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C A Strott

Publications and source records attributed to C A Strott.

At least 37 records · Page 2Linked to original sources
PubMed1992

Purification and identification of the heat-stable factor required for pregnenolone-binding protein activity. Evidence that the factor is adenosine 3',5'-diphosphate.

This paper presents data identifying adenosine 3',5'-diphosphate (3',5'-ADP) as the small heat-stable factor essential for the active steroid binding complex of the adrenocortical pregnenolone-binding protein (PBP). Factor activity obtained from the boiled supernatant of partially purified PBP was isolated by high performance liquid chromatography using weak anion-exchange and hydrophobic (C18) chromatography sequentially. The purified material retained characteristic factor activity and presented a UV spectrum identical to that for authentic 3',5'-ADP. Mass spectroscopic analysis of the isolated factor revealed an M-H ion of appropriate mass (m/z = 426) and a decomposition pattern for the M-H ion that was consistent with the structure of 3',5'-ADP. The studies presented here demonstrate that authentic 3',5'-ADP can categorically substitute for factor prepared from the soluble fraction of the guinea pig adrenal. Specifically, 3',5'-ADP potentiated ligand binding of partially purified native PBP and restored binding capacity to alkaline phosphatase-inactivated PBP in a dose-dependent manner. As is the case for adrenocortical factor activity, these effects were negated by pretreating the 3',5'-ADP with calf intestinal alkaline phosphatase. Other nucleotides similarly tested, including ADP isomers, were ineffective as factor substitutes. The sulfated form of 3',5'-ADP (i.e. 3'-phosphoadenosine 5'-phosphosulfate) demonstrated some potential for restoring binding capacity to phosphatase-inactivated PBP; however, this compound was clearly inhibitory rather than stimulatory for native PBP activity. Taken collectively, the data overwhelmingly demonstrate that 3',5'-ADP is in fact the molecule required by the PBP for high affinity steroid binding complex formation. It is not yet known whether 3',5'-ADP acts allosterically or contributes directly to the structure of the steroid binding site.

Adenosine Diphosphate↗
PubMed1992

Molecular cloning and expression of a full-length complementary DNA encoding the guinea pig adrenocortical estrogen sulfotransferase.

Complementary DNA for the guinea pig adrenocortical estrogen sulfotransferase (EST) has been cloned and expressed. Oligonucleotides, based on amino acid sequences of the purified 34-kilodalton protein, were synthesized and used to generate a specific probe by polymerase chain reaction for screening a guinea pig adrenal cDNA library. The polymerase chain reaction rapid amplification of cDNA ends procedure was employed to obtain the 3' and 5' cDNA ends, and a full-length cDNA was constructed. The cloned cDNA consists of 1192 base pairs and encodes a protein of 296 amino acids with a calculated molecular mass of 35,161 daltons. A computer search of the protein data banks revealed significant homology with several sulfotransferases: 71% with bovine placental estrogen sulfotransferase, 52% with rat liver phenol sulfotransferase, 35% with rat liver hydroxysteroid sulfotransferase, and 36% with rat liver senescence marker protein 2. The EST cDNA was inserted into the pcDNA I eukaryotic expression vector and transfected into COS-7 cells. The successful expression of EST cDNA in COS-7 cells was ascertained by Western blot analysis using antibody generated against the protein used to obtain the original amino acid sequence. Additionally, the expressed protein was clearly functional. Only after transfection with EST cDNA was there detectable estradiol sulfotransferase activity in COS-7 cell cytosol. The expressed EST had a single pI of 6.4, whereas native guinea pig adrenocortical EST exhibits four primary charge isoforms. The majority of adrenocortical EST activity focuses as a broad bimodal band in the pH range of 6.6-6.2; additionally, three other discrete immunocross-reactive isoforms are present with pIs of 5.5, 5.4, and 5.2. Antibodies generated against each individual isoform cross-react with all the other isoforms and with the expressed protein. These isoforms were previously reported to be isomers of a pregnenolone-binding protein; however it is now evident that the isoforms and antibodies raised against them are EST specific. Under high stringency hybridization conditions, EST mRNA was only detected in the adrenal gland, where two mRNA species of 1.4 and 1.8 kilobases were evident; when low stringency conditions were used, a faint 1.4-kilobase band was also detected in the liver. Primer extension analysis revealed that the multiple mRNAs do not arise from differential transcription initiation sites, and genomic Southern blot analysis indicated that the multiple mRNAs arise from a single gene.

