Christine Gervy Decoster

A mechanism in the control of intracellular CAMP level: the activation of a calmodulin-sensitive phosphodiesterase by a rise of intracellular free calcium

The intracellular concentration of cAMP results from the balance between its synthesis by adenylate cyclase and its catabolism by the system of cyclic nucleotide phosphodiesterases. Positive regulation of the cAMP system by activation of adenylate cyclase has been the focus of most of the research on the regulation of the level of this nucleotide. With regard to negative controls, a direct inhibition of adenylate cyclase by a-adrenergic, cholinergic agonists and several peptides is now well characterized and accounts for multiple negative controls of cAMP generation (Jakobs et al., 1980). It is thus often assumed now that intracellular concentration of cAMP is only controlled at the level of its synthesis. Such a concept is an oversimplification as it neglects the potential of controls at the level of cAMP catabolism. Phosphodiesterases are rather complex enzymes consisting of multiple soluble and particulate forms (reviewed by Beavo et al., 1982). It has been demonstrated that they are distinct non-intercon-

Absence of human chorionic somatomammotropin during pregnancy associated with two types of gene deletion.

SummaryComplete absence of human somatomammotropin (hCS) was demonstrated in two patients experiencing an otherwise uneventful pregnancy. After delivery, DNA was prepared from the neonate blood or from the placenta and the integrity of the hCS-hGH gene cluster was investigated by Southern blotting and hybridization with an hCS cDNA probe. Patient 1 was found to be homozygous for a deletion involving hCS-A, hGH-V, and hCS-B. Patient 2 was a double heterozygote, with one chromosome bearing the same deletion as that of patient 1, while in the other, only the hCS-A gene was missing. Considerations relative to the frequency of the defect are derived from the present results.

Effects of carbamylcholine and ionophore A-23187 on cyclic 3',5'-AMP and cyclic 3',5'-GMP accumulation in dog-thyroid slices.

Carbamylcholine and acetylcholine through a muscarinic type of receptor, KCl, ionophore A-23187 and NaF increased cyclic GMP accumulation in dog-thyroid slices. These effects were abolished in calcium-depleted slices, which findings confirm that Ca2+ is required for cyclic GMP accumulation. All these agents depressed the accumulation of cyclic AMP in TSH-stimulated slices. KCl and NaF depressed cyclic AMP accumulation in TSH-treated slices even when they had been depleted of Ca2+. This suggests a cyclic GMP- and Ca2+-independent mechanism. The absence of inhibition of the effects of the ionophore, NaF and KCl in the presence of atropine suggests that these drugs do not act by inducing the release of acetylcholine in the slices. The effects of carbamylcholine and ionophore A-23187 on cyclic GMP accumulation and protein iodination were reversible; the inhibitions of TSH-induced cyclic AMP accumulation and secretion were non-competitive and were not accompanied by a depression of ATP levels. All these effects were greatly decreased in the absence of extracellular Ca2+. These data suggest that carbamylcholine and ionophore A-23187 act mainly by increasing the influx of extracellular Ca2+ in thyroid cells. However, the persistence of some carbamylcholine effect in the absence of Ca2+ in the medium suggests that this agent may also trigger the release of Ca2+ from an intrafollicular pool. The kinetics of action of carbamylcholine are compatible with a role of cyclic GMP in the inhibition of cyclic AMP accumulation. However, with the ionophore, the depression of cyclic AMP accumulation was much longer than the rise of cyclic GMP, which suggests a mechanism independent of cyclic GMP.

Tumor promoters as probes of protein kinase C in dog thyroid cell: Inhibition of the primary effects of carbamylocholine and reproduction of some distal effects

