Effects of glucocorticoids on the beta-adrenergic adenylate cyclase system of pig skin

Glucocorticoids, genes and brain function

The identification of key genes in transcriptomic data constitutes a huge challenge. Our review of microarray reports revealed 88 genes whose transcription is consistently regulated by glucocorticoids (GCs), such as cortisol, corticosterone and dexamethasone, in the brain. Replicable transcriptomic data were combined with biochemical and physiological data to create an integrated view of the effects induced by GCs. The most frequently reported genes were Errfi1 and Ddit4. Their up-regulation was associated with the altered transcription of genes regulating growth factor and mTORC1 signaling (Gab1, Tsc22d3, Dusp1, Ndrg2, Ppp5c and Sesn1) and progression of the cell cycle (Ccnd1, Cdkn1a and Cables1). The GC-induced reprogramming of cell function involves changes in the mRNA level of genes responsible for the regulation of transcription (Klf9, Bcl6, Klf15, Tle3, Cxxc5, Litaf, Tle4, Jun, Sox4, Sox2, Sox9, Irf1, Sall2, Nfkbia and Id1) and the selective degradation of mRNA (Tob2). Other genes are involved in the regulation of metabolism (Gpd1, Aldoc and Pdk4), actin cytoskeleton (Myh2, Nedd9, Mical2, Rhou, Arl4d, Osbpl3, Arhgef3, Sdc4, Rdx, Wipf3, Chst1 and Hepacam), autophagy (Eva1a and Plekhf1), vesicular transport (Rhob, Ehd3, Vps37b and Scamp2), gap junctions (Gjb6), immune response (Tiparp, Mertk, Lyve1 and Il6r), signaling mediated by thyroid hormones (Thra and Sult1a1), calcium (Calm2), adrenaline/noradrenaline (Adcy9 and Adra1d), neuropeptide Y (Npy1r) and histamine (Hdc). GCs also affected genes involved in the synthesis of polyamines (Azin1) and taurine (Cdo1). The actions of GCs are restrained by feedback mechanisms depending on the transcription of Sgk1, Fkbp5 and Nr3c1. A side effect induced by GCs is increased production of reactive oxygen species. Available data show that the brain's response to GCs is part of an emergency mode characterized by inactivation of non-core activities, restrained inflammation, restriction of investments (growth), improved efficiency of energy production and the removal of unnecessary or malfunctioning cellular components to conserve energy and maintain nutrient supply during the stress response.

Adenylate cyclase induces intracellular Ca2+ increase in single human epidermal keratinocytes of the epidermal sheet as measured by digital imaging microscopy using Fura 2-AM

Intracellular Ca2+ ([Ca2+]i) is thought to act as a second messenger of transmembrane signalling systems. However, no measurement of [Ca2+]i has been made in intact epidermal keratinocytes. We have developed a method for measuring [Ca2+]i in human keratinocytes from pure epidermal sheet by the application of digital imaging fluorescence microscopy with the use of Fura 2-AM. Normal human pure epidermal sheets were obtained by dispase treatment. Epinephrine and salbutamol induced transient [Ca2+]i increases. Propranolol, a beta-antagonist, inhibited this response, while prazosin and yohimbine (alpha 1- and alpha 2-antagonists, respectively) did not affect the response. Histamine and adenosine, also receptor agonists of the epidermal adenylate cyclase system, induced a similar [Ca2+]i increase, as did forskolin, a direct activator of adenylate cyclase. These data coincide with those previously presented for cultured human epidermal keratinocytes, and reveal that adenylate cyclase activation induces an increase of [Ca2+]i in intact epidermal cells. This technique enables the kinetics of [Ca2+]i in various skin disorders to be investigated.

Regulation of beta 2-adrenergic receptors in keratinocytes: glucocorticoids increase steady-state levels of receptor mRNA in foetal rat keratinizing epidermal cells (FRSK cells)

