Inactivation of potassium-evoked adrenomedullary catecholamine release in the presence of calcium, strontium or BAY-K-8644

The rate of catecholamine release from cat adrenal glands perfused with Krebs solution containing 59 mM K declined exponentially during the first few minutes of depolarization. The rate of decline was considerably slower when Ca was substituted by Sr. The late addition of Ca, Sr or the Ca-channel activator BAY-K-8644 evoked a revival of secretion when catecholamine release was inactivated by prior K depolarization; the revival of secretion was independent of the depolarization time. These data demonstrate that inactivation of catecholamine release is specifically dependent on Ca; the modulatory role of Ca on secretion seems to be exerted at a step distal to the transmembraneous Ca channel.     

Characterization of a Dopaminergic Receptor that Modulates Adrenomedullary Catecholamine Release

Nicotine evokes the release of catecholamines from bovine adrenal glands perfused with oxygenated Krebs-bicarbonate solution. Two 2-min pulses of 5 microM nicotine, at 40-min intervals (S1 and S2), gave net catecholamine outputs of 45.2 +/- 3.6 and 29.1 +/- 3.5 micrograms/8 min, respectively. Apomorphine (1 or 10 microM) markedly inhibited catecholamine release during S2 to 9.1 +/- 2.2 and 0.5 micrograms/8 min, respectively. Haloperidol (0.5 microM) reversed the inhibitory effects of apomorphine. Haloperidol alone enhanced catecholamine release induced by nicotine to 67.9 +/- 7.9 micrograms/8 min. [3H]Spiperone binds to adrenomedullary membranes with a KD of 0.24 nM and a Bmax of 117 fmol/mg of protein. Whereas spiperone and haloperidol potently displaced such binding, 3,4-dihydroxyphenylethylamine (dopamine) and sulpiride were poorer displacers, and SCH23390, prazosin, phenoxybenzamine, propranolol, BAY-K-8644, and nitrendipine did not displace [3H]spiperone bound. These data strongly suggest that, as in the cat, the bovine adrenal medulla chromaffin cell contains a dopaminergic receptor that modulates the catecholamine secretory process triggered by stimulation of the nicotinic cholinoceptor. Such a receptor seems to be of the D2 type and might be involved in a sympatho-adrenal cooperative mechanism contributing to the maintenance of cardiovascular homeostasis during stressful situations as well as to the pathogenesis of hypertension. If so, selective dopaminergic agonists might prove clinically useful in the treatment of hypertension.     

M2 muscarinoceptor-associated ionophore at the cat adrenal medulla

Atropine and pirenzepine displaced 3H-quinuclydinyl-benzylate binding and inhibited methacholine-evoked catecholamine release with a similar order of potencies, atropine being 200 fold more potent than pirenzepine. In contrast to high-K, methacholine-evoked 45Ca uptake or catecholamine release were not blocked by (+)PN200-110. Bay-K-8644 did not modify the secretory response to methacholine either in the presence of Ca or Sr but potentiated K-evoked secretion. In depolarized glands, methacholine still evoked its usual secretory response. The results suggest that muscarinic stimulation of cat adrenal chromaffin cells stimulates Ca entry though an ionophore other than voltage-dependent Ca channels; such ionophore seems to be chemically operated through a M2 muscarinoceptor.     

Catecholamine secretion by isolated adrenal cells.

Isolated adrenal cells were prepared by collagenase digestion of guinea pig adrenal glands. Acetylcholine stimulates the secretion of catecholamines by these isolated adrenal cells. Acetylcholine-stimulated catecholamine secretion is inhibited by cholinergic blocking agents (atropine and hexamethonium) and by local anaesthetics (tetracaine), and is dependent upon the concentration of Ca2+ in the incubation medium. In the presence of Ca2+, catecholamine secretion is also stimulated by two divalent cation ionophores, A23187 and X-537A. Cyclic nucleotides and 5'-nucleotides cause a small, non-specific stimulation of catecholamine secretion. These results indicate that isolated adrenal cells are a useful system in which to study catecholamine secretion, and support the hypothesis that increased Ca2+ entry into chromaffin cells is a sufficient stimulus for catecholamine secretion.     

