AIP inactivation leads to pituitary tumorigenesis through defective Gαi-cAMP signaling.

The aryl hydrocarbon receptor interacting protein (AIP) is a tumor-suppressor gene underlying the pituitary adenoma predisposition. Thus far, the exact molecular mechanisms by which inactivated AIP exerts its tumor-promoting action have been unclear. To better understand the role of AIP in pituitary tumorigenesis, we performed gene expression microarray analysis to examine changes between Aip wild-type and knockout mouse embryonic fibroblast (MEF) cell lines. Transcriptional analyses implied that Aip deficiency causes a dysfunction in cyclic adenosine monophosphate (cAMP) signaling, as well as impairments in signaling cascades associated with developmental and immune-inflammatory responses. In vitro experiments showed that AIP deficiency increases intracellular cAMP concentrations in both MEF and murine pituitary adenoma cell lines. Based on knockdown of various G protein α subunits, we concluded that AIP deficiency leads to elevated cAMP concentrations through defective Gαi-2 and Gαi-3 proteins that normally inhibit cAMP synthesis. Furthermore, immunostaining of Gαi-2 revealed that AIP deficiency is associated with a clear reduction in Gαi-2 protein expression levels in human and mouse growth hormone (GH)-secreting pituitary adenomas, thus indicating defective Gαi signaling in these tumors. By contrast, all prolactin-secreting tumors showed prominent Gαi-2 protein levels, irrespective of Aip mutation status. We additionally observed reduced expression of phosphorylated extracellular signal-regulated kinases 1/2 and cAMP response element-binding protein levels in mouse and human AIP-deficient somatotropinomas. This study implies for the first time that a failure to inhibit cAMP synthesis through dysfunctional Gαi signaling underlies the development of GH-secreting pituitary adenomas in AIP mutation carriers.

Interactions of dihydralazine with furosemide in hypertonic patients.

In 9 hypertensive patients stage II we studied whether dihydralazine, which is known to increase the renal blood flow, influences the elimination of furosemide (40 mg i.v.) when given additionally over a period of 2 weeks (75 mg daily). The results were compared with data from 9 healthy volunteers. The most important alterations in hypertonics were significantly increased half-lives (28.0 +/- 3.7 and 35.1 +/- 5.7 min), distribution coefficients (0.105 +/- 0.017 and 0.132 +/- 0.028 ml/g) and unchanged plasma clearances (2.62 +/- 0.33 and 2.59 +/- 0.27 ml min-1 X kg-1). Pretreatment with dihydralazine resulted in normalization of distribution coefficients (0.134 +/- 0.027 and 0.102 +/- 0.020 ml/g), decrease in plasma clearance (2.55 +/- 0.29 and 2.08 +/- 0.23 ml min-1 X kg-1) without alterations in half-lives (36.3 +/- 6.0 and 34.2 +/- 7.0 min). The authors conclude that the effects after dihydralazine co-medication are only distribution mediated.

The influence of the acetylator phenotype for the clinical use of dihydralazine.

Dihydralazine is a substrate of the human N-acetyltransferase. Therefore the acetylator phenotype could influence the pharmacodynamic response of dihydralazine and/or side effects of this drug. In this study it could be shown that: among patients with dihydralazine incompatibility slow acetylators preponderated; the risk of early side effects was higher in females than in males; and the ratio of fast/slow acetylators was higher in dihydralazine treated patients than in patients treated with other antihypertensives. Dihydralazine should be given very cautiously to female hypertonic patients that are slow acetylators.

Superinduction of tyrosine aminotransferase in RLC-cells.

Actinomycin D, administered to RLC cells which were pretreated with the glucocorticoid dexamethasone phosphate, causes superinduction of tyrosine aminotransferase. By the addition of actidione it could be proved that the superinduction takes place because of the decreased activity of the tyrosine aminotransferase-degrading enzymes.

Influence of L-tryptophan on the activity of tryptophan oxygenase in rat liver slices.

Earlier experiments in vivo with adrenalectomized rats showed that for the induction of tryptophan oxygenase and tyrosine aminotransferase small doses of cortisone acetate and the corresponding substrate are necessary. We performed the similar experiments in vitro with liver slices from adrenalectomized rats which were pretreated with cortisone acetate in vivo. Studies with alpha-amanitine and cordycepin--given in vivo--showed, that the synthesis of m -RNA for tryptophan oxygenase after application of 1 mg/kg cortisone acetate lasted for less than 2 h. The results obtained in vitro were very similar to those reported earlier. Maximum activity is obtained in the presence of the substrate L-tryptophan. When adding other amino acids instead of the substrate no effect can be observed. The same is true also for actinomycin D. In the presence of puromycin and cycloheximide the enzyme activity decreases.

[Effect of substrate and small doses of cortisone on the induction of Tryptophan 2,3-dioxygenase (author's transl)]. / Wirkung von Substrat und kleinen Dosen Cortison auf die Induktion der Tryptophan-2,3-Dioxygenase

A number of enzymes are induced by steroid hormones. In this paper the reaction of tryptophan 2,3-dioxygenase is further analyzed. In particular we show in which way the substrate and low doses of cortisone cause an induction. 1) For the induction of tryptophan 2,3-dioxygenase in adrenalectomized rats by 2.5 mg cortisone/kg, the presence of the substrate is necessary as well. Under these conditions an induction of the enzyme can already be registered in the presence of 12.5 mg L-tryptophan/kg. 2) In animals treated before with cortisone, the enzyme maximum appears 30 min after L-tryptophan injection, The enhancement of enzyme activity in animals which are treated with 2.5 mg cortisone/kg before is blocked by actidione only until 30 min after L-tryptophan injection. 3) Experiments with antibodies in animals treated with a low dosis of cortisone show that L-tryptophan acts mainly via enzyme degradation or the saturation with the coenzyme hematin, respectively.

Influence of a new virostatic compound on the induction of enzymes in rat liver.

The virostatic compound N,N-diethyl-4-[2-(2-oxo-3-tetradecyl-1-imidazolidinyl)-ethyl]-1-piperazinecarboxamide-hydrochloride (5531) was analyzed as to its effect on the induction of tryptophan-pyrrolase and tyrosineaminotransferase in rat liver. 1. The basic activity of the enzymes was not influenced by the substance either in normal or in adrenalectomized animals. 2. The induction of the enzymes by cortisone increased in the presence of the compound whereas the substrate induction remained unchanged. 3. The induction of tyrosine-aminotransferase by dexamethasonephosphate in tissue culture is inhibited if the dose of compound 5531 is higher than 5 mug/ml.

[The importance of the substrate for the induction of tyrosine-alpha-ketoglutarate-transaminase in RLC-cells (author's transl)]. / Dei Bedeutung des Substrates bei der Induktion der Tyrosin-alpha-Ketoglutarat-Transaminase in RLC-Zellen

1. Dexamethasone phosphate causes approximately a threefold increase of the tyrosine-alpha-ketoglutarate transaminase in the culture of RLC cells. 2. The induction of the enzyme depends on the presence of L-tyrosine. Omission of L-leucine or L-tryptophan, respectively, has no effect. 3. Omission of L-tyrosine influences the activity of the lactate dehydrogenase and malate dehydrogenase not at all and that of the glucose-6-phosphate-dehydrogenase only to a small extent. 4. In the absense of L-tyrosine an superinduction takes also place by actinomycin.