Pieter De Moor

Influence of the Vitamin D-binding Protein on the Serum Concentration of 1,25-Dihydroxyvitamin D3: SIGNIFICANCE OF THE FREE 1,25-DIHYDROXYVITAMIN D3 CONCENTRATION

The influence of the serum binding protein (DBP) for vitamin D and its metabolites on the concentration of its main ligands, 25-hydroxyvitamin D(3) (25-OHD(3)) and 1,25-dihydroxyvitamin D(3) (1,25-[OH](2)D(3)) was studied. The concentration of both 1,25-(OH)(2)D(3) and DBP in normal female subjects (45+/-14 ng/liter and 333+/-58 mg/liter, mean+/-SD, respectively; n = 58) increased during the intake of estro-progestogens (69+/-27 ng/liter and 488+/-90 mg/liter, respectively; n = 29), whereas the 25-OHD(3) concentration remained unchanged. A positive correlation was found between the concentrations of 1,25-(OH)(2)D(3) and DBP in these women. At the end of pregnancy, the total concentrations of 1,25-(OH)(2)D(3) (97+/-26 ng/liter, n = 40) and DBP (616+/-84 mg/liter) are both significantly higher than in nonpregnant females and paired cord serum samples (48+/-11 ng/liter and 266+/-41 mg/liter, respectively). A marked seasonal variation of 25-OHD(3) was observed in pregnant females and their infants, whereas in the same samples the concentrations of both DBP and 1,25-(OH)(2)D(3) remained constant throughout the year. The free 1,25-(OH)(2)D(3) index, calculated as the molar ratio of this steroid and DBP, remains normal in women taking estro-progestogens, however, and this might explain their normal intestinal calcium absorption despite a high total 1,25-(OH)(2)D(3) concentration. In pregnancy the free 1,25-(OH)(2)D(3) index remains normal up to 35 wk of gestation, but during the last weeks of gestation, the free 1,25-(OH)(2)D(3) index increases in both circulations. A highly significant correlation exists between the (total and free) 25-OHD(3) and 1,25-(OH)(2)D(3) concentrations in maternal and cord serum both at 35 and 40 wk of gestation.

Stimulation effect of neurotransmitters on the aromatization of testosterone by Sertoli cell-enriched cultures

The aromatization of testosterone has been studied in Sertoli cell-enriched cultures derived from 19-day-old rats. It was found that, besides dbcAMP and FSH, several neurotransmitters have a stimulatory effect. At a concentration of 10(-5) M, the strongest effects were noted with L-isoproterenol, L-norepinephrine, L-epinephrine and D,L-synephrine. Some stimulation was observed with dopamine, whereas histamine, melatonin and serotonin as well as acetylcholine and pilocarpine were ineffective. Experiments with alpha- and beta-adrenergic antagonists suggest that beta 2- and maybe also alpha-receptors are involved. The same maximal level of stimulation was generally observed for dbcAMP, FSH and isoproterenol. No further increase in activity was obtained with combinations of these compounds. It is concluded that adrenergic agonists may play a role in testicular development and function.

Comparative study of the affinity of the serum vitamin d-binding protein

Abstract The affinity and capacity of the serum vitamin D-binding protein for 25-hydroxyvitamin D 3 and 1,25-dihydroxyvitamin D 3 were studied. The association constant (M −1 ) at 4°C for 25-hydroxyvitamin D 3 was about 5 × 10 8 at pH 7.4 in all species (man, monkey, rat and chick) except for a 10-fold higher affinity in the toad. At pH 8.6 a tenfold increase in affinity for 25-hydroxyvitamin D 3 was observed in the mammalian species but not in the chick or the toad. The association constant (M −1 ) of the serum vitamin D-binding protein for 1,25-dihydroxyvitamin D 3 at 4°C and pH 7.4 was about 1.5 × 10 7 in man, monkey and chick and was tenfold higher in rat and toad. At pH 8.6 only a slight increase in affinity for 1,25-dihydroxyvitamin D 3 was observed. The serum binding capacity for 25-hydroxyvitamin D 3 and 1,25-dihydroxyvitamin D 3 was in the micromolar order in all species except for a 100-fold lower capacity in the toad. The genetic heterogeneity of the human and rat vitamin D-binding protein did not affect its affinity or capacity for both vitamin D metabolites.

Ammonium sulfate precipitation as a tool for the study of androgen receptor proteins in rat prostate and mouse kidney

Ammonium sulfate precipitation has been used for the separation of bound and free steroids in rat prostate and mouse kidney cytosol equilibrated with tritiated androgens. A high affinity, low capacity binding protein has been identified in the 35% saturation precipitate. Biochemical and physiological data indicate that this protein is identical with the previously described 8-10 S androgen receptor. It has been demonstrated that this receptor protein binds 17 beta - hydroxy-5alpha-androstan-3-one (DHT) and testosterone in both tissues. The apparent dissociation constant (Kd) of the prostatic receptor for DHT and of the renal receptor for testosterone is 1-2 nM. The number of binding sites equals 57 and 23 fmoles/mg protein in prostate and kidney respectively. Dterminations of apparent inhibition constants (Ki) for 26 steroidal and non-steroidal compounds suggest that the binding sites in these tissues is similar or identical.

