Effects of prostaglandins Fα on dog thyroid cyclic AMP level and function

Prostaglandins F_1α and F_2α, at high concentrations (≥28 μM) enhanced cyclic AMP accumulation in dog thyroid slices. At lower concentrations, they inhibited the cyclic AMP accumulation induced by thyrotropin (TSH), prostaglandin E₁, and cholera toxin. This effect was rapid in onset and of short duration, calcium-dependent and suppressed by methylxanthines. Prostaglandin F_α also inhibited TSH-induced secretion and activated iodine binding to proteins. These characteristics are similar to those of carbamylcholine action, except that prostaglandins F did not enhance cyclic GMP accumulation. The effect of prostaglandin F_α was not inhibited by atropine, phentolamine and adenosine deaminase and can therefore not be ascribed to an induced secretion of acetylcholine, norepinephrine or adenosine. It is suggested that prostaglandins F act by increasing influx of extracellular Ca²⁺. Arachidonic acid also inhibited the TSH-induced cyclic AMP accumulation. However this effect was specific for TSH, it was enhanced in the absence of calcium and was not inhibited by methylxanthines or by indomethacin at concentrations which completely block its conversion to prostaglandin F_α. Arachidonic acid action is sustained. This suggests that arachidonic acid inhibits thyroid adenylate cyclase at the level of its TSH receptor and that this effect is not mediated by prostaglandin F_α or any other cyclooxygenase product.     

Effects of prostaglandins and other drugs on the cyclic AMP content of cultured bone cells

Prostaglandins of the E-series (PGE₁ and PGE₂) may be involved in disease-related, localized loss of bone. E-prostaglandins increase the cyclic AMP content of many cells; and, to determine if their effects on bone are mediated by cyclic AMP, we examined the effects of E-prostaglandins and of other agents on the cyclic AMP content of cultured bone cells. PGE₂ produced a rapid, marked and dose-related increase in the cyclic AMP content of confluent monolayers of bone cells isolated from newborn rat calvaria. At 2.8 × 10⁻⁶ M, PGE₁ and PGE₂ had approximately the same effect, while the effect of PGF_2α was much less pronounced. In the presence of theophylline, PGE₂ had a more marked effect than parathyroid hormone (PTH) and the combination of PGE₂ and PTH had a synergistic effect. The divalent, cationic, ionophore, A23187, produced an increase in cellular cyclic AMP and had an additive effect in combination with PGE₂. Synthetic salmon calcitonin (CT), which inhibits the bone resorptive effect of PGE₂, increased cellular cyclic AMP and had an additive effect in combination with PGE₂. A prostaglandin antagonist, SC-19220, partially inhibited the resorptive effect of PGE₂ and reduced its effect on cellular cyclic AMP. The calcium antagonist, D600, inhibited the bone resorptive effects of PGE₂ but had no effect on increased cellular cyclic AMP produced by PGE₂.The marked effect of PGE₂ on bone cell cyclic AMP suggests that this action is involved in the mechanism of PGE₂-related bone loss. The fact that agents with different effects on PGE₂-induced increases in cellular cyclic AMP can inhibit its resorptive actions, suggests that PGE₂-induced changes in cyclic AMP may be related less to its resorptive actions than to its inhibitory effect on bone formation.     

Effects of prostaglandins on cyclic AMP levels in isolated cells from developing chick limbs

Effects of prostaglandins (PGs) on accumulation of cyclic AMP (cAMP) in the presence of a phosphodiesterase inhibitor were investigated in cells isolated from avian limb buds at various stages of development. Cells were responsive to PGE2 at the earliest stage investigated (stage 20-21) which was well in advance of specific cytodifferentiation of limb tissues. At three later stages (24-25; 26-28; 30-32), the responsiveness of cells isolated from the developing skeletal anlagen of the limb progressively increased coincident with the differentiation and maturation of the cartilage phenotype. Cells isolated from stage 26-28 cartilage rods were responsive also to prostacyclin (PGI2); however, the response produced was only about 50% of the response to an equivalent concentration of PGE2. Cells were not responsive to either PGF2 alpha or 6-keto PGF1 alpha, at concentrations of 30-33 micrograms/ml demonstrating a degree of specificity for PGE2 and PGI2. In the absence of the phosphodiesterase inhibitor, PGE2 increased cAMP accumulation two-fold over the controls and produced a concentration-dependent response between 0.3-30 micrograms/ml. The results demonstrate that PGs are capable of modulating cAMP levels of undifferentiated limb mesenchymal cells as well as embryonic cartilage cells and suggest a role for these compounds in limb chondrogenesis.     