Adrenal Cortex↗
PubMed1991

Adrenocortical nuclear progesterone-binding protein: identification by photoaffinity labeling and evidence for deoxyribonucleic acid binding and stimulation by adrenocorticotropin.

Nuclei of the guinea pig adrenal cortex contain a protein that specifically binds progesterone and that, biochemically, is clearly distinct from the classical progesterone receptor. The adrenocortical nuclear progesterone-binding protein has now been purified more than 2000-fold by steroid-affinity chromatography with a 75% yield. The purified protein preparation demonstrated three major bands on sodium dodecyl sulfate-polyacrylamide gel of 79K, 74K, and 50K. To determine which of the three might represent the progesterone-binding protein, steroid photoaffinity labeling was performed which resulted in the specific and exclusive labeling of a 50K band. Thus, the adrenocortical nuclear progesterone-binding protein appears to be distinct from the classical progesterone receptor not only biochemically, but also on the basis of molecular size. To test whether the adrenocortical nuclear progesterone-binding protein can be hormonally stimulated, guinea pigs were treated with ACTH. The chronic administration of ACTH caused a 4- to 6-fold increase in the specific progesterone binding capacity without a change in the binding affinity. There appeared to be no significant difference in nuclear progesterone binding between the zona fasciculata and zona reticularis. This finding suggests a mediating role for the progesterone-binding protein in ACTH action. In addition, the nuclear progesterone-binding protein bound to nonspecific DNA sequences, further suggesting a possible transcriptional regulatory role.

Adrenal Cortex↗
PubMed1991

Adrenocortical pregnenolone-binding protein activity requires a small heat-stable factor: evidence that regulation by phosphorylation/dephosphorylation occurs at the level of the factor, not the protein.

The steroid-binding capacity of the adrenocortical pregnenolone-binding protein (PBP) is effectively destroyed by extreme temperature (boiling water for 2-5 min); however, the boiled preparation contains a factor that potentiates ligand binding when readded to native PBP. Treatment of the boiled fraction with calf intestinal alkaline phosphatase at pH 9 reverses the stimulatory effect on PBP activity. Additionally, if native PBP is first incubated with alkaline phosphatase, which converts it to a nonbinding form, activity can be fully restored in a dose-dependent manner by the addition of the boiled preparation. The factor (itself devoid of binding capacity) can also be generated by exposing native PBP to acidic conditions (pH 4). The molecule is small (mol wt, less than 2000), as judged by Sephadex G-25 gel filtration and equilibrium dialysis. It is not retained on Concanavalin-A-Sepharose and is not extractable with a variety of organic solvents. The factor remains active after lyophilization and has a net negative charge at pH 7.4 (determined by DEAE-cellulose chromatography). While the binding capacity of native PBP is destroyed by a variety of proteases, the heat-stable factor is unaffected by similar treatment. Additionally, factor activity is not susceptible to RNase, DNase, or lipase digestion. Thus, the protein moiety of the PBP has an absolute requirement for a distinct phosphorylated heat-stable factor for expression of ligand-binding activity, and it may be through this factor that binding activity is regulated. It is not yet known whether the factor is acting allosterically or actually functions as part of the steroid-binding site.

Adenosine Triphosphate↗
PubMed1990

Regulation of adrenocortical pregnenolone-binding protein activity by phosphorylation/dephosphorylation. Phosphatase-mediated inactivation is reversed by cytosolic kinase.

