Increased Phenylethanolamine N-methyltransferase Activity Research Articles

Glucocorticoid induction of epinephrine synthesizing enzyme in rat skeletal muscle and insulin resistance.

Rat skeletal muscle contains two enzymes which can make epinephrine: phenylethanolamine N-methyltransferase (PNMT) and nonspecific N-methyltransferase. We studied the time-course and mechanism by which the glucocorticoid dexamethasone increases muscle PNMT activity. We also examined the hypothesis that increased muscle E synthesis may contribute to glucocorticoid-induced insulin resistance. Dexamethasone (1 mg/kg s.c. for 12 d) increased muscle PNMT activity seven-fold but did not change NMT activity. Immunotitration with an anti-PNMT antibody indicated that the PNMT elevation was due to increased numbers of PNMT molecules. Dexamethasone rapidly increased PNMT activity and this elevation was largely maintained 6 d after glucocorticoid treatment stopped. Muscle epinephrine levels were transiently elevated by dexamethasone. Dexamethasone-treated rats had elevated insulin levels after a glucose load, and chronic administration of the PNMT inhibitor SKF 64139 reversed this increase. Chronic SKF 64139 improved glucose tolerance in normal rats. Dexamethasone induced muscle synthesis of the epinephrine-forming enzyme PNMT. A PNMT inhibitor lowered insulin levels in glucocorticoid-treated rats and glucose levels in untreated rats. These findings are compatible with antagonism of insulin-mediated glucose uptake by epinephrine synthesized in skeletal muscle.

Adrenal phenylethanolamine N-methyltransferase induction in relation to glucocorticoid receptor dynamics: evidence that acute exposure to high cortisol levels is sufficient to induce the enzyme.

Glucocorticoids (GCs) are thought to regulate, in a permissive fashion, the basal activity of adrenal medullary phenylethanolamine N-methyltransferase (PNMT). However, it is unclear whether a large short-term increase in GC release, such as occurs during an acute stress response, may also play a role in PNMT regulation. The present study investigated how the GC influence over PNMT activity varies in relation to dynamic changes in the hormone-receptor signal. Using [3H]dexamethasone (DEX) and [3H]RU 28362 as radioligands, we have confirmed the presence of GC receptors in bovine adrenal medullary cells. A concentration-dependent decline in soluble GC receptor sites and an increase in nuclear uptake of [3H]DEX were found in response to GC levels as low as 5 x 10(-8) M. The loss of soluble sites plateaued between 5 x 10(-8) and 10(-6) M cortisol, with further losses occurring at 10(-5) and at 10(-4) M. The functional consequence of GC receptor binding was confirmed by measuring PNMT activity following 3-day exposure to cortisol. The pattern of PNMT induction was similar to that seen with GC receptor occupancy; at cortisol concentrations between 10(-8) and 10(-5) M, PNMT induction was at a plateau, with a further increase in activity at 10(-4) M. The increase in PNMT activity following 3-day exposure to low (10(-7) M) and high (5 x 10(-5), 10(-5) M) cortisol was blocked by the GC receptor antagonist RU 38486, suggesting a GC receptor-mediated event. Finally, a short (2 h) pulse of GC, which mimics the time course of physiological elevation of GC following acute stress, elevated adrenal medullary PNMT activity measured 3 days later. Therefore, our results provide novel evidence that short-term exposure of adrenal medullary cells to high cortisol levels can elevate PNMT activity.

