Restoration of fertility in a woman with giant prolactinoma in response to cabergoline treatment.

SUMMARY: A 32-year-old woman presented with primary amenorrhoea, prolactin (PRL) level of 154 150 mIU/L and was diagnosed with a giant pituitary adenoma measuring maximum 6.2 cm. Cabergoline (CAB) treatment at a dose of 0.5 mg/week was prescribed to the patient. The treatment decreased the tumour size after 3 months (MRI scans of the brain) and brought back to normal the level of the PRL (345 mIU/L) after 6 months of CAB treatment. After 7 months of CAB treatment, menarche was achieved, and after 12 months, the patient became pregnant. She discontinued taking CAB at 4-week gestation. The pregnancy resulted in a missed miscarriage at 6-7 weeks; an abortion was conducted by the vacuum aspiration method. The MRI scans of the brain did not show any tumour enlargement. After 18 months from the start of the treatment the patient got pregnant for the second time. At 25-week gestation an MRI scan of the brain was conducted which did not show any increase in the tumour size. At 38 weeks the patient delivered a healthy full-term girl via C-section. The patient chose not to breastfeed and resumed CAB therapy after the delivery. During the treatment, the PRL level returned to the normal range and the menstrual cycle was restored. After 3 years the patient got pregnant for the third time. The patient did not receive CAB during the pregnancies; the examination did not show any tumour enlargement. Further MRI scans did not show any tumour growth. CAB therapy was effective in normalization of the PRL level, tumour shrinkage, menarche and pregnancy-induction which led to the birth of healthy children in a woman with primary amenorrhoea and a giant prolactinoma invading the skull base bones. LEARNING POINTS: Giant prolactinomas are very rarely found in women. Cabergoline therapy can be effective in the normalization of the PRL level, tumour shrinkage, menarche induction in a woman with primary amenorrhoea, and giant prolactinoma. Cabergoline therapy can be effective in pregnancy induction which leads to the birth of children in a woman with giant prolactinoma. Cabergoline discontinuation did not trigger tumour enlargement during pregnancy.

[Structural organization of a hexamer of glutamate dehydrogenase. 3. Effect of the coenzyme and substrate on the urea-induced dissociation and inactivation of the hexamer]. / Strukturnaia organizatsiia geksamera glutamatdegidrogenazy. 3. Vliianie kofermenta i substrata na indutsiruemye mochevinoi dissotsiatsiiu i inaktivatsiiu geksamera.

Effects of coenzyme (NADH) and substrate (2-oxoglutarate) on the urea-induced dissociation and inactivation of immobilized phosphopyridoxyl derivative of bovine liver glutamate dehydrogenase (L-glutamate-NAD(P)-oxidoreductase, EC 1.4.1.3) have been studied. Urea at concentration 3.0 to 4.0 M in the presence of NADH induced dissociation of the enzyme's hexamer to catalytically inactive immobilized dimer. In the presence of both NADH and 2-oxoglutarate at the urea concentration 1.0 to 2.0 M the hexamer dissociated to the conformationally stable immobilized trimer possessing 60% catalytic activity of the hexamer. Studies of regulatory properties of the immobilized trimer showed that the allosteric inhibition of glutamate dehydrogenase by GTP was realized on the level of trimers, where the subunits interact through identical heterological contacts.

[Structural organization of glutamate dehydrogenase hexamer. 1. Immobilization on sepharose as a model for analysis of structural-functional characteristics of the enzyme]. / Strukturnaia organizatsiia geksamera glutamatdegidrogenazy. 1. Immobilizatsiia na sefaroze s tsel'iu polucheniia modeli dlia izucheniia strukturno-funktsional'nykh osobennostei fermenta.

Bovine liver glutamate dehydrogenase (L-glutamate-NAD(P)-oxidoreductase, EC 1.4.1.3) and its radioactive phosphopyridoxyl derivative were covalently immobilized on Sepharose CL-4B with different degrees of cyanogen bromide activation. The catalytical and regulatory properties of the immobilized samples of the enzymes were studied. It was shown that the enzymes were immobilized through a single subunit of hexamer when sepharose was activated by small amounts of cyanogen bromide (less than 5 mg per 1 ml of gel). In this case, the immobilization did not alter the catalytical and regulatory properties of glutamate dehydrogenase. The immobilized radioactive phosphopyridoxyl derivative of glutamate dehydrogenase completely imitated the immobilized native enzyme and can be used as a convenient model for structural and functional investigation of catalytically active hexamer of glutamate dehydrogenase.