The pregnenolone-binding protein (PBP) in guinea pig adrenocortical cytosol is inactivated (converted to a nonsteroid-binding form) by incubation with calf intestinal alkaline phosphatase at pH 9. Previously bound pregnenolone does not prevent this inactivation, and dephosphorylation causes dissociation of bound ligand from the protein. Cytosolic PBP, partially purified PBP, and highly purified PBP are equally susceptible to alkaline phosphatase-mediated inactivation. No change in apparent molecular weight or immunoreactivity is evident by Western blot analysis. Loss of pregnenolone-binding capacity of cytosolic PBP (but not partially purified PBP) could be reversed by inhibiting the phosphatase, lowering the pH to approximately 7, and adding ATP to the incubation. Reactivation is absolutely and specifically dependent upon ATP, which restores binding capacity in a concentration-dependent manner. Other nucleoside triphosphates, including the nonhydrolyzable ATP analogue adenosine 5'-(beta, gamma-imido)triphosphate, as well as cAMP and cGMP are ineffectual as cofactors for reactivation. These data strongly implicate a cytosolic kinase which is apparently inactivated or separated from PBP during purification. Preliminary investigations indicate that the reactivating kinase is not cAMP-dependent, but may have a requirement for calcium and/or calmodulin. The identification of phosphorylation/dephosphorylation as the regulatory mechanism for steroid binding should prove pivital in elucidating the functional role of PBP.

Adrenal Cortex↗
PubMed1990

Charge isoforms of the adrenocortical pregnenolone-binding protein: influence of phosphorylation on isoformation and binding activity.

Isoelectric focusing of the Mr 34,000 pregnenolone-binding protein (PBP) isolated from the guinea pig adrenal cortex has revealed multiple charge isoforms. Alkaline phosphatase treatment resulted in the disappearance of the pI 5.4 isoform associated with the appearance of pI 5.9 and pI 6.1 isoforms; this alteration in the charge-isoform pattern of the PBP correlated with a loss in pregnenolone-binding activity. This finding appears to be novel for intracellular steroid-binding proteins and has not been demonstrated for steroid receptors, a well-studied group of phosphoproteins. Resolution of the PBP by nondenaturing polyacrylamide gel electrophoresis produced two radioactive peaks of [3H]pregnenolone in an equilibrium system, while only one peak was present in a nonequilibrium system, suggesting high- and low-binding affinity forms of PBP. Isoelectric focusing of highly purified PBP resolved multiple forms of Mr 34,000 proteins with pI values ranging from 6.4 to 5.2. Two of the Mr 34,000 charge isoforms were isolated, and each was used to generate polyclonal antibodies; both antisera were crossreactive against all forms of Mr 34,000 PBP. Western blot analysis revealed that the PBP was present in both the fasciculata and reticularis of the adrenal cortex, though the isoform patterns were not identical for the two zones. Additionally, the pregnenolone-binding activity was approximately 10-fold greater in the zona reticularis. In vitro alkaline phosphatase treatment of the PBP abolished pregnenolone-binding activity and caused an alteration in the charge-isoform pattern for PBP in the zona reticularis, where pregnenolone binding is high, to resemble the pattern found for the zona fasciculata, where pregnenolone binding is low. The results indicate that phosphorylation/dephosphorylation regulates pregnenolone-binding activity and influences the pattern of the PBP isoformation. The data further suggest that the pI 5.4 isoform may be the active steroid-binding molecule.

Adrenal Cortex↗
PubMed1990

Immunocytochemical localization of the 34 KD pregnenolone-binding protein to fasciculata and reticularis cells and a novel 32 KD protein specific for reticularis cells in guinea pig adrenal cortex.

Two proteins were isolated and purified from guinea pig adrenal cortex: a 34 KD protein that specifically binds pregnenolone (product of the rate-limiting step in steroidogenesis), and a novel co-purifying 32 KD protein that has not been characterized. Specific antisera were generated and used for immunocytochemical analysis. The 34 KD and 32 KD proteins were specific for the adrenal cortex and were absent from other tissues, including the testis. The 34 KD pregnenolone binding protein (PBP) was localized to zona fasciculata and zona reticularis cells and absent from zona glomerulosa cells. Thus, the PBP was absolutely correlated with ACTH-regulated steroidogenic cells, whereas steroidogenic cells regulated by other peptide hormones did not contain the PBP. This finding suggests a functional relationship between the PBP and ACTH. A second interesting finding was that a novel 32 KD co-purifying protein localized to the zona reticularis and was absent from the zona glomerulosa and the zona fasciculata. The 32 KD protein can therefore serve as an excellent marker for the reticularis cell of the adrenal cortex.