Voltage-dependence of nitrendipine provides direct evidence for dihydropyridine receptor coupling to calcium channels in intact cat adrenals

Nitrendipine behaves as a powerful inhibitor of catecholamine release in perfused cat adrenal glands stimulated with pulses of Ca (0.5 mM) in high K (118 mM). Its blocking ability is considerably enhanced if, before Ca stimulation, the adrenomedullary tissue is impregnated with nitrendipine in depolarizing (IC50 = 0.99 nM) as opposed to hyperpolarizing (IC50 = 214 nM) conditions. 3H-nitrendipine binding to adrenomedullary tissue was considerably enhanced in depolarization; blockade of 45Ca uptake into and catecholamine secretion from the same glands was also enhanced in depolarized tissues. This study shows for the first time the a good correlation between these three parameters in the same intact preparation, providing direct evidence for a functional coupling between dihydropyridine receptors, Ca channels and secretion.     

Ryanodine Inhibits Caffeine-Evoked Ca2+ Mobilization and Catecholamine Secretion from Cultured Bovine Adrenal Chromaffin Cells

The effects of ryanodine, a selective inhibitor of the Ca(2+)-induced Ca2+ release mechanism, on caffeine-evoked changes in cytosolic Ca2+ concentration ([Ca2+]i) and catecholamine secretion were investigated using cultured bovine adrenal chromaffin cells. Caffeine (5-40 mM) caused a concentration-dependent transient rise in [Ca2+]i and catecholamine secretion in Ca2+/Mg(2+)-free medium containing 0.2 mM EGTA. Ryanodine (5 x 10(-5) M) alone had no effect on either [Ca2+]i or catecholamine secretion. Although the application of ryanodine plus caffeine caused the same increase in both [Ca2+]i and catecholamine secretion as those induced by caffeine alone, ryanodine (4 x 10(-7) - 5 x 10(-5) M) irreversibly prevented the increase in both [Ca2+]i and catecholamine secretion resulting from subsequent caffeine application over a range of concentrations. The secretory response to caffeine was markedly enhanced by replacement of Na+ with sucrose in Ca2+/Mg(2+)-free medium, and this enhanced response was also blocked by ryanodine. Caffeine was found to decrease the susceptibility of the secretory apparatus to Ca2+ in digitonin-permeabilized cells. These results indicate that caffeine mobilizes Ca2+ from intracellular stores, the function of which is irreversibly blocked by ryanodine, resulting in the increase in catecholamine secretion in the bovine adrenal chromaffin cell.     

Alamethicin channel permeation by Ca2+, Mn2+ and Ni2+ in bovine chromaffin cells.

Alamethicin causes a concentration-dependent increase of [Ca2+]i in suspensions of bovine adrenal chromaffin cells loaded with fura-2. The basal levels of Cai2+ (234 +/- 37 nM; n = 4) increased to a maximum of 2347 +/- 791 nM (n = 3) with 100 micrograms/ml alamethicin. In the presence of 1 mM Cae2+ the increase reached a plateau within about 2-5 s. This increase was due to Ca2+ entry into chromaffin cells, since in the absence of Cae2+ alamethicin did not modify [Ca2+]i. This contrasts with ionomycin (1 microM) which produced a Cai2+ transient even in the absence of Cae2+. Mn2+ ions also entered chromaffin cells in the presence of alamethicin, as measured by the quenching of fura-2 fluorescence following excitation at 360 nm. Resting chromaffin cells had a measurable permeability to Mn2+ which was drastically increased by cell depolarization by K+ (50 mM) addition. This suggests that Mn2+ is able to permeate voltage-dependent Ca2+ channels. Ni2+ uptake into either resting or K(+)-stimulated chromaffin cells was undetectable, but addition of alamethicin induced rapid uptake of this cation. The alamethicin-induced entry of Ni2+ was decreased by 50 mM K+. Overall, the results are compatible with the formation by alamethicin of ion channels in chromaffin cell plasma membranes.     

The effect of etorphine on nicotine- and muscarine-induced catecholamine secretion from perfused rat adrenal glands

The effect of etorphine on nicotine and muscarine-mediated catecholamine (CA) release from isolated perfused rat adrenal glands was investigated. Nicotine increased CA secretion at the low concentration of 0.5 micrograms while higher concentrations of muscarine (5 micrograms) were required. Moreover, muscarine released primarily epinephrine (EP) from rat adrenal glands while nicotine released norepinephrine (NE) and Ep. Etorphine inhibited NE and EP release evoked by nicotine to the same extent, whereas, muscarine-mediated release of NE and EP was not affected. Mecamylamine and verapamil inhibited nicotine but not muscarine-induced CA secretion. Our results suggest that etorphine preferentially interacts with nicotinic receptors on rat adrenal chromaffin cell membranes.     

