Glucocorticoids, adrenocorticotropichormone and related polypeptides on myocardial sensitivity to noradrenaline

Adrenocortical function in the postoperative pediatric cardiac surgical patient

PURPOSE OF REVIEW

Corticosteroids are frequently used in the postoperative care of children with congenital heart disease. This review describes the function of the adrenocortical axis in this population and the effects of corticosteroids on cardiovascular function. In addition, it examines the diagnosis of adrenal insufficiency in this population and provides an overview of recent studies on the use of steroids in treating hemodynamic instability in these children.

RECENT FINDINGS

Corticosteroids improve hemodynamic parameters in children with shock following congenital heart surgery. This improvement may be due to treatment of adrenal insufficiency or from direct cardiovascular effects of corticosteroids. The diagnosis of adrenal insufficiency in this population is challenging as low cortisol levels do not consistently correlate with adverse outcomes.

SUMMARY

Because of the lack of evidence delineating what the normal adrenocortical function is in this population, cortisol levels alone are not sufficient to justify treating with steroids in this population. Corticosteroids are beneficial in improving hemodynamics in children with shock after congenital heart surgery, but the adverse effects of the therapy in this context are not fully known. Prospective trials are necessary to clarify which patients may benefit from steroid therapy and to examine long-term effects of steroids.

Regulation of equine lymphocyte beta-adrenoceptors under the influence of clenbuterol and dexamethasone

In 12 healthy horses, the effects of the beta2-agonist clenbuterol and the glucocorticoid dexamethasone on the lymphocyte beta2-adrenoceptor density and affinity (determined by (-)-[125I]-iodocyanopindolol binding) as well as its responsiveness (assessed by lymphocyte cyclic AMP [cAMP] responses to 10 micromol/l (-)-isoprenaline) were studied. Clenbuterol treatment, 2 x 0.8 microg/kg/day i.v. for 12 days, decreased significantly ICYP binding sites by approximately 30-40%; concomitantly, lymphocyte cAMP response to (-)-isoprenaline was reduced. After withdrawal of clenbuterol, beta2-adrenoceptor density and responsiveness gradually increased, reaching predrug levels after 4 days. The effects of dexamethasone on clenbuterol-induced desensitisation were further investigated. Administration of dexamethasone (1 x 0.1 mg/kg/day, i.v. for 5 days) immediately after clenbuterol withdrawal accelerated beta2-adrenoceptor recovery: only 24 h after administration dexamethasone restored the number of binding sites and cAMP response to (-)-isoprenaline to levels statistically indistinguishable from values before clenbuterol treatment. Three days after dexamethasone administration, lymphocyte beta2-adrenoceptors were further increased about 2-fold the pretreatment values, and this increase declined gradually after dexamethasone withdrawal, reaching baseline values after 4 days. Furthermore, in groups exposed simultaneously to both drugs, dexamethasone completely prevented clenbuterol-induced decrease in lymphocyte beta2-adrenergic receptor density and responsiveness. No significant change was observed in the dissociation constant for ICYP in any of the situations. We conclude that dexamethasone (glucocorticoids) can reverse and prevent Clenbuterol-induced desensitisation (down-regulation) of the lymphocyte beta2-adrenoceptors and therefore, a combined therapy with clenbuterol and dexamethasone may be potentially beneficial in horses suffering from chronic obstructive pulmonary disease (COPD).

Rapid neuromodulation by cortisol in the rat paraventricular nucleus: an in vitro study

1. We have used a range of in vitro electrophysiological techniques to investigate the mechanism of rapid cortisol neuromodulation of parvocellular neurones in the rat paraventricular nucleus. 2. In our study, we found that cortisol (10 microM) increased spontaneous action-current firing frequency to 193%. This effect was insensitive to the glucocorticoid intracellular-receptor antagonist mifepristone. 3. Cortisol (0.1-10 microM) had no detectable effects on whole-cell GABA current amplitudes, or GABA(A) single-channel kinetics. 4. Cortisol (10 microM) inhibited whole-cell potassium currents in parvocellular neurones by shifting the steady-state activation curve by 14 mV to the right. 5. Additionally, in a cell line expressing both the glucocorticoid intracellular receptor and recombinant, fast inactivating potassium channels (hKv1.3), cortisol (1 and 10 microM) inhibited potassium currents by shifting their steady-state activation curves to the right by 12 mV (10 microM cortisol). This effect was also insensitive to the cortisol antagonist, mifepristone. 6. These data suggest that inhibition of voltage-gated potassium channels may contribute to the rapid neuromodulatory effects of cortisol, possibly by direct interaction with the ion channel itself.