[Structural organization of glutamate dehydrogenase. 2. Inactivation and dissociation of immobilized hexamer induced by urea]. / Strukturnaia organizatsiia geksamera glutamatdegidrogenazy. 2. Izuchenie inaktivatsii i dissotsiatsii immobilizovannogo geksamera pod vliianiem mocheviny.

The urea-induced inactivation and dissociation of catalytically active hexamer of glutamate dehydrogenase (L-glutamate-NAD(P)-oxidoreductase, EC 1.4.1.3) from bovine liver were studied using radioactive phosphopyridoxyl derivative of the enzyme immobilized on cyanogen bromide-activated Sepharose CL-4B. It is shown that at neutral pH (7.0-7.8) urea causes dissociation of glutamate dehydrogenase to directly yield catalytically inactive immobilized monomers rather than hexamer's stable fragments at the same time. At pH 8.9 or 5.6 the urea-induced is accompanied by the formation of conformationally stable immobilized dimers or trimers, respectively. The trimers are catalytically active, whereas the dimers did not exhibit any enzymatic activity. The data obtained led to suggestion that the hexamer consists of three either equivalent dimers (3 alpha 2) or of two equivalent trimers (2 alpha 3).

[Cooperative inactivation of glutamate dehydrogenase of 2,2,6,6- tetramethyl-4-oxopiperidine-1-oxyl. Interpretation of results within the scope of a hexamer model with equivalent subunit orientation]. / Kooperativnaia inaktivatsiia glutamatdegidrogenazy 2,2,6,6- tetrametil-4-oksopiperidin-1-oksilom. Interpretatsiia resul'tatov v ramkakh modeli geksamera s ékvivalentnoi orientatsiei sub''edinits.

It was shown that the blockage of epsilon-amino group of Lis-126 residue by 2,2,6,6-tetramethyl-4-oxo-piperidine-1-oxyl (TMPO) leads to the cooperative inactivation of glutamate dehydrogenase (L-glutamate-NAD(P)-oxidoreductase, EC 1.4.1.3). The data concerning cooperative inactivation of the enzyme are interpreted by the model of hexamer with identical orientation of subunits. It was shown that the modification of any of enzyme subunits is accompanied by an inactivation of the hexamer's fragment which is a dimer, with subunits interacting reciprocally by means of isological contacts.

[Modification of glutamate dehydrogenase by pyridoxal-5'-phosphate. Study of the cooperative type of inhibition by GTP]. / Modifikatsiia glutamatdegidrogenazy piridoksal'-5'-fosfatom. Izuchenie kooperativnogo kharaktera ingibirovaniia GTP.

The character of allosteric inhibition of glutamate dehydrogenase by GTP was studied. The derivative of the enzyme not capable of being polymerized was taken as a model. It was shown that: in the absence of NADH every protomer of this derivative can bind one molecule of GTP; in the presence of NADH the additional binding site for GTP was induced; the modification of the enzyme derivative by pyridoxal-5-phosphate in the presence of NADH and alpha-ketoglutarate blocked the NADH-induced GTP binding site and the disappearance of positive kinetic cooperativity induced by GTP was observed; to achieve the inhibitory action of GTP the binding of the effector to only one (NADH-induced) site was enough; the role of GTP binding to the NADH-induced site is to provide better affinity of the effector to the "inhibitory" centre; the positive kinetic cooperativity of inhibition of glutamate dehydrogenase by GTP depends probable on the cooperative character of interaction between the two molecules of GTP to each protomer of the enzyme.

[Modification of glutamate dehydrogenase by pyridoxal-5'-phosphate. Study of the structural organisation of the hexamer and its possible role in the realization of GTP action]. / Modifikatsiia glutamatdegidrogenazy piridoksal'-5'-fosfatom. Izuchenie strukturnoi organizatsii geksamera i ego vozmozhnoi roli v realizatsii deistviia GTP.