Adrenal Cortex↗
PubMed1990

The nuclear conversion of pregnenolone to progesterone and subsequent binding to the nuclear progesterone-binding protein in the guinea pig adrenal cortex: a possible regulatory role for the pregnenolone-binding protein.

Progesterone, which is normally produced in the endoplasmic reticulum, was found to be rapidly degraded in the cytosolic fraction of the guinea pig adrenal cortex in vitro. Assuming this finding reflects what happens in vivo raises a question as to the source of progesterone for interacting with a nuclear progesterone-binding protein (P4-BP) that exists in this model system. It was subsequently found that pregnenolone, which in contrast to progesterone is relatively stable in the cytosol, was converted to progesterone by endogenous nuclear 3 beta-ol dehydrogenase. It was also determined that the nuclear-derived progesterone specifically bound to the nuclear P4-BP which is distinct from the classical progesterone receptor. The guinea pig adrenocortical cytosol contains a specific pregnenolone-binding protein (P5-BP) that could be virtue of its pregnenolone binding activity regulate the conversion of pregnenolone to progesterone in the nuclear compartment and thereby reduce the binding of progesterone to the nuclear P4-BP. A partially purified P5-BP preparation markedly inhibited the nuclear conversion of pregnenolone to progesterone and reduced the binding of progesterone to the nuclear P4-BP (P5-BP did not directly inhibit binding of progesterone to the nuclear P4-BP). The ability of P5-BP to inhibit the conversion of pregnenolone to progesterone was destroyed by heat and alkaline phosphatase treatment. The binding of pregnenolone to the P5-BP, as previously reported, is regulated by phosphorylation/dephosphorylation, and alkaline phosphatase-treated P5-BP loses the ability to bind pregnenolone; this process can be reversed by a cytosolic kinase. This provides a mechanism for controlled release of bound steroid. These results suggest that P5-BP regulates the nuclear conversion of pregnenolone to progesterone and thus the binding of progesterone to the nuclear P4-BP.

Adrenal Cortex↗
PubMed1989

Calmodulin-binding proteins in subcellular fractions of zones of the adrenal cortex.

The guinea pig adrenal cortex consists of a steroidogenic ACTH-responsive outer zone and an ACTH-unresponsive inner zone. It has been suggested that calmodulin plays an important role in ACTH-stimulated steroidogenesis. Thus, in an effort to examine the calmodulin 'system' in the guinea pig adrenal cortex model, Ca2+-dependent binding of calmodulin to proteins in subcellular fractions of the outer and inner zones was examined by the [125I]iodocalmodulin overlay technique and compared to similar studies utilizing pancreas, brain and liver tissue. Although the general pattern of calmodulin-binding proteins was similar for the two adrenocortical zones, quantitatively there was a striking difference with greater binding in the outer zone; this was particularly noteworthy for the mitochondrial fraction. The two most prominent calmodulin-binding proteins isolated from cytosol by calmodulin-Sepharose column chromatography had Mr of 60,000 and 47,000. The size of these two proteins suggested the presence of Ca2+/calmodulin-dependent protein kinase II. Western blot analysis, however, failed to demonstrate calmodulin kinase II in either zone, although it was clearly detectable in brain cytosol. The 60 K calmodulin-binding protein in the adrenal cortex also suggested the presence of the calmodulin-binding A subunit of the Ca2+/calmodulin-stimulated protein phosphatase, calcineurin. Western blot analysis did reveal the presence of calcineurin in the outer adrenocortical zone; it was not detectable, however, in the inner adrenocortical zone. The relation between the striking zonal differential for calmodulin-binding proteins and the zonal differential in ACTH-stimulated steroidogenesis in the guinea pig adrenal cortex will require further investigation.