Glucocorticoid effects on phenylethanolamine N-methyltransferase (PNMT) in explants of embryonic rat medulla oblongata

Although glucocorticoid hormones have important roles in the development of neurotransmitter systems in cells derived from the neural crest, it is not known whether they have parallel effects on neuronal development in the brain. To address this tissue, we have established an in vitro system of fetal medulla oblongata (MO) to follow development of the epinephrine-synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT). Embryonic MO was explanted from E13 or E18 embryos and maintained for up to 3 weeks. Successful culture of adrenergic neurons was possible only in explants taken from young embryos, since E18 explants failed to develop. In E13 explants, immunoreactivity to both PNMT and tyrosine hydroxylase, the rate limiting enzyme in catecholamine synthesis, was observed. PNMT catalytic activity which was barely detectable at the time of explanation increased markedly during the first week in vitro. To study the effects of glucocorticoids on PNMT development in central neurons, MO explants were grown in glucocorticoid deficient medium in which rat serum from adrenalectomized rats was substituted for human placental serum. Addition of natural glucocorticoids, cortisol or corticosterone, or the mineralcorticoid, deoxycorticosterone, during the third culture week had no effect on PNMT activity. Dexamethasone (DEX), a synthetic glucocorticoid, also had no effect on PNMT during the first or second weeks in culture. However, addition of DEX during the third culture week resulted in a doubling of PNMT activity. However, attempts to block the DEX effect during the third week or to block the increase in PNMT activity during the first week in control cultures with the glucocorticoid receptor antagonist, dexamethasone 21-mesylate, were unsuccessful. These results suggest that PNMT in central neurons does not require glucocorticoids for ontogeny during the embryonic period. This is in contrast to PNMT in adrenal medulla which requires glucocorticoids for normal development during both the embryonic and postnatal periods. More generally, these studies suggest that development of the same neurotransmitter phenotype in brain and periphery may be differentially regulated.

Distribution of phenylethanolamine-N-methyltransferase in the rat heart: effect of 6-hydroxydopamine

The distribution of phenylethanolamine-N-methyltransferase (PNMT), the epinephrine-forming enzyme in the adult rat heart atria and ventricles was studied. The activity of the enzyme in the hearts of adult rats is very low; a significantly higher activity was found in the atria than in the ventricles. A significant increase in PNMT activity was found in all heart areas examined in 6-hydroxydopamine-treated rats compared to vehicle-treated rats. The increased PNMT activity might reflect compensatory or adaptation processes secondary to the destruction of the peripheral sympathetic nerve terminals.

Expression and development of phenylethanolamine N-methyltransferase (PNMT) in rat brain stem: Studies with glucocorticoids

To study the differentiation of adrenergic (epinephrine-synthesizing) neurons in brain, the initial appearance and ontogeny of phenylethanolamine N-methyltransferase (PNMT), a specific marker of the adrenergic phenotype, were studied with immunocytochemistry and catalytic assay. The appearance of immunoreactivity to dopamine β-hydroxylase (DBH-IR), an enzyme common to the noradrenergic and adrenergic phenotypes, was also studied. DBH-IR was initially observed on embryonic Day 13 (E13) in cells located on the ventrolateral floor and wall of the rhombencephalon. A day later (E14), PNMT-IR cells and PNMT catalytic activity were observed in the rhombencephalon suggesting that, as in the adrenal gland, noradrenergic expression precedes adrenergic expression. The PNMT-IR cells were presumed to be precursors of C1 neurons since they were located in the ventrolateral medulla oblongata. Cells located in the wall of the medulla which appeared to be migrating ventrally to the C1 group also contained PNMT-IR. On E15, cells which had PNMT-IR processes coursing through the germinal zone were observed dorsally near the fourth ventricle. Although the location of the C1 cell group was apparent when PNMT was initially expressed, the dorsal C2 and C3 adrenergic cell groups were not evident until late in gestation on E19. Even in the term embryo there appeared to be PNMT-IR cells which had not yet reached their final destination. On E14 and E15, PNMT-IR cells were also observed on the floor of the pons just rostral to the pontine flexure. However, these were not observed in older embryos, suggesting that transient expression of PNMT occurs in brain, as well as in the periphery. To determine whether glucocorticoids regulate brain PNMT, we examined the effects of altered glucocorticoid levels. In contrast to PNMT in the sympathetic nervous system, PNMT activity in medulla oblongata was not affected in neonates or adults by the decrease in glucocorticoids following adrenalectomy or hypophysectomy. Conversely, elevation of glucocorticoids by hormonal treatment did not alter PNMT in neonates. Notably, however, treatment of pregnant rats with dexamethasone on E18–E21, but not earlier, increased PNMT activity in the fetal brain stem. These observations suggest that PNMT expression and development is regulated by different factors in cells derived from neural crest and tube. PNMT is expressed earlier in brain than in adrenal and sympathetic ganglia. Further, the development of PNMT in the periphery, but not in the brain, is dependent on maintenance of physiological levels of glucocorticoids. Our studies also elucidate three similarities in central and peripheral PNMT development: (1) in both adrenal and brain, adrenergic expression follows noradrenergic expression, (2) in both brain and periphery, PNMT is transiently expressed in some cells, and (3) glucocorticoid treatment of pregnant rats increases PNMT in the embryonic brain and sympathetic nervous system. Finally, we have observed a critical period during which glucocorticoid treatment increases PNMT activity in the brain.

