Adenylate Cyclase-cyclic AMP System Research Articles

Carl and Gerty Cori: A collaboration that changed the face of biochemistry.

Carl Cori and Gerty Cori elucidated basic biochemical mechanisms involved in the utilization of energy by muscle and liver, first at Roswell Park Cancer Institute and then at Washington University. In 1929, they formulated the Cori cycle, the process by which glycogen is converted to glucose in liver and is then reconverted to glycogen in muscle. They later found that glycogen breakdown yielded glucose-1-phosphate (Cori ester) and lactate, key intermediates in the cycle; they also established that lactic acid provided the energy employed in muscle contraction. They later discovered phosphorylase, the enzyme that catalyzed glycogen breakdown. After purifiying and crystallizing muscle phosphorylase, they identified two forms of the enzyme and defined their respective roles in metabolic regulation. These studies emboldened other scientists to advance our knowledge of fundamental regulatory processes such as the adenylate cyclase-cyclic AMP system and enzyme phosphorylation. The Coris also built a world-renowned Department of Biochemistry at Washington University, which included seven future Nobelists. In 1947, the Coris were awarded the Nobel Prize, with Gerty Cori being the first American woman to win this prestigious honor.

Interaction between Platelet-Aggregating Response and Vasoconstrictive Response to Platelet Activating Factor.

It is very important to know under medical treatment which kinds of platelet agonists participate in abnormal platelet-blood vessel interactions. The present study, focusing on platelet activating factor (PAF) was undertaken in an attempt to investigate its action on platelet aggregating response and vasocontractile response to noradrenaline (NA-R). We used autologous platelets and isolated perfused arterial segments from Japanese white rabbits. Firstly, typical tracings of platelet aggregating response to PAF were increased in a dose-dependent fashion, which remained constant and long-lasting. Secondly, noradrenaline (NA) at 5 to 25 ng elicited an initially augmented response in the presence of platelet rich plasma (PRP) with PAF, followed by gradually attenuated responses. Based on the light transmission intensity, platelet aggregation did not seem to be directly or strictly linked to vasocontractile response. Pretreatment with either dibutyryl cyclic AMP (DBcAMP) or indomethacin (IM, a cyclo-oxygenase inhibitor) clearly caused reductions in NA-R as well as platelet aggregation in the presence of PRP with collagen, whereas platelet aggregation and NA-R in the presence of PRP with PAF were scarcely influenced by pretreatment with either DBcAMP or IM. Thus, it seems reasonable to conclude that, in contrast to the response to collagen, platelet aggregation response to PAF was almost indifferent to the adenylate cyclase-cyclic AMP system and the cyclo-oxygenase metabolic pathway.

Epixenosomes, peculiar epibionts of the ciliateEuplotidium itoi: Involvement of membrane receptors and the adenylate cyclase-cyclic AMP system in the ejecting process

The extrusive apparatus is the most prominent and complex structure of epixenosomes. In the present paper the mechanisms activating its ejecting process were investigated by means of in vivo treatments and cytochemical procedures at the ultrastructural level. The results obtained clearly demonstrated that the ejecting process in epixenosomes is triggered by the detection of external signals through membrane receptors and the consequent activation of the adenylate cyclase-cyclic AMP system as a transduction mechanism. The membrane receptors coming into play have an affinity for soybean agglutinin and have a precise localization at the top of the organism, just where a membrane interruption appears as a first step in the whole process. The factors that trigger ejection in nature are still unknown. In the laboratory, ejection was obtained in the presence of adrenalin, which has been proved to bind to the same receptors shown to have affinity for soybean agglutinin. So epixenosomes appear to possess specific binding molecules for a mammalian hormone in the appropriate location, i.e., in the plasma membrane, and this hormone induces a precise biological response. These results are particularly interesting if we consider that epixenosomes are enigmatic organisms in which prokaryotic and eukaryotic characteristics appear to coexist.

