Substrate-dependent effect of 1-34 human parathyroid hormone fragment, dibutyryl cAMP and cAMP on gluconeogenesis in rabbit renal tubules

In the presence of 0.5 mM extracellular Ca2+ concentration both 1-34 human parathyroid hormone fragment (0.5 micrograms/ml) as well as 0.1 mM dibutyryl cAMP stimulated gluconeogenesis from lactate in renal tubules isolated from fed rabbits. However, these two compounds did not affect glucose synthesis from pyruvate as substrate. When 2.5 mM Ca2+ was present the stimulatory effect of the hormone fragment on gluconeogenesis from lactate was not detected but dibutyryl cAMP increased markedly the rate of glucose formation from lactate, dihydroxyacetone and glutamate, and inhibited this process from pyruvate and malate. Moreover, dibutyryl cAMP was ineffective in the presence of either 2-oxoglutarate or fructose as substrate. Similar changes in glucose formation were caused by 0.1 mM cAMP. As concluded from the 'crossover' plot the stimulatory effect of dibutyryl cAMP on glucose formation from lactate may result from an acceleration of pyruvate carboxylation due to an increase of intramitochondrial acetyl-CoA, while an inhibition by this compound of gluconeogenesis from pyruvate is likely due to an elevation of mitochondrial NADH/NAD+ ratio, resulting in a decrease of generation of oxaloacetate, the substrate of phosphoenolpyruvate carboxykinase. Dibutyryl cAMP decreased the conversion of fracture 1,6-bisphosphate to fructose 6-phosphate in the presence of both substrates which may be secondary to an inhibition of fructose 1,6-bisphosphatase.     

Two-dimensional 1H-NMR study of the 1-34 fragment of human parathyroid hormone

The complete assignment of resonances in the proton nmr spectrum of the 1-34 amino acid fragment of human parathyroid hormone [hPTH(1-34)], determined using a combination of one- and two-dimensional nmr techniques at 500 MHz, is described. In particular, homonuclear Hartmann-Hahn experiments, recorded in H2O and D2O, are used to resolve ambiguities in the connectivities between the highly overlapped resonances in the aliphatic region of the spectrum. One-dimensional multiple quantum filtering experiments are used to identify serine and phenylalanine spin systems. Analyses of the through-bond and through-space connectivities in the alpha H-NH fingerprint regions of the correlated spectroscopy (COSY) and nuclear Overhauser effect spectroscopy (NOESY) spectra lead to the assignment of resonances to specific amino acid residues in the polypeptide. Examination of the observed NOE cross peaks indicates that hPTH(1-34) has no detectable secondary structural elements in aqueous solution.     

Demonstration that cyclic adenosine 3',5'-monophosphate mediates the lipolytic action of parathyroid hormone.

Studies were carried out with rat epididymal fat pads first to compare the effects of the synthetic N-terminal 1-34 peptide of bovine parathyroid hormone and of the native hormone to determine whether this portion of the molecule is responsible for the lipolytic action of the hormone and second to determine whether this biologic action of parathyroid hormone is mediated by cyclic adenosine 3',5'-monophosphate. The N-terminal polypeptide was as effective as the native hormone in stimulating lipolysis in the concentration range between 10(-8) M and 10(-6) M. Parathyroid hormone stimulated lipolysis by isolated fat cells. The concentration of cyclic adenosine 3',5'-monophosphate in the fat pads was significantly increased by the hormone (10(-6)M). Lipolytic stimulation by parathyroid hormone (10(-6)M) was diminished by insulin (100 muU/ml) and prostaglandin E1 (1 mug/ml), both of which are known inhibitors of lipolysis. The findings indicate that the amino-terminal 1-34 peptide portion of parathyroid hormone is responsible for the lipolytic action and that this effect is mediated through cyclic adenosine 3',5'-monophosphate.     

Effect of treadmill exercise on plasma and urinary cyclic adenosine 3'5'-monophosphate.

The effect of treadmill exercise on plasma and urinary cyclic adenosine 3'5' monophosphate levels (cyclic AMP) was studied in twelve healthy subjects. Plasma cyclic AMP levels were found to be markedly elevated without significant changes in urinary cyclic AMP or cyclic AMP/creatine ratio. Most likely altered plasma glucagon and catecholamine levels were responsible for these changes.     

