small amounts of NESP55, but the levels as measured by radioimmunoassay were five times lower. The distribution of NESP55 mRNA was similar to preproenkephalin mRNA which previously was shown to be confined to adrenaline-producing cells of the adrenal medulla. The present study indicates that stimulation of adrenergic cells will release significantly higher amounts of NESP55. The functional implications of this preferential secretion, however, have yet to be discovered.

The role of the pituitary-thyroid axis in the developmental regulation of enkephalin-containing peptides in the superior cervical ganglia and adrenal of the fetal sheep

We have postulated that sympathetic neurones may be one source of circulating enkephalins in the fetus. Therefore, we have investigated the effects of increasing gestational age on the content of the enkephalin-containing peptides in the superior cervical ganglia (SCG) of the fetal sheep during late gestation. We have also investigated the role of the pituitary-thyroid axis in the coordinate regulation of enkephalin-containing peptides within the fetal sympathoadrenal system. We found an increase (P < 0.05) in the content of Free Met-O-Enkephalin between 85 and 105 days (d) (0.46 +/- 0.12 nmoles/SCG) and 116 and 125 d (0.93 +/- 0.12 nmoles/SCG), and the SCG content of Free Met-O-Enkephalin remained elevated throughout the remainder of gestation. The fetal SCG content of Total Met-O-Enkephalin also increased significantly between 85 and 105 d (2.8 +/- 0.5 nmoles/SCG) and 116 and 125 d (7.1 +/- 1.2 nmoles/SCG). There was, therefore, no change in the ratio of Total:Free Met-O-Enkephalin content of the SCG between 85 and 145 d. There were no significant effects of fetal hypophysectomy with or without thyroxine (T4) replacement on the content of Free Met-O-Enkephalin (intact, 1.11 +/- 0.18 nmoles; hypophysectomy (HX) + Sal, 1.41 +/- 0.25 nmoles; HX + T4, 1.08 +/- 0.27 nmoles) or Total Met-O-Enkephalin (intact, 3.03 +/- 0.90 nmoles; HX + Sal, 4.03 +/- 0.22 nmoles; HX + T4, 3.53 +/- 0.88 nmoles) in the fetal SCG. The adrenal contents of Free and Total Met-O-Enkephalin were, however, significantly reduced after fetal hypophysectomy and these effects were not altered by replacement with T4 after fetal hypophysectomy. In summary, we have demonstrated for the first time that enkephalin-containing peptides are present in the SCG of the fetal sheep and that the SCG enkephalin content increases between 85 and 125 days gestation. We have found no evidence that there is a change in the post-translational processing of the enkephalin precursor to Free Met-Enkephalin within the SCG during the second half of gestation. In contrast to the fetal SCG, maintenance of adrenal enkephalin content in late gestation is dependent on the presence of an intact fetal pituitary, but is independent of the circulating concentrations of thyroxine.

Thyroxine replacement after hypophysectomy alters the pattern of enkephalin localisation in the adrenal medulla of the fetal sheep

It has been suggested that a pituitary-derived or -dependent factor may suppress enkephalin peptide synthesis in the central noradrenaline- containing cells of the sheep adrenal medulla in late gestation. We have investigated the effect of thyroxine (T4) replacement after fetal hypophysectomy on the localisation of enkephalin peptides within the peripheral adrenaline- and central noradrenaline-containing regions of the adrenal medulla of the fetal sheep. Fetal hypophysectomy (HX) was performed in 12 fetal sheep at 105-108 days gestation (term = 145 +/- 3 days gestation). T4 (40 micrograms/kg/24h) (HX + T4) or saline (HX + Sal) were infused between 110 and 140 days gestation. Adrenal glands were collected from the HX + T4, HX + Sal groups and from a group of intact fetal sheep (n = 4) for immunohistochemistry using anti- met-enkephalin and an avidin-biotin staining system. In adrenals from intact fetal sheep, there was intense positive staining for met-enkephalin in the peripheral adrenaline-containing region and sparse staining for enkephalins in the central noradrenaline-containing region. In contrast, in the HX + Sal group, enkephalin staining was uniformly present throughout the peripheral and central regions of the adrenal medulla. In the HX + T4 group, however, the staining density of met-enkephalin was higher within the adrenaline cells of the peripheral rim of the medulla than in the central medullary region. We have demonstrated that T4 replacement after fetal hypophysectomy restores the normal ontogenetic pattern of localisation of enkephalin peptides within the fetal adrenal. We postulate that T4 acts either indirectly via neural mechanisms or directly at the noradrenaline-containing cells to mediate the suppression of enkephalin staining within the central noradrenaline-containing region of the adrenal medulla of the fetal sheep in late gestation.