Dexamethasone-induced cardiogenic shock rescued by percutaneous cardiopulmonary support (PCPS) in a patient with pheochromocytoma

A 52-year-old man with pheochromocytoma had cardiogenic shock and was rescued using a percutaneous cardio pulmonary supporting system. After recovery, diagnostic tests including metaiodobenzylguanidine scintigraphy and computed tomography, revealed the pheochromocytoma which was confirmed by histology. It was postulated that the acute episode was induced by intra-joint dexamethasone, which increased the production of epinephrine and augmented the sensitivity of cardiomyocytes for catecholamine, thereby inducing the cardiomyopathy.

Randomised trial of dopamine compared with hydrocortisone for the treatment of hypotensive very low birthweight infants

AIM

To compare the efficacy of hydrocortisone with dopamine for the treatment of hypotensive, very low birthweight (VLBW) infants.

METHODS

Forty infants were randomly allocated to receive either hydrocortisone (n = 21) or dopamine (n = 19).

RESULTS

All 19 infants randomised to dopamine responded; 17 of 21 (81%) did so in the hydrocortisone group. Three of the four non-responders in the hydrocortisone group had clinically significant left to right ductal shunting. The incidence of bronchopulmonary dysplasia, retinopathy of prematurity, intraventricular haemorrhage, necrotising enterocolitis, symptomatic patent ductus arteriosus, hyperglycaemia, sepsis (bacterial or fungal) or survival did not differ between groups. The adrenocorticotrophic hormone (ACTH) stimulated plasma cortisol activity, either before or after treatment, did not differ between the two groups of infants. Although a significant difference in efficacy between dopamine and hydrocortisone was not noted (P = 0.108), there were four treatment failures in the hydrocortisone group, compared with none in the dopamine group.

CONCLUSION

Both hydrocortisone and dopamine are effective treatments for hypotension in very low birthweight infants.

Characterization of beta-endorphin- and alpha-MSH-related peptides in rat heart

POMC-derived peptides and mRNA have been identified in heart tissue, although POMC processing has not been fully characterized. In the present study, we found that beta-lipotropin and ACTH were localized in rat heart, although they were almost entirely converted to beta-endorphin- and alpha-MSH-related peptides. Ion exchange HPLC analysis revealed that beta-endorphin(1-31) was further processed to alpha-N-acetyl-beta-endorphin(1-31), which comprised 35.9 +/- 0.1% of total immunoreactivity, and smaller amounts of beta-endorphin(1-27), beta-endorphin(1-26), and their alpha-N-acetylated derivates. The predominant alpha-MSH immunoreactive peptides coeluted with alpha-MSH and N,O-diacetyl-alpha-MSH by reverse-phase HPLC, although small amounts of ACTH(1-13)-NH2 were also present. Thus, multiple forms of beta-endorphin and alpha-MSH are localized in rat heart. beta-Endorphin(1-31) is a minor constituent, however, indicating that nonopioid beta-endorphin peptides predominate.

Glucocorticoid-recognizing and -effector sites in rat liver plasma membrane. Kinetics of corticosterone uptake by isolated membrane vesicles--I. Binding and transport

To gain insight into the mechanisms governing cellular uptake of glucocorticoids, we studied the binding and membrane transport of corticosterone (B) on a highly purified plasma membrane fraction from rat liver that was homogenized using a gentle, isotonic procedure. The fraction was mostly in the form of right-side out and osmotically active vesicles that were free of intracellular glucocorticoid receptors (GCR), transcortin (CBG) and ATP. Our uptake and binding studies carried out at 22 degrees C with [3H]B in physiological concentrations resulted in the following findings: (1) unlabeled B competed with [3H]B for uptake by the membrane vesicles; half-maximal competition of specific uptake was achieved with a 10- to 11-fold molar excess of unlabeled B. (2) [3H]B uptake was a saturable process of unusual kinetics (multiple sigmoidity); modified Scatchard plots revealed three significantly different apparent Kd-values of 1.3, 4.7 and 17.3 nM, corresponding to free B in the blood of non-stressed rats (4-16 nM). (3) Osmotic shrinkage of the vesicles led to a linear decrease in specific uptake, while non-specific uptake was independent of vesicle volume. Passive diffusion of [3H]B took place in leaky, but not in intact, vesicles. Reversible binding to, and mediated transport through, the membrane were interdependent parts of a strongly linked process. B was accumulated inside the vesicle up a concentration gradient by an active transport that followed first-order kinetics (Kt:3.9 nM); for its statistically reliable mathematical formulation and kinetic analysis, a replot was developed that revealed that relative accumulation increased with decreasing external hormone concentration. (4) Comparative binding studies disclosed that the apparent Kd-values (86.5 +/- 7.3 and 77.0 +/- 14.3 nM, respectively) of the [3H]B interactions with CBG and GCR did not differ (P greater than 0.3). These findings permit the conclusion that a plasma membrane-inserted carrier for B, effectively operating at physiological concentrations in the blood, is involved in a functional and regulatory manner in the biological action of glucocorticoids.