Glucocorticoid receptors and regulation of phenylethanolamine-N- methyltransferase activity in cultured chromaffin cells

Glucocorticoids are known to regulate the enzyme phenylethanolamine-N-methyltransferase (PNMT) in the adrenal medulla of the rat and are thereby thought to control the synthesis of epinephrine. We have examined the details of this relationship in a simplified system, chromaffin cell primary cultures derived from bovine adrenal medulla. Cultured chromaffin cells were found to have a cytosolic, high affinity, saturable glucocorticoid-binding protein with the steroid specificity of a classical glucocorticoid receptor and a Kd of approximately 1 nM. Treatment of cultured cells with dexamethasone or hydrocortisone at any time up to 21 days in culture increased PNMT activity in the soluble fraction of the cell. The concentration of hormone required to produce a half-maximal response was 10 nM dexamethasone when cells were cultured in the presence of 5% fetal calf serum, or 1 nM in a defined serum-free medium. These dose-response relationships are consistent with mediation of this effect by the glucocorticoid receptor. Unexpectedly, however, the glucocorticoid-induced increment in PNMT activity was not inhibited by cycloheximide at concentrations up to 50 microM, and an acceleration of protein synthesis by insulin treatment did not augment the glucocorticoid effect on PNMT. Treatment of the cells with dexamethasone (100 microM) prevented the decline in the epinephrine-to-norepinephrine ratio seen over time in culture, an effect consistent with increased PNMT activity. However, there was no effect of dexamethasone on the ability of the cells to secrete catecholamines in response to stimulation with high KCl or 30 microM nicotine.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucocorticoid regulation of phenylethanolamine N-methyltransferase (PNMT) in organ culture of superior cervical ganglia.

Glucocorticoid regulation of the adrenergic enzyme, phenylethanolamine N-methyltransferase (PNMT) was studied in organ cultures of the superior cervical ganglion (SCG) from newborn rats. Although PNMT catalytic activity was present in control ganglia, enzyme levels were too low to allow visualization of PNMT immunofluorescent cells. Addition of dexamethasone (DEX) or corticosterone to the medium resulted in a large increase in PNMT activity and bright PNMT immunoreactive (PNMT-IR) staining in cells resembling small, intensely fluorescent (SIF) cells. Addition of non-glucocorticoid steroids was ineffective. Exposure to a brief, 2-hr pulse of DEX (10(-6) M) in vitro elicited the same increase in PNMT as continual exposure to DEX. Studies using metabolic inhibitors demonstrated that the steroid-dependent increase in PNMT activity required both protein and RNA synthesis. Furthermore, the increase was inhibited by cytochalasin B and by the glucocorticoid receptor antagonists, DEX 21-mesylate and cortisol 21-mesylate. These observations suggest that glucocorticoids increase PNMT protein in SIF cells by interacting with specific steroid receptors that undergo translocation to the nucleus.