The catalytic and regulator properties of glutamate dehydrogenase by modification of Lys-126 residue by puridoxal-5'-phosphate was studied. The phosphopyridoxyl derivative of the enzyme with blocked NADH-induced binding site of GTP not capable of being polymerized was taken as a model. It was shown that: blocking the epsilon-amino group of Lys-126 residue brings to a simultaneous inactivation of the enzyme and desensibilization of its residual activity to GTP action; the modification of Lys-126 residue and resulting inactivation of the enzyme and desensibilization to GTP action were non-cooperative processes, with equal values of pseudofirst order rate constants; modification of Lys-126 residue of any of hexamer's protomer results in the desensibilization to GTP action on one of the contacting, catalytically active protomers. The experimental dependence of the inhibition degree of the enzyme by GTP upon the average number of modified residues of Lys-126 is explained by the model of the hexamer of glutamate dehydrogenase with identical interlocation of any of the protomers in relation to the one in contact.

[Identification of a glutamate dehydrogenase amino acid residue modified by 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl. Study of the type of inactivation of a catalytically active enzyme oligomer in modification]. / Identifikatsiia aminokislotnogo ostatka glutamatdegidrogenazy, modifitsiruemogo 2,2,6,6-tetrametil-4-oksopiperidin-1-oksilom. Izuchenie kharaktera inaktivatsii kataliticheski aktivnogo oligomera fermenta pri modifikatsii.

It has been shown that 2,2,6,6-tetramethyl-4-oxo-piperidine-1-oxyl selectively blocks epsilon-amino group of Lys126 residue in bovine liver glutamate dehydrogenase (L-glutamate NAD(P) oxydoreductase, EC 1.4.1.3). Modification of this residue in one of the six promoters of catalytically active hexamer is accompanied by the loss of about half of the enzymatic activity. The enzyme inactivation caused by modification has a cooperative character.

[Effect of bivalent copper ions on the catalytic properties of bovine liver glutamate dehydrogenase]. / Vliianie dvukhvalentnogo iona medi na katalitichskie svoistva glutamatdegidrogenazy pecheni byka.

The effects of bivalent copper ions on the activity of bovine liver glutamate dehydrogenase (L-glutamate NAD (P) oxidoreductase, EC 1.4.1.3) were studied. Cu2+ effectively interacts with the enzyme; this interaction is accompanied by a loss of the enzyme activity in the reaction of reductive amination of alpha-ketoglutarate. The data obtained are indicative of a similar type of the enzyme inhibition by GTP and copper ions.

[Bovine liver glutamate dehydrogenase modified by 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl: enzymatic activity and catalytic properties]. / Modifikatsiia glutamatdegidrogenary pecheni byka 2,2,6-6-tetrametil-4-okso-piperidin-1-oksilom. Vliianie na aktivnost' i kataliticheskie svoistva.

When modified by 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (TMPO) bovine liver glutamate dehydrogenase (L-glutamate NAD(P) oxidoreductase, E. C. 1.4.1.3) looses its catalytical activity and sensitivity to allosteric inhibitor GTP. The stoicheiometry of the binding of TMPO to glutamate dehydrogenase has been studied--each protomer bound one molecule of TMPO. It is supposed that TMPO reacts with lysine residue located in the enzyme's active center.

[Purification and some physico-chemical properties of glutamate dehydrogenase from beef brain]. / Ochistka glutamatdegidrogenazy iz mozga byka i ee nekotorye fiziko-khimicheskie svoistva.

A procedure for purification of glutamate dehydrogenase (GDH; L-glutamate NAD(P) oxidoreductase, EC 1.4.1.3) from beef brain has been developed. The enzyme preparation obtained has the specific activity of 6.7 units per mg of protein (192-fold enhance with a 30% yield of total activity of the homogenate). In some of its physico-chemical properties (pH optimum of catalyzed reactions, molecular weight, subunit structure, thermal stability) the brain GDH is identical to the enzyme from beef liver. The Km values for most of the coenzymes and substrates for the enzyme studied do not exceed those for beef liver enzyme more than 1,5--2-fold. The only exception is the Km value for glutamate, which in the case of brain GDH is 4 times less than that for the liver enzyme. The results obtained suggest that upon interaction with NAD the brain GDH reveals a relatively higher affinity for L-glutamate and L-ketoglutarate as compared to the liver enzyme.