Glucocorticoids increase the beta-adrenergic adenylate cyclase response of epidermal keratinocytes. Using FRSK cells, a cultured cell line of foetal rat keratinocytes, the regulatory mechanism of the beta-adrenergic augmentation effect was investigated. Treatment with dexamethasone (1 x 10(-6) M increase by 1.5-fold the beta-adrenergic adenylate cyclase response of FRSK cells. The effect was observed at 6 h incubation and remained for at least 48 h. The prostaglandin E-adenylate cyclase response was also increased 1.5-fold by glucocorticoid treatment. Neither the adenosine-adenylate cyclase response nor cholera toxin- or forskolin-induced cyclic AMP accumulations were altered. Northern blot hybridization showed that levels of the beta 2-adrenergic receptor mRNA increased within 3 h, while actin-, Gs-alpha, Gi-2 alpha, Gi-3 alpha mRNA levels were unchanged. Testosterone, 17 beta-oestradiol, and progesterone had no effect on either the beta 2-adrenergic adenylate cyclase response or the expression of beta 2-adrenergic receptor mRNA. The increase in the numbers of the beta-adrenergic receptors was visualized by immunofluorescence with an antibody specific for the beta 2-adrenergic receptor. Our results indicate that glucocorticoids regulate the beta 2-adrenergic adenylate cyclase response of FRSK cells through the enhanced expression of the receptor.

Cholera toxin- and forskolin-induced cyclic AMP accumulations of pig skin (epidermis). Modulation by chemicals which reveal the beta-adrenergic augmentation effect

Effects of cholera toxin and forskolin on pig epidermal adenylate cyclase system were investigated. Both agents increased cyclic AMP levels of epidermis. Marked accumulations were observed in the presence of cyclic AMP phosphodiesterase inhibitor, isobutylmethylxanthine (IBMX). It has been known that hormone-stimulated adenylate cyclase responses are modified by various chemical treatments. Following long term incubation with hydrocortisone, Ro10-1670, and colchicine, the epidermal beta-adrenergic adenylate cyclase response was increased without the alteration of cyclic AMP phosphodiesterase activity. Adenosine-, and histamine-adenylate cyclase responses were unchanged by hydrocortisone treatment, and were decreased by Ro10-1670 and colchicine treatments. Following the long term incubation with these chemicals, effects of cholera toxin and forskolin were investigated. Colchicine-treated skin revealed the increased cholera toxin-, and forskolin-induced cyclic AMP accumulations. Neither hydrocortisone- nor Ro10-1670-treated skin revealed alterations of cholera toxin-, and forskolin-effect. The stimulatory effect of colchicine on the cholera toxin-, and forskolin-effect was observed at doses of the beta-adrenergic augmentation effect. Our results indicate that among the chemicals which reveal the beta-adrenergic augmentation effect, colchicine is unique in that it also increases cholera toxin-, and forskolin-induced cyclic AMP accumulations of epidermis.

Studies of glucocorticoid enhancement of the capacity of hepatocytes to accumulate cyclic AMP

Pretreatment of cultured rat hepatocytes with dexamethasone markedly enhanced the acute cAMP response to glucagon, isoproterenol or forskolin. The effect of dexamethasone was apparent within 3-6 hr and was maximal after 20-30 hr. The amplification of the cAMP response to glucagon could also be produced by other glucocorticoids, with relative potency dexamethasone much greater than methylprednisolone greater than hydrocortisone. The increased cAMP response was associated with a reduced cAMP phosphodiesterase activity in cell lysates and a reduced effect of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine in intact cells, indicating that the glucocorticoid pretreatment reduced cAMP degradation. However, the increase in response to glucagon in glucocorticoid-treated cells was relatively larger than the increase in forskolin response and also larger than the decrease in phosphodiesterase activity, suggesting that other factors in addition to down-regulation of phosphodiesterases was responsible for the effect. Cycloheximide abolished the difference in phosphodiesterase activity and cAMP response between dexamethasone-treated and control cells. The results suggest that the glucocorticoids increase the ability of hepatocytes to accumulate cAMP due to protein synthesis-dependent processes which at least in part involve reduced degradation of cAMP.

The epidermal G1-chalone: an endogenous tissue-specific inhibitor of epidermal cell proliferation

An apparently macromolecular factor is isolated from aqueous skin extracts which inhibits DNA synthesis in vivo and in vitro with high efficacy (ID50 in vivo 0.2 pmol/g, in vitro 0.2 pM) and in a highly specific manner showing a point of attack in the late G1-phase of the cell cycle (epidermal G1-chalone). Preliminary characterization indicates an unusual highly amphipathic structure consisting of amino acids and carbohydrate. Despite its apparent molecular weight of approximately 10 kD the chalone is stable against denaturing agents and most enzymes, including proteases. An inverse correlation between chalone responsiveness of mouse epidermis in vivo and the development of hyperplasia due to injury indicates an important role of the factor in the regulation of tissue homeostasis. According to its physicochemical and biological properties the epidermal G1-chalone appears not to be related to other endogenous inhibitors of epidermal cell proliferation such as the pentapeptide pyroGlu-Glu-Asp-Ser-GlyOH and transforming growth factor beta (TGF beta).