The binding of 17β-hydroxy-5α-androstan-3-one to the steroid-binding β-globulin in human plasma, as studied by means of ammonium sulphate precipitation

Abstract The binding of 17β-hydroxy-5α-androstan-3-one (dihydrotestosterone, DHT) to the steroid-binding β-globulin (SBβG) in human plasma was evaluated by means of three parameters, based on ammonium sulphate precipitation of this globulin. 1. The ratio of precipitated to non-precipitated 3H-DHT (DHT-precipitation index) was measured after incubation of a tracer amount of 3H-DHT in the presence of the plasma sample diluted with a solution of bovine albumin. 2. By adding various amounts of DHT the ratio of precipitated to non-precipitated DHT was studied as a function of the precipitated amount of DHT, using a Scatchard-type binding plot. From this plot the DHT-binding capacity of the precipitated protein could be derived. 3. The DHT-binding capacity of the precipitated protein was estimated more directly by measurement of the precipitated amount of DHT after incubation of the plasma sample with an excess of DHT and after repetition of the precipitation step. This method was chosen for further study. Normal values for the DHT-binding capacity of SBβG were 1.07 ± 0.37 (SD) μg per 100 ml in 24 men, 1.76 ± 0.59 (SD) μg per 100 ml in 18 women and 12.55 ± 1.74 (SD) μg per 100 ml during pregnancy (n = 11).

Desensitization of cultured rat sertoli cells by follicle-stimulating hormone and by l-isoproterenol

When Sertoli cell-enriched cultures derived from 19-day-old Wistar rats are exposed to FSH or L-isoproterenol, cAMP accumulates in the medium. Previous contact of cultured cells with either one of these agents results in a reversible state of desensitization. During secondary stimulation up to 20 times less cAMP accumulates in the medium and in the cells. The extent of desensitization depends on the concentration of FSH or L-isoproterenol to which the cells have been exposed and on the duration of this previous contact. Pre-incubation with FSH results in cross-desensitization for L-isoproterenol. Comparable heterologous desensitization is not observed after pre-incubation with L-isoproterenol. This suggests that down-regulation of the respective receptors cannot be the only explanation. Refractoriness can also be induced by dbcAMP. This opens the possibility that cAMP itself contributes to the homologous and heterologous desensitization process.

Hormonal control of phosphodiesterase activity in cultured rat Sertoli cells.

Phosphodiesterase activity was studied in cultures derived from 19-day-old rats and enriched with Sertoli cells. Pretreatment of such cultures with follicle-stimulating hormone or L-isoproterenol increased cAMP-phosphodiesterase activity 5.2 and 2.0 times, respectively. cGMP-phosphodiesterase activity was not affected. Similar effects were observed in freshly isolated cells. The stimulatory effect was enhanced by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine and was mimicked by cholera toxin and dbcAMP. Increased activity was observed after a latent period of 1 h. Stimulation was blocked by cycloheximide and actinomycin D. The enzyme had an apparent Km for cAMP of 1.4 micro M. Its activity was enhanced by Mg2+ but not by Ca2+. It is concluded that phosphodiesterases play an important role in the hormonal control of Sertoli-cell function and may contribute to the refractory state of these cells after stimulation with various agonists.

Adrenal cortical hormones in the spermatic vein of 95 patients with left varicocele.

Adrenocortical hormones were measured in the peripheral and spermatic venous blood samples, taken simultaneously at the time of a high vasoligation for left varicocele in 95 patients.

Interconversion between 17β-hydroxy-5α-androstan-3-one (5α-dihydrotestosterone) and 5α-androstane-3α,17β-diol: Tissue specificity and role of the microsomal NAD: 3α-hydroxysteroid oxidoreductase

Abstract The tissue specificity of the microsomal NAD: 3α-hydroxysteroid oxidoreductase has been investigated. A striking correlation is observed between the responsiveness of the investigated tissues to 3α-andros-tanediol on the one hand and the activity of the NAD: 3α-hydroxysteroid oxidoreductase as well as their ability to convert 3α-androstanediol into 5α-dihydrotestosterone on the other hand.

More familial leukaemia in ALL patients with both unexplained high transcortin levels and an HLA antigen Cw3

Summary. In a group of 74 adult ALL patients 25 had a transcortin level ±3 SD above the normal mean, 15 expressed an HLA‐Cw3 antigen and 11 combined both characteristics. In this subgroup of 11 ALL patients, five had familial leukaemia, i.e. at least one relative with acute leukaemia or lymphoma. On the other hand, only three examples of familial leukaemia were found in a series of 59 ALL patients with one or none of these two characteristics (relative risk: 15.6; P<0.001).