Interleukin-1-induced corticosterone release occurs by an adrenergic mechanism from rat adrenal gland

Interleukin-1 (IL-1) has been shown to stimulate corticosterone release from the adrenal gland directly, and indirectly through activation of the hypothalamic-pituitary-adrenal axis. The aim of this paper was to determine whether IL-1-stimulated corticosterone release occurs indirectly through the local release of catecholamines from the rat adrenal gland. To accomplish this, experiments were conducted on both quartered rat adrenal glands and primary cultures of dispersed adrenal cells. Incubation of quartered adrenals with adrenocorticotropic hormone (ACTH, 10(-12) to 10(-8) M) or IL-1 beta (10(-12) to 10(-8) M) resulted in dose-dependent increases (P less than 0.05) in corticosterone release. Corticosterone release stimulated by 10(-8) M doses of ACTH and IL-1 beta began to rise 30 min after incubation and peaked at 2 h. In primary cultures of adrenal cells, IL-1 alpha and IL-1 beta elevated corticosterone release after a 24-h incubation period. ACTH elevated corticosterone levels at 4 and 24 h. The stimulatory effect of IL-1 on corticosterone release was mimicked by epinephrine (10(-6) M), and was selectively blocked by the alpha-adrenergic antagonist phentolamine (10(-5) M). The beta-adrenergic antagonist propranolol (10(-5) M) did not change IL-1-induced corticosterone release. Neither phentolamine nor propranolol had an effect on ACTH-stimulated corticosterone release. Both IL-1 alpha and IL-1 beta significantly increased (P less than 0.05) epinephrine levels after a 24-h incubation period compared with media-treated controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression cloning of a common receptor for parathyroid hormone and parathyroid hormone-related peptide from rat osteoblast-like cells: a single receptor stimulates intracellular accumulation of both cAMP and inositol trisphosphates and increases intracellular free calcium

Parathyroid hormone (PTH), a major regulator of mineral ion metabolism, and PTH-related peptide (PTHrP), which causes hypercalcemia in some cancer patients, stimulate multiple signals (cAMP, inositol phosphates, and calcium) probably by activating common receptors in bone and kidney. Using expression cloning, we have isolated a cDNA clone encoding rat bone PTH/PTHrP receptor from rat osteosarcoma (ROS 17/2.8) cells. The rat bone PTH/PTHrP receptor is 78% identical to the opossum kidney receptor; this identity indicates striking conservation of this receptor across distant mammalian species. Additionally, the rat bone PTH/PTHrP receptor has significant homology to the secretin and calcitonin receptors but not to any other G protein-linked receptor. When expressed in COS cells, a single cDNA clone, expressing either rat bone or opossum kidney PTH/PTHrP receptor, mediates PTH and PTHrP stimulation of both adenylate cyclase and phospholipase C. These properties could explain the diversity of PTH action without the need to postulate other receptor subtypes.

A G protein-linked receptor for parathyroid hormone and parathyroid hormone-related peptide

The complementary DNA encoding a 585-amino acid parathyroid hormone-parathyroid hormone-related peptide (PTH-PTHrP) receptor with seven potential membrane-spanning domains was cloned by COS-7 expression using an opossum kidney cell complementary DNA (cDNA) library. The expressed receptor binds PTH and PTHrP with equal affinity, and both ligands equivalently stimulate adenylate cyclase. Striking homology with the calcitonin receptor and lack of homology with other G protein-linked receptors indicate that receptors for these calcium-regulating hormones are related and represent a new family.

Cyclic adenosine 3',5'-monophosphate (cAMP)-dependent and cAMP-independent regulation of parathyroid hormone receptors on UMR 106-01 osteoblastic osteosarcoma cells

