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At least 379 records · Page 21Linked to original sources
PubMed1996

Vesicle-associated membrane protein 2 is essential for cAMP-regulated exocytosis in rat parotid acinar cells. The inhibition of cAMP-dependent amylase release by botulinum neurotoxin B.

Amylase exocytosis of the parotid gland is mediated by intracellular cAMP. To investigate whether cAMP-dependent secretion has a mechanism similar to that of regulated neuroexocytosis, we examined the expression of synaptosome-associated proteins. In rat parotid acinar cells, we found 25 (p25) and 18 kDa (p18) proteins reacted with antibodies against Rab3A and vesicle-associated membrane protein 2 (VAMP-2), respectively. On the other hand, syntaxin 1 and SNAP-25, which interact with VAMP-2 at synapses, were undetectable. Rab3A-like p25 and VAMP-2-like p18 were also expressed in other exocrine acinar cells. The latter was localized at secretory granule membranes, and the former was detected in secretory granule and cytosolic fractions. The antibody against VAMP-2 used in this study did not react with cellubrevin, and p18 was cleaved with botulinum neurotoxin B. Thus, we identified p18 as VAMP-2. Botulinum neurotoxin B inhibited the cAMP-induced amylase release from streptolysin O-permeabilized acinar cells. Therefore, VAMP-2 is required for cAMP-regulated amylase release in rat parotid acinar cells. This is the first report that VAMP-2 is involved in regulated exocytosis that is independent of Ca2+.

Amylases↗
PubMed1996

Phosphorylation and activation of a cAMP-specific phosphodiesterase by the cAMP-dependent protein kinase. Involvement of serine 54 in the enzyme activation.

A cAMP-specific phosphodiesterase (PDE4D3) is activated in rat thyroid cells by TSH through a cAMP-dependent phosphorylation (Sette, C., Iona, S., and Conti, M.(1994) J. Biol. Chem. 269, 9245-9252). This short term activation may be involved in the termination of the hormonal stimulation and/or in the induction of desensitization. Here, we have further characterized the protein kinase A (PKA)-dependent phosphorylation of this PDE4D3 variant and identified the phosphorylation site involved in the PDE activation. The PKA-dependent incorporation of phosphate in the partially purified, recombinant rat PDE4D3 followed a time course similar to that of activation. Half-maximal activation of the enzyme was obtained with 0.6 microM ATP and 30 nM of the catalytic subunit of PKA. Phosphorylation altered the Vmax of the PDE without affecting the Km for cAMP. Phosphorylation also modified the Mg2+ requirements and the pattern of inhibition by rolipram. Cyanogen bromide cleavage of the 32P-labeled rat PDE4D3 yielded two or three major phosphopeptide bands, providing a first indication that the enzyme may be phosphorylated at multiple sites in a cell-free system. Site-directed mutagenesis was performed on the serine residues present at the amino terminus of this PDE in the context of preferred motifs for PKA phosphorylation. The PKA-dependent incorporation of 32P was reduced to the largest extent in mutants with both Ser13 --> Ala and Ser54 --> Ala substitutions, confirming the presence of more than one phosphorylation site in rat PDE4D3. While substitution of serine 13 with alanine did not affect the activation by PKA, substitution of Ser54 completely suppressed the kinase activation. Similar conclusions were reached with wild type and mutated PDE4D3 proteins expressed in MA-10 cells, where the endogenous PKA was activated by dibutyryl cAMP. Again, the PDE with the Ser54 --> Ala substitution could not be activated by the endogenous PKA in the intact cell. These findings support the hypothesis that the PDE4D3 variant contains a regulatory domain target for phosphorylation at the amino terminus of the protein and that Ser54 in this domain plays a crucial role in activation.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1998

Gene-specific transcriptional activity of the insulin cAMP-responsive element is conferred by NF-Y in combination with cAMP response element-binding protein.