Difference in the Effectiveness of Ca2+ to Evoke Catecholamine Secretion Between Adrenaline-and Noradrenaline-Containing Cells of Bovine Adrenal Medulla

Abstract: Differential adrenaline (Ad) and noradrenaline (NA) secretions evoked by secretagogues were investigated using digitonin-permeabilized adrenal chromaffin cells, cultured adrenal chromaffin cells, and perfused adrenal glands of the ox. In digitonin-permeabilized cells, Ca²⁺ (0.8-160 μM) caused a concentration-dependent increase in catecholamine secretion, which was characterized by a predominance of NA over Ad secretion. Acetylcholine (10-1,000 μM), high K⁺ (14-56 μM), and bradykinin (0.1-1,000 μM) all were confirmed to induce the release of more NA than Ad at all concentrations used. There was no apparent difference in the ratios of NA/Ad between Ca²⁺-induced catecholamine secretion from digitonin-permeabilized cells and those induced by secretagogues from cultured cells. Qualitatively the same result was obtained in the secretory responses to acetylcholine and high K⁺ in perfused adrenal glands. These results indicate that the effectiveness of Ca²⁺ for catecholamine secretion is higher in the secretory apparatus of NA cells than in that of Ad cells of the bovine adrenal medulla. This may be one of the reasons why the secretagogues cause a predominance of NA secretion over Ad secretion in the bovine adrenal medulla.     

Mechanism of dissociation of cortisol and adrenal androgen secretion after removal of adrenocortical adenoma in patients with Cushing's syndrome

We investigated the mechanism of dissociation of cortisol and dehydroepiandrosterone sulfate (DHEA-S) secretion by the adrenal glands after the removal of an adrenal gland containing an adrenocortical adenoma in a patient with Cushing's syndrome. After removal of the adrenocortical adenoma, the serum cortisol rapidly decreased from 24.6 +/- 6.4 micrograms/dl (mean +/- SD, n = 6) to 0.7 +/- 0.5 micrograms/dl. Serum DHEA-S levels were 15 +/- 14 micrograms/dl and 6 +/- 9 micrograms/dl before and after surgery, respectively, and significantly lower than the control values. Serum cortisol levels reverted to normal levels 1.5 to 3 years after the surgery. On the other hand, DHEA-S levels reverted to normal 5 to 7 years after the serum cortisol levels had normalized. Monolayer cultures of normal human adrenal cells obtained at adrenalectomy in patients with advanced breast cancer and atrophic adrenal cells adjacent to the adrenocortical adenoma in patients with Cushing's syndrome were used to study the mechanism of the dissociation of cortisol and DHEA-S secretion. ACTH caused significant increases in the productions of pregnenolone (P5), progesterone (P4), 17-hydroxypregnenolone (17-OH-P5), 17-hydroxyprogesterone (17-OH-P4), DHEA, DHEA-S, androstenedione (delta 4-A), and cortisol. The amounts of 17-OH-P5 and 17-OH-P4 produced by ACTH in atrophic adrenal cells were significantly greater than those in normal adrenal cells. The amounts of DHEA, DHEA-S and delta 4-A produced by ACTH in atrophic adrenal cells were significantly smaller than those of normal adrenal cells. The conversion rate of 17-OH-[3H]P5 to 17-OH-[3H]P4 and 11-deoxy-[3H] cortisol was higher in atrophic adrenal cells than in normal adrenal cells, but the conversion rate to [3H]DHEA, [3H]DHEA-S and [3H]delta 4-A was significantly lower in atrophic adrenal cells than in normal adrenal cells. These results suggest that the dissociation of cortisol from DHEA-S after the removal of adrenocortical adenoma is a probably due to diminished C17,20-lyase activity in the remaining atrophic adrenal gland.     

Capsaicin, a pungent principle of hot red pepper, evokes catecholamine secretion from the adrenal medulla of anesthetized rats

Using a direct monitoring system for catecholamine (CA) secretion into the adrenal vein, we have demonstrated that capsaicin (CAP) evokes CA secretion from the adrenal medulla of pentobarbital-anesthetized rats. A significant increase in epinephrine (E) secretion was seen in rats infused with CAP (200 micrograms/kg, i.v.) without a detectable lag after the infusion. Norepinephrine (NE) secretion evoked by CAP was fairly weak compared with E secretion. The secretion of E evoked by CAP was dose-amount dependent. The stimulation of E release by CAP was barely detectable at 20 micrograms/kg, half-maximal at 100 micrograms/kg, and maximal at 600 micrograms/kg. When CAP (200 micrograms/kg) was infused into rats, the weight-ratio of E to NE was significantly higher (47.6) than when acetylcholine (12.5 micrograms/kg) was infused (13.0). These results indicate that CAP can evoke CA secretion from the adrenal medulla of rats.     