The osteoblast-like cells, UMR 106-01, express PTH receptors that are coupled to adenylate cyclase. Recently, we reported the isolation of a UMR 106-01 subclone, UMR 4-7, that is stably transfected with a Zn(++)-inducible mutant of the regulatory subunit of protein kinase A. Incubation of UMR 4-7 cells with Zn++ renders the cells unresponsive to cAMP agonists. This subclone, therefore, seemed particularly suitable for studies of PTH receptor regulation. In UMR 106-01 cells, PTH receptors are strikingly down-regulated by pretreatment with 8-Br-cAMP or 3-isobutyl-1-methylxanthine for 2 days. In UMR 4-7 cells, this effect is totally prevented by prior and concurrent treatment with Zn++. Zn++ addition to UMR 106 cells does not modify these responses. Treatment with the PTH agonist [Nle8,18,Tyr34]bovine PTH(1-34)NH2 [(NlePTH(1-34)] also markedly down-regulates PTH receptors in UMR 106 cells, but this effect is only partially inhibited in Zn(++)-induced UMR 4-7 cells. At high doses, the PTH antagonist, [Nle8,18,Tyr34]bovine PTH(3-34)NH2 [NlePTH(3-34)] also (partially) reduces PTH receptor availability. Receptor regulation by NlePTH(3-34) is not blocked in the cAMP-resistant cells, however. Coincubation of submaximal doses of NlePTH(1-34) (1 nM) with NlePTH(3-34) (1 microM) reduces receptor availability more than when the cells are exposed to either ligand alone. This decrease is only partially inhibited in Zn(++)-induced UMR 4-7 cells. In contrast to its additive effect on receptor regulation, NlePTH(3-34) efficiently competes for binding to the PTH receptor in UMR 106-01 cells and antagonizes the stimulatory effects of NlePTH(1-34) on both intracellular cAMP accumulation and gene expression driven by a transiently transfected synthetic cAMP-responsive enhancer. In conclusion, homologous down-regulation of PTH receptors is mediated by activation of both cAMP-dependent (via protein kinase A) and cAMP-independent pathways. PTH activates both pathways, whereas the effect of NlePTH(3-34) appears to be exclusively cAMP-independent. These results give new insights into mechanisms of PTH receptor regulation.

Specific, high-affinity binding sites for angiotensin II on Mycoplasma hyorhinis

Mycoplasmataceae are known to express various proteins that are similar to those present in mammals. We report a strain of Mycoplasma hyorhinis isolated from opossum kidney cells with specific, high-affinity binding sites for human angiotensin II (Kd = 5.1 +/- 1.9 nM). In contrast, two strains of M. hominis revealed no specific binding. These binding sites resembled mammalian angiotensin II receptors by their high affinity and by their sensitivity to dithiothreitol. However, they are different from mammalian angiotensin II receptors in that they bind angiotensin I with high affinity (Kd = 1.6 +/- 0.29 nM) but not angiotensin III (Kd approximately 330,000 nM). [125I]-angiotensin II binding was not inhibited by angiotensin receptor subtype antagonists DuP 753 and CGP 42112A but it was sensitive to bacitracin and aprotinin. Positions Asp1, Ile5, His6 and Pro7 were essential for binding to M. hyorhinis as deletion of these residues led to a more than 10,000-fold decrease in affinity.

Properties of amino-terminal parathyroid hormone-related peptides modified at positions 11-13

Biological properties of amino-terminal PTHrP analogues modified in the region 11-13 were examined using ROS 17/2.8 cells. [Leu11,D-Trp12,Arg13,Tyr36]PTHrP(1-36)amide had a 17-fold lower binding affinity for the receptor (apparent Kd: 5 x 10(-8) M) than [Tyr36]PTHrP(1-36)amide or [Arg11,13,Tyr36]PTHrP(1-36)amide (apparent Kd for both: 2 x 10(-9) M). Moreover, it is only a weak partial agonist despite completely inhibiting radioligand binding. [Leu11,D-Trp12,Arg13,Tyr36,Cys38]PTHrP(7-3 8) and PTHrP(7-34)amide had similar receptor affinities (apparent Kds: 5 x 10(-8) M and 8 x 10(-8) M), while that of [Nle8,18,Tyr34]bPTH(7-34)amide was more than 10-fold lower (apparent Kd: 2 x 10(-6) M). These changes in biological properties suggest that high affinity receptor binding requires both amino- and carboxyl-terminal domains of the PTHrP(1-36) sequence and/or intramolecular interactions which are impaired by the D-Trp substitution for Gly12.

Expression of human parathyroid hormone-(1-84) in Escherichia coli as a factor X-cleavable fusion protein

Recombinant human parathyroid hormone (hPTH)-(1-84) was obtained from Escherichia coli using a cleavable fusion protein strategy. The fusion protein contains residues 1-138 of human growth hormone as the amino-terminal region and residues 1-84 of hPTH as the carboxyl-terminal region. A 7-residue linker containing the recognition/cleavage sequence of the site-specific blood coagulation protease activated factor X (factor Xa) joins the two regions. Intact hPTH-(1-84) is released from this fusion protein by cleavage in vitro with factor Xa. The fusion protein was produced at a high level and formed inclusion bodies which allowed it to be easily purified by low speed centrifugation, with a yield of approximately 50 mg/liter of culture. After factor Xa cleavage and high performance liquid chromatography purification, highly purified hPTH was obtained, with a final yield of 1.5-3 mg/liter. Physical and biological characterization of the purified hormone demonstrated that it was intact and active hPTH-(1-84).