Adrenal Cortex↗
PubMed1989

Nuclear progesterone-binding protein in the guinea pig adrenal cortex: distinction from the classical progesterone receptor.

Nuclei purified from the guinea pig adrenal cortex contain a specific progesterone-binding activity which, based on enzyme degradation studies, appears to be proteinaceous. Saturation analysis revealed a Kd of about 15 nM and a binding capacity of about 33 pmol/mg DNA. The activity of the nuclear binding protein was specific essentially for progestational steroids; the two most potent progesterone competitors were 5 alpha-pregnane-3,20-dione and medroxyprogesterone (17 alpha-hydroxy-6 alpha-methylprogesterone), while 17 beta-estradiol, testosterone, cortisol, and other related steroids were poor competitors. The adrenocortical nuclear progesterone-binding protein was present to an equal extent in both male and female guinea pigs. The adrenocortical nuclear progesterone-binding protein differed from the classical progesterone receptor in that 1) the affinity of the adrenocortical binding protein for progesterone is an order of magnitude lower; 2) the potent synthetic progestin R5020 binds less tightly to the adrenocortical progesterone-binding protein; 3) the adrenocortical progesterone-binding protein is not modulated by estrogenic activity; 4) the adrenocortical progesterone-binding protein is more stable at 37 C; 5) the adrenocortical nuclear progesterone-binding protein is not salt extractable; and 6) Western blot analysis has revealed that an antiprogesterone receptor monoclonal antibody, which recognizes the guinea pig uterine classical nuclear progesterone receptor, does not recognize the adrenocortical nuclear progesterone-binding protein. Thus, the guinea pig adrenocortical nucleus contains a type of progesterone-binding protein that appears to be clearly different from the classical progesterone receptor.

Adrenal Cortex↗
PubMed1988

Phosphorylation of calmodulin on threonine residue(s) by cytosol prepared from the adrenal cortex.

During the course of experiments examining Ca2+/calmodulin-dependent protein phosphorylation by cytosol prepared from the outer and inner zones of the guinea pig adrenal cortex, it appeared that the calmodulin added to incubation mixtures was undergoing phosphorylation. This was subsequently confirmed by immunoprecipitation following phenyl-Sepharose purification of the phosphocalmodulin. The phosphorylation of calmodulin was maximal in the absence of calcium, and markedly increased by the presence of poly-basic amino acids. Phosphoamino acid analysis revealed that calmodulin was phosphorylated exclusively on threonine residue(s). It was of interest to note that the phosphorylation of calmodulin was always considerably more intense with the cytosol prepared from the inner adrenocortical zone than with cytosol prepared from the outer zone.

Adrenal Cortex↗
PubMed1988

Adrenocortical pregnenolone-binding protein: identification and antibody development.

Pregnenolone-binding activity isolated from the cytosol of the guinea pig adrenal cortex appears to correspond to a Mr 34,000 protein when examined by SDS-polyacrylamide gel electrophoresis during different stages of purification. To verify this finding the Mr 34,000 protein band was eluted from the SDS gel and used to generate a polyclonal antibody. Immobilized anti 34,000 IgG on protein A-Sepharose was found to extract pregnenolone-binding activity from solution in contrast to pre-immune IgG and an antibody raised against a Mr 30,000 protein isolated simultaneously. In addition, protein eluted from the protein A-anti 34,000 IgG complex exhibited the expected molecular weight of 34,000 when examined on an SDS gel. These results, thus, confirm that the pregnenolone-binding protein is indeed a protein of Mr 34,000.

Adrenal Cortex↗
PubMed1988

Calcium-dependent protein kinase activity and protein phosphorylation in zones of the adrenal cortex.