Gonadotropins and cyclic adenosine 3',5'-monophosphate (cAMP) alter the morphology of cultured human granulosa cells

Morphological changes in human granulosa cells in culture were observed by phase, fluorescent, scanning electron and transmission electron microscopy following the addition of human chorionic gonadotropin (hCG), luteinizing hormone (LH), 8-bromocyclic adenosine 3',5'-monophosphate (cAMP) and cytochalasins B and D. In response to these agents, polygon-shaped granulosa cells with granular cytoplasm became rounded, leaving fingerlike processes attached to the substratum and adjacent cells. The changes in cell shape were accompanied by a centripetal movement of mitochondria and lysosomes to a perinuclear location. The morphological alterations appeared to be mediated by cyclic AMP and to be the result of a dismantling and reorganization of microfilament-containing stress fibers. Follicle-stimulating hormone (FSH), prolactin (PRL), growth hormone (GH), and human placental lactogen (hPL) did not provoke cell shape changes. We conclude that tropic hormones capable of stimulating progestin secretion by luteinized granulosa cells cause a change in cell structure in vitro which leads to a redistribution of organelles involved in steroid synthesis. The possible relationship of the cytoskeleton to steroidogenesis is considered.     

Changes in adenosine 3',5'-monophosphate induced by parathyroid hormone and theophylline in the developing rat renal cortex

To test the biochemical responsiveness of developing rat renal cortex to parathyroid hormone (PTH), intracellular concentrations of adenosine 3′,5′-monophosphate (cyclic AMP) were measured. Renal cortical slices from 10-day-, 20-day-, and 12-week-old animals contained higher concentrations of cyclic AMP when incubated in the presence of theophylline than in its absence. In the absence of theophylline, tissue from all three age groups responded to PTH with dose-dependent increases in cyclic AMP. In the presence of theophylline the response of tissue from 10-day-old animals was greater than that of 12-week-old animals.It is suggested that the differential effect of theophylline with respect to age may be the result of higher turnover rates of cyclic AMP in the young animals.     

Effect of adenosine 3':5'-monophosphate and guanosine 3':5'-monophosphate on RNA release from isolated nuclei.

The addition of physiological concentrations of either cAMP or cGMP stimulated the release of RNA from isolated prelabeled rat liver nuclei to a fortified cytosol in a cell-free system. The released RNA was shown to be primarily mRNA by its binding to oligo(dT)-cellulose and its sedimentation profile. Treatment of rats with cAMP or cGMP 30 min prior to the preparation of cyclic nucleotides on the cell-free system. Cyclic nucleotides stimulation of RNA release occurred in systems prepared from resting rat liver, Novikoff hepatoma, and Morris hepatoma 5123D, but not the 18-h regenerating liver. The response of the cell-free system to added cyclic nucleotides reflected the in vivo concentration of these substances in the tissues from which the system was prepared. Those with high in vivo levels were not stimulated while those with lower levels did respond to added cyclic nucleotides. Neither cAMP nor cGMP had an appreciable effect on rRNA release.     

Two novel stimuli of cyclic adenosine 3',5'-monophosphate (cAMP) in human lymphocytes.

Polystyrene latex particles (PLP) and zymosan particles (ZP), two commonly employed phagocytic stimuli, were noted to bind to purified human peripheral blood lymphocytes. This interaction was not accompained by ingestion but did lead to a marked increase in intracellular cyclic AMP. The cAMP response to PLP was proportional to the particle cell ratio which, in turn, correlated with the number of membrane-associated particles. After the addition of PLP to lymphocytes, the cAMP response occurred within 2 min, peaked between 4 and 15 min, and returned to baseline by 30 to 60 min. The cAMP response to ZP was similar in onset and duration to that seen with PLP but was less marked (2- to 4-fold vs 25- to 50-fold) and more variable in magnitude. This is probably a reflection of the smaller number of cells interacting with ZP. At high PLP to cell ratios almost all of the lymphocytes bound PLP but only 10 to 28% of the mixed lymphocyte population bound ZP. Two lines of evidence established conclusively that the cAMP response was taking place in the lymphocytes themselves rather than in contaminating cells. 1) When lymphocytes were purified additionally by filtration through a nylon wool column (99 to 100% lymphocytes), they were found to undergo a similar cAMP response to PLP. Since the nylon filtration procedure also removes almost all of the B cells, this further indicates that T cells are capable of undergoing the response. 2) Immunofluorescence studies with anti-cAMP antibody revealed an increase in intralymphocytic cAMP which was primarily adjacent to the site of PLP or ZP attachment. The likely explanation of this data is that PLP and ZP perturb the lymphocyte surface leading to regional activation of membrane-bound adenylate cyclase and subsequent cAMP accumulation. Although the physiologic significance of these observations remains to be determined, the results: 1) provide histologic confirmation for the concept of cAMP compartmentablization, 2) clarify conflicting results regarding the localization of cAMP accumulation during the phagocytosis of PLP by mixed leukocyte populations, and 3) suggest that this experimental system may allow an analysis of the mechanism by which perturbations of the lymphocyte surface modulate cAMP.     