Effects of concanavalin A and neuraminidase on cyclic AMP levels and 14C-1-glucose oxidation in dog thyroid slices.

Treatment with concanavalin A at 100 micron/ml or higher concentrations significantly increased 14C-1-glucose oxidation in dog thyroid slices as reported in other tissues. This treatment exerted no effect on tissue cyclic AMP levels. Neuraminidase at the same concentrations also had similar effects on these parameters. Neither concanavalin A nor neuraminidase at the concentrations up to 100 microng/ml had the TSH effect on both tissue cyclic AMP and 14C-1-glucose oxidation. These results indicate that modification of carbohydrate moieties of glycoproteins on the cell surface may cause an increase in glucose metabolism without any critical effect on cyclic AMP system and in the process of TSH response.     

Effects of prostaglandins and other drugs on the cyclic AMP content of cultured bone cells.

Prostaglandins of the E-series (PGE1 and PGE2) may be involved in disease-related, localized loss of bone. E-prostaglandins increase the cyclic AMP content of many cells; and, to determine if their effects on bone are mediated by cyclic AMP, we examined the effects of E-prostaglandins and of other agents on the cyclic AMP content of cultured bone cells. PGE2 produced a rapid, marked and dose-related increase in the cyclic AMP content of confluent monolayers of bone cells isolated from newborn rat calvaria. At 2.8 X 10(-6) M, PGE1 and PGE2 had approximately the same effect, while the effect of PGF2alpha was much less pronounced. In the presence of theophylline, PGE2 had a more marked effect than parathyroid hormone (PTH) and the combination of PGE2 and PTH had a synergistic effect. The divalent, cationic, ionophore, A23187, produced an increase in cellular cyclic AMP and had an additive effect in combination with PGE2. Synthetic salmon calcitonin (CT), which inhibits the bone resorptive effect of PGE2, increased cellular cyclic AMP and had an additive effect in combination with PGE2. A prostaglandin antagonist, SC-19220, partially inhibited the resorptive effect of PGE2 and reduced its effect on cellular cyclic AMP. The calcium antagonist, D600, inhibited the bone resorptive effects of PGE2 but had no effect on increased cellular cyclic AMP produced by PGE2. The marked effect of PGE2 on bone cell cyclic AMP suggests that this action is involved in the mechanism of PGE2-related bone loss. The fact that agents with different effects on PGE2-induced increases in cellular cyclic AMP can inhibit its resorptive actions, suggests that PGE2-induced changes in cyclic AMP may be related less to its resorptive actions than to its inhibitory effect on bone formation.     

Interactions between parathyroid hormone and prostaglandins on renal cortical cyclic AMP

Effects of parathyroid hormone (PTH) and several prostaglandins (PGs) on cyclic AMP (cAMP) metabolism were studied and compared in isolated renal cortical tubules from male hamsters. Both production and intracellular degradation of cAMP were increased by PTH and each of the PGs tested (PGE2, PGE1, PGI2). Production of cAMP was increased to similar levels by maximal concentrations of PTH and each PG, however, degradation of cAMP was significantly higher in response to PTH than with any of the PGs. This difference in intracellular degradation of cAMP was responsible for the much higher concentrations of cAMP in renal cortical tubules exposed to PGs (PGE1, PGE2, PGI2) than to PTH. Submaximal amounts of each PG produced additive increases in cAMP concentrations in the presence of maximal amounts of PTH. Additivity of the combined responses was lost, however, as the PGs concentrations reached their maxima. The results suggest that renal PGs (PGE2 and PGI2) may modulate the effects of PTH on cAMP concentrations in renal cortical tubules.     