Preparation and characterization of [N alpha-(4-azido-2-nitrophenyl)Ala1,Tyr36]-parathyroid hormone related peptide (1-36)amide: a high-affinity, partial agonist having high cross-linking efficiency with its receptor on ROS 17/2.8 cells

The synthesis, purification, and structural analysis of the major compounds resulting from photoderivatization of [Tyr36]-parathyroid hormone related peptide (1-36)amide [[Tyr36]PTHrP(1-36)amide] are described. The reaction of the synthetic peptide with 4-fluoro-3-nitrophenyl azide under nonaqueous conditions yields three major products (peaks D-1, D-2, and G), which were purified to homogeneity by reverse-phase high-performance liquid chromatography. Subsequent amino acid analysis showed that the peptides of peaks D-1 and G each lack one lysine residue, while the peptide in peak D-2 lacks one alanine residue, suggesting that these residues are chemically modified by photoderivatization. Sequence analysis of the photoderivatized peptides revealed that compounds D-1 and G were derivatized on Lys13 and Lys11, respectively. Compound D-2 was N-blocked, indicating that this compound is derivatized on the alpha-amino function of Ala1. Both Lys residues of D-2 were quantitatively recovered upon sequencing after digestion with endoproteinase Glu-C. Compounds D-2 and G had apparent KdS of 1 X 10(-9) M and 0.6 X 10(-9) M, respectively, for their receptors on ROS 17/2.8 cells, which are identical with or similar to that of the underivatized [Tyr36]PTHrP(1-36)amide. Compound G had the same adenylate cyclase stimulating potency as the underivatized, synthetic [Tyr36]PTHrP(1-36)amide, whereas compound D-2 was only a partial agonist, having about 25% of the maximal cAMP production. Compound D-1, which is modified on Lys13, retained only 2-4% of its receptor binding affinity and biological activity relative to that of its parent compound.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of fully active biotinylated parathyroid hormone analogs. Application to fluorescence-activated cell sorting of parathyroid hormone receptor bearing cells

[Nle8,18,Tyr34]bPTH-(1-34)amide (NlePTH) was biotinylated using sulfosuccinimidyl 6-(biotinamido)hexanoate, in dimethyl sulfoxide, and the multiple resulting peptides peaks were separated by reverse-phase high performance liquid chromatography. Their biological activities were compared with those of NlePTH, the parent compound, in radioreceptor and cAMP accumulation bioassays using rat osteosarcoma 17/2.8 cells; the earliest two eluting products, bioPTH 1 and 2, were equipotent, a third, bioPTH 3, was only 10% as potent, and the remaining, later eluting derivatives all were less than 0.1% as active. Competitive avidin binding assays using [3H]biotin suggested that bioPTH 1 and 2 had a single biotin congener per molecule, while bioPTH 3 contained two biotin residues. Upon Edman degradation, bioPTH 1 contained biotin on the lysine at position 13 of NlePTH; bioPTH 2's biotin was on the lysine at position 26 (or 27) and bioPTH 3 had biotins on lysines at both positions 13 and 26 (or 27). Avidin tagged with 125I, peroxidase, or fluorescein isothiocyanate was detected on bone-derived cells which had been incubated initially with bioPTH 2 (1, 10, and 100 nM) for 4 h, but not when NlePTH (1 microM) was added with bioPTH 2. A fluorescence-activated cell sorter detected a symmetrical shift in fluorescence of bone-derived cells incubated with 10 nM of bioPTH 2 and 10 micrograms/ml fluorescein isothiocyanate-avidin. Addition of a 30-fold molar excess of NlePTH, or omission of bioPTH 2, completely reversed this fluorescence shift, and no shift in fluorescence was seen with cells lacking PTH receptors. This fully active, high affinity biotinylated PTH-derivative should prove useful in the study of PTH receptor-bearing cells.

Inactivation of pertussis toxin-sensitive guanyl nucleotide-binding proteins increase parathyroid hormone receptors and reverse agonist-induced receptor down-regulation in ROS 17/2.8 cells