Substance P Protects Against Desensitization of the Nicotinic Response in Isolated Adrenal Chromaffin Cells

Substance P, a peptide endogenous to the splanchnic nerve, is known to inhibit the acetylcholine-and nicotine-induced release of catecholamines from isolated adrenal chromaffin cells. In the present study the effect of substance P on desensitization of catecholamine release from these cells was examined. Substance P (10(-5) M) completely protected against desensitization of catecholamine release produced by acetylcholine at 37 degrees C or 23 degrees C and by nicotine at 23 degrees C; substance P also afforded appreciable protection against nicotine-induced desensitization at 37 degrees C. The peptide had no effect on K+-induced desensitization of catecholamine release. Like substance P, d-tubocurarine also prevented nicotinic desensitization. Substance P prevented both of two components of nicotinic desensitization, i.e. the Ca2+-dependent component and the Ca2+-independent, depletion-independent component of desensitization. Substance P had little effect on subsequent catecholamine uptake, indicating that substance P's protection against desensitization is a result of facilitation of catecholamine release rather than inhibition of catecholamine reuptake. Nicotine-induced catecholamine release and nicotinic desensitization of catecholamine release were Na+-independent, although substance P's inhibition of nicotine-induced catecholamine release was reduced by extracellular Na+. These in vitro studies suggest a similar role for substance P in vivo: substance P's protection against nicotinic desensitization may ensure a maintained output of adrenal catecholamines during stress, when the splanchnic nerve releases large amounts of acetylcholine.     

Oxytocin inhibits ACTH and peripheral catecholamine secretion in the urethane-anesthetized rat

Oxytocin (OT) generally has a stimulatory effect on ACTH secretion both in vitro and in vivo. As part of a study of ACTH-releasing factors in hypophysial portal blood, the effects of i.v. OT administration on plasma ACTH levels were tested in urethane-anesthetized rats. Surprisingly, i.v. injection of 10 micrograms OT lowered plasma ACTH levels by about 35% (P less than 0.01). It was reasoned that this paradoxical inhibition of ACTH secretion by OT might be mediated by inhibition of the unusually high rate of peripheral catecholamine secretion in this model. Measurement of plasma catecholamines before and after i.v. administration of 10 micrograms OT revealed a 53% inhibition of EPI (P less than 0.01) and 43% inhibition of NE (P less than 0.05). Administration of the beta-adrenergic antagonist propranolol (400 micrograms) 15 min before the beginning of the experiment completely blocked the inhibitory effects of OT on ACTH secretion and in fact unmasked the stimulatory effects of OT normally seen in conscious animals and in vitro. Superfused bisected adrenal glands exposed to 10(-6) M OT for 10 min secreted more than 30% less EPI and NE than control adrenals suggesting that the inhibition of EPI and NE secretion by OT in vivo occurs, at least in part, directly at the level of the adrenal. The data support the hypothesis that peripheral catecholamines may at times be directly involved in the control of ACTH secretion and also suggest that OT, which has recently been identified in the adrenal medulla, may have important paracrine functions in the regulation of adrenal catecholamine secretion.     

Internal Ca2+ Mobilization by Muscarinic Stimulation Increases Secretion from Adrenal Chromaffin Cells Only in the Presence of Ca2+ Influx

The cytosolic free Ca2+ concentration ([Ca2+]in) in single cat and bovine adrenal chromaffin cells was measured to determine whether or not there was any correlation between the [Ca2+]in and the catecholamine (CA) secretion caused by muscarinic receptor stimulation. In cat chromaffin cells, methacholine (MCh), a muscarinic agonist, raised [Ca2+]in by activating both Ca2+ influx and intracellular Ca2+ mobilization with an accompanying CA secretion. In bovine cells, MCh elevated [Ca2+]in by mobilizing intracellular Ca2+ but did not cause CA secretion. The MCh-induced rise in [Ca2+]in in cat cells was much higher than that in bovine cells, but when Ca2+ influx was blocked, the rise was reduced, with a concomitant loss of secretion, to a level comparable to that in bovine cells. Intracellular Ca2+ mobilization due to muscarinic stimulation substantially increased secretion from depolarized bovine and cat cells, where a [Ca2+]in elevated above basal values was maintained by a continuous Ca2+ influx. These results show that Ca2+ released from internal stores is not effective in triggering secretion unless Ca2+ continues to enter across the plasma membrane, a conclusion suggesting that secretion depends on [Ca2+]in in a particular region of the cell.     