The acute effects of phorbol esters, used as probes of protein kinase C activation, were studied on dog thyroid slices incubated in vitro. The derivatives used were: tetradecanoylphorbol acetate (TPA), phorbol-12,13, didecanoate (PDD), phorbol-12,13-diacetate (PDA), and phorbol dibutyrate (PDBu) and as inactive controls, phorbol itself, phorbol-12, myristate and phorbol-13, acetate, in concentrations ranging from 5.10(-8) to 5.10(-6) mol/L. The active phorbol esters had no effect on basal cyclic AMP concentrations; they inhibited cyclic AMP accumulation induced by prostaglandin E1 but not that induced by thyrotropin (TSH) 1 mU/mL and forskolin 10 mumol/L. Phorbol esters like carbamylcholine acutely stimulated iodide organification and inhibited the stimulation of hormone secretion resulting from TSH, Cholera Toxin, forskolin, and Bu2-cyclic AMP action. These metabolic effects did not require the presence of extracellular Ca++, and could not be antagonized by Ca++ depletion or manganese addition. The active phorbol esters abolished the cyclic AMP independent increased PI turnover induced by TSH 10 mU/mL or carbamylcholine (Cchol) 10(-6) mol/L but did not affect the basal incorporation of 32P into phosphatidylinositol. They reduced the 45Ca efflux from preloaded slices below basal levels and blocked the increased 45Ca release induced by TSH and Cchol. They also inhibited the increase in cyclic GMP concentrations resulting from Cchol action but not the effect of the ionophore A23187 (10(-5) mol/L) nor the basal levels of cyclic GMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth hormone release after desipramine in depressive illness

SummaryThe effect of i.m. administration of 75 mg of desipramine on growth hormone (GH) secretion was investigated in a sample of 87 patients with major depressive disorders and in 31 normal controls. The GH response was lower in depressed females compared to depressed males, but no such difference was present in controls. In the premenopausal female group, GH response was significantly lower in depressed patients than in controls. No significant difference was found between normal males and male depressed patients. In the premenopausal group, no difference emerged between endogenous and nonendogenous depressed women.

Effects of prostaglandins F alpha on dog thyroid cyclic AMP level and function.

Prostaglandins F1 alpha and F2 alpha, at high concentrations (greater than or equal to 28 microM) 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 alpha also inhibited TSH-induced secretion and activated iodide 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 alpha 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 alpha. 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 alpha or any other cyclooxygenase product.

In vitro effects of arachidonic acid and of inhibitors of its metabolism on the dog thyroid gland

Incubation of dog thyroid tissue with arachidonic acid (10 to 200 microM) led to the following events: --low conversion to prostaglandins E2 and F2 alpha: 0.07% and 0.02% per hour and 100 mg tissue, respectively --inhibition of the stimulatory effect of low concentrations of TSH on thyroid secretion: the secretory effect of supra-maximal concentrations of TSH and of dB-cAMP was unaffected --inhibition of the cyclic AMP accumulation induced by TSH: this effect was inhibited neither by indomethacin nor by ETYA; cyclic AMP accumulation in response to cholera toxin or PGE1 was unaffected --no effect on cyclic GMP level --stimulation of thyroid proteins iodination. ETYA, but not indomethacin, depressed the iodination of thyroid proteins in resting and stimulated tissue. These data show that arachidonic acid-or a metabolite-can modulate thyroid responsiveness to TSH and suggest that lipoxygenase-products of arachidonic acid metabolism could be involved in thyroid proteins iodination.

Desensitization of carbamylcholine-mediated cyclic GMP accumulation in dog thyroid slices

Previous studies have shown that carbamylcholine through a muscarinic receptor increases Ca2+ influx and consequently cGMP accumulation in dog thyroid slices. A first exposure to carbamylcholine induced desensitization of the cGMP response to a further exposure to this agent. The aim of this work was to investigate the role of carbamylcholine, extracellular calcium or intracellular cGMP in this desensitization. The effect of various combinations of these factors has been studied. Carbamylcholine in the absence of calcium, with and without cGMP accumulation, did not desensitize. On the other hand, an increase in intracellular calcium and its consequent cGMP accumulation did not desensitize carbamylcholine-induced cGMP accumulation either. Previous exposure of dog thyroid cells to carbamylcholine in the presence of calcium slightly decreased ionophore A23187-induced cGMP accumulation. Carbamylcholine desensitization is thus mainly homologous and bears on a step prior to cGMP synthesis. These data suggest that both carbamylcholine interaction with its receptor and extracellular calcium are necessary for desensitization. cGMP is not sufficient for this effect but its possible role is not excluded.

Negative regulation of cyclic-AMP levels by carbamylcholine in dog thyroid is not mediated by cyclic-GMP

Carbamylcholine, through calcium, enhances cyclic-GMP accumulation and depresses cyclic-AMP accumulation in TSH stimulated dog thyroid. The results presented show that compounds which can be transformed to nitric oxide increase cyclic-GMP accumulation in the dog thyroid. These compounds do not require extracellular calcium for their action. In thyroid stimulated by TSH, these compounds do not depress AMP accumulation. Cyclic-GMP is not the main intracellular signal involved in the negative regulation of cyclic-AMP levels in dog thyroid.