Modulation of cyclic AMP production by strial marginal cells from gerbil in culture

To further investigate the role of marginal cells (MCs) in the secretion of endolymph and because of the limitations encountered in investigating these cells in vivo, we used primary cultures of MCs derived from explants of gerbil stria vascularis and investigated modulation of the adenylate cyclase-cyclic AMP system. After 10 days on type I collagen coated plastic dishes, a confluent monolayer of epithelial-like cells was obtained which exhibited the morphologic and immunohistochemical features of the native marginal cells. The cyclic AMP (cAMP) content was determined at 37°C, after 5 min of incubation with various agents, in the presence of a specific inhibitor of type III cAMP-dependent phosphodiesterase, RO 20–1724. The adenylate cyclase-cAMP system was associated with β 2-adrenergic receptors. The cAMP content was increased by isoproterenol (23-fold), a β-agonist, but not by octopamine, an α-agonist, and the affinity for ICI 118.551, a specific β 2-antagonist, was greater than for CGP 20712A, a specific β 1-antagonist (Kd: 0.03 × 10 −6 M and 15 × 10 −6 M respectively). The cAMP content was maximally increased by prostaglandin E 2 > β 2-adrenergic agonist > vasopressine type 2 receptor agonist (26-, 23-, and 3-fold the basal cAMP content, respectively). The present study demonstrates that cultured marginal cells retain some of their in vivo properties including a modulated enzymatic cAMP system. This culture model should allow further in-depth investigation of the function of marginal cells.

A cyclic AMP mechanism mediates the serotonin-induced increase in glutamic acid decarboxylase activity in the preoptic area and hypothalamus.

Previous studies have shown that the injection of 5-hydroxytryptamine (5-HT) into the third ventricle of rats on the afternoon of proestrus increases glutamic acid decarboxylase (GAD) activity in the preoptic area and the hypothalamus. In the present report we examine the adenylate cyclase-cyclic AMP (cAMP) system as mediator of that effect. The increase in GAD activity induced by intraventricular injection of 5-HT was completely blocked by injecting an antiserum against cAMP into the third ventricle 30 min earlier, whereas an injection of serum from normal rabbits was ineffective. On the contrary, activation of adenylate cyclase activity by intraventricular injection of forskolin increased GAD activity, an effect that was also blocked by anti-cAMP serum. Anti-cAMP serum also lowered GAD activity in the preoptic area and hypothalamus when injected on the morning of proestrus but not when injected in the afternoon, when the values of GAD activity were already low. The results suggest that a cAMP mechanism may be involved in the changes in preoptic-area and hypothalamic GAD activity such as the rise in enzyme activity induced by intraventricular injection of 5-HT.

Ultrastructural localization of adenylate cyclase activity in chicken osteoclasts.

Using lead citrate as a capture reagent and adenylate-(beta, gamma-methylene) diphosphate (AMP-PCP) as a substrate, we localized adenylate cyclase activity on the non-ruffled border plasma membrane of approximately half of the osteoclasts on trabecular bone surfaces in the tibial metaphyses of chickens fed a low (0.3%)-calcium diet. The enzyme was not detectable in osteoclasts when chickens were fed a normal calcium diet. Activity was observed on the entire plasma membrane of detached osteoclasts that were situated between osteoblasts on the bone surface and blood vessels in the marrow cavity. Detection of activity on detached osteoclasts required the presence of an activator, implying lower levels in these cells than in those with ruffled borders. Staining was greater on the lateral sides of osteoblasts and osteoclasts when they were in contact with each other. Reaction specificity was indicated by the demonstration of stimulation by forskolin, guanylate-(beta, gamma-methylene) diphosphate (GMP-PCP), dimethylsulfoxide, and NaF, inhibition by alloxan and 2',5'-dideoxyadenosine, and absence of activity when sections were incubated in substrate-free medium or when GMP-PCP replaced AMP-PCP as a substrate. The finding of adenylate cyclase in osteoclast plasma membrane provides structural evidence that the adenylate cyclase-cyclic AMP system has a role in regulation of osteoclast cell function. The low-calcium diet appears to have resulted in increased amounts of adenylate cyclase in osteoclasts.

内耳電位とホルモン

Recent studies of hormones in the inner ear are described. The possibility that hormones act on the cochlea through the adenylate cyclase-cyclic AMP system and through the regulation of blood flow in the cochlea is dicussed, though no direct evidence supporting this hypothesis yet exists. The action of hormones on the vestibule is still unknown. In the endolymphatic sac, direct evidence supporting the action of catecholamines on the endolymphatic sac has recently been obtained. Our recent study revealed that catecholamines change the oxygen-dependent positive DC potential in the endolymphatic sac of the guinea pig in a reversible manner. The involvement of aldosterone in regulating the functions of the endolymphatic sac has also been suggested. It is assumed that the endolymphatic sac may be an important tissue for hormonal regulation in the inner ear.