The guinea pig adrenal cortex is composed of two chromatically distinct concentric zones. The steroidogenic response to ACTH by the two zones is likewise distinct: ACTH stimulates cholesterol side-chain cleavage activity in the outermost zone, but fails to do so in the inner zone. This despite the fact that adenylate cyclase activation by ACTH and cAMP formation are similar for the two zones. To further examine this model, protein kinase activity and protein phosphorylation have been examined. It was found that the cAMP-dependent, Ca2+/phospholipid-dependent, and Ca2+/calmodulin-dependent protein kinase activities were significantly higher in the outer zone than in the inner zone by 70, 60 and 800%, respectively. Although the physiological meaning of a zonal difference in protein kinase activity is not as yet clear, the marked difference in Ca2+/calmodulin-dependent protein kinase activity between the inner and outer zones correlates well with the marked difference in steroidogenesis that exists between the two zones. Of the Ca2+/calmodulin-dependent protein kinases known to exist, there is preliminary evidence to suggest the presence of kinase III in the guinea pig adrenal cortex. Protein phosphorylation induced by the three kinase systems in the two adrenocortical zones revealed notable differences in phosphoprotein patterns. In addition, it was found that exogenous calmodulin was phosphorylated and that the kinase responsible for this was more active in the inner zone.

Adrenal Cortex↗
PubMed1987

Differential activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase in zones of the adrenal cortex.

Cholesterol metabolism and steroidogenesis in the outer (zona fasciculata/glomerulosa) and inner (zona reticularis) zones of the adrenal cortex were examined in the guinea pig. It is known from previous studies that the content of cholesterol in the inner zone is considerably lower than that in the outer zone, although basal low density lipoprotein (LDL) receptor activity is similar in the two zones. To further explore cholesterol metabolism in the guinea pig adrenal cortex, the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-limiting step in cholesterol synthesis, has been examined for which this paper forms the initial report. It was found that the basal specific activity of HMG-CoA reductase was similar in the outer and inner adrenocortical zones (approximately 230 pmol mevalonate formed/min X mg microsomal protein). The administration of ACTH caused 4- and 5-fold increases in HMG-CoA reductase activity in the outer and inner zones, respectively. In fact, the increase in HMG-CoA reductase activity with ACTH treatment was always greater for the inner zone than for the outer zone. This is in contrast to LDL receptor activity, which does not increase in the inner zone as it does in the outer zone with ACTH treatment. When dexamethasone was administered, HMG-CoA reductase activity decreased in the outer zone by about 50%, while there was no change in reductase activity in the inner zone. The latter finding is similar to what happens with LDL receptor activity during dexamethasone administration. Why suppression of endogenous ACTH had no effect on HMG-CoA reductase activity in the inner zone while exogenous ACTH administration caused a marked increase in enzyme activity is not clear, but may be related to phosphorylation/dephosphorylation mechanisms. Based on the use of sodium fluoride in solutions to block HMG-CoA reductase phosphatase, evidence is presented which indicates that a pharmacological dose of ACTH alters the phosphorylation/dephosphorylation status of HMG-CoA reductase in the inner adrenocortical zone, but not in the outer cortical zone.

Adrenal Cortex↗
PubMed1986

Cyclic AMP-dependent protein kinase activity and protein phosphorylation in zones of the adrenal cortex.

Steroidogenesis is not stimulated by ACTH in the inner zone of the guinea pig adrenal cortex; adenylate cyclase is normally stimulated. To further explore the lack of a steroidogenic response to ACTH in the inner zone, cAMP-dependent protein kinase activity and protein phosphorylation were examined in the outer and inner adrenocortical zones. To summarize: total cAMP-dependent protein kinase activity was 40% higher in the outer zone than in the inner zone; of the total cAMP-dependent protein kinase activity, cytosol contained 80% for the outer and 70% for the inner zone. In both zones only the type II isozyme was present. Qualitative and quantitative differences in protein phosphorylation were noted for the two zones.

Adrenal Cortex↗
PubMed1986

Low-density lipoprotein receptor activity in the guinea pig adrenal cortex. II. Zonal response to aminoglutethimide and 17 alpha-ethinylestradiol.