Modulation of myosin isoenzyme populations and activities of monoamine oxidase and phenylethanolamine-N-methyltransferase in pressure loaded and normal rat heart by swimming exercise and stress arising from electrostimulation in pairs.

The question of whether the effects of physical exercise on the heart of 15-weeks normotensive and hypertensive rats can be modulated by additional stressors was studied. Intermittent swimming (33-35 degrees C water, maximum 2 X 1.5 h/day, 2-6 weeks) was employed as a model of exercise. Electrostimulation of rats in pairs (maximum 2 X 1.5 h/day, 6 weeks) served as a model leading predominantly to stress. When the above procedures were combined, electrostimulation in pairs was performed in one session and was followed up by swimming. The myosin isoenzyme population was used as a marker of changes in contractile performance of myofibrils. Activities of the catecholamine-degrading enzyme monoamine oxidase (MAO) and the adrenaline-synthesizing enzyme phenylethanolamine-N-methyltransferase (PNMT) served to monitor chronic alterations of catecholamine turnover in myocardium. Redistribution in favour of VM-1 (ventricular myosin isoenzyme 1) occurred as early as 2 weeks after the onset of intermittent swimming and was observed under several experimental conditions. The redirection of genetic expression of the isoenzymes was not linked to the presence of an increased ratio of right to left ventricular weight, most probably arising from intermittent hypoxia during drownproofing. The myosin isoenzyme population of swimming spontaneously hypertensive rats (SHR) resembled that of sedentary Wistar rats. The enzyme activities of MAO and PNMT were both significantly reduced following 6 weeks intermittent swimming in Wistar rats and SHR. This can most probably be attributed to the exercise component of swimming which, on average, led to reduced catecholamine turnover in heart. Electrostimulation of rats in pairs for 6 weeks, which resulted in aggressivity and aggressions, did not alter the myosin isoenzyme population in Wistar rats; in SHR, it further augmented the proportion of VM-3 (ventricular myosin isoenzyme 3), which had already increased in the sedentary state. Furthermore, electrostimulation increased PNMT activity, but did not affect MAO activity. Electrostimulation in pairs, followed by swimming, altered the myosin isoenzyme population in the same way as did swimming alone. However, the activities of PNMT and MAO seemed to be governed by the routine involving stress and not by the exercise routine. This demonstrates that stressors supplementing exercise can decisively modify or even prevent reactions of the organism in response to exercise.(ABSTRACT TRUNCATED AT 400 WORDS)

A new group of neurons in hypothalamus containing phenylethanolamine N-methyltransferase (PNMT) but not tyrosine hydroxylase

Intraventricular injection of colchicine in rat results in the appearance within hypothalamus of numerous neurons containing the adrenaline-synthesizing enzyme, phenylethanolamine N-methyltransferase, but not the other catecholamine biosynthetic enzymes. Increased PNMT staining in hypothalamus was paralleled by an increase in PNMT activity measured in micropunch preparations. Immunotitration demonstrated that this increase was due to accumulation of specific enzyme protein. The finding that hypothalamic neurons express PNMT without tyrosine hydroxylase suggests that such neurons may produce methylated amines other than adrenaline.

Tetrahydroisoquinolinecarboxylic acids and regulation of phenylethanolamine N-methyltransferase in cultured adrenal medulla

Explants of rat adrenal medullae, cultured for up to 48 hr in the presence of 3′,4′-deoxynorlaudanosolinecarboxylic acid (DNLCA) or α-methyltyrosine, exhibited a 69% increase in phenylethanolamine N-methyltransferase (PNMT) activity as measured in dialyzed homogenates. A related tetrahydroisoquinoline, norlaudanosolinecarboxylic acid (NLCA), when added to the medium did not elevate PNMT activity. No increase in the amount of PNMT was detected by immunochemical titration of homogenates from DNLCA-treated cultured medulla, nor were there changes in rates of synthesis or degradation of the enzyme. Although DNLCA is an inhibitor of tyrosine 3-monooxygenase, it had no effect on PNMT activity when added directly to an incubation mixture in vitro. Kinetic analyses of dialyzed homogenates from explants cultured in the presence of DNLCA revealed that the V max of PNMT was higher than that of control tissue. There was no decrease in K m after DNLCA treatment. The increase in PNMT activity appears to be a compensatory response to depletion of medullary catecholamines by DNLCA or α-methyltyrosine.