Interactions between parathyroid hormone and prostaglandins on renal cortical cyclic AMP

Effects of parathyroid hormone (PTH) and several prostaglandins (PGs) on cyclic AMP (cAMP) metabolism were studied and compared in isolated renal cortical tubules from male hamsters. Both production and intracellular degradation of cAMP were increased by PTH and each of the PGs tested (PGE₂, PGE₁, PGI₂). Production of cAMP was increased to similar levels by maximal concentrations of PTH and each PG, however, degradation of cAMP was significantly higher in response to PTH than with any of the PGs. This difference in intracellular degradation of cAMP was responsible for the much higher concentrations of cAMP in renal cortical tubules exposed to PGs (PGE₁, PGE₂, PGI₂) than to PTH. Submaximal amounts of each PG produced additive increases in cAMP concentrations in the presence of maximal amounts of PTH. Additivity of the combined responses was lost, however, as the PGs concentrations reached their maximas. The results suggest that renal PGs (PGE₂ and PGI₂) may modulate the effects of PTH on cAMP concentrations in renal cortical tubules.     

Effects of substance P on thyroidal cyclic AMP levels and thyroid hormone release from canine thyroid slices

A neuropeptide, substance P (1-50 microM) caused a prompt but transient rise in tissue cyclic AMP levels and also increased the release of thyroid hormones from canine thyroid slices. While norepinephrine markedly inhibited the stimulation by TSH of such parameters as reported previously, substance P had no effect. These results suggest that substance P may play a regulatory role in thyroid gland functions in a manner different from norepinephrine.     

Effects of arachidonic acid and prostaglandins on lung function in the intact dog

The effects of the prostaglandin (PG) precursor, arachidonic acid (AA), and the primary PG's, PGF2alpha, and PGD2, on lung function were compared in 39 intact-chest, paralyzed, artificially ventilated dogs. Intravenous AA decreased dynamic compliance (Cdyn) and functional residual capacity and increased airway resistance (Rl) and transpulmonary pressure at end-passive expiration. The decrease in Cdyn correlated closely with a rise in pulmonary arterial pressure (Ppa). Indomethacin abolished airway and vascular responses to AA, but did not attenuate responses to the PG's. The effects of AA, PGD2, and PGF2alpha on lung function and Ppa were similar, whereas PGE2 had little effect. Vagotomy attentuated the RL increase in response to AA, PGE2alpha, and PGD2 and the Cdyn decrease in response to the PG's. The effects of the PG's on compliance were greater than those produced by mechanically increasing pulmonary venous pressure. The present studies suggest that the PG precursor is rapidly converted to agents that have marked effect on both pulmonary vessels and airways, particularly peripheral airways, in the dog.     

Metabolism of cyclic AMP in isolated renal tubules: Effects of prostaglandins and parathyroid hormone

Concentrations of cyclic AMP (cAMP) were increased in isolated renal cortical tubules from hamsters by both parathyroid hormone (PTH) and prostaglandin E₁ (PGE₁) with maximal effects of PGE₁ being 6–8 fold greater than those of PTH during a 10 min period. However, cAMP concentrations in cells treated with 1-methyl-3-isobutylxanthine (MIX) were increased with maximal concentrations of either hormone to the same degree. Similar effects of both hormones were observed on adenylate cyclase activity in renal homogenates. Simultaneous addition of hormones produced changes in both cAMP concentrations in intact tubules as well as adenylate cyclase activity of homogenates which were not completely additive. Degradation of cAMP, estimated in intact tubules as the difference in cAMP levels in the presence and absence of MIX, was increased by both hormones, however, changes were 2–3 fold greater in tubules exposed to PTH than to PGE₁. Neither hormone directly altered cAMP phosphodiesterase (PDE) activity in either 30,000 x g supernatant or pellets from renal cortical homogenates.The results suggest that both hormones increase the production of cAMP in renal cortical tubules and may share a common target cell type in this response. Degradation of cAMP, however, is differentially effected by the two hormones, probably reflecting differences exerted on intracellular mechanisms regulating the enzymatic hydrolysis of cAMP.     

Cell membrane mechanism of action of prostaglandins E1 and F2 alpha on thrombocyte function

PGE1 and PGF2 alpha were shown to exert an opposite action on Na, K-ATPase activity and protein fluorescence of the platelet membranes. The effect of the prostaglandins appeared to be unidirectional as regards the erythrocytic membranes. The prostaglandins were demonstrated to increase viscosity of the lipid bilayer and its permeability by uni- and bivalent cations.     