We examined mechanisms of down-regulation of PTH receptors and desensitization of the PTH-stimulated increase in intracellular cAMP in clonal rat osteosarcoma cells, ROS 17/2.8. ROS cells treated with 10 nM [Nle8,Nle18,Tyr34] bovine (b) PTH-(1-34) amide (NlePTH) for 3 days showed loss of specific PTH binding and PTH-stimulated cAMP accumulation to 10% of that in vehicle-treated control cells. Treatment of these cells with both 0.5 mM 8-bromo-cAMP (8-Br-cAMP) and 1 mM methylisobutylxanthine or 100 ng/ml cholera toxin for 3 days elicited no change in either of these responses. Treatment with 10 nM NlePTH for 3 days did not modify the cAMP accumulation stimulated by 30 microM forskolin or 1 micrograms/ml cholera toxin, indicating that agonist-specific desensitization of PTH-stimulated cAMP accumulation is not due to diminished activity of either the stimulatory guanyl nucleotide regulatory subunit (Gs) or the catalytic subunit of the adenylate cyclase. Treatment of ROS cells with pertussis toxin (PT; 10 ng/ml) for 12, 24, 48, and 72 h increased specific PTH binding by 21%, 28%, 35%, and 39%. The increase in PTH binding was associated with a parallel increase in PTH-stimulated cAMP accumulation and was due to an increase in the number of PTH receptors. PTH receptor affinity remained constant (apparent Kd = 0.3 nM). PT treatment of the cells partially blocked agonist-specific PTH receptor down-regulation. PT catalyzed ADP ribosylation of 41K and 39K membrane proteins, consistent with the alpha-subunits of Gi and Go, respectively. In conclusion, agonist-induced PTH receptor down-regulation in ROS 17/2.8 cells is cAMP independent and can be reversed by PT treatment. PTH receptor expression in these cells appears to be under tonic inhibitory control by mechanisms involving a PT-sensitive G protein(s).

Non-homologous sequences of parathyroid hormone and the parathyroid hormone related peptide bind to a common receptor on ROS 17/2.8 cells

We and others have recently shown that amino terminal sequences of parathyroid hormone (PTH) and parathyroid hormone related peptide (PTHrP), which share a 62% homology within the first 13 residues, bind to the same receptor on ROS 17/2.8 cells. The remaining PTHrP sequence is markedly different from PTH, suggesting that receptor binding may be dependent on the first 13 amino acids of either peptide. However, since the amino acid residues 14-34 have previously been recognized as an important binding domain for PTH, conformational similarity within this portion's secondary structure of both peptides could contribute to their capacity to bind to the same receptor. To test this hypothesis, we synthesized [Tyr36,Cys38]PTHrP-(14-38) and [Tyr34]bPTH(14-34)NH2, and studied binding of both peptides to the common PTH/PTHrP receptor on ROS 17/2.8 cells. Radioiodinated, HPLC-purified [Nle8,18, Tyr34]bPTH(1-34)NH2 (NlePTH) and [Tyr36]PTHrP-(1-36)NH2 were used to functionally define receptor binding requirements. [Tyr36,Cys38]PTHrP(14-38) and [Tyr34]bPTH(14-34)NH2 competed with 125I-NlePTH for binding sites on ROS 17/2.8 cells with apparent Kds of 10 microM and 50 microM respectively. Both peptides also competed with 125I-[Tyr36]PTHrP(1-36)NH2 with apparent Kds of 30 microM and 10 microM respectively. In the same assay system, NlePTH and [Tyr36,Cys38]PTHrP(1-38)inhibited binding of either radioiodinated ligand with apparent Kds of 0.3 and 1.0 nM. These studies indicate that although [Tyr34]bPTH(14-34)NH2 and [Tyr36,Cys38]PTHrP(14-38) share virtually no sequence homology, their secondary structures must be sufficiently similar to permit binding to a common PTH/PTHrP receptor.

Parathyroid hormone causes translocation of protein kinase-C from cytosol to membranes in rat osteosarcoma cells

PTH binds to specific receptors that are coupled to adenylate cyclase and activate cAMP-dependent protein kinase. Since it has been shown that PTH activates phospholipid inositol metabolism, we investigated whether PTH influences protein kinase-C (PKC) activity in rat osteosarcoma (ROS) cells 17/2.8 that contain a large number of PTH receptor. Incubation of ROS cells with PTH or phorbol 12-myristate 13-acetate (PMA) for 1-30 min caused a rapid and transient decrease in PKC activity in the cytosol, which was associated with a transient increase in PKC activity in the membrane fraction. After 1, 5, 15, and 30 min of incubation with PTH, cytosolic PKC activity decreased to 57%, 74%, 84%, and 93% of the control value, whereas membrane PKC activity increased to 156%, 122%, 111%, and 106% of the control value, respectively. After PMA treatment for 1, 5, 15, and 30 min, cytosolic PKC activity decreased by 81%, 74%, 63%, and 44%, whereas membrane-bound PKC activity increased by 83%, 44%, 28%, and 17%, respectively. The effects of PTH and PMA on PKC were dose dependent, with ED50 values of 0.3 nM PTH and 4 nM PMA. Chronic treatment of ROS cells for 3 days with PMA caused depletion of total PKC activity in cytosolic and membrane fractions to less than 10% of that in control cells. Conversely, chronic treatment of ROS cells with PTH did not deplete PKC. In addition, chronic treatment of ROS cells with PTH inhibited the responsiveness of PKC activity to subsequent acute PTH challenge, but not to acute PMA challenge, suggesting specific desensitization of this response by PTH. Activation of cytosolic PKC by diolein, phosphatidylserine, and calcium caused phosphorylation of many cytosolic proteins, including those having apparent mol wt of 39K, 35K, 33K, 25K, 19K, and 16K. Pretreatment of ROS cells with PTH resulted in a transient decrease in the phosphorylation of these cytosolic proteins by PKC. This decrease in cytosolic protein phosphorylation by treatment with PTH is temporally associated with PTH-stimulated translocation of PKC activity from the cytosol to the membranes. These data suggest a potential role for PKC in the mechanism of action of PTH in ROS cells.