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.

Kappa opioids exert a strong antiproliferative effect on PC12 rat pheochromocytoma cells

Pheochromocytomas synthesize several types of opioids and their receptors. Opioids affect the proliferation rate of normal and tumoral cells. We have previously shown that the PC12 rat pheochromocytoma cells synthesize multiple opioids. The aim of the present work was to study the effect of opioids on the proliferation of these pheochromocytoma cells. Thus, the effect of several opioid agonists and antagonists was examined on basal and EGF-induced PC12 cell proliferation. The kappa opioid agonists dynorphin A, U-69593, and U-50488 suppressed basal proliferation in a dose-dependent manner. The effect of kappa opioids was blocked by the general opioid antagonist naloxone and the selective kappa antagonist nor-binaltorphimine. Furthermore, both opioid antagonists given alone had a strong stimulatory effect, a findings suggesting that the proliferation of PC12 cells is under tonic inhibition by locally produced kappa opioids. Finally, the mu-opioid agonist DAGO and the delta and mu agonists DADLE and DSLET were ineffective.

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.

Neural mediation of the cardiovascular responses to intrathecal administration of substance P in the rat: slowing of the cardioacceleration by an adrenal opioid factor

Substance P, given intrathecally at the second (T2) or ninth (T9) thoracic level in the anesthetized rat, increased heart rate, arterial pressure and circulating catecholamines. At T9 in adrenalectomized animals and at T2 in intact animals, the cardioacceleration was more abrupt than in intact animals injected at T9 suggesting that the adrenals are not necessary for the cardiovascular responses and that the adrenals may have released a factor which slows the neurally mediated cardioacceleration. As opioids are co-released with catecholamines from the adrenals, naloxone (10 mg/kg i.v.) or nalorphine HCl (which does not cross the blood-brain barrier; 10 mg/kg s.c.) was given 5 min before administration of substance P at T9 in intact rats. In both groups the cardioacceleration was similar to that elicited in adrenalectomized animals, indicating that the adrenal factor was opioid and that its action was peripheral rather than central. When propranolol (10 mg/kg i.v.) was given 3 or 15 min before, substance P increased arterial pressure but heart rate was unchanged, indicating that the opioid factor was not slowing the cardioacceleration by a direct effect on the heart. The results indicate that intrathecal administration of substance P produces a neurally mediated increase in arterial pressure and heart rate and induces the release of an adrenal opioid factor which slows the neurally-mediated cardioacceleration by an action in the periphery. This indicates a functional interaction between humoral and neural sympathetic mechanisms regulating the cardiovascular system.

Coordinate and differential regulation of proenkephalin A and PNMT mRNA expression in cultured bovine adrenal chromaffin cells: responses to cAMP elevation and phorbol esters