Endogenous cyclic AMP in thyroid cell culture. Effect of thyroid-stimulating hormone and dibutyryl cyclic AMP

We have studied the variations of endogenous cyclic AMP levels in thyroid cells cultured over a period of 7 days in several conditions: in the presence of thyroid-stimulating hormone or dibutyryl cyclin AMP which both promote the aggregation of isolated cell into follicles, and in their absence when cells develop as a typical monolayer. In follicle-forming cells, the cyclic AMP level was found to rise during the first day of culture, then to fall rapidly. In monolayer-forming cells, the cyclic AMP content slightly increases attaining the same level as found in other cells at the fourth day, which remains stable till the seventh day. We have investigated the response of these cells to the acute effect of thyroid-stimulating hormone: only cells cultured in the presence of dibutyryl cyclic AMP retain the capability of increasing their cycli AMP concentration whereas monolayer-forming cells do not preserve this quality of thyroid cells.     

Prostacyclin stimulation of dog arterial cyclic AMP levels

Prostacyclin (PGI₂) dose-dependently increases the adenosine 3′,5′-cyclic monophosphate (cyclic AMP) levels in canine femoral, carotid, and canine and bovine coronary arteries. The prostacyclin-stimulation is enhanced by phosphodiesterase inhibitors, and is readily measurable after 60 sec incubation. The prostaglandin endoperoxide PGH₂, but not PGH₁, also elevates cAMP levels in femoral arteries. Inhibition of arterial prostacyclin synthetase with 28 μM 9,11-azoprosta-5,13-dienoic acid (azo analog I) blocks the PGH₂-stimulation of cAMP accumulation. Azo analog I does not attenuate a direct PGI₂ stimulation, indicating that the PGH₂ dependent elevation of cAMP is due to conversion of PGH₂ to PGI₂ by the artery. PGI₂ and PGE₁ increase cyclic AMP levels and relax dog femoral and bovine coronary arteries, while PGE₂, which actually contracts bovine coronary arteries, has no effect on arterial cyclic AMP levels. The significance of the PGI₂-stimulation of arterial cyclic AMP is not known, but it is probably related to relaxation of arterial strips.     

Interrelationships between prostaglandins, cyclic AMP and steroids in ovulation.

Ovulation is a complex phenomenon, involving a series of biochemical events within the ovary, leading to the rupture of the follicle. This paper summarizes recent studies in our laboratory of some of these biochemical changes using the rabbit as an experimental model. It has been shown in our laboratory that isolated Graafian follicles obtained from oestrous rabbits synthesize steroids and cyclic AMP when incubated in vitro. Luteinizing hormone added to the incubation medium increased steroidogenesis and cyclic AMP synthesis many fold. When follicles were isolated from rabbits at different times following the ovulatory stimulus (mating or HCG injection) it was found that the in vitro response to LH in terms of steroidogenesis and cylcic AMP synthesis was lost as ovulation approached. In contrast, when prostaglandins (PGF and PGE) were measured in rabbit Graafian follicles it was found that the PGF and PGE levels increased as ovulation approached. From these data and from reports in the literature, we have developed a hypothetical model for ovulation in the rabbit which may help in a better understanding of the ovulatory process.     

Rat osteogenic sarcoma cells: Effects of some prostaglandins, their metabolites and analogues on cyclic AMP production

Cyclic AMP production by freshly isolated cells, from a ³²P-induced transplantable rat osteogenic sarcoma, was stimulated by PGE₁, PGE₂ and to a less extent by PGF_2α and PGA₂. In the case of PGE₂, the cyclic AMP content of cells was miximal within 5 min. The 13, 14-dihydro derivatives of PGE₁, PGE₂ and PGF_2α had approximately 40% of the activity of the parent prostaglandin whilst, in every case, the metabolites (15-keto and 13,14-dihydro-15-keto) had very little activity. Two prostaglandin endoperoxide analogues (U44069 and U46619) had only 10% of the activity of an equimolar dose of PGE₂. The data presented in this paper demonstrates similarities between the responses of these cells and cells derived from bony tissue in terms of the ability of prostaglandins to stimulate bone resorption in tissue culture.