Effects of dopamine and synthetic atrial natriuretic polypeptide on the release of norepinephrine and epinephrine from the adrenal medulla of rats

We evaluated the effects of dopamine (DA) and synthetic atrial natriuretic polypeptide (ANP) on the release of catecholamines (CA) from the adrenal medulla. Adrenal glands of male Wistar rats were superfused with Ringer's solution saturated with 95%, O2, 5% CO2 by the use of a continuous flow incubation system, and norepinephrine (NE) and epinephrine (E) concentrations in the perfusate were continuously measured by high pressure liquid chromatography with fluorescent reaction. And the effects of DA and ANP on the CA release were evaluated. Next the effects of metoclopramide (MC), dopamine (D2) antagonist, and glucagon were added in the Ringer's solution, and the changes of NE and E in the perfusate were determined. Basal secretion of NE and E were 0.02-0.04 ng/mg.wet weight/min and 0.05-0.1 ng/mg.wet weight/min, respectively. DA remarkably decreased both NE and E release, and the suppressive effect was dependent on DA concentration in the perfusate. MC clearly raised NE and E release as well as glucagon. The increasing effect of MC was perfectly suppressed by 10(-4) M of DA. But the effect of glucagon was not blocked by the same dose of DA. Alpha rANP (10(-5)M) slightly decreased the releases of NE and E from adrenal medulla, and the magnitude of the effect of rANP was smaller than that of DA. MC significantly increased NE and E release even when the adrenal gland was superfused with Ringer's solution containing 10(-5)M of rANP. These data suggest that the release of CA from adrenal medulla may be regulated by DA, and that the receptors specifically binding to DA may exist in adrenal medulla as well as sympathetic presynaps. We concluded that DA (but not ANP) may play an important role in controlling (suppressing) the activity of sympathoadrenomedullary system.     

Ontogeny of enkephalin and catecholamine-synthesizing enzymes in the primate fetal adrenal medulla

Adrenal medullary cells in adult primates contain catecholamines and several neuropeptides. Among these peptides are several products of the three opiate precursor proteins: proenkephalin, prodynorphin, and proopiomelanocortin. We used immunocytochemistry to study the ontogeny of leu-enkephalin and the catecholamine-synthesizing enzymes dopamine beta-hydroxylase and phenylethanolamine N-methyltransferase in adjacent sections of 14 fetal rhesus and 31 fetal human adrenal glands. The adrenal medulla of a 24-week-old human fetus as well as medullas of 11 134- to 172-day-old rhesus fetuses were immunopositive with all 3 antisera employed. Furthermore, in thin serial sections of these glands, dopamine beta-hydroxylase, phenylethanolamine N-methyltransferase, and leu-enkephalin appeared to be colocalized in the same cells of the adrenal medulla. Twenty-six adrenals from fetuses 15-26 weeks stained lightly with one or more of the antisera. Dopamine beta-hydroxylase could be detected at 15 weeks, followed by leu-enkephalin and phenylethanolamine N-methyltransferase at 18-19 weeks. The role of the enkephalins during fetal life or in the adaptation to extrauterine life is not yet clear. In adults, enkephalins are cosecreted with catecholamines in response to stress. Our results suggest that the fetal adrenal may be capable of cosecretion of catecholamines and enkephalins, at least by the end of the second trimester of gestation.     

Interaction between epinephrine, prostaglandin E, and met-enkephalin in the regulation of insulin release in man

Prostaglandin E (PGE), epinephrine and metenkephalin are three endogenous substances normally present in the endocrine pancreas which have been reported to inhibit glucose-induced insulin secretion in normal humans. To evaluate possible synergistic interactions between these inhibitory agents upon the regulation of insulin release in man, we examined the effects of PGE, epinephrine and the long-acting met-enkephalin analogue FK 33-824, given alone or in combination, upon glucose-induced insulin secretion in normal man. The infusion of the three agents at doses known to affect insulin secretion (10 micrograms/min, 15 ng/kg/min, 0.5 mg im, respectively) produced the expected inhibitory effects upon insulin responses to an intravenous glucose challenge. The infusion of the three agents at doses which did not produce per se any significant change of insulin responses to glucose (5 micrograms/min, 5 ng/kg/min, 0.2 mg i.m., respectively), caused a significant inhibition of this response when given in combination. In particular, the acute insulin response to glucose decreased from a control value of 50 +/- 9 microU/ml to a value of 21 +/- 6 microU/ml (p less than 0.02). The inhibitory effect of epinephrine (15 ng/kg/min) upon glucose-induced insulin secretion was partially reversed by sodium salicylate, an inhibitor of endogenous prostaglandin synthesis, which increased but not normalized, either the acute insulin response and the glucose disappearance rates. Similarly, the negative effect of FK 33-824 upon glucose-induced insulin secretion was reversed by sodium salicylate. Similar findings were also obtained with indomethacin, another structurally unrelated inhibitor of endogenous prostaglandin synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Protein kinase-C in the human fetal adrenal gland