Cyclic AMP stimulates insulin gene transcription through a cAMP response element (CRE). In the present study the insulin CRE-binding proteins and their functions were investigated. A mutational analysis of nuclear protein binding in electrophoretic mobility shift assays in combination with specific antisera showed that in the CRE of the rat insulin I gene the imperfect CRE octamer-like sequence TGACGTCC interacts weakly with CREB and overlaps with two sequence motifs (TTGTTGAC and CCAAT) that bind winged helix-like proteins and the transcription factor NF-Y, respectively. Transient transfection of wild-type and mutant insulin CRE-reporter fusion genes and the inactivation of cellular CREB or NF-Y by overexpression of the dominant negative mutants KCREB or NF-YA29, respectively, indicate that cAMP inducibility of the insulin CRE is mediated by CREB or closely related proteins; however, NF-Y binding to the insulin CRE confers constitutive, basal activity and decreases the ability of CREB to mediate cAMP-stimulated transcription and calcium responsiveness. Results from these studies demonstrate that NF-Y binds to the insulin CRE and modulates the function of CREB. Together with the nonpalindromic sequence of the CRE octamer motif, the interaction of NF-Y with CREB may be responsible for the gene-specific transcriptional activity of the insulin CRE and explain why it has considerable basal activity but is less responsive to cAMP stimulation than others.

Animals↗
PubMed2002

cAMP-dependent protein kinase types I and II differentially regulate cAMP response element-mediated gene expression: implications for neuronal responses to ethanol.

We have shown that ethanol induces translocation of cAMP-dependent protein kinase (PKA) to the nucleus, cAMP response element-binding protein (CREB) phosphorylation, and cAMP response element-mediated gene transcription in NG108-15 cells. However, little is known about which PKA types regulate this process. We show here that under basal conditions NG108-15 cells contain type I PKA (CbetaRIbeta) primarily in cytosol and type II PKA (CalphaRIIbeta) in the particulate and nuclear fractions. Antagonists of both type I and type II PKA inhibit forskolin- and ethanol-induced cAMP response element-mediated gene transcription. However, only the type II PKA antagonist inhibits forskolin-induced Calpha and ethanol-induced Calpha and RIIbeta translocation to the nucleus and CREB phosphorylation; the type I antagonist is without effect. Our data suggest that forskolin- and ethanol-induced CREB phosphorylation and gene activation are differentially mediated by the two types of PKA. We propose that type II PKA is translocated and activated in the nucleus and induces CREB phosphorylation that is necessary but not sufficient for gene transcription. By contrast, type I PKA is activated in the cytoplasm, turning on a downstream pathway that activates other transcription cofactors that interact with phosphorylated CREB to induce gene transcription.

Cell Nucleus↗
PubMed2002

Mechanisms of FOXC2- and FOXD1-mediated regulation of the RI alpha subunit of cAMP-dependent protein kinase include release of transcriptional repression and activation by protein kinase B alpha and cAMP.

We have reported recently that mice overexpressing the forkhead/winged helix transcription factor FOXC2 are lean and show increased responsiveness to insulin due to sensitization of the beta-adrenergic cAMP-PKA(+) pathway and increased levels of the RI alpha subunit of cAMP-dependent protein kinase (PKA) (Cederberg, A., Grønning, L. M., Ahren, B., Taskén, K., Carlsson, P., and Enerbäck, S. (2001) Cell 106, 563-573). In this present study, we reveal that FOXC2 and a related factor, FOXD1, specifically activate the 1b promoter of the RI alpha gene in adipocytes and testicular Sertoli cells, respectively. By deletional mapping, we discovered two different mechanisms by which the Fox proteins activated expression from the RI alpha 1b promoter. In 3T3-L1 adipocytes, an upstream region represses promoter activity under basal conditions. Bandshift experiments indicate that overexpression of FOXC2 promotes the release of a potential repressor from this region. In Sertoli cells, sequences downstream of the transcription start sites mediate the activating effect of FOXD1, and protein kinase B alpha/Akt1 strongly induces this effect. Furthermore, we show that an inactive FOXD1 mutant lowers the cAMP-mediated induction of the RI alpha 1b reporter construct. In summary, winged helix transcription factors of the FOXC/FOXD families function as regulators of the RI alpha subunit of PKA and may integrate hormonal signals acting through protein kinase B and cAMP in a cell-specific manner.

3T3 Cells↗
PubMed1998

An inverted cAMP response element mediates the cAMP induction of the ovine beta 1-adrenergic receptor gene.