Relaxation response of isolated canine veins to agents that act on the adenylate cyclase-cyclic AMP system: further investigation

The present study was undertaken to clarify whether there is a deficiency in the relaxation mediated by the adenylate cyclase-cyclic AMP (cAMP) system in the portal vein as compared to the saphenous vein. Longitudinal strips of the portal vein and helical preparations of the saphenous vein were used. The relaxation response to various agents was examined under conditions such that the venous preparations were previously contracted by methoxamine in equipotent concentrations (EC 80), i.e., 10 −6 M for portal vein and 10 −5 M for saphenous vein. The saphenous vein relaxed fully in response to isoproterenol but the portal vein relaxed only to 29% of the maximum relaxation induced by papaverine 10 −4 M. However, dibutyryl cAMP and 8-bromo-cAMP, membrane permeable derivatives of cAMP, 3-isobutyl-1-methylxanthine and papaverine, phosphodiesterase inhibitors, and forskolin, a direct stimulator of adenylate cyclase, relaxed portal and saphenous veins similarly though with quantitative differences. The results suggest that there is no profound deficiency in the adenylate cyclase-cAMP system but there may be a deficiency in the coupling between surface β-adrenoceptors and adenylate cyclase or there may be a low density of β-adrenoceptors in the portal vein.

Electrical parameters of the toad skin: Effects of forskolin

Forskolin stimulated short-circuit current (SCC) and transepitelial electrical conductance (G) in the isolated skin of the toad Bufo arenarum in a concentration-dependent manner, between 1.0 x 10(-6) and 2.4 x 10(-5) M. At the latter concentration, glandular secretion appeared to be stimulated also. The increase in G was considerably greater in skins bathed in Ringer solution than in solutions containing no chloride. The increased SCC was abolished by amiloride, a specific blocker of sodium transport in amphibian membranes, irrespective of the anion present in the solution bathing the skin. G was also decreased by amiloride to control values in skins bathed in solutions without chloride, but remained elevated in the presence of Cl-. The increase in SCC following exposure to forskolin, 4.4 x 10(-6) M, was not altered when furosemide, a specific blocker of chloride transport, was present in the Ringer solution bathing the dermal side of the skin. The response to forskolin, 2.4 x 10(-5) M, however, was significantly decreased by dermal furosemide; the inhibitor was ineffective in the absence of chloride. The data indicate that forskolin acts on at least two sites: stratum granulosum cells (the main pathway for sodium transport, and an alternate site, responsible for the increase in permeability to chloride. In addition, at high concentration of the agent, glandular secretion is also stimulated. The data suggest that the adenylate cyclase-cyclic AMP system is involved in the regulation of the permeability of the toad skin to sodium and chloride, probably by separate cell types.

Regulatory subunits of cyclic AMP-dependent protein kinase: presence in granules and secretion by exocrine and endocrine cells.

Cyclic AMP-dependent protein kinase (cAPK) is the intracellular mediator of signal transduction events involving the adenylate cyclase-cyclic AMP system. A monoclonal antibody (MAb BB1) to the type II regulatory subunit (RII) of cAPK was used in a post-embedding immunogold-labeling procedure to determine the ultrastructural localization of RII in several different secretory cells of the rat. Label was present in nuclei, especially over the heterochromatin, and in the cytoplasm, particularly in areas containing rough endoplasmic reticulum. Immunolabeled RII was also present in secretory granules of the parotid gland, exocrine and endocrine pancreas, seminal vesicle, anterior and intermediate pituitary, and intestinal endocrine cells. Photoaffinity labeling of parotid saliva, pancreatic and seminal fluids with the cyclic AMP analogue, 32P-labeled-8-azido-cyclic AMP, revealed the presence of cyclic AMP-binding proteins with electrophoretic mobilities similar to those of authentic cAPK regulatory subunits. These results confirm our previous observations on the localization of cAPK regulatory subunits in the rat parotid using polyclonal antibodies, and extend them to a number of other exocrine and endocrine cells. The apparent widespread occurrence of cAPK subunits in secretory granules and secretory fluids suggests that cAPK may be involved in specific intragranular regulatory and/or phosphorylation events, or that it has an unidentified extracellular function.