The parathyroid hormone-like peptide associated with humoral hypercalcemia of malignancy and parathyroid hormone bind to the same receptor on the plasma membrane of ROS 17/2.8 cells

[Tyr36]human adenylate cyclase stimulating peptide (1-36)-NH2, an amino-terminal analog of a tumor peptide which is associated with hypercalcemia of malignancy, and [Nle8, Nle18, Tyr34]bovine parathyroid hormone (PTH)-(1-34)-NH2 both bind with similar affinities to receptors on rat osteosarcoma cells, ROS 17/2.8, when either of the peptides is used as the radioligand. Pretreatment of the cells with either peptide down-regulates available binding sites for either radioligand and desensitizes the cAMP accumulation stimulated by either peptide. Prior exposure of the cells to dexamethasone increases these responses to both peptides. Photoderivatized radioiodinated [Tyr36]human adenylate cyclase-stimulating peptide (1-36)-NH2 and [Nle8, Nle18, Tyr34]bovine PTH-(1-34)-NH2 both specifically label a Mr = 80,000 membrane protein on ROS 17/2.8 cells. The intensity of labeling this receptor band by either photoprobe is reduced by co-incubation with either peptide over the same dose range. Equivalent dose-dependent down-regulation of receptors which bind both photoprobes is also found when ROS 17/2.8 cells are preincubated with either peptide. Dexamethasone increases the intensity of receptor labeling. Our findings strongly indicate that both peptides recognize the same plasma membrane receptor on ROS 17/2.8 cells. Although the physiological function(s) of human adenylate cyclase-stimulating peptide is unknown, these results could explain why its biological actions on mineral ion metabolism so closely simulate those of PTH and raise interesting questions about the general biological and evolutionary significance of the use of the same receptor by chemically distinct peptides.

Calcium-dependent control of corticotropin release in rat anterior pituitary cell cultures

The role of calcium in the stimulation of ACTH secretion by CRF and other regulators was studied in rat anterior pituitary cells. Incubation of cultured pituitary cells in normal calcium with CRF, vasopressin, angiotensin II, or norepinephrine increased the rate of ACTH release for up to 45 min and then became constant for up to 3 h. In the absence of extracellular calcium, the initial rate of stimulated secretion was unaffected, but after 45 min the secretion rate decreased by 40% for CRF and to a greater extent for the other stimuli. Addition of calcium after 90 min in calcium-free medium restored the CRF-stimulated ACTH release rate to the control value. The absence of extracellular calcium had no effect on CRF-stimulated cAMP accumulation, but intracellular calcium depletion by preincubation of the cells with EGTA completely inhibited CRF-stimulated cAMP production and ACTH release. The voltage-dependent calcium channel antagonist nitrendipine and the calcium channel agonist BK 8644 had little effect on the CRF-stimulated ACTH release rate, while they, respectively, inhibited and enhanced the stimulation by vasopressin and high potassium. In calcium-depleted cells incubated with the calcium ionophore A23187, CRF stimulation of cAMP production and ACTH release were dependent upon extracellular calcium concentrations from 0.1-100 microM. These findings have defined two phases in the stimulation of ACTH release by CRF and cAMP-independent stimuli in cultured pituitary cells: an early phase with a rapid increase in the ACTH release rate which is independent of extracellular calcium, and a late phase of constant secretion rate, with partial extracellular calcium dependence for the stimulation by CRF and complete calcium dependence for the stimulation by non-cAMP-mediated stimuli.

Phorbol 12-myristate 13-acetate and vasopressin potentiate the effect of corticotropin-releasing factor on cyclic AMP production in rat anterior pituitary cells. Mechanisms of action