We identified an inverted, functional cAMP response element (CRE) located at--1599 bp relative to the translation start site within the ovine beta 1-adrenergic receptor (beta 1 AR) gene promoter. In transfection studies with SK-N-MC cells, a 40-bp oligonucleotide containing the potential CRE, beta 1 AR-CRE, conferred a 3- to 4-fold increase in luciferase activity mediated by cAMP. The induction was mimicked by co-transfecting the cells with a vector overexpressing the alpha-catalytic subunit of the cAMP-dependent protein kinase (PKA) without treatment, and was blocked by overexpressing a PKA inhibitor (PKI). In electrophoretic mobility shift assays, a discrete binding pattern was shown in cell nuclear extract probed with the 40 bp beta 1 AR-CRE. The binding was shown to be specific and supershifted by addition of a CRE binding protein (CREB-1) antibody. These data demonstrate that cAMP mediates the induction of beta 1 AR gene expression by interacting with an inverted CRE within the promoter region. This is the first reported functional CRE among all beta 1 AR genes.

Animals↗
PubMed1989

Bi-directional regulation of dephosphorylation of cAMP-dependent phosphorylated proteins by cAMP and calcium in permeabilized rat heart cells.

We studied the regulation of dephosphorylation of cAMP-dependent phosphorylated proteins of isolated, permeabilized (skinned) myocardial cells from adult rat. Staurosporine, a potent inhibitor of protein kinase, inhibited cAMP-dependent phosphorylation of phospholamban and troponin-I, the key proteins in the control of contraction and relaxation of the myocardial cells. Staurosporine antagonized the stimulatory action of cAMP on the spontaneous beating of the myocytes accompanied by dephosphorylation of phospholamban but not of troponin-I at pCa 7-8. In cold ATP dilution experiments with apparent stoppage of protein phosphorylation, dephosphorylation of phospholamban was accelerated both by Ca2+ and staurosporine but that of troponin-I took place only in the presence of Ca2+ ion (pCa less than 6.5). These phenomena suggest a bi-directional regulation of dephosphorylation of the key proteins by the intracellular messengers cAMP and Ca2+.

Adenosine Triphosphate↗
PubMed1995

cAMP-cAMP receptor protein complex: five binding sites in the control region of the Escherichia coli mannitol operon.

The control region of the mannitol (mtl) operon of Escherichia coli has been shown to contain five cAMP receptor protein (CRP) binding sequences, the most yet reported for any operon. A DNA fragment encompassing the entire mtl operon regulatory region was generated by PCR, and the binding of the cAMP-CRP complex was studied. Using restrictional analysis to separate, delineate and destroy the various putative CRP binding sites, all five sites were shown to be functional for CRP binding in vitro. Four of these sites bound the cAMP-CRP complex with high affinity while the fifth site (the most distal relative to the transcriptional start site) bound the complex with lower affinity. Simultaneous binding of cAMP-CRP complexes to several of these sites was demonstrated. The results serve to identify and define five dissimilar CRP binding sites in a single operon of E. coli. A model for mtl operon transcriptional initiation and repression complexes is presented.

Base Sequence↗
PubMed1991

A novel function of the cAMP-CRP complex in Escherichia coli: cAMP-CRP functions as an adaptor for the CytR repressor in the deo operon.

Unlike classical bacterial repressors, the CytR repressor of Escherichia coli cannot independently regulate gene expression. Here we show that CytR binding to the deoP2 promoter relies on interaction with the master gene regulatory protein, CRP, and, furthermore, that cAMP-CRP and CytR bind co-operatively to deoP2. Using mutant promoters we show that tandem, properly spaced DNA-bound cAMP-CRP complexes are required for this co-operative binding. These data suggest that CytR forms a bridge between tandem cAMP-CRP complexes, and that cAMP-CRP functions as an adaptor for CytR. The implications of this new version of negative control in E. coli on bacterial gene expression and on combinatorial gene regulation in higher organisms are discussed.

Bacterial Proteins↗
PubMed1993

A novel cAMP-dependent regulatory region including a sequence like the cAMP-responsive element, far upstream of the human CYP21A2 gene.