The Study of Direct Effect of Methimazole on Thymidine Incorporation in FRTL-5 Cells

During the course of treatment of Graves' disease with the anti-thyroid drug, methimazole (MMI), a decrease in a patient's goiter size is sometimes observed. Using rat thyroid cell strain, FRTL-5, the direct effect of MMI on thyroid cell growth was investigated. FRTL-5 cells (2 X 10(5)) were cultured for 48 hours with TSH, (Bu)2 cAMP or forskolin in the presence of [3H]-thymidine. All three stimulators increased cell growth, expressed as [3H]-thymidine incorporation into DNA in a dose-dependent fashion. When FRTL-5 cells were cultured for 48 hours in the presence of MMI at 10(-6)-10(-3) M with these stimulators (TSH 250 microU/ml, (Bu)2 cAMP 10(-3) M, forskolin 10(-5) M), [3H]-thymidine incorporation was suppressed in dose-dependent fashions (MMI 10(-5) M-10(-3) M). From the present study, it is suggested that methimazole directly modulates thyroid cell growth induced by thyroid growth stimulators which are involved in adenylate cyclase-cyclic AMP system and that the site of its action exists beyond cAMP production.

"In vitro" study on release of cyclic AMP and thyroid hormone in autonomously functioning thyroid nodules.

The TSH effect on slice and the incubation medium cyclic AMP levels and T3 and T4 released from 8 autonomously functioning thyroid nodules (AFTN) and their respective perinodular (PN) tissues were examined. The thyroid slices were incubated in Eagle's Medium containing TSH (5 to 100 mU/ml) for 60 min and 300 min for tissue cyclic AMP generation and for cyclic AMP, T3 and T4 release, respectively. Basal cyclic AMP levels were not different either in AFTN and in PN slices or into the incubation medium. In both tissues TSH produced a similar cyclic AMP generation. In contrast, cyclic AMP released into the incubation medium was significantly higher in AFTN than in PN tissues, after TSH stimulation. Basal T3 values and TSH-stimulated T3 release in AFTN were not different from PN tissue. However, basal T4 levels were significantly higher in AFTN than in PN tissue as well as T4 released in response to TSH. In addition, T3/T4 ratio was lower in AFTN than in PN tissues. The cyclic AMP released into the incubation medium correlated with both T3 and T4 release in PN tissue but in the AFTN tissue no correlations were found. These findings suggest that the adenylate cyclase-cyclic AMP system is more sensitive to TSH-stimulation in AFTN when compared with PN tissue and that AFTN tissue has a preferential T4 secretion.

Adenylate cyclase and cyclic AMP in the ciliate Euplotes crassus: Involvement in both cell cycle and sexual reproduction

AbstractIn this paper the presence and the possible activity of adenylate cyclase‐cyclic AMP (AC‐cAMP) system has been investigated through cell cycle and sexual reproduction of the ciliate Euplotes crassus. For this purpose cytochemical studies for AC demonstration at the ultrastructural level were carried on. Moreover, “in‐vivo” experiments were performed by adding different substances to the cell cultures: alloxan (inhibitor of AC), theophylline (inhibitor of phosphodiesterase), exogenous cAMP, and cholera toxin (which maintains AC in an active state). The results obtained are indicative that cAMP is a “regulatory factor” acting during cell cycle as E. crassus cells are not able to undergo macronuclear DNA synthesis in the presence of theophylline. As concerns sexual reproduction both cytochemical observation and “in‐vivo” experiments are suggestive of a rapid activation of AC upon mixing strains of different mating types. This activation, which lasts only for the initial part of the waiting period, appears to be necessary for pair formation.

Adenylate cyclase-cyclic AMP system in pure epidermis isolated by use of dispase.

AbstractEpidermal adenylate cyclase systems following dispase treatment were investigated. Dispase is a bacterial neutral protease obtained from Bacillus polymyxa. Following the treatment with dispase, the epidermal sheet is easily peeled off the dermis. Dispase‐treated pure epidermal sheets were shown to contain three major (beta‐adrenergic‐, adenosine‐, and histamine‐) receptor adenylate cyclase systems. Without phosphodiesterase inhibitors, the intracellular cyclic AMP (cAMP) level reached the maximal level at 3 min. This effect was markedly enhanced by the addition of cAMP phosphodiesterase inhibitor. Among these epidermal adenylate cyclase systems, the most marked cAMP accumulation was observed by histamine, followed by adenosine, and then by epinephrine. The separation of epidermis and dermis following dispase treatment revealed that epidermis contained most of the beta‐adrenergic response (87%), whereas the dermis retained a significant proportion of adenosine (26%) and histamine (40%) responses when 0.3 mm thickness skin was studied.Specific antagonists of epinephrine, adenosine, and histamine inhibited the effects of these agents completely. The simultaneous addition of two stimulators into the incubation medium resulted in an additive effect.Beta‐augmentations by hydrocortisone, colchicine, and retinoid all remained in the dispase‐treated pure epidermal sheets, but beta‐augmentations by these drugs were spoiled by trypsin treatment.These results indicate that dispase‐treated pure epidermis contains three major (beta‐adrenergic‐, adenosine‐, and histamine‐) specific and independent receptor adenylate cyclase systems. Dispase is a very useful tool for investigating the metabolism and regulatory system of keratinocytes without any significant damage to epidermal membrane receptor systems.