The potentiation of corticotropin-releasing factor (CRF)-stimulated cAMP production by vasopressin (VP) in the pituitary cell was investigated by studies on the interaction of CRF, VP, and the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA) on cAMP, adenylate cyclase and phosphodiesterase. Addition of VP or PMA (0.01-100 nM) alone did not alter cellular cAMP content, but markedly increased the effect of 10 nM CRF with ED50 of about 1 nM. Treatment of the cells with 200 ng/ml pertussis toxin for 4 h increased CRF-stimulated cAMP accumulation by 3.2-fold, an effect that was not additive to those of VP and PMA. Incubation of pituitary cells with 2 mM 1-methyl-3-isobutylxanthine increased CRF-stimulated cAMP accumulation and decreased the relative effect of VP and PMA, suggesting that the actions of VP and PMA are partially due to inhibition of phosphodiesterase. This was confirmed by the demonstration of a 30% inhibition of the low-affinity phosphodiesterase activity in cytosol and membranes prepared from cells preincubated with VP or PMA. In intact cells, following [3H]adenine prelabeling of endogenous ATP pools, measurement of adenylate cyclase in the presence of 1-methyl-3-isobutylxanthine showed no effect of VP and PMA alone, but did show a 2-fold potentiation of the effect of CRF. Measurement of adenylate cyclase in pituitary homogenates by conversion of [alpha-32P]ATP to [32P]cAMP showed a paradoxical GTP-dependent inhibition by VP of basal and CRF-stimulated adenylate cyclase activity, suggesting that the VP receptor is coupled to an inhibitory guanyl nucleotide-binding protein. Pertussis toxin pretreatment of the cells prevented the VP inhibition of adenylate cyclase activity observed in pituitary cell homogenates. These findings indicate that besides inhibition of phosphodiesterase, VP has a dual interaction with the pituitary adenylate cyclase system; a direct inhibitory effect, manifested only in broken cells, that is mediated by a receptor-coupled guanyl nucleotide-binding protein, and a physiologically predominant indirect stimulatory effect in the intact cell, mediated by protein kinase C phosphorylation of one of the components of the CRF-activated adenylate cyclase system.

Synthetic atrial natriuretic factors (ANFs) stimulate guanine 3',5'-monophosphate production but not hormone release in rat pituitary cells: peptide contamination with a gonadotropin-releasing hormone agonist explains luteinizing hormone-releasing activity of certain ANFs

The effects of atrial natriuretic factors (ANFs) on anterior pituitary hormone secretion and cyclic nucleotide production were investigated in cultured rat pituitary cells. ANF had no effect on ACTH, GH, PRL, and TSH release or on cAMP production either on basal hormone levels or during stimulation of their secretion by the appropriate releasing factor. However, ANF markedly stimulated cGMP production in both mixed anterior pituitary cells and enriched anterior pituitary cell populations fractionated by centrifugal elutriation. Unexpectedly, certain ANF preparations, Bachem rat ANF-(5-28) and rat ANF-(5-25), markedly stimulated LH release from cultured anterior pituitary cells and gonadotroph-enriched elutriated pituitary cells. The same ANFs also displaced [125I-D-Lys6]GnRH ethylamide from binding to anterior pituitary membranes with potencies similar to their LH-releasing activities. Immunoprecipitation of ANF with a specific antiserum abolished the effect of ANF on cGMP production, but did not change the effect of ANF on LH release. In conclusion, ANF did not affect anterior pituitary hormone secretion or cAMP production, but stimulated cGMP formation. The effect of certain ANF preparations on LH release appears to be attributable to peptide contamination with a potent GnRH agonist.

Role of arachidonic acid in the regulation of adrenocorticotropin release from rat anterior pituitary cell cultures

In addition to cAMP-dependent mechanisms, stimulation of pituitary ACTH secretion by various stimuli, including CRF, may involve phospholipid and arachidonic acid turnover. To determine the role of phospholipase A2 activation in corticotroph function, we studied the effect of exogenous arachidonic acid, phospholipase A2, and the phospholipase A2 activator melittin on ACTH release in cultured rat anterior pituitary cells. Incubation with 1-100 micron arachidonic acid, 0.01-1 micron melittin, 0.1-10 U/ml phospholipase A2, and 0.01-10 nM CRF caused dose-dependent increases in ACTH release to 8.1 +/- 1.1- (+/- SE), 16.2 +/- 0.9-, 13.6 +/- 1.2-, and 2.9 +/- 0.3-fold; respectively. The participation of the major pathways of arachidonic acid metabolism in the control of ACTH release was analyzed in cells treated with nordihydroguaiaretic acid, a lipoxygenase inhibitor; indomethacin, a cycloxygenase inhibitor; and 5,8,11,14-eicosatetraynoic acid, an inhibitor of both pathways. The effects of arachidonic acid, melittin, and CRF were partially blocked by 10 micron nordihydroguaiaretic acid and 5,8,11,14-eicosatetraynoic acid, but were significantly enhanced by 10 micron indomethacin. These results suggest that arachidonic acid is mainly metabolized through the lipoxygenase pathway to a stimulatory metabolite and, to a lesser extent, through the cycloxygenase pathway to an inhibitory metabolite. Arachidonic acid release from anterior pituitary cells labeled with [3H]arachidonic was analyzed during cell column perifusion and stimulation by CRF and other secretagogues. Two-minute pulses of CRF (10 nM), vasopressin (10 nM) and phorbol 12-myristate 13-acetate (100 nM) caused immediate 1.5- to 2-fold increases in [3H]arachidonic acid release, and melittin (100 nM) caused a 5-fold increase in [3H]arachidonic acid release. The ability of both exogenously added and endogenously generated arachidonic acid to stimulate ACTH secretion, together with the stimulation of arachidonic acid release by ACTH secretagogues and the attenuation of stimulated ACTH release by lipoxygenase blockers, indicate that lipoxygenase products of arachidonic acid metabolism participate in the control of ACTH secretion.