The expression of proenkephalin A (ProEnk A) mRNA and phenylethanolamine N-methyltransferase (PNMT) mRNA in response to cAMP analogues, forskolin and phorbol esters was examined in cultures of bovine adrenal chromaffin cells. Exposure of chromaffin cells to 1 mM dibutyryl cAMP for 24 h increased significantly the levels of ProEnk A mRNA, with no significant effect on the levels of PNMT mRNA. Cells exposed to the tumor promoting phorbol esters (phorbol 12-myristate 13-acetate, phorbol 12,13-dibutyrate or 4-beta-phorbol 12,13-didecanoate) for 12 h differentially activated PNMT mRNA and ProEnk A mRNA expression. The levels of PNMT mRNA were dramatically elevated in response to low concentrations (10(-9) to 10(-8)M) of these phorbol esters, but these increases were diminished at higher concentrations (10(-7) to 10(-6) M) of the phorbol esters. These responses were synergistically potentiated by dexamethasone (1 microM), a synthetic glucocorticoid. None of these effects was seen with the biologically inactive phorbol ester, 4-alpha-phorbol 12,13-didecanoate. By contrast, the expression of ProEnk A mRNA was activated by the tumor promoting phorbol esters in a concentration-dependent manner. The results of this study demonstrate a differential stimulatory effect of second messenger mechanisms in the control of PNMT and ProEnK A mRNA expression and provide further evidence for an independent control for the enkephalin and adrenaline synthesis in these cells.

Coordinate and differential regulation of proenkephalin A and PNMT mRNA expression in cultured bovine adrenal chromaffin cells: responses to secretory stimuli

The expression of proenkephalin A (ProEnk A) mRNA and phenylethanolamine N-methyltransferase (PNMT) mRNA in response to nicotine and to a number of secretagogues was examined in cultured bovine adrenal chromaffin cells. Prolonged incubation with nicotine (10 microM) resulted in a 2-fold increase in ProEnk A mRNA but had no significant effect on the level of PNMT mRNA. Similarly, prolonged stimulation with high K+ (56 mM) induced a time-dependent elevation in the level of ProEnk A mRNA reaching 4-fold basal level after 24 h incubation. By contrast, the level of PNMT mRNA was not changed by treatment with high K+. The increase in the level of ProEnk A mRNA by high K+ was abolished by the presence of 10 microM D600, a calcium channel blocker. Unlike the effects of high K+, treatment of the cells with the sodium channel activator veratridine significantly elevated the levels of both ProEnk A and PNMT mRNA. This increase in ProEnk A and PNMT mRNA levels was however less affected by D600. Stimulation of the cells with Ba2+ (1.1 mM) also stimulated the levels of ProEnk A and PNMT mRNA and this action required the presence of extracellular Ca2+. This was in contrast to the effect of Ba2+ in stimulating catecholamine secretion, which was inhibited by Ca2+ and enhanced in Ca2(+)-free buffer. The results of the present study indicate that membrane depolarization and entry of extracellular Ca2+ play an important role on the regulation of ProEnk A and PNMT mRNAs, in addition to their well-known actions on hormone secretion. Furthermore, these results suggest that the expression of ProEnk A mRNA and PNMT mRNA are under independent regulation in response to secretory stimulation.

Developmental expression of proenkephalin A mRNA and phenylethanolamine N-methyltransferase mRNA in foetal sheep adrenal medulla

The ontogenic expression of proenkephalin A (ProEnk A) mRNA and phenylethanolamine N-methyltransferase (PNMT) mRNA was examined in the foetal sheep adrenal medulla by the use of specific oligodeoxyribonucleotide probes. Northern blot analysis of RNA extracts from foetal adrenals demonstrated that ProEnk A mRNA was expressed as early as 60 days of gestation, a time at which the foetal adrenal is not functionally innervated. In situ hybridization on sections of foetal adrenals revealed that at 110-140 days gestation ProEnk A mRNA was expressed in chromaffin cells at the outer margin of the adrenal medulla but at earlier stages of gestation (e.g. 95 days) appeared to be expressed homogeneously throughout the whole of the adrenal medulla. In comparison, PNMT mRNA was expressed preferentially in cells at the outer margin of the adrenal medulla from the earliest stage detectable. Both PNMT mRNA and ProEnk A mRNA co-localized in cells at the outer margin of foetal adrenal of late gestations (110-140 days), a similar pattern to that seen in the adult adrenal medulla. These results indicate that, as with adult animals, in foetuses of late gestation, adrenal enkephalins are co-stored within adrenaline cells. It is likely therefore that enkephalins are co-released from the foetal adrenal with adrenaline in response to intra-uterine stress.