The fetal zone (FZ) of the human fetal adrenal gland undergoes rapid growth and exhibits a high rate of steroidogenesis throughout fetal life. In addition to cAMP-dependent processes regulating steroidogenesis and possibly growth of the FZ, evidence is accumulating that cAMP-independent mechanisms are also involved. The purpose of this study was to determine if the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), a potent stimulator of protein kinase-C activity, stimulates steroidogenesis in FZ cells and to characterize protein kinase-C activity in FZ, neocortex zone, and anencephalic adrenal tissues. Adrenal glands were obtained from first and second trimester abortions and two anencephalic fetuses. The FZ was dissected from the neocortex. In some experiments, dispersed FZ cells were incubated in the presence and absence of ACTH and TPA for 3 h. TPA and ACTH stimulated steroidogenesis 2- and 5-fold, respectively. In other experiments, the separated zones and anencephalic adrenal tissues were homogenized, and the homogenates were subjected to DEAE-cellulose column chromatography. A single peak with phospholipid- and calcium-dependent activity was found. Subcellular distribution studies demonstrated greatest activity in the cytosolic fraction. The specific activity of protein kinase-C was significantly greater in FZ than neocortex zone, whether expressed per mg protein or per microgram DNA content. The activity in anencephalic tissue was low. In addition, protein kinase-C (80,000-dalton molecular size protein) was detected in adrenal tissues after electrophoresis and immunoblotting using an antibody directed against protein kinase-C. Greater amounts of protein kinase-C were detected in FZ tissue than in NC or anencephalic adrenal tissue. These results indicate that the lower activities of protein kinase-C in neocortex and anencephalic adrenal tissues were due to low amounts of enzyme rather than inactive enzyme. In summary, TPA-stimulated steroidogenesis in fetal zone cells and fetal zone cells contained greater activity and a greater amount of protein kinase-C than neocortex cells. Minimal activity and enzyme protein were found in anencephalic tissues. These results suggest that cAMP-independent mechanisms may play a role in fetal adrenal steroidogenesis.     

Enkephalin- and somatostatin-like immunoreactivities in human adrenal medulla and pheochromocytoma.

By using the Coons indirect immunofluorescence technique, enkephalin-like immunoreactivity with a granular localization was observed in human adrenal medullary gland cells and pheochromocytomas. In two of the tumors and in a few adrenal gland cells, a somatostatin-like peptide could also be identified. Catecholamine cell types were visualized on adjacent sections with antisera to the synthesizing enzymes dopamine-beta-hydroxylase [DBH; dopamine beta-monooxygenase; 3,4-dihydroxyphenylethylamine, ascorbate: oxygen oxidoreductase (beta-hydroxylating), EC 1.14.17.1] and phenylethanolamine-N-methyltransferase (PNMT; noradrenalin N-methyltransferase; S-adenosyl-L-methionine:phenylethanolamine N-methyltransferase, EC 2.1.1.28). In the normal adrenal medulla more DBH- than PNMT-immunoreactive gland cells were observed. In the adrenal pheochromocytoma both DBH- and PNMT-positive cells were seen, whereas the two extra-adrenal tumors contained only DBH. These findings correlated well with plasma catecholamine measurements. Finally, enkephalin immunoreactive fibers and somatostatin immunoreactive cells were observed in a sympathetic ganglion extirpated together with one of the tumors.     

Plasma norepinephrine and epinephrine in acromegaly.

Plasma norepinephrine and epinephrine concentrations were measured, in the supine resting position and in response to standing, in 10 unselected patients with active acromegaly, in 2 effectively treated acromegalic patients with normal serum growth hormone concentrations and in 15 nonacromegalic normal subjects. Plasma catecholamine concentrations were not significantly related to serum growth hormone levels or to the diastolic blood pressure in the acromegalic patients. Mean (+/- SE) plasma norepinephrine concentrations rose from 211 +/- 28 pg/ml supine to 501 +/- 65 pg/ml after 10 minutes standing in the active acromegalic patients and from 210 +/- 20 pg/ml supine to 502 +/- 54 pg/ml after 10 min standing in the normal subjects. Corresponding plasma epinephrine concentrations were 33 +/- 6 and 60 +/- 14 pg/ml in the acromegalics and 57 +/- 7 pg/ml in the normals. Thus, no abnormality in basal or stimulated plasma catecholamine concentrations was found in acromegalic patients.     