Deletion mutants in the 5' upstream sequence of the human CYP21A2 gene demonstrated a novel regulatory DNA element responsible for cAMP-dependent expression of the gene in the transient expression system using Y-1 cells (mouse adrenocortical tumor cell line). This regulatory element (-2574 to -2489 bp) was also found to exhibit a strong enhancer activity through heterologous promoters in response to cAMP and to contain a sequence like the cAMP-responsive element (CRE) and a CAAT-like sequence. The CRE-like sequence has a five-base motif (5'-TGACG-3') of the palindromic CRE consensus (TGACGTCA). Competitive gel mobility shift assays using nuclear extracts of bovine adrenal cortex with sequences typical of the binding sites for the binding proteins of CRE and the CAAT-like sequence revealed that these binding proteins, or related factors, bound to their cognate DNA binding sites in the upstream enhancer region of the CYP21A2 gene. These two enhancer elements and their cognate binding factors cooperate with previously identified tissue-specific enhancers (adrenal-specific protein factor and Ad4-like sequences) and their binding factors to express a high level of cAMP-responsive expression of the CYP21A2 gene.

Adrenal Cortex↗
PubMed1991

Action of mercurials on 3H-cAMP binding to the regulatory subunit-II of cAMP-dependent protein kinase.

Binding of the regulatory subunit type II (RII) of adenosine 3',5'-cyclic monophosphate (cAMP) dependent protein kinase was inhibited by Hg2+ with an IC50 value of 0.31 microM. Methyl mercury, p-chloromercuribenzoic acid (PCMB), and 5,5'-dithiobis-2-nitrobenzoic acid (DTNB) also inhibited cAMP binding with IC50 values of 70-80 microM for organic mercurials and 130 microM for DTNB. Addition of 1 mM 2-mercaptoethanol and 1 M cysteine to the assay mixture reversed these inhibitions. N-ethylmaleimide (NEM) showed little effect on the binding. On the other hand, Hg2+ and methyl mercury markedly suppressed enzymatic activity of the catalytic subunit. The IC50 value was 0.13 microM for Hg2+ and 0.15 microM for organic mercurials. Scatchard plots of kinetic analysis data for the cAMP binding revealed a noncompetitive type of inhibition by mercurials and DTNB. It is suggested that blockade of sulfhydryl groups resulted in the inhibition of cAMP binding to the RII subunit, which might result in preserving the association of the RII subunit and the catalytic subunits and in preventing further inactivation of the catalytic subunit by Hg2+.

Animals↗
PubMed2005

Fluorescence quenching and kinetic studies of conformational changes induced by DNA and cAMP binding to cAMP receptor protein from Escherichia coli.

Cyclic AMP receptor protein (CRP) regulates the expression of more then 100 genes in Escherichia coli. It is known that the allosteric activation of CRP by cAMP involves a long-distance signal transmission from the N-terminal cAMP-binding domain to the C-terminal domain of CRP responsible for the interactions with specific sequences of DNA. In this report we have used a CRP mutant containing a single Trp13 located in the N-terminal domain of the protein. We applied the iodide and acrylamide fluorescence quenching method in order to study how different DNA sequences and cAMP binding induce the conformational changes in the CRP molecule. The results presented provide evidence for the occurrence of a long-distance conformational signal transduction within the protein from the C-terminal DNA-binding domain to the N-terminal domain of CRP. This conformational signal transmission depends on the promoter sequence. We also used the stopped-flow and Forster resonance energy transfer between labeled Cys178 of CRP and fluorescently labeled DNA sequences to study the kinetics of DNA-CRP interactions. The results thus obtained lead to the conclusion that CRP can exist in several conformational states and that their distribution is affected by binding of both the cAMP and of specific DNA sequences.

Binding Sites↗
PubMed1993

Complex transcriptional control of the sigma s-dependent stationary-phase-induced and osmotically regulated osmY (csi-5) gene suggests novel roles for Lrp, cyclic AMP (cAMP) receptor protein-cAMP complex, and integration host factor in the stationary-phase response of Escherichia coli.

osmY (csi-5) is a representative of a large group of sigma s-dependent genes in Escherichia coli that exhibit both stationary-phase induction and osmotic regulation. A chromosomal transcriptional lacZ fusion (csi-5::lacZ) was used to study the regulation of osmY. We show here that in addition to sigma s, the global regulators Lrp, cyclic AMP (cAMP) receptor protein-cAMP complex (cAMP-CRP), and integration host factor (IHF) are involved in the control of osmY. All three regulators negatively modulate the expression of osmY, and they act independently from sigma s. Stationary-phase induction of osmY in minimal medium can be explained by stimulation by sigma s combined with a relief of Lrp repression. Stationary-phase induction of osmY in rich medium is mediated by the combined action of sigma s, Lrp, cAMP-CRP, and IHF, with the latter three proteins acting as transition state regulators. The transcriptional start site of osmY was determined and revealed an mRNA with an unusual long nontranslated leader of 244 nucleotides. The regulatory region is characterized by a sigma 70-like -10 promoter region and contains potential binding sites for Lrp, CRP, and IHF. Whereas sigma s, Lrp, CRP, and IHF are clearly involved in stationary-phase induction, none of these regulators is essential for osmotic regulation of osmY.