Adenylate cyclase system of human trichilemmoma cell line

The adenylate cyclase system of an established human trichilemmoma cell line was investigated. Stimulators of human epidermal adenylate cyclase system, epinephrine, histamine, adenosine, and prostaglandin E increased cyclic AMP levels of the trichilemmoma cells. The effects of epinephrine, histamine, and adenosine were inhibited by the addition of propranolol (a beta-adrenergic antagonist), cimetidine (histamine H2-antagonist), and theophylline (adenosine-receptor antagonist), respectively. The epinephrine, histamine, and prostaglandin E effects were augmented by the addition of cyclic AMP (cAMP) phosphodiesterase inhibitor, isobutylmethylxanthine (IBMX); the adenosine effect was augmented by another phosphodiesterase inhibitor, papaverine. Without the addition of these phosphodiesterase inhibitors, the maximal accumulations were observed at 3 min incubation. Following this, the cAMP content returned to the basal level, and the cells did not respond to repeated stimulations with the same initial stimulator. This fact indicates receptor-specific refractoriness. For example, epinephrine-pretreated cells did not respond to epinephrine, but retained their sensitivity to histamine. It has been known that normal epidermal keratinocytes are regulated in vitro by glucocorticoids, colchicine, and retinoids, resulting in the augmentation of their beta-adrenergic response. Only hydrocortisone treatment on the trichilemmoma cells resulted in the augmentation of the beta-adrenergic response. Although the established human trichilemmoma cell line has similar adenylate cyclase systems as normal epidermis, it apparently has lost some of the regulatory mechanism of the beta-adrenergic response.

Glucocorticoid-induced modulation of the beta-adrenergic adenylate cyclase response of epidermis: its relation to epidermal phospholipase A2 activity

It has been suggested that glucocorticoids produce their biologic effects through the synthesis of phospholipase A2 inhibitor protein (lipocortin) in various cell systems. Recent studies from our laboratory revealed that glucocorticoids augment the beta-adrenergic adenylate cyclase response of epidermis and that this effect depends on a protein synthesis mechanism. In order to elucidate the possible mechanism of this glucocorticoid effect in terms of phospholipase A2 activity, an in vitro pig skin incubation system was employed. Mepacrine, a phospholipase A2 inhibitor, augmented the beta-adrenergic adenylate cyclase response of epidermis as glucocorticoids. The effect of mepacrine was stronger and was observed earlier than that of glucocorticoid (hydrocortisone). The addition of both mepacrine and hydrocortisone at their optimal concentrations in the incubation medium, resulted in neither an additive nor a synergistic effect on the beta-adrenergic augmentation. On the other hand, melittin, a phospholipase A2 stimulator, depressed the beta-adrenergic adenylate cyclase response. The addition of both melittin and hydrocortisone in the incubation medium resulted in the inhibition of the hydrocortisone-induced beta-adrenergic augmentation effect. Following long-term incubation with hydrocortisone, the epidermal phospholipase A2 activity was significantly decreased. These results indicate that glucocorticoids might affect the beta-adrenergic adenylate cyclase response of epidermis through the synthesis of phospholipase A2 inhibitor protein (lipocortin) as in other cell systems.

Dimethyl sulfoxide-induced augmentation of adenosine-adenylate cyclase response of pig skin epidermis

Adenosine-adenylate cyclase response in pig skin epidermis showed a specific increase after long-term (24 h) incubation in the presence of 0.5%-1% dimethyl sulfoxide (DMSO). There was no significant difference between control and DMSO-treated epidermis with regard to cyclic AMP (cAMP) phosphodiesterase activity. DMSO had no effect on the basal cAMP levels of epidermis; beta-adrenergic and histamine-adenylate cyclase responses were not affected. The direct addition of DMSO at the time of incubation with various adenylate cyclase stimulators (adenosine, epinephrine, and histamine) had no effect on agonist-induced cAMP accumulation effects. It was concluded that DMSO affected epidermal keratinocytes during long-term incubation, resulting in a specific increase in the adenosine-adenylate cyclase response. Although the biological significance of this DMSO effect remains to be determined, it should be kept in mind when using DMSO as a solvent for various chemicals in the experiments dealing with epidermal keratinocytes in vitro.