Melittin-induced alteration of epidermal adenylate cyclase responses

Using an in vitro pig skin-slice incubation system, we investigated the effect of melittin, a phospholipase A2 (PLA2) stimulator, on the adenylate cyclase-cyclic AMP (cAMP) system. Significant decreases of various epidermal (beta-adrenergic, adenosine, and histamine) adenylate cyclase responses were observed as early as 1 h following the melittin treatment (50 micrograms/ml). The effect of melittin was concentration-dependent and the minimal concentration of melittin was 10 micrograms/ml for the inhibition of the beta-adrenergic adenylate cyclase response, whereas more than 50 micrograms/ml concentration was required for the inhibition of the adenosine and histamine adenylate cyclase responses. There was no significant difference in either low or high Km cAMP phosphodiesterase activity between control and melittin-treated skin. The beta-adrenergic augmentation effect by various chemicals (colchicine and Ro10-1670, an active form of Ro10-9359) were suppressed by the simultaneous addition of melittin in the incubation medium. Our data indicate that melittin affects not only on the beta-adrenergic adenylate cyclase system but also on the adenosine and histamine adenylate cyclase systems. However, the beta-adrenergic system was shown to be more sensitive to melittin than the other receptor adenylate cyclase systems.

Secretory activity in salt glands of birds and turtles: stimulation via cyclic AMP.

O2 consumption in tissue slices from the nasal salt gland of the duck and the lachrymal salt gland of Malaclemys is stimulated by methacholine, a stimulation that is inhibited by bumetanide and by ouabain. In addition, the calcium ionophore A23187 mimics the action of methacholine in stimulating this secretion-related O2 consumption in both glands, suggesting a second-messenger role for this ion in the cholinergic response. However, the adenylate cyclase activator, forskolin, and the cyclic AMP analogue, 8-cpt-cAMP, also stimulate ouabain-sensitive and bumetanide-sensitive O2 consumption in both the duck gland and the Malaclemys gland. It is suggested that the mechanism of salt secretion in the Malaclemys lachrymal gland conforms to that previously described for other extrarenal salt-secreting tissues in nonmammalian vertebrates and, as in the bird gland, is subject to a cholinergic regulation potentially acting via changes in intracellular calcium. In addition to this, secretory activity in both the avian and the turtle glands can be stimulated by a previously undisclosed adenylate cyclase-cyclic AMP system. The identity of the primary signal for such a system is not known, nor is the nature of any interrelationship between the two second-messenger systems that have been identified in these glands.

Characterization of Thyroid Follicular Cell Apical Plasma Membrane Peroxidase Using Monoclonal Antibody

Thyroid peroxidase (TPO) located in the apical plasma membrane of follicular cells was investigated by means of a membrane-immunofluorescent technique. The epitope of TPO recognized by a murine monoclonal antibody (mAb 30.1.2) was identified on the apical membrane surface. Trypsinization removed TPO immunoreactivity and enzymatic activity after 60 min of incubation at 37 degrees C. The epitope reappeared on the apical membrane surface after short term culture for 120 min without the addition of TSH. With TSH the time required for reappearance was only 30 min. TPO activity was regenerated under both conditions. Since dibutyryl cyclic AMP could not accelerate the reappearance of the epitope, it was thought that TPO reappearance is mediated by other than the adenylate cyclase-cyclic AMP system.

Effect of dihydroergocryptine and dihydroergocristine on cyclic AMP accumulation and prolactin release in vitro: evidence for a dopaminomimetic action.