Amino Acid Sequence↗
PubMed1997

Maximization of transcription of the serC (pdxF)-aroA multifunctional operon by antagonistic effects of the cyclic AMP (cAMP) receptor protein-cAMP complex and Lrp global regulators of Escherichia coli K-12.

The arrangement of the Escherichia coli serC (pdxF) and aroA genes into a cotranscribed multifunctional operon allows coregulation of two enzymes required for the biosynthesis of L-serine, pyridoxal 5'-phosphate, chorismate, and the aromatic amino acids and vitamins. RNase T2 protection assays revealed two major transcripts that were initiated from a promoter upstream from serC (pdxF). Between 80 to 90% of serC (pdxF) transcripts were present in single-gene mRNA molecules that likely arose by Rho-independent termination between serC (pdxF) and aroA. serC (pdxF)-aroA cotranscripts terminated at another Rho-independent terminator near the end of aroA. We studied operon regulation by determining differential rates of beta-galactosidase synthesis in a merodiploid strain carrying a single-copy lambda[phi(serC [pdxF]'-lacZYA)] operon fusion. serC (pdxF) transcription was greatest in bacteria growing in minimal salts-glucose medium (MMGlu) and was reduced in minimal salts-glycerol medium, enriched MMGlu, and LB medium. serC (pdxF) transcription was increased in cya or crp mutants compared to their cya+ crp+ parent in MMGlu or LB medium. In contrast, serC (pdxF) transcription decreased in an lrp mutant compared to its lrp+ parent in MMGlu. Conclusions obtained by using the operon fusion were corroborated by quantitative Western immunoblotting of SerC (PdxF), which was present at around 1,800 dimers per cell in bacteria growing in MMGlu. RNase T2 protection assays of serC (pdxF)-terminated and serC (pdxF)-aroA cotranscript amounts supported the conclusion that the operon was regulated at the transcription level under the conditions tested. Results with a series of deletions upstream of the P(serC (pdxF)) promoter revealed that activation by Lrp was likely direct, whereas repression by the cyclic AMP (cAMP) receptor protein-cAMP complex (CRP-cAMP) was likely indirect, possibly via a repressor whose amount or activity was stimulated by CRP-cAMP.

3-Phosphoshikimate 1-Carboxyvinyltransferase↗
PubMed2000

Dual transcriptional regulation of the Escherichia coli phosphate-starvation-inducible psiE gene of the phosphate regulon by PhoB and the cyclic AMP (cAMP)-cAMP receptor protein complex.

We have shown that the Escherichia coli phosphate-starvation-inducible psiE gene is regulated by both phosphate and the carbon source by using both lacZ and chloramphenicol acetyltransferase gene (cat) fusions. Yet, under all conditions tested, a single transcriptional start site lying 7 bp downstream of a predicted -10 region was revealed by primer extension analysis. DNase I footprinting showed that the PhoB transcriptional-activator protein protects two predicted pho boxes lying upstream of and near the -35 promoter region. Similar analysis showed that the cyclic AMP (cAMP)-cAMP receptor protein (cAMP-CRP) complex binds a region that overlaps with the downstream pho box. These results, together with measurements of the in vivo psiE promoter activity under various conditions, show that expression of the psiE gene is under direct positive and negative control by PhoB and cAMP-CRP, respectively.

Bacterial Proteins↗
PubMed1984

Ca2+ dependence of positive inotropic responses of guinea pig isolated cardiac preparations to cAMP-generating and cAMP-independent agonists.