Topical PUVA treatment increases epidermal beta-adrenergic adenylate cyclase responsiveness

The effects of topical PUVA treatment on the epidermal cyclic AMP system were investigated. 8-methoxypsoralen (8-MOP), 0.3% in ethanol was applied to the backs of pigs which were then irradiated with UVA. A significant increase in the epidermal beta-adrenergic adenylate cyclase response was observed 24 h after low (1.1 J/cm2) and moderate (2.1 J/cm2) dose irradiation. There was no significant change in the adenosine- or histamine-mediated adenylate cyclase responses. 8-MOP application or UVA irradiation alone had no effect on the beta-adrenergic adenylate cyclase response. PUVA treatment with a higher irradiation dose (4.2 J/cm2) produced no increase in the beta-adrenergic response and adenosine- and histamine-mediated adenylate cyclase responses were decreased. Cyclic AMP phosphodiesterase activity was decreased by PUVA treatments using UVA doses of 1.1 and 2.1 J/cm2; however, the change was not statistically significant. The increased beta-adrenergic response was also observed in the presence of the cyclic AMP phosphodiesterase inhibitor, isobutylmethylxanthine. These results indicate that epidermal adenylate cyclase responsiveness is affected by topical PUVA treatment in vivo.

"Ischemic" rise of epidermal cyclic AMP is a beta-adrenergic adenylate cyclase-dependent process

The endogenous level of epidermal cyclic AMP does not remain constant but increases rapidly and transiently after removal of the tissue; this is known as the "ischemia" effect. UVB-irradiated epidermis which shows increased beta-adrenergic response revealed an increased ischemia effect, while psoriatic involved epidermis which shows decreased beta-adrenergic response revealed a decreased ischemia effect. Because of the similar rise-and-fall pattern between the ischemia effect and the beta-adrenergic response, the mechanism of the ischemia effect was investigated, especially in terms of the beta-adrenergic relationship. The ischemic rise of epidermal cyclic AMP was well preserved after 6 h pretreatment at 4 degrees C, and, following the pretreatment, the skin markedly increased its cyclic AMP level by the 37 degrees C treatment with 1 mM isobutylmethyl xanthine. The addition of propranolol or cimetidine at the time of 37 degrees C treatment (following the 4 degrees C pretreatment) had no effect on the ischemia effect; both skin groups markedly increased their cyclic AMP levels to an extent similar to that of the control skin. However, the addition of propranolol at the time of both preincubation (at 4 degrees C) and incubation (at 37 degrees C) markedly decreased the ischemic rise of cyclic AMP. Similar treatment by cimetidine had no effect on the ischemia effect. There was no significant difference in cyclic AMP phosphodiesterase activities among skin groups by propranolol or cimetidine pretreatment. These results indicate that the so-called ischemic rise of epidermal cyclic AMP is actually the beta-adrenergic adenylate cyclase-dependent process. Our results also indicate that the magnitude of the "ischemic" rise of cyclic AMP is generally parallel to the beta-adrenergic responsiveness of epidermis.

Effects of retinoids on the cyclic AMP system of pig skin epidermis

Although retinoids reveal various biologic and biochemical activities on epidermal keratinocytes, their effects on the epidermal cyclic AMP (cAMP) system has been less well characterized. In order to elucidate the relation between them, an in vitro pig skin-slice incubation system was employed. After a long-term (up to 24 h) incubation in vitro, control skin responded to epinephrine only slightly. The addition of Ro 10-1670, an active derivative of Ro 10-9359 (etretinate) in the incubation medium, resulted in an increase of the beta-adrenergic adenylate cyclase response of epidermis. On the other hand, histamine-induced cAMP accumulation was decreased by the retinoid treatment after long-term incubation. The augmentation of the beta-adrenergic response was observed at 1 microM concentration and the maximal effect was observed at 10 microM. There was no significant difference in cAMP phosphodiesterase activities between the control and retinoid-treated skin. The effect was also observed by the addition of all-trans-retinoic acid, retinol, and Ro 10-9359; the latter two compounds revealed much lesser effects. The addition of combinations of various drugs (Ro 10-1670 and hydrocortisone; Ro 10-1670 and colchicine) resulted in more marked (additive or synergistic) effects than the single addition of each chemical. On the other hand, the addition of Ro 10-1670 and all-trans-retinoic acid resulted in neither additive nor synergistic effect, suggesting that they probably work on the same site. Our data indicate that the epidermal beta-adrenergic adenylate cyclase response is modulated by retinoids probably as an independent mechanism stimulated by glucocorticoids or colchicine.