Effects of trypsin on secretion stimulated by micromolar Ca2+ and phorbol ester in digitonin-permeabilized adrenal chromaffin cells

1. Catecholamine secretion from digitonin-treated chromaffin cells is stimulated directly by micromolar Ca2+ in the medium. The permeabilized cells are leaky to proteins. 2. In this study trypsin (30-50 micrograms/ml) added to cells after digitonin treatment completely inhibited subsequent Ca2+-dependent catecholamine secretion. The same concentrations of trypsin did not inhibit secretion from permeabilized cells if trypsin was present only prior to cell permeabilization. 3. The data indicate that trypsin entered digitonin-treated chromaffin cells which were capable of undergoing secretion and that an intracellular, trypsin-sensitive protein is involved in secretion. Chymotrypsin was less potent but had effects similar to those of trypsin. 4. The enhancement of Ca2+-dependent secretion from permeabilized chromaffin cells induced by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) was inhibited by trypsin added simultaneously with Ca2+ to permeabilized cells at concentrations (3-10 micrograms/ml) which had little or no effect on Ca2+-dependent secretion from cells untreated with TPA. Ca2+-dependent secretion in TPA-treated cells was reduced by trypsin only to the level that would have occurred in cells not treated with TPA. Trypsin reduced the large TPA-induced increment of membrane-bound protein kinase C.     

Diadenosine Tetraphosphate Is Co-Released with ATP and Catecholamines from Bovine Adrenal Medulla

Secretion of adenosine(5')tetraphospho(5')adenosine (Ap4A) and ATP from perfused bovine adrenal glands stimulated with acetylcholine or elevated potassium levels was measured and compared with that of catecholamines. We have found a close correlation between the release of Ap4A and catecholamines elicited with all the secretagogues used in the presence of either Ca2+ or Ba2+, suggesting co-release of both constituents from the chromaffin granules. By contrast, ATP secretion, as measured with luciferase, showed a significantly different time course regardless of the secretagogue used. ATP secretion consistently decreased after 1-2 min of stimulation at a time when Ap4A and catecholamine secretions were still increasing. Measures of degradation of injected [3H]ATP to the gland during stimulation showed little difference in the level of uptake or decomposition of ATP throughout the pulse. However, a reexamination of ATP secretion by monitoring its products of degradation (AMP, adenosine, and inosine) by HPLC techniques showed that Ap4A, ATP, and catecholamines are indeed secreted in parallel from the perfused adrenal gland.     

Inhibition of voltage-gated Ca(2+) current by PACAP in rat adrenal chromaffin cells.

It is well established that pituitary adenylate cyclase-activating polypeptide (PACAP) can stimulate catecholamine biosynthesis and secretion in adrenal chromaffin cells. Recent studies from this laboratory demonstrated that PACAP pretreatment inhibits nicotine (NIC)-induced intracellular Ca(2+) transients and catecholamine secretion in porcine adrenal chromaffin cells. Mechanistically, this effect is mediated by protein kinase C (PKC), and based on indirect evidence, is thought to primarily target voltage-gated Ca(2+) channels. The present study used whole-cell patch-clamp analysis to test this possibility more directly in rat chromaffin cells. Consistent with the porcine data, pretreatment with PACAP or with phorbol ester [phorbol myristate acetate (PMA)] significantly suppressed NIC-induced intracellular Ca(2+) transients and catecholamine secretion in rat chromaffin cells. Exposure to PACAP and PMA significantly reduced peak Ca(2+) current in rat cells. The effects of both PACAP and PMA on Ca(2+) current could be blocked by treating cells with the PKC inhibitor staurosporine. Exposure to selective channel blockers demonstrated that rat chromaffin cells contain L-, N- and P/Q-type Ca(2+) channels. PACAP pretreatment significantly reduced Ca(2+) current gated through all three channel subtypes. These data suggest that PACAP can negatively modulate NIC-induced catecholamine secretion in both porcine and rat adrenal chromaffin cells.     