The effects of procedures which diminish Ca2+ influx into myocardial cells on responses of isolated cardiac preparations to cAMP-independent histamine H1 receptor stimulation and cAMP-generating beta-receptor stimulation were measured. The histamine response of guinea pig left atria, which appears to be primarily mediated by H1 receptors, was depressed to a greater extent than was the response of this preparation to isoproterenol by decreasing the extracellular Ca2+ concentration, and by the Ca2+ influx blocker D-600. Similarly, while the H1 agonist 2-pyridylethylamine dihydrochloride (PEA) produced increases in tension of a similar magnitude as the partial beta-agonist salbutamol in both left atria and in papillary muscles, responses of both preparations to PEA were depressed to a significantly greater extent by decreasing the extracellular Ca2+ concentration than were responses to salbutamol. Overall, both the basal developed force of papillary muscles and the responses of these preparations to H1 and beta-receptor stimulation appeared to be less depressed by decreasing the extracellular Ca2+ concentration than were those of left atria. These results indicate that responses mediated via cAMP-independent H1 receptors, like those arising from alpha-receptor stimulation, are more sensitive to procedures which diminish Ca2+ influx than are responses arising from stimulation of cAMP-generating beta-receptors. This may reflect differences in the mechanisms by which stimulation of H1, alpha-, and beta-receptors give rise to positive inotropic responses. In addition, left atria may be more dependent than papillary muscles on extracellular Ca2+ for the support of contraction.

Albuterol↗
PubMed1990

Identification of a 50-kDa Ca-, cAMP-, and cGMP-dependent epithelial phosphoprotein as a cAMP regulatory protein.

Multiple second messengers, presumably acting via protein phosphorylation mechanisms, regulate flounder intestinal ion transport. We recently reported [C. Toskulkao, N. T. Nash, K. Leach, and M. C. Rao. Am. J. Physiol. 258 (Cell Physiol. 27): C879-C888, 1990] that this tissue possesses adenosine 3',5'-cyclic monophosphate (cAMP)- and guanosine 3',5'-cyclic monophosphate (cGMP)-specific protein kinases, types II and III Ca-calmodulin kinases, and very low levels of protein kinase C. These results correlate with ion transport studies in which cGMP and Ca were shown to inhibit salt absorption, cAMP to increase anion permeability, and phorbol esters to have no effect. In the present study we characterized in detail a 50-kDa protein the phosphorylation of which is regulated by more than one second messenger. The 50-kDa (pI 5.2) phosphoprotein is present in both the cytosol (50 kDa-C) and particulate (50 kDa-P) fractions and appears to be regulated by Ca, cAMP, and cGMP. Although the pI and Mr of the regulated proteins are identical, there are differences in the regulation of 50 kDa-P and 50 kDa-C. The phosphorylation of 50 kDa-P is high in the basal state, and Ca and cGMP enhance this. cAMP has a biphasic effect, increasing it at low and decreasing it at high protein concentrations. The isoquinoline derivatives H-8 [50% effective dose (ED50) approximately 2.3 microM] and H-7 (ED50 approximately 45 microM) inhibit basal 50 kDa-P phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1984

Effect of testosterone on gonadotropin response to DBcAMP, cAMP binding, and cAMP production in pituitary cultures.

The role of testosterone (T) in the modulation of pituitary follicle-stimulating hormone (FSH) and luteinizing hormone (LH) sensitivity to DBcAMP was examined in the pituitary monolayer cultures prepared from intact young female rats. Hormone contents in media and cell homogenates were determined by radioimmunoassays. Incubation with 8 and 4 mM DBcAMP for 4 h consistently induced a significant (P less than 0.05) increase in FSH and LH release, respectively. Pretreatment with 10 nM T for 4 days reduced the minimal dose of DBcAMP required to stimulate FSH release (2 vs. 8 mM) but had no effect on the DBcAMP-induced LH release. Data indicate that T treatment for 4 or 7 days stimulated total FSH contents (sum of hormone contents in medium and cells). Similarly, incubation with 10 mM DBcAMP for 4 h significantly increased total FSH content per dish in both the T-treated and non-T-treated cultures. Neither T nor DBcAMP had any effect on LH production under these conditions. Intracellular cAMP was significantly increased to three- to eightfold of control after T treatment for 3 or 6 h, respectively. Furthermore, cAMP-binding activities were significantly increased after T treatment for 1 or 4 days (174 or 422% of control). Our previous data indicate that estrogen increases LH production, cAMP binding, cAMP production, and LH sensitivity to DBcAMP, and these data indicate that T exerts stimulatory effects on FSH in a similar fashion. These results support the concept that the two gonadotropins are regulated independently via different gonadal steroids.

Animals↗