Mechanisms of glucocorticosteroid action in bronchial asthma

Although their precise mechanisms of action are undefined, the usefulness of CCS in the treatment of asthma is unquestioned. It is clear that they act at multiple sites. Among the general actions of CCS felt to be applicable to asthma are their ability to facilitate beta-adrenergic responsiveness and to suppress inflammation. More specific actions relevant to asthma are their inhibition of eicosanoid formation (e.g., reduction in leukotriene formation), prevention and reversal of LPR (probably through CCS anti-inflammatory effects), and reduction in mucus secretion. Actions that have not yet been clarified but that may be useful include possible reductions in airway hyperreactivity (or at least the prevention of increases in reactivity superimposed upon overreactive airways) and suppression of basophil (but not mast cell) mediator release.

Ultraviolet radiation augments epidermal beta-adrenergic adenylate cyclase response

Pig skin was irradiated in vivo with fluorescent sunlamp tubes (peak emission at 305 nm). A significant increase in epidermal beta-adrenergic adenylate cyclase response was observed as early as 12 h following 1-2 minimum erythema doses (MEDs) UVB exposure, which lasted at least 48 h. The augmentation of adenylate cyclase response was relatively specific to the beta-adrenergic system and there was no significant difference in either adenosine- or histamine-adenylate cyclase response of epidermis. The increased beta-adrenergic adenylate cyclase response was less marked at higher doses of UVB exposure (5 MEDs); in the latter condition, a significant reduction in adenosine- or histamine-adenylate cyclase response was observed. There was no significant difference in either low- or high-Km cyclic AMP phosphodiesterase activity between control and UVB-treated skin at 1-2 MEDs. Our data indicate that the epidermal adenylate cyclase responses are affected in vivo by UVB irradiation, which might be a significant regulatory mechanism of epidermal cyclic AMP systems.

Modulation of pig epidermal adenylate-cyclase responses by protein-synthesis inhibitors: its relation to glucocorticoid and colchicine effects

The effects of protein-synthesis inhibitors (actinomycin D, puromycin, and cycloheximide) on epidermal adenylate-cyclase responses were investigated. When pig skin (epidermis) was incubated in RPMI-1640 medium, the beta-adrenergic adenylate-cyclase response (epinephrine-induced cyclic-AMP accumulations) decreased, whereas the adenosine and histamine responses increased after long-term (up to 48 h) incubation. The addition of actinomycin D or puromycin to the incubation medium resulted in a marked increase in epinephrine-induced cyclic-AMP accumulations and a decrease in adenosine- and histamine-induced cyclic-AMP accumulations. Cycloheximide had a weak effect on the epinephrine response, and had apparently stronger effects on the adenosine and histamine responses than actinomycin D or puromycin. Histologically, various degenerative changes of keratinocytes (with or without acantholytic changes) were observed after long-term incubation with these protein-synthesis inhibitors. Both low- and high-Km cyclic-AMP phosphodiesterase activities were moderately decreased by the protein-synthesis inhibitors. However, augmentation effects on the beta-adrenergic response were also observed in the presence of the cyclic-AMP phosphodiesterase inhibitor, theophylline. We have described previously similar augmentation effects on the beta-adrenergic response caused by glucocorticoids and colchicine. Comparison of the effects of these chemicals with those of protein-synthesis inhibitors revealed that the most marked effects on the beta-adrenergic response were produced by actinomycin D, puromycin and colchicine; glucocorticoid had a moderate effect (hydrocortisone), while cycloheximide had only a weak effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucocorticoid-induced alteration of beta-adrenergic adenylate cyclase response of epidermis