Effect of fetal hypophysectomy on the localization of the catecholamine biosynthetic enzymes and enkephalins in the adrenal medulla of the fetal sheep

We have investigated the effect of fetal hypophysectomy on the localization of dopamine B-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT) and enkephalin-containing peptides in the fetal sheep adrenal, using immunocytochemical techniques. Staining with anti-DBH was observed throughout the adrenal medulla in the intact (140-146 days of gestation) and hypophysectomized fetal sheep (147-164 days of gestation) and the newborn lamb (10-12 days after birth). In the adrenal medulla of the late-gestation intact fetal sheep and newborn lamb, positive staining with anti-PNMT was observed in the peripheral rim of medullary cells adjacent to the adrenal cortex. After hypophysectomy, there was intense positive staining with anti-PNMT in the peripheral adrenal medullary cells and a small and variable proportion of central adrenal medullary cells were stained with anti-PNMT. In the adrenal gland of the intact fetal sheep and the newborn lamb, there was intense staining with anti-enkephalin in the peripheral rim of adrenal medullary cells. Staining with anti-enkephalin was less intense in the central medullary cells of the adrenal gland of the intact fetal sheep and the 10- to 12-day-old newborn lamb, and many unstained central medullary cells were present. After hypophysectomy, intense positive staining with anti-enkephalin was observed throughout the entire fetal adrenal medulla. Therefore, the fetal pituitary, either directly or indirectly through the adrenal cortex, plays a role in regulating the pattern of localization of both PNMT and enkephalin in the fetal sheep adrenal.     

Circadian rhythms of epinephrine and norepinephrine in man

The diurnal rhythms of plasma epinephrine and norepinephrine were investigated in a group of normal young men. Sleep, posture, illumination, and food intake were monitored. Plasma epinephrine demonstrated a statistically significant diurnal rhythm, with a mean amplitude of 14 +/- 1.6 (+/- SE) pg/ml superimposed on a mean level of 43 +/- 5.3 pg/ml. The trough occurred at 03.20 h +/- 35 min. Plasma norepinephrine had a significant diurnal rhythm, with a mean amplitude of 111 +/- 19 pg/ml superimposed on a mean level of 413 +/- 25 pg/ml, with the trough occurring at 02.20 h +/- 30 min. There was a significant correlation between the two rhythms at zero phase shift, with a pooled value for the group of r = 0.49. Epinephrine levels had no direct relationship to sleep or posture, whereas norepinephrine levels were significantly higher with upright posture and higher when the men were awake than when asleep. Our results indicate that circadian variations in the sympathetic-adrenal medullary system are not explained by a single controlling influence and that the norepinephrine rhythm can be accounted for as a direct response to changes in posture and sleep, whereas the epinephrine rhythm is probably controlled by a circadian oscillator.     

Influence of age on diurnal rhythms of adrenal norepinephrine, epinephrine, and corticosterone levels in soft-shelled turtles (Lissemys punctata punctata)

An investigation was made of what role aging plays on diurnal rhythms of norepinephrine, epinephrine, and corticosterone contents in the adrenal gland of soft-shelled turtles. To resolve this problem, juvenile and adult soft-shelled turtles were sacrificed at four different time intervals (0600, 1200, 1800, and 2400 hr) and adrenal hormonal levels were measured by spectrofluorometer. The findings revealed that peak norepinephrine, epinephrine, and corticosterone values were observed at 2400, 0600, and 2400 hr, respectively, and trough values for all the hormones were found at 1200 hr in both juvenile and adult animals. Thus, diurnal rhythms for all the hormones studied exist in both juvenile and adult animals. It is suggested that aging apparently has no influence on diurnal variations of adrenal hormones in turtles.     

Differences in the neuronal removal of circulating epinephrine and norepinephrine

Neuronal uptake is an important mechanism for the removal of norepinephrine, but its contribution to the removal of epinephrine is unknown. This study compared the neuronal removal of circulating epinephrine and norepinephrine by examination of the cardiac extractions or plasma clearances of [3H]norepinephrine and endogenous or 3H-labeled epinephrine in healthy subjects, patients with cardiovascular disorders, and subjects administered desipramine to block neuronal uptake. In rabbits the plasma clearances of [3H]epinephrine and [3H] norepinephrine by neuronal uptake and the formation of dihydroxyphenylglycol (DHPG) from simultaneously infused [3H] norepinephrine and epinephrine were compared. In normal patients 51 +/- 3% of plasma epinephrine was extracted during one pass through the coronary circulation, significantly less than the cardiac extraction of [3H]norepinephrine (78 +/- 1%). In patients with cardiovascular disorders extractions of epinephrine (34 +/- 3%) remained lower than those of [3H]norepinephrine (63 +/- 2%). After desipramine, cardiac extraction of epinephrine was reduced to 12 +/- 2% and [3H]norepinephrine to 20 +/- 3%. In subjects infused simultaneously with [3H]epinephrine and [3H] norepinephrine, desipramine reduced the cardiac extraction of [3H]epinephrine by 28 +/- 6%, significantly less than the 49 +/- 7% reduction in [3H]epinephrine extraction; the plasma clearance of [3H]epinephrine was reduced by 4 +/- 5%, significantly less than the 20 +/- 6% reduction in [3H]norepinephrine clearance. In rabbits desipramine reduced the plasma clearance of [3H] epinephrine by 18%, significantly less than the 42% reduction in [3H]norepinephrine clearance; production of DHPG from epinephrine was less than half the production of [3H]DHPG from [3H]norepinephrine. The above differences indicated that epinephrine was removed 44-64% less avidly than norepinephrine by uptake into and metabolism within sympathetic neurons.