Differentiation of adrenomedullary catecholamine synthesizing enzyme responses to repeated immobilization in hybrid rats

The response of adrenomedullary catecholamine synthesizing enzymes to repeated immobilization was studied in hybrid (F 1) offspring of 2 inbred rat strains (LEW and F344). Immobilization-induced increases in tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyl-transferase (PNMT) activities in one of the parental strains (F344) previously were shown to be dependent upon intact adrenal gland innervation but independent of the pituitary gland, while responses in the other parental strain (LEW) were independent of adrenal innervation but dependent upon pituitary function. Factors determining immobilization-induced increases in adrenal enzymes of F 1 offspring were enzyme-specific. Increased PNMT activity was pituitary dependent in F 1 rats, whereas increased TH and DBH activities after immobilization were dependent upon an intact adrenal gland innervation. These results suggest that the factor(s) regulating PNMT responses are differentiable from those regulating TH and DBH responses. The results also indicate that analysis of PNMT responses to immobilization in backcross populations is feasible, and could indicate whether strain-specific response mechanisms are heritable.

DIFFERENTIAL EFFECTS OF α-METHYLDOPA, CLONIDINE AND HYDRALAZINE ON NOREPINEPHRINE AND EPINEPHRINE SYNTHESIZING ENZYMES IN THE BRAINSTEM NUCLEI OF SPONTANEOUSLY HYPERTENSIVE RATS

Repeated administrations of clonidine to spontaneously hypertensive rats (SHR) markedly lowered dopamine β-hydroxylase (DBH) activity in the locus coeruleus (LC) and increased it in the spinal intermediolateral cell column (IML), while α-methyldopa tended to lower the enzyme activity in the medullary nucleus tractus solitarii (NTS) and A1 cell areas. Clonidine-induced inhibition of 3H-norepinephrine binding to crude cerebral membranes of SHR or Kyoto Wistar rats (KWR) as a measure of α-receptor agonist activity was 7 times greater than that of (±)α-methyl-(±)-norepinephrine. Clonidine and hydralazine significantly lowered phenylethanolamine N-methyltransferase (PNMT) activity elevated in the nucleus hypothalamicus posterior (NHP) of SHR to the level of KWR, and both drugs or α-methyldopa consistently increased PNMT in the nucleus paraventricularis (NPA). Peripherally active hydralazine also increased PNMT activity in the NTS, and antagonized the activity elevated in the A1 cell area of SHR to the level of KWR. In conclusion, clonidine selectively lowers DBH activity in the LC, while α-methyldopa appears to decrease the enzyme activity in the medullary NTS and A1 cell areas, suggesting different sites of action of both drugs. The decreased DBH activity in these nuclei may be related to stimulation of respective α-noradrenergic receptors. Elevating effects of all three drugs on PNMT activity in the NPA may be due to decreased baroreceptor afferent impulses to the nucleus after a fall in blood pressure.

Increased brain stem and decreased hypothalamic adrenaline-forming enzyme after acute and repeated immobilization stress in the rat.

The effects of immobilization stress on the activity of the adrenaline-forming enzyme, phenylethanolamine N-methyltransferase (PNMT), have been studied in discrete areas of the rat brain stem and hypothalamus. The changes in brain PNMT activity varied with the duration of the stress, were localized to a few brain areas, and the direction of the change varied with the area considered. PNMT was increased after acute immobilization in several areas of the brain stem: A2 area, the anterior part of the nucleus tractus solitarius, and the locus coeruleus. After 7 days of stress, significantly increased PNMT activity was found only in the A2 area and in the cerebellum. In the anterior hypothalamic nucleus, immobilization stress repeated for seven days resulted in a significant decrease in methyltransferase activity. These results implicate discrete, localized adrenaline-forming neurons in the central regulation of the stress response.