It has been reported that the beta-adrenergic adenylate cyclase system of the pig epidermis is regulated by glucocorticoids, resulting in the augmentation of epinephrine-induced cyclic-AMP accumulations. Using this phenomenon, we compared the glucocorticoidal potency of three typical glucocorticoids: hydrocortisone, prednisolone and dexamethasone. There was a considerable variation in the magnitude of the glucocorticoid-induced augmentation of the beta-adrenergic response when pig skin that had been obtained on different occasions was used. In each experimental series (using the same pig skin), however, the maximal augmentation effects obtained with these glucocorticoids were approximately the same. The potent glucocorticoid, dexamethasone, demonstrated its effect at lower concentrations than were required for prednisolone, while hydrocortisone required a much higher concentration before its effect was detectable. Thus, despite considerable variations in the magnitude of the glucocorticoid effects, the concentrations required for the glucocorticoid effect were closely associated with the established glucocorticoidal potency which has previously been described.

Colchicine-induced alteration of hormone-stimulated cyclic AMP synthesis in pig skin (epidermis)

Effects of colchicine on the epidermal adenylate cyclase systems were investigated. When pig skin (epidermis) was incubated in RPMI 1640 medium without the addition of serum, the beta-adrenergic adenylate cyclase response (epinephrine-induced cyclic AMP accumulations) gradually decreased, whereas adenosine and histamine responses remained high or increased during the long-term (up to 48 h) incubation period. The addition of colchicine (1 mumol/liter) in the incubation medium resulted in an increase in the beta-adrenergic responsiveness and a decrease in adenosine and histamine responsivenesses. The effects of colchicine were both time- and concentration-dependent; they could be observed after 9-12 h incubation, and the maximal effect was obtained at a concentration of 0.1 mumol/liter. Similar effects were observed by the addition of another microtubule-disruptive agent, vinblastine. On the other hand, cytochalasin B, which affects the microfilament system, apparently decreased the beta-adrenergic response and increased adenosine and histamine responses during the long-term incubation period. The addition of serum in the incubation medium resulted in essentially the same effect as that of colchicine; in the presence of serum, colchicine-treated skin responded much more markedly to epinephrine (and much less to adenosine and histamine) than the control skin after 24- and 48-h incubation. Previously we reported that hydrocortisone has similar potentiating effects on the beta-adrenergic system of epidermis. The comparison of the effects of both compounds revealed that colchicine had a stronger effect than hydrocortisone, and furthermore, the simultaneous addition of both compounds (colchicine and hydrocortisone) in the incubation medium resulted in the more marked increase of beta-adrenergic response than the single addition of each chemical. Our overall results, coupled with the finding that hydrocortisone has no toxic effects on the adenosine- or histamine-adenylate cyclase system of epidermis, suggest that colchicine affects epidermal adenylate cyclase systems probably through a mechanism that is independent of glucocorticoid (hydrocortisone) effect.

Regulation of beta-adrenergic adenylate cyclase responsiveness of pig skin epidermis by suboptimal concentrations of epinephrine

Although receptor-specific refractoriness has been suggested to be one of the regulatory mechanisms of epidermal adenylate cyclase systems, its physiologic significance has been a subject of controversy because of the requirement of unusually high concentrations of agonists to induce refractoriness. In order to determine whether the epidermal adenylate cyclase system is regulated through a refractoriness mechanism by suboptimal concentrations of receptor agonists, this study was undertaken using pig skin epidermal adenylate cyclase systems. Pretreatment of pig skin with 0.1-1 microM epinephrine in vitro resulted in the reduction of the maximal epinephrine response (epinephrine-induced cyclic AMP accumulations) to various degrees without alterations in either low or high Km cyclic AMP phosphodiesterase activities. Repeated pretreatments were shown to be more effective in inducing refractoriness than a single pretreatment. Apparently there was no change in the Km value for epinephrine, suggesting that the decrease in epinephrine response represents a reduction in the number but not in the affinity of functional beta-adrenergic adenylate cyclase receptor sites. This refractoriness by low concentrations of catecholamine pretreatment was specific to the beta-adrenergic system, since there was no reduction in histamine response after the epinephrine pretreatment. These results indicate that the epidermal beta-adrenergic adenylate cyclase system is regulated by much lower concentrations of catecholamine than were previously described. It was suggested that physiologic fluctuations of plasma catecholamine levels might have a profound effect on epidermal beta-adrenergic adenylate cyclase responsiveness, resulting in the alteration of the minimal catecholamine level required for the successive activation of cyclic AMP-dependent protein kinase, which is the predominant target of cyclic AMP in epidermis.