Biphasic inhibition of adrenocorticotropin release by corticosterone in cultured anterior pituitary cells

The inhibition of ACTH secretion by glucocorticoids in vivo is biphasic, with rapid early suppression followed by transient recovery and a late inhibitory phase. To evaluate whether this biphasic effect of glucocorticoids occurs at the pituitary level, the effects of corticosterone (B) on stimulated ACTH release were analyzed in rat anterior pituitary cell cultures. Preincubation with 1 microM B inhibited the ACTH response to 10 nM CRF in a biphasic manner, with rapid inhibition after 10-40 min of preincubation, followed by partial recovery between 40-80 min, and a later phase of inhibition after 80-140 min. Preincubation with B for 40 or 120 min caused a dose-dependent suppression of CRF-stimulated ACTH release, with ED50 values of 416 +/- 21 and 45 +/- 12 nM B, respectively. Pretreatment with B also caused a biphasic inhibitory effect on the stimulatory action of vasopressin, angiotensin II, and norepinephrine on ACTH release. However, addition of these stimuli in combination with CRF surmounted B inhibition of CRF-stimulated ACTH release. B also inhibited the ACTH-releasing effects of postreceptor stimuli, including 8-bromo-cAMP, phorbol 12-myristate 13-acetate, and 1,2-dioctanoylglycerol. In the presence of cycloheximide (10 microM), the early inhibitory effect of B was unchanged, but the delayed effect was decreased. Whereas preincubation with B for 40 min inhibited ACTH release, but not total intracellular plus released ACTH, preincubation for 120 min decreased both released and total ACTH. These findings demonstrate that the two inhibitory effects of B on ACTH release differ in their kinetics, steroid sensitivity, and dependence on protein synthesis. The inhibitory effect of B on ACTH responses to stimuli with different mechanisms of action suggests that the suppressive effects of B are mainly exerted at a site distal to the formation of the second messengers involved in hormonal activation of ACTH release.

beta-Endorphin in genetically hypoprolactinemic rat: IPL nude rat

Beta-endorphin has been reported to regulate not only stress- and suckling-induced but also basal prolactin secretion. In the aim to better evaluate the endogenous beta-endorphin-prolactin interrelation, we measured beta-endorphin levels in a new rat strain, genetically hypoprolactinemic and characterized by a total lack of lactation: IPL nude rat. Beta-endorphin was measured using a specific anti-h-beta endorphin in plasma and extracts of anterior and neurointermediate lobes of the pituitary, hypothalamus and brain. Pituitary extracts were also chromatographed on Sephadex G50 column. Results obtained showed that in IPL nude females on diestrus and males, the beta-endorphin contents of the neurointermediate lobe was significantly lower than in normal rats, while the values found in the other organs and plasma were similar. However, elution pattern of the anterior pituitary extract from male rats showed greater immunoactivity eluting as I125 h-beta-endorphin than in normal rat; this was not the case for the female rat. These results are consistent with a differential regulation of beta-endorphin levels of anterior and neurointermediate lobe by catecholamines. Moreover they suggest that PRL secretion was more related to neurointermediate beta-endorphin.

Involvement of protein kinase C in the regulation of adrenocorticotropin release from rat anterior pituitary cells

