Daniel T. Baran

1,25 dihydroxyvitamin d-induced inhibition of3H-25 hydroxyvitamin D production by the rachitic rat liverin vitro

SummaryThe effect of the vitamin D metabolites 1,25 dihydroxyvitamin D (100 pg/ml) and 25-hydroxyvitamin D (30 ng/ml) on hepatic production of3H-25 hydroxyvitamin D was investigated using rachitic liver perfusions and homogenates. 1,25 dihydroxyvitamin D inhibited hepatic3H-25 hydroxyvitamin D production in the liver perfusion (3.6 ± 0.4 vs 2.0 ± 0.5 pmol/liver,P<0.05) and in liver homogenates (11.9 ± 0.6 vs 10.1 ± 0.4 pmol/g liver protein/3 h,P<0.02). Inhibition was time and dose dependent. 25-hydroxyvitamin D inhibited production in liver homogenates (11.9 ± 0.6 vs 9.2 ± 0.1 pmol/g liver protein/3 h,P<0.05) but not in the intact liver (3.6 ± 0.4 vs 3.4 ± 0.5 pmol/liver). The data indicate that 1,25 dihydroxyvitamin D is able to feedback regulate the production of its precursor, 25-hydroxyvitamin D. Although 25-hydroxyvitamin D also inhibits its own production in liver homogenates, it failed to alter total production in the intact liver, suggesting that this metabolite may require immediate access to the vitamin D 25-hydroxylase, located on the microsomes and mitochondria, to induce inhibition.

Lithium inhibition of bone mineralization and osteoid formation.

Lithium chloride administration to growing rats, which resulted in circulating lithium levels of 1.4 meq/liter, was attended by significant suppression of bone mineralization and organic matrix synthesis as assessed by tetracycline labeling and histological quantitation of osteoid, respectively. These effects of lithium were not associated with changes in animal behavior, nor were there any significant differences in blood levels of calcium, phosphorus, alkaline phosphatase, creatinine, pH, or parathyroid hormone. The data suggest that lithium inhibition of bone mineralization is secondary to suppression of osteoid formation.

Alpha-aminoisobutyric acid transport in human leukemic lymphocytes: in vitro characteristics and inhibition by cortisol and cycloheximide

We have studied the transport of alpha-aminoisobutyric acid (AIB)-3-(14)C and its response to cortisol and cycloheximide in vitro in blood lymphocytes from untreated patients with chronic lymphocytic leukemia. The accumulation of AIB-3-(14)C increased in a linear fashion for 60 min, and reached an apparent steady state in 120 min. The initial rate of AIB accumulation (V(o)) varied from 1.1 to 10.2 mumoles/kg cell H(2)O per min in cells from 16 different patients; however, V(o) was reproducible in cells from five of six patients which were studied repeatedly over 1-9 months, and correlated positively with the lymphocyte count (r = 0.51, P = < 0.01). Virtually total inhibition of protein synthesis with cycloheximide was found to decrease the accumulation of AIB in cells from four patients which had high rates of AIB transport, but had no effect on transport in cells from four patients which accumulated AIB more slowly. These results indicate that active transport depends, in part, upon the presence of labile protein with a turnover rate which varies among different cell populations. Treatment with 10 muM cortisol for 240 min in vitro reduced the initial rate of AIB-3-(14)C accumulation (V(o)) by 43.4+/-4.1% (SE) (range, 9-66%) in cells from 16 patients. The degree of inhibition did not vary appreciably over a 9 month period in four of five patients. The effect of cortisol was proportional to its starting concentration, and developed at low concentrations (0.1-1.0 muM). Cortisol appears to decrease AIB accumulation by inhibiting active uptake, since it neither enhanced the exodus of AIB, nor inhibited apparently nonsaturable transport. Inhibition was noncompetitive in type, suggesting that cortisol decreases the total capacity of the active transport mechanism.Cortisol inhibited AIB transport indirectly by a process which involved de novo protein synthesis, since inhibition (a) appeared only after 60 min of treatment, (b) was present in treated cells which were subsequently incubated for 60 min in cortisol-free medium, and (c) failed to develop during simultaneous blockade of protein synthesis with cycloheximide, even when cycloheximide itself did not decrease AIB transport.