Dihydropyridine Modulation of the Chromaffin Cell Secretory Response

Prolonged perfusion of cat adrenal glands with Krebs-bicarbonate solutions containing nicotine, muscarine, or excess K rapidly increased the rate of catecholamine output proportional to the concentrations of secretagogue used. The secretory responses to nicotine or high K reached a peak and declined to almost basal rates of secretion after about 10 min of stimulation. The dihydropyridine Ca channel agonist Bay K 8644 potentiated markedly the secretory responses to 1 microM nicotine and to 17.7 mM K but not to higher concentrations of these secretagogues. The muscarinic response did not decrease with time and was modestly potentiated by Bay K 8644. Similar curves were obtained with 17.7 mM K plus Bay K 8644 and with 59 mM K alone. CGP28392, another agonist, was about 10 times less potent than Bay K 8644 in potentiating the secretory responses to 17.7 mM K. Bay K 8644 also potentiated the release of [3H]noradrenaline evoked by stimulation of cultured bovine adrenal chromaffin cells with 17.7 mM K or 2 microM nicotine but not with higher concentrations of K or nicotine. Dihydropyridine Ca channel antagonists reversed the effects of Bay K 8644 with the following order of potency: niludipine greater than nifedipine = nimodipine greater than nitrendipine. The secretory rates from intact chromaffin cells treated with the Ca ionophores X537A or A23187, or those evoked by Ca-EGTA buffers from digitonin-permeabilized cells, were not affected by Bay K 8644. These results are compatible with the following conclusions: Bay K 8644 selectively potentiates catecholamine secretory responses mediated through the activation of voltage-sensitive Ca channels; during nicotine or high-K stimulation, Ca gains access to the cell interior through a common permeability pathway, the Ca channel.(ABSTRACT TRUNCATED AT 250 WORDS)     

IGF1 and 2 in two models of adrenal growth

Insulin-like growth factors (IGFs) 1 and 2 were measured in the adrenal glands of rats undergoing either compensatory growth following left unilateral adrenalectomy or adrenal regeneration following bilateral adrenal enucleation. In normal rat adrenal gland, the tissue concentration of IGF2 (7.45 +/- 0.99 pg/micrograms protein) wa higher than IGF1 (1.26 +/- 0.23 pg/micrograms protein), both peptides being more abundant in the inner zones of the adrenal gland compared to the capsule-glomerulosa. During compensatory growth of the right adrenal gland, IGF1 and 2 increased significantly compared with control right adrenal glands at 24 h following left unilateral adrenalectomy (P less than 0.001). At 68 h, the increase remained significant for IGF1 (P = 0.012). The two peptides were measured in the regenerating adrenal gland at 7, 14 and 21 days following bilateral enucleation. Whilst there was a trend towards an increase in the IGF1 and 2 content of regenerating adrenal glands, the increase was significant only for IGF2 in the left adrenal gland at 21 days following enucleation. Plasma IGF1 and 2 did not increase compared to controls during the experiments (110.97 +/- 1.95 and 46.33 ng/ml, respectively), suggesting that the changes in tissue IGF reflect increased local production during rapid growth of the adrenal gland.     

Age-Related Bidirectional Changes in Neuropeptide Y Peptides in Rat Adrenal Glands, Brain, and Blood

Age-related changes in neuropeptide Y (NPY) regulation were studied in rat adrenal glands, brains, and blood by radioimmunoassay and biochemical characterization using reversed phase HPLC and gel filtration chromatography. NPY immunoreactivity (pmol/g tissue +/- SEM) in rat adrenal glands increased from 7 +/- 1 (6 weeks old) to 1,500 +/- 580 (69 weeks old). Biochemical characterization by HPLC showed that this increase was due to those of NPY and methionine sulfoxide NPY. In contrast, in rat brain, NPY content decreased in an age-dependent manner specifically in striatum, hippocampus, medulla oblongata, and spinal cord and the sulfoxide form was not detected. In rat blood, the circulating level of NPY was high (3-5 pmol/ml plasma +/- SEM) but did not change significantly with age or by adrenal demedullation. Only a small increase of the sulfoxide form of NPY was observed in aged rat plasma. The age-dependent changes in regulation and modification of NPY in adrenal glands and in specific brain areas may have physiological relevance in the regulation of catecholamine release from adrenal glands and some brain functions during aging.