Prostaglandin stimulation of adenosine 3',5'-monophosphate accumulation in cultured chondrocytes in the presence or absence of parathyroid hormone

The effect of prostaglandin analogues on the cyclic AMP level in cultured chondrocytes were examined. Prostaglandin E1 at 0.4 to 30 microM, increased the intracellular concentration of cyclic AMP in chondrocytes. Its effect was rapid, being evident within 1 min and reaching a maximum in 10 to 20 min. The maximum level was sustained until 30 min after its addition and then decreased gradually. Prostaglandin D2 and E2 also increased the cyclic AMP level in chondrocytes, but they had less effect than prostaglandin E1. Prostaglandin A1 had no effect on the nucleotide level in chondrocytes, although they markedly increased the level in fibroblasts. The time course of stimulation of cyclic AMP accumulation in chondrocytes by prostaglandin E1, D2 or E2 was quite different from that by parathyroid hormone (PTH): the effect of prostaglandin was slower and more sustained than that of PTH. PTH potentiated the effect of prostaglandin E1, E2, or D2 on the cyclic AMP level in chondrocytes and that the combined effects of prostaglandin and PTH were more than additive. Addition of an inhibitor of cyclic nucleotide phosphodiesterase with prostaglandin, PTH or both produced a synergistic effect on the accumulation of cyclic AMP in the chondrocytes. These findings suggest that prostaglandin E1, E2, and D2 increase the synthesis of cyclic AMP and that the combined effect of the prostaglandins and PTH on the cyclic AMP level in chondrocytes is partly attributed to the synergistic synthesis of cyclic AMP in the cells.     

Anabolic effects of recombinant human parathyroid hormone (1 - 84) and synthetic human parathyroid hormone (1 - 34) on the mandibles of osteopenic ovariectomized rats with maxillary molar extraction.

In rodent osteoporosis models such as ovariectomized (OVX) rats, intermittently administered human parathyroid hormone (hPTH) has an anabolic effect in vertebrae and long bones. In the present experiments, subcutaneously injected hPTH(1 - 34) or hPTH(1 - 84) dose- and time-dependently increased bone mineral density (BMD) as measured by dual energy X-ray absorptiometry in mandibles, L2 to L4 vertebrae and femurs of such rats. The highest dose (15.9 nmol/kg, s. c.) of either peptide given four times weekly for 10 weeks completely reversed the effects of overiectomy on BMD. Significant elevation in lumbar BMD after 10 weeks was observed with hPTH(1 - 34) or hPTH(1 - 84) at 1.1 nmol/kg, whereas hPTH(1 - 34) at 1.1 and 4.2 nmol/kg significantly increased BMD of the whole bone and the metaphysis of the femur and the diaphysis of the bone, respectively. In contrast, significant effects of hPTH(1 - 84) administration on BMD increase in the femur were observed at 4.2 and 15.9 nmol/kg in the whole bone and the metaphysis, and in the diaphysis, respectively. Maxillary molar extraction left mandibular BMD in rats with intact ovaries unchanged, but significantly decreased mandibular BMD in OVX rats. Administration of hPTH(1 - 84) for 10 weeks in OVX rats without or with extraction significantly increased BMD in the mandibular molar region at doses of 15.9 and 4.2 nmol/kg, respectively, indicating that efficacy was increased by extraction. A significant BMD increase in the molar region in OVX rats with extraction occurred at only 1.1 nmol/kg of hPTH(1 - 34) and 4.2 nmol/kg of hPTH(1 - 84). Also, BMD of the ramus region was increased by administration of both peptides to a lesser extent than that of the molar region in these rats. Thus, intermittent administration of hPTH, especially hPTH(1 - 34), has an anabolic effect on bone, particularly alveolar bone. Such treatment may increase alveolar bone mass in postmenopausal women with osteoporosis.