Low-density lipoprotein (LDL) receptor activity and the concentration of cholesterol were measured in the outer (glomerulosa/fasciculata) and inner (reticularis) zones of the adrenal cortex of the guinea pig to examine the relation between cholesterol content and LDL receptor activity. While the concentration of cholesterol was 2-3-times higher in the outer cortical zone, the maximum high-affinity binding capacity for LDL was essentially the same for the two zones, or slightly higher for the inner zone. Adrenocorticotrophic hormone (ACTH) caused a significant increase in LDL receptor activity only in the outer zone, but led to a reduction in the cholesterol content in both adrenocortical zones. The treatment of animals with 17 alpha-ethinyl-estradiol also resulted in a reduction of cholesterol in both adrenocortical zones, but an increase in LDL receptor number only in the outer zone. The latter effect was partially reversed by the administration of dexamethasone. Aminoglutethimide, which was used in a dose that did not block steroidogenesis but did block the hydrolysis of cholesteryl esters in response to ACTH, did not prevent the ACTH-induced increase in LDL receptor number in the outer zone. Thus, the number of LDL receptors was increased in the zona fasciculata by ACTH in the absence of a reduction in cellular cholesterol content, while the number of LDL receptors in the zona reticularis was not increased by ACTH even in the face of a reduction in cellular cholesterol. Exclusive of the experiments employing aminoglutethimide, when the cellular cholesterol content was plotted against LDL binding activity, an excellent inverse correlation was revealed for the zona fasciculata, but essentially no correlation was noted for the zona reticularis. It is concluded that the outer and inner cortical zones of the guinea pig adrenal are quite distinct in the nature of their LDL receptor activity and regulation: the LDL receptor of the outer zone appears to function in a way similar to what has been reported for the whole adrenal cortex of other species in that receptor number correlates with tissue cholesterol content and is primarily regulated by ACTH; the LDL receptor number of the inner zone, however, does not correlate with tissue cholesterol content and is apparently not regulated by ACTH.

Adrenal Cortex↗
PubMed1986

Low density lipoprotein receptor activity in the guinea pig adrenal cortex. I. Zonal characterization and response to adrenocorticotropin.

The binding of [125I]iodo-low density lipoprotein ([125I]iodo-LDL) to isolated membranes was determined for the outer (glomerulosa/fasciculata) and inner (reticularis) zones of the guinea pig adrenal cortex. Binding of [125I]iodo-LDL to membranes from both zones was found to be highly specific and dependent on the presence of divalent cations, such as calcium. Saturation analysis revealed that the maximum high affinity binding capacity was similar for both zones under control conditions (approximately 400 ng/mg protein). When ACTH was administered, however, the maximum high affinity binding capacity increased in the outer zone by at least 3-fold, while there was no significant change for the inner zone. It was also noted that dexamethasone administration decreased [125I]iodo-LDL high affinity binding activity to less than half the control level in the outer zone without altering the binding activity in the inner zone. The cholesterol content in the outer zone was 2-3 times greater than that in the inner zone. When ACTH was administered, the concentration of cholesterol decreased significantly in both zones. Thus, ACTH appeared to influence cholesterol metabolism in the outer and inner adrenocortical zones, but was able to modulate LDL receptor activity only in the outer zone.

Adrenal Cortex↗
PubMed1985

Adenylate cyclase activity and cyclic AMP production in the outer and inner zones of the adrenal cortex.

It has been reported that cells isolated from the inner zone of the guinea pig adrenal cortex fail to have a steroidogenic response to ACTH. To further explore this, adenylate cyclase activity of membrane particles and cAMP production by cells prepared from the inner and outer adrenocortical zones were determined. The cAMP response to ACTH and forskolin was similar for cells from both zones. Basal adenylate cyclase activity was significantly higher in the inner zone; and while absolute responses to ACTH, GppNHp, GTP, NaF, and forskolin were greater for the inner zone, relative responses were similar for the two zones. These observations suggest that the inner zone of the guinea pig adrenal cortex may have a defect in ACTH action at a step(s) beyond cAMP formation.

Adenylyl Cyclases↗