Footshock stress-induced supersensitivity to isoprenaline in the isolated pacemaker of the rat: effects of the compounds RU-38486 and RU-28362

1. Three daily sessions of inescapable footshock stress of 30 min duration each increased the sensitivity of the isolated pacemaker of the rat to the chronotropic effect of isoprenaline. 2. The effect of inescapable footshock stress on the sensitivity of the isolated rat pacemaker to the chronotropic effect of isoprenaline was prevented by the daily administration of the compound RU-38486, a potent antiglucocorticoid which blocks the cytosolic receptor for corticosterone. 3. The administration of the compound RU-28362, a potent agonist of the cytosolic receptor for corticosterone, during 3 days to rats which were not submitted to footshock stress induces supersensitivity to the chronotropic effect of isoprenaline. 4. It is concluded that corticosterone plays an important role in the qualitative control of the rat pacemaker beta-adrenoceptor population during adaptation to repeated footshock stress.

Adrenocorticotropin binding sites in rat cardiac tissue

Using the ACTH analog [125I-Tyr23,Phe2,Nle4] ACTH(1-24), the existence of specific binding sites for ACTH in atrial membrane preparations was demonstrated. The dissociation constants (Kd), determined by Scatchard analysis were not significantly different for membrane preparations of adrenal gland or atrial tissue (being 6.40 x 10(-12)M and 8.86 x 10(-12)M respectively). No binding was observed to membrane preparations from kidney or lung. While the binding of the ACTH(1-24) analog to atrial membranes was inhibited by ACTH(1-24), it was not affected by norepinephrine or epinephrine. It was proposed that the ACTH(1-24) analog may bind to sites located on the adrenergic nerve endings associated with the cardiac tissue, and that such binding would interfere with the neuronal reuptake of the catecholamines.

The adrenocorticotropic hormone (ACTH)-induced reversal of hemorrhagic shock

Adrenocorticotropic hormone (ACTH), while having negligible effects on cardiovascular function in the intact animal, induces a potent and sustained reversal of an otherwise invariably, rapidly fatal condition of hemorrhage-induced hypovolemic shock, in rats and dogs. The main site(s) of action are at the peripheral level; however, subsidiary site(s) of action in the CNS cannot be excluded. The studies on the mechanism of action indicate that the ACTH-induced reversal of hemorrhagic shock (a) is an extra-hormonal, adrenal-independent effect, because it is not affected by adrenalectomy and is shared by many ACTH-fragments practically devoid of corticotropic activity; (b) is antagonized by morphine in a surmontable way; (c) needs the functional integrity of the sympathetic nervous system (it is prevented by guanethidine, reserpine, and clonidine) and the availability of peripheral alpha-adrenoceptors (it is antagonized by dibenamine, prazosin and yohimbine, but not by practolol); (d) requires the integrity of afferent vagal fibers (it is almost completely abolished by vagotomy); (e) involves central cholinergic networks (it is antagonized by atropine sulphate, but not by atropine methyl bromide; and it is prevented by the intracerebroventricular injection of hemicholinium-3); (f) is associated with a massive increase in the volume of circulating blood, likely due to a mobilization from peripheral pooling sites (it is largely prevented by splenectomy or by suprahepatic veins ligature, and is associated with a restoration of the venous blood flow in peripheral vascular beds and with a normalization of venous PO2); (g) is associated with a restoration of heart and spleen adrenoceptors, whose number is significantly decreased during hemorrhagic shock. The survival time of hemorrhage-shocked animals, which is 26 +/- 3 min in controls, is greatly prolonged (44 +/- 18 h) by ACTH, provided that the treatment is made within 5-10 min after bleeding. Finally, in animals treated with ACTH within 5-10 min after bleeding, blood reinfusion retains its effectiveness and reverse shock even if performed 2-5 h later.