Cortisol-induced inhibition of amino acid transport in thymic lymphocytes: Kinetic parameters: relation to ATP levels and protein synthesis; and specificity

1. 1. α-Aminoisobutyric acid accumulation in rat thymic lymphocytes increased in linear fashion for 10 min and reached an apparent steady state in 60 min. α-Aminoisobutyric acid was transported by concentrative and non-concentrative processes. Cortisol inhibited only the concentrative process. Inhibition was non-competitive, indicating a decrase in the total capacity of the active transport mechanism. The effect of cortisol on α-aminoisobutyric acid transport was evident only after 60–90 min of treatment but preceeded the appearance of reductions in cellular ATP by an additional 60–90 min, suggesting that cortisol inhibition of α-aminoisobutyric acid transport was not caused by the decrease in ATP. 2. 2. Inhibition of protein synthesis with cycloheximide reduced α-aminoisobutyric acid uptake without decreasing cellular ATP, pointing to the participation of labile proteins in the active transport of α-aminoisobutyric acid which are not related to ATP metabolism. Inhibition of α-aminoisobutyric acid transport caused by cortisol and cycloheximide together was no greater than that caused by each agent alone. Moreover, cortisol failed to decrease cellular ATP levels during simultaneous exopsure of thymic lymphocytes to cycloheximide. Hence, inhibition of α-aminoisobutyric acid transport and reduction of ATP content are separate manifestations of cortisol action, each arising by a process which depends upon de novo protein synthesis. 3. 3. Inhibition of α-aminoisobutyric acid transport by cortisol appeared to be related to its glucocorticoid activity sicne (a) low concentrations (0.1 μM and 1.0 μM) were inhibitory, yet steroids devoid of glucocorticoid activity (progresterone, cortisone and testosterone) were non-inhibitory at the same concentrations, and (b) 11-deoxy-cortisol (cortexolone), which is known to impede the binding of glucocorticoids to cellular receptors, appreciably reduced the degree of inhibition caused by cortisol. High concentrations of progesterone and cortisone (10 μM) inhibited α-aminoisobutyric acid transport slightly suggesting that the decrease in α-aminoisobutyric acid uptake caused by 10 μM cortisol might reflect both specific (glucocorticoid-related) and non-specific effects.

Phenobarbital-induced Alterations in the Metabolism of [3H]Vitamin D3 by the Perfused Rachitic Rat Liver In Vitro

Anticonvulsant therapy of seizure disorders in man is associated with the development of complications involving bone and mineral metabolism including hypocalcemia, elevated serum immunoreactive parathyroid hormone levels, and increased amounts of unmineralized bone or osteoid. The latter has been attributed to a reduction in serum-25-hydroxycholecalciferol levels resulting from increased hepatic metabolism of vitamin D. Using an in vitro recycling hepatic perfusion system, we have demonstrated that 5 d of phenobarbital treatment increases the hepatic production of [(3)H]25-hydroxyvitamin D(3) (4.3+/-0.3 vs. 3.3+/-0.2%/h, P <0.025) without affecting the biliary excretion of radioactivity. Furthermore, rachitic livers perfused with blood obtained from animals treated with phenobarbital for 5 d also manifested an increase in [(3)H]25-hydroxyvitamin D(3) production (4.6+/-0.5 vs. 3.3+/-0.2%/h, P < 0.02). Addition of phenobarbital or its major metabolite, p-hydroxyphenobarbital, directly to the perfusion apparatus had no effect on [(3)H]25-hydroxyvitamin D(3) production. Phenobarbital treatment was also attended by a decrease in the intrahepatic content of [(3)H]vitamin D(3) (11.7+/-0.4 vs. 17.5+/-0.7 dpm/mg liver protein, P < 0.001) without alterations in the content of [(3)H]25-hydroxyvitamin D(3). The data collectively suggest that the increased hepatic conversion of [(3)H]vitamin D(3) to [(3)H]25-hydroxyvitamin D(3) attending phenobarbital treatment is secondary to stimulation of the hepatic 25-hydroxylation system(s) by a metabolite of phenobarbital other than p-hydroxyphenobarbital and/or by metabolic alterations resulting from phenobarbital therapy.

Hypophyseal Metastatic Renal Cell Carcinoma and Pituitary Adenoma. Case Report and Review of the Literature

A patient with a remote history of nephrectomy for renal ceil carcinoma presented with a visual field defect. At surgery, a metastasis from the hypernephroma and an adenoma were found coexisting in the anterior pituitary gland. Although hypernephromas are known to act as “recipient” tumors in cases in which two primary neopiasms coexist, it is unusual for a renal ceil carcinoma to metastasize into another tumor.