Dihydroergocryptine and dihydroergocristine, two C-9, 10-hydrogenated ergot alkaloids, inhibited in a concentration-dependent manner prolactin release and cyclic AMP accumulation in cultured anterior pituitary cells. The inhibitory effect of dihydroergocryptine was more potent and started at lower concentrations than that of dihydroergocristine. Haloperidol and pimozide, two dopamine receptor antagonists, completely abolished the inhibitory activity of the ergot alkaloids. The involvement of the adenylate cyclase-cyclic AMP system in the inhibitory action of the two compounds was demonstrated by the antagonism by pertussis toxin of the reduction of both prolactin release and cyclic AMP accumulation produced by dihydroergocryptine and dihydroergocristine.

Inhibition of prolactin release and blockade of adenohypophyseal cell cyclic AMP accumulation are two dissociable effects of dopaminergic and non-dopaminergic drugs

The secretion of PRL by the anterior pituitary gland is under a tonic inhibitory control exerted by dopamine (DA). However, the mechanism(s) involved in the inhibition of PRL secretion is not clearly defined. Several recently published papers supported the hypothesis that DA inhibits the release of PRL through blockade of the pituitary adenylate cyclase-cyclic AMP system. We have recently demonstrated that sodium ions are essential for dopaminergic inhibitory action on PRL secretion. The present paper reports the effects, in the presence or in the absence of Na +, of either DA, bromocriptine, apomorphine or 2 anticalmodulin drugs, penfluridol and W-7, on cyclic AMP accumulation by rat adenohypophyseal cells in primary culture. Studies with dopaminergic agonists show that in the presence of Na + inhibition of both PRL and cyclic AMP is obtained at 15 and 30 min, while in the absence of the ion a dissociation exists between the inhibition of PRL release which is completely abolished, and that of cyclic AMP content which is still present. Dose-response studies done in the presence of Na + show the existence of a good correlation between hormone and nucleotide effects of dopaminergic agonists while, in the absence of Na +, a dissociation is observed between the inhibition of PRL release, which is completely suppressed, and that of cyclic AMP accumulation which is slightly or not at all decreased. The inhibitory effects of penfluridol after 15 and 30 min of incubation were not suppressed by Na + removal, although its hormonal actions were slightly decreased. On the contrary, W-7 inhibition of cyclic AMP accumulation was drastically reduced in the absence of Na +, while inhibition of PRL release was enhanced after 30 min of incubation. These results confirm that Na + is essential for dopaminergic agonists to inhibit PRL release, and suggest that the inhibitory effect is not directly due to blockade of the adenylate cyclase-cyclic AMP system since they are two dissociable phenomena.

Thyroid cell responses to thyrotropin and 12- O-tetradecanoyl-phorbol-13-acetate: Translocation of protein kinase C and phosphorylation of thyroid cell polypeptide substrates

Not all of the effects of thyroid-stimulating hormone (TSH) on the thyroid are mediated by activation of the adenylate cyclase-cyclic AMP system, indicating that other control systems must also exist. Although a calcium-phospholipid-dependent protein kinase (protein kinase C) and specific substrates had been identified in thyroid tissue, their responsiveness to TSH and other stimulators has not been determined. In thyroid cells which had been preloaded with [ 32P]orthophosphate, TSH and 12- O-tetradecanoyl-phor-bol-13-acetate (TPA) increased the phosphorylation of a 33K polypeptide substrate within 5 min in a dose-dependent fashion. The effect was observed with 1 mU/ml TSH and 3 n m TPA and was maximal with 100 mU/ml TSH and 100 n m TPA. The biologically inactive analog of TPA, 4α-phorbol, had no effect. Isobutylmethylxanthine (IBMX) decreased the phosphorylation of the 33K polypeptide and inhibited the effect of TSH and TPA, indicating that the phosphorylation is not mediated by cyclic AMP. TSH and IBMX, but not TPA, augmented phosphorylation of a 38K polypeptide, suggesting involvement of cyclic AMP. In contrast TPA, but not TSH, increased the phosphorylation of 58K and 28K polypeptides. TSH, but not TPA or 4α-phorbol, elevated the cyclic AMP level of thyroid slices. Incubation of thyroid slices with TSH or TPA significantly decreased protein kinase C activity in the 100,000 g cytosol fraction and increased it in an extract of plasma membranes. The effect was present within 5 min and was maximal by 30 min. The effect was observed with 100 mU/ml TSH or 1 n m TPA. The stimulation by TSH or TPA of protein kinase C and its translocation from the cytosol to the plasma membranes of thyroid tissue may provide another mechanism for control of thyroid Cell metabolism.