Effect of circadian rhythm on the neuronal uptake and sensitivity to the inotropic action of norepinephrine by rat atria

The circadian rhythm for plasma corticosterone was determined. Animals were then killed at times corresponding to high and low periods of the circadian rhythm in plasma corticosterone. Myocardial sensitivity to norepinephrine was measured at these time periods as the ED50 of the catecholamine, obtained using electrically driven rat atria. The uptake of 3H-norepinephrine by spontaneously beating atria was also measured at both time periods. A circadian variation in the uptake of 3H-norepinephrine by the rat atria was observed. This variation in uptake was associated with a variation in plasma corticosterone, but was not associated with any change in myocardial sensitivity to norepinephrine.

Effect of (1-24)adrenocorticotrophin on the uptake of 3H-norepinephrine by the rat atria

Spontaneously beating rat atria were incubated with 3H-norepinephrine both in the presence and absence of (1-24)ACTH. A significant reduction in the uptake and retention of radioactivity was found in atria pretreated with (1-24)ACTH. A kinetic study of the uptake process showed similar Km values for both the control (24.1 x 10(-8) M) and (1-24)ACTH pretreated (22.2 x 10(-8) M) groups, but a significantly different Vmax. The Km values were similar to that reported for the neuronal reuptake process (Uptake 1). It was concluded that the ACTH-induced enhanced myocardial sensitivity to catecholamines previously reported, could be explained in part on the basis of an inhibition of neuronal uptake by (1-24)ACTH. The inhibition of neuronal uptake by (1-24)ACTH was dose-dependent.

ACTH increases noradrenaline release in pithed rabbits with electrically stimulated sympathetic outflow

ACTH 0.03-1 microgram/kg per min i.v. increased the noradrenaline spillover rate (the rate at which endogenous noradrenaline enters into plasma) and the plasma noradrenaline concentration in pithed rabbits with electrically stimulated sympathetic outflow. ACTH 0.1 and 1 microgram/kg per min decreased the mean arterial pressure (MAP). The effects of ACTH persisted in animals treated with propranolol. Corticosterone 10 micrograms/kg per min had no effect on the neurochemical and circulatory parameters. ACTH 0.03 and 1 microgram/kg per min increased plasma corticosterone and cortisol concentrations; the two doses of ACTH had approximately the same effect. The plasma corticosterone concentration reached after infusion of corticosterone 10 micrograms/kg per min was about twice that obtained after ACTH 0.03 or 1 microgram/kg per min. In a second series of experiments, a pressor dose of noradrenaline (1 or 2 micrograms/kg per min) was infused i.v. into pithed rabbits. ACTH 0.03 and 1 microgram/kg per min decreased blood pressure and increased heart rate in these animals. The results suggest that high doses of ACTH increase noradrenaline release by an action on postganglionic sympathetic neurons. The effect is probably not mediated through adrenal steroids. In addition, ACTH seems to decrease MAP and to increase heart rate through postsynaptic vascular and myocardial effects.

ACTH 1-24-induced potentiation of norepinephrine contractile responses in aortic strips from spontaneously hypertensive (SH) and normotensive (WKY) rats

Norepinephrine (NE)-induced contractile responses were less in aortic strips from SH compared to WKY rats. ACTH 1-24 potentiated NE responses in both SH and WKY aortic strips. This effect was more potent in SH aortic strips. NE-induced contractions in SH aortic strips were less sensitive to changes in external Ca2+ levels than were those of WKY aortic strips. ACTH 1-24 did not potentiate NE responses under low external Ca2+ conditions in SH aortic strips or under high external Ca2+ conditions in WKY aortic strips. The greater sensitivity of NE responses following ACTH 1-24 in SH aortic strips may imply that this peptide is modulating a mechanism related to an impaired contractility and that Ca2+ plays a key role in the observed effects.

Natriuretic and hypertensive activities reside in a fragment of ACTH

The hypertensive and natriuretic effects of chronic administration of adrenocorticotrophic hormone (ACTH) cannot be duplicated by the administration of glucocorticoids and/or mineralocorticoids. We investigated the effects of a fragment of this hormone (ACTH4-10) and an analog of the fragment (D-Phe7) ACTH4-10 and found them to have pressor and cardioaccelerator actions in rats as determined by bolus intravenous (i.v.) injections of 30 to 1000 nmol/kg. The pressor and cardioaccelerator effects of (D-Phe7) ACTH4-10 were attenuated by alpha-receptor (phentolamine) and beta-receptor (metoprolol) antagonists. The cardiovascular actions of ACTH4-10 were produced in adrenalectomized or ganglionic-blocked (with mecamylamine) rats. At a lower dose (7 nmol/kg i.v.), ACTH4-10 was natriuretic and had a pattern of activity similar to that of a larger ACTH fragment, alpha-melanocyte-stimulating hormone. Extraadrenal effects of the intact ACTH molecule or the in vivo production of an ACTH4-10-like fragment from ACTH may contribute to the hypertensive and natriuretic actions associated with this hormone.