The involvement of protein kinase C in normal corticotroph function was studied by analysis of the effects of the phorbol ester derivative phorbol 12-myristate-13-acetate (PMA) and the synthetic diacylglycerol dioctanoylglycerol (DOG) on basal and stimulated ACTH release in cultured rat anterior pituitary cells. Incubation of rat pituitary cells with increasing concentrations of PMA or DOG caused dose-related increases in ACTH release up to 13.4 +/- 2.1- and 10.1 +/- 0.9-fold, respectively, similar to that caused by CRF (9.8 +/- 1.6-fold). Also, stimulation of endogenous diglyceride formation by phospholipase C (100 mU/ml) stimulated ACTH release by 2.5 +/- 0.1-fold. In cells incubated with maximum stimulatory concentrations of CRF (10 nM) or 8-bromo-cAMP (8-Br-cAMP; 5 mM), addition of either 100 microM DOG or 100 nM PMA caused significantly higher ACTH responses than those obtained with CRF, 8-Br-cAMP, DOG, or PMA alone. 8-Br-cAMP (5 mM) and 10 nM CRF significantly increased the effect of 100 nM PMA by 1.4 +/- 0.2- and 1.5 +/- 0.1-fold, respectively. Combinations of 10 nM CRF with either vasopressin (VP) or angiotensin II (AII) increased ACTH secretion to values higher than those produced by CRF, VP, or AII alone. However, addition of maximal stimulatory concentrations of VP or AII (10 nM) did not further increase the effects of either PMA alone or PMA/CRF combinations, indicating that their mechanisms of action may be similar to that of PMA. These results indicate that in addition to the established cAMP-dependent mechanism, stimulation of ACTH release in normal pituitary cells may be elicited by activation of protein kinase C. The evidence also suggests that protein kinase C is involved during stimulation of ACTH release by the cAMP-independent regulators VP and AII and in the synergistic effects of VP and AII with CRF on the corticotroph.

The value of beta-lipotrophin measurement during the short metyrapone test in patients with pituitary diseases and in Cushing's syndrome

Serum 11-deoxycortisol (S) determination has been used to evaluate the pituitary adrenal response to the short metyrapone (MTP) test. The validity of this indirect evaluation of corticotrophin ACTH reserve has been questioned since the MTP-induced S elevation may reflect a passive accumulation rather than an ACTH activated adrenal response. The purpose of this study was to evaluate the usefulness of serum beta-lipotrophin (beta-LPH) measurement during the short midnight MTP test (30 mg/kg body weight) in patients with pituitary diseases (n = 36) and in patients with Cushing's syndrome (n = 8). In 28/36 patients with pituitary diseases both S and beta-LPH concentrations were increased normally by MTP. In 8/36 patients the beta-LPH response was lacking, while their serum S concentrations increased significantly. The absence of beta-LPH response to MTP in these 8 patients was in good agreement with the diagnosis of ACTH insufficiency because in 7 of them the cortisol response to insulin induced hypoglycaemia was also insufficient. In the 8 patients with Cushing's syndrome serum S concentration increased following MTP administration in all the cases. In 2 with adrenal adenoma the increase of S level was an ACTH-independent phenomenon, since beta-LPH level was undetectable both before and after MTP administration. In 2 patients with ectopic ACTH secretion, the basal beta-LPH concentrations were high and remained unmodified by MTP administration. In the 4 patients with Cushing's disease, MTP administration resulted in a dramatic increase of beta-LPH concentration. We conclude that beta-LPH measurement improves the utility of the short MTP test for investigation of pituitary adrenal function.

Increased plasma concentration of N-terminal beta-lipotrophin and unbound cortisol during pregnancy

The plasma concentration of N-terminal beta-lipotrophin (beta-LPH), total and protein unbound cortisol, progesterone and the transcortin (CBG) binding parameters have been measured in 21 women in the early follicular phase and in 70 pregnant women at various stages of pregnancy. Results showed that the plasma CBG binding capacity and the concentrations of total cortisol and progesterone increased significantly at each trimester of pregnancy while the plasma concentration of unbound cortisol increased significantly only in the 2nd and the 3rd trimesters of pregnancy. In addition, a significant increase of N-terminal beta-LPH level was observed during the 3rd trimester. By chromatography, it is demonstrated that during the 3rd trimester of pregnancy the beta-LPH/gamma-LPH molar ratio decreases dramatically and that the increase of N-terminal beta-LPH concentration is mainly due to a two fold increase in gamma-LPH concentration.

Twenty-four hour melatonin secretory pattern in men with idiopathic hemochromatosis

In idiopathic hemochromatosis, iron deposits in endocrine tissue can be associated with hormonal disorders including hypogonadism. We have studied the functional status of the pineal gland in this disease in relation to gonadotrophin levels and cortisol rhythm. Plasma melatonin, luteinizing hormone (LH) and cortisol concentrations were measured by radioimmunoassay every 20 min over a 24 hr period in nine men with idiopathic hemochromatosis aged 36 to 66 years. In six patients a circadian melatonin rhythm was present. The 24 hr means were in the normal range in three patients, and varied below the control values in two patients and above the control values in one patient. These variations seemed unrelated to gonadotrophin status. In the three other patients no plasma melatonin rhythm was observed; two patients with gonadotrophin insufficiency had low melatonin levels, and one with normal gonadotrophin function had high melatonin concentrations. In all cases, the plasma cortisol rhythm was normal. We concluded that the circadian melatonin rhythmicity can be disturbed in some cases of idiopathic hemochromatosis without relationship to the cortisol rhythm and associated endocrine disorders.