Dihydralazine and catecholamine-synthesizing enzymes in spontaneous hypertension

Dihydralazine treatment which lowered blood pressure in young rats from the Lyon Hypertensive Strain (LHS), did not change phenylethanolamine-N-methyltransferase (PNMT) activity, but decreased tyrosine hydroxylase and dopamine-β-hydroxylase activities in the C 2 medullary region. These data suggest that the increase in PNMT activity, previously described for this strain, is not a consequence of the developing hypertension and that hypotensive treatment could inactivate some catecholaminergic neurons of the medulla oblongata.

Effect of stress on newborn hypothalamic phenylethanolamine- N-methyltransferase

1. 1. Assays of phenylethanolamine- N-methyltransferase (PNMT) activity of rat hypothalami revealed that PNMT was present at birth, even though only in traces, and gradually increased during the first two postnatal months. 2. 2. Exposure to recurrent stressful situations increased PNMT activity in a statistically significant manner. 3. 3. Persistence of stressful situations resulted in a higher PNMT of adult rats as compared to adult controls. 4. 4. Assays of hypothalamic tissue cultures led to the conclusion that part of the increase of PNMT activity resulted from temporary potentiation of PNMT by local factors, and part from induction of protein synthesis. 5. 5. One of the submolecular chain reactions generated by stress and able to induce protein synthesis was identified as: release of ACTH during stress, activation of local adenylate cyclase by ACTH to synthesize cyclic AMP. When released, this cyclic AMP increased the local ratio of cyclic AMP/cyclic GMP, a process known to induce protein synthesis.

Influence of repeated injections of estradiol during late pregnancy upon enzymes of monoamine metabolism and biosynthesis in the rat

The effects of repeated injections of estradiol to pregnant rats upon activities of enzymes catechol-O-methyltransferase (COMT), monoamine oxidase (MAO) and phenylethanolamine-N-methyltransferase (PNMT) in the adrenal gland have been reported. Both the enzymes of monoamine metabolism, MAO and COMT showed declines in activity after estradiol treatment. Estradiol increased PNMT activity when the results were expressed in cpm/adrenal gland. Adrenal noradrenaline stores declined significantly in pregnant females receiving estradiol treatment but adrenaline did not show any marked change. These observations were further tested by the perfusion of 3H-adrenaline to estradiol treated and normal pregnant females. Estradiol pretreatment significantly increased physiological accumulation of the tracer by the adrenals. The transformation of 3H-adrenaline to 3H-metadrenaline did not show any change howsoever 3H-acid metabolites were greatly decreased after pretreatment of estradiol. The results provide evidence that estradiol administration during pregnancy inhibits enzymes of monoamine metabolism and stimulate enzyme PNMT to some extent. The uptake of labelled adrenaline increases significantly following administration of estradiol to pregnant females.

Effects of dexamethasone on phenylethanolamine N-methyltransferase and adrenaline in the brains and superior cervical ganglia of adult and neonatal rats.

Abstract— Phenylethanolamine N‐methyltransferase (PNMT) activity assayed by a sensitive radiochemical method was found to be distributed unevenly in the adult rat brain. Highest activities of this enzyme were located in the medulla and the hypothalamus. Small amounts of adrenaline were identified in the hypothalamus using a sensitive enzymatic radiochemical assay procedure, whereas in the medulla and other brain regions the values for adrenaline were at the limits of the sensitivity of the assay for this amine. The daily administration of dexamethasone (1 mg/kg) to adult rats for 13 days significantly increased PNMT activity in medulla and hypothalamus and also increased the adrenaline content of the hypothalamus. Five daily injections of dexamethasone (0·1 mg/kg) to newborn rats did not alter the PNMT activity or the catecholamine content of the brain, but markedly increased the PNMT activity and adrenaline content of superior cervical ganglia. Higher doses of dexamethasone given to newborn rats (6 daily injections of 1 mg/kg) increased PNMT activity both in the medulla and in the hypothalamus.