Corticosterone secretion in the rat after DSP-4 treatment

Functioning of the hypothalamo-pituitary-adrenocortical axis was assessed in rats treated with DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine), a selective noradrenergic neurotoxin. Although adrenal weights were slightly increased 10 days after DSP-4 injection, basal plasma corticosterone levels were unaltered compared to those of control animals. Moreover, the elevation of corticosterone levels induced by the stress of ether inhalation did not appreciably differ from that in control rats. These various results suggest that DSP-4 treatment has no marked effect on the normal functioning of the hypothalamo-pituitary-adrenocortical axis.

Facilitatory effect of adrenocorticotropic hormone and related peptides on Ca2+-dependent noradrenaline release from sympathetic nerves

Strips of rabbit pulmonary artery and aorta were incubated with [3H]noradrenaline and subsequently superfused. Tritium overflow from strips superfused with physiological salt solution was stimulated either electrically (usually at a frequency of 2 Hz) or by tyramine 1 mumol/l and overflow from strips superfused with Ca2+-free solution containing K+ 54.7 mmol/l was stimulated by introduction of Ca2+ 1.6 mmol/l. In most of the experiments (stimulation by electrical impulses or CaCl2) neuronal and extraneuronal uptake and beta-adrenoceptors were blocked by cocaine, corticosterone and propranolol, respectively. The electrically evoked overflow of 3H-labelled substances from pulmonary artery and aorta was increased by adrenocorticotropic hormone. In the pulmonary artery, the adrenocorticotropic hormone--induced increase in impulse--evoked overflow (and contraction) was the more pronounced, the lower the frequency of stimulation (6, 2 and 0.66 Hz: 360 impulses). The electrically evoked overflow of 3H-labelled substances was also increased by alpha-melanocyte-stimulating hormone and porcine adrenocorticotropic hormone, but was not affected by adrenocorticotropic hormone. Adrenocorticotropic hormone also facilitated the Ca2+-evoked overflow of 3H-labelled substances promoted by high K+, but it did not affect the Ca2+-independent tyramine-evoked overflow. Adrenocorticotropic hormone did not alter the percentages of [3H]noradrenaline and 3H-labelled metabolites contained in electrically or tyramine-evoked overflow of 3H-labelled substances. In conclusion, adrenocorticotropic hormone and fragments of adrenocorticotropic hormone cause an increase in stimulation-evoked, Ca2+-dependent noradrenaline release from postganglionic sympathetic nerve fibres, probably by activating presynaptic receptors for adrenocorticotropic hormone.

Electrophysiological and contractile responses of canine atrial tissue to adrenocorticotropin

The direct extra-adrenal actions of adrenocorticotropin 1-39 (ACTH) on electrical (E) and mechanical (M) characteristics of canine atrial tissues (AT) were investigated in in vitro experiments. One hundred twenty-five mU/ml of ACTH 1-39 significantly augmented the catecholamine induced positive inotropism as seen by shortening the time to peak tension (10.6%, p = 0.01) and increasing peak isometric tension (3.5 times, p = 0.001). Effects on the M responses were inhibited by propranolol (10(-6) M) (P). ACTH did not significantly modify action potential E or M parameters during cholinergic receptor antagonism or alpha-adrenergic receptor antagonism. Existence of a specific ACTH receptor was demonstrated using 125I radioiodinated ACTH 1-24. Significant binding of 125I-ACTH to AT was observed. Intracellular C-AMP levels were also measured in AT using radioimmunoassay. Tissues were exposed to 125mU/ml ACTH 1-39 plus combinations of norepinephrine (10(-6) M) (NE) and P. ACTH alone did not elevate intracellular C-AMP levels. NE increased C-AMP levels were not further increased by ACTH. Exposure to antagonist returned elevated C-AMP levels to control values. In conclusion (1) ACTH augments the NE induced M positive inotropism of the beta adrenergic receptor system. (2) ACTH specifically binds to AT and (3) ACTH does not utilize the C-AMP second messenger system.