EFFECTS OF DEXAMETHASONE ON NEUROTRANSMITTER ENZYMES IN CHROMAFFIN TISSUE OF THE NEWBORN RAT

—Dexamethasone administration to newborn rats resulted in an increase in phenylethanolamine N-methyltransferase activity in superior cervical ganglia. The same treatment resulted in a decrease in tyrosine hydroxylase and choline acetyltransferase activities. The decline in choline acetyltransferase activity after dexamethasone treatment was only seen when the drug was given before 5 days of age. When dexamethasone was given to pregnant rats it caused an age-dependent decrease in choline acetyltransferase in the adrenals, superior cervical ganglia and para-aortic chromaffin tissue of the offspring. These results suggest that dexamethasone administration may delay the development of the preganglionic neurons of sympathetic ganglia. This in turn would delay the development of tyrosine hydroxylase but not phenylethanolamine N-methyltransferase.

Influence of corticosterone on the stress-induced elevation of phenylethanolamine- N-methyl transferase activity in the avian adrenal

The mechanism of adrenal phenylethanolamine- N-methyl transferase (PNMT) elevation occurring in the avian stress response was evaluated in 8- to 9-wk-old White Leghorn cockerels. The nonspecific stressor used in this study was a single 3-hr period of immobilization. The following physiological parameters were measured: (1) plasma and adrenal concentrations of epinephrine (E) and norepinephrine (NE); (2) plasma concentration of corticosterone (B); and (3) adrenal PNMT activity. It was found that if an inhibitor of B biosynthesis (Metopirone) was administered prior to the restraint period, the elevation in adrenal PNMT activity normally occurring with immobilization was prevented. The Metopirone-treated group also showed significantly smaller adrenal and plasma levels of E after restraint as compared to the non-drug-treated group. In contrast there was no significant difference between the restrained control group and the restrained group given Metopirone in their plasma and adrenal levels of NE. Puromycin given prior to immobilization was also effective in preventing the increased PNMT activity seen with immobilization. The administration of a large dose of B did not alter the blocking action of puromycin on PNMT elevation. The plasma concentrations of E and NE were also significantly smaller in the restrained group given puromycin as compared to the non-drug-treated restrained group. It is concluded that B does cause an increase in PNMT activity during the avian stress response and that this increase in activity provides a means for replenishing the adrenal with E under the condition of stress. The regulation of PNMT activity by B appears to be by enzyme induction.

Phenylethanolamine- N-methyl transferase activity in the avian adrenal following immobilization or adrenocorticotropin

The acute response of the avian adrenal to stress was evaluated by quantitatively measuring the adrenal and plasma levels of the major adrenal hormones (corticosterone (B), epinephrine (E), and norepinephrine (NE) along with assaying the adrenal activity of phenylethanolamine- N-methyltransferase (PNMT) in 8- to 9-week-old White Leghorn cockerels. The nonspecific stressor used in this study was a single 3-hour period of immobilization or a single dose of adrenocorticotropin (ACTH). It was found that the administration of ACTH or immobilization resulted in a significant increase in plasma E and NE concentrations with an accompanying decrease in their adrenal levels. ACTH-trcatment or immobilization was also effective in significantly increasing plasma B concentration and adrenal PNMT activity, but had no effect on the adrenal level of B. It is suggested that the rapid increase in PNMT activity, occurring with the acute application of stressors in chickens, may provide a means of sustaining an increased outflow of E in times of “stress.” The role that B may play in the elevation of PNMT, occurring in the avian stress response, is also discussed.