Samarendra N. Baksi

Chronic vitamin D deficiency in the weanling rat alters catecholamine metabolism in the cortex

The effect of a vitamin D deficient (--D), vitamin D replete (150 I.U. D3 twice weekly) and normal rat diets for 4 weeks in weanling male rats on the steady-state concentration in several brain sites of dopamine (DA), norepinephrine (NE), and dihydroxyphenylacetic acid (DOPAC) was investigated. The areas of the central nervous system assayed were the brainstem, cerebellum, cerebral cortex, hypothalamus-median eminence, and striatum. The results indicate that DA content of cortex and hypothalamus significantly increased in the --D group compared to the normal diet or D replete groups. The concentrations of DOPAC and NE in the cortex of both --D and D replete rats increased significantly compared to normal diet group. Plasma calcium level was significantly lower in --D group compared to the normal diet or vitamin D replete groups.

Vitamin D metabolism in bullfrogs and Japanese quail: Effects of estradiol and prolactin

Abstract Estradiol benzoate injection (5 mg/kg im daily) in the bullfrog for 15 days significantly increased both the plasma calcium level and the in vitro renal production of 1,25-dihydroxyvitamin D 3 [1,25-(OH) 2 D 3 ] from 25-hydroxyvitamin D 3 [25-(OH)D 3 ]. A lower dose (3 mg/kg im daily for 6 days) failed to show significant responses. Ovine prolactin injection (0.5 mg/kg im twice daily for 5 days) in Japanese quail also significantly increased both the plasma calcium level and the in vitro renal production of 1,25-(OH) 2 D 3 . A higher dose of prolactin (1.0 mg/kg in twice daily for 4.5 days) also stimulated in vitro renal production of 1,25-(OH) 2 D 3 and depressed that of 24,25-(OH) 2 D 3 but did not increase the plasma calcium significantly. On the other hand, a hypercalcemic dose of ovine prolactin (0.5 mg/kg im daily for 9 days) in the bullfrog failed to elicit any stimulation of in vitro renal production of 1,25-(OH) 2 D 3 . Bullforg kidney homogenates do not contain an inhibitor of the 25-(OH)D 3 -1-hydroxylase enzyme, as has been observed in homogenates prepared from mammalian kidneys.

Does estradiol stimulate in vivo production of 1,25-dihydroxyvitamin D3 in the rat?

Abstract Female rats were injected with estradiol benzoate (3 mg/kg daily) or corn oil for 8 days before receiving 325 picomoles of 25-[26,27 3 H]-hydroxyvitamin D 3 intravenously. Eighteen hours later lipids were extracted from plasma, gut mucosa and kidneys and vitamin D 3 metabolites were separated using Sephadex LH-20 and chloroform: hexanes (65:35) column chromatography. Estradiol treatment increased 1,25-[26,27- 3 H]-dihydroxyvitamin D 3 content in all three isssues.

Acute effect of estradiol on the renal vitamin D hydroxylases in Japanese quail

Abstract It has been reported previously by us and others that in vivo estradiol administration stimulates in vitro 1,25-(OH) 2 D 3 production in the Japanese quail and chicken. The present investigation was done to study the dose- and time-response relationships of estradiol-induced stimulation of in vitro 1,25-(OH) 2 D 3 production. In addition, the reported permissive role of androgen in this response was studied. Four-week-old immature female Japanese quail, either primed with testosterone propionate (5 mg/kg) or without androgen priming, were injected i.m. with three different doses (0.01, 0.1 and 1.0 mg/kg) of estradiol benzoate dissolved in 95 % ethanol. One, 4,12 and 24 hr after in vivo estradiol injection, kidney homogenates were incubated with tritiated 25-(OH)D 3 . The results were similar whether or not the birds were primed with androgen. Under both conditions all three doses of estradiol stimulated l,25-(OH) 2 D 3 , and inhibited 24,25-(OH) 2 D 3 , production at 12 and 24 hr with one exception (0.01 mg/kg dose at 12 hr in androgen-primed birds). At 4 hr these responses were seen only at the higher doses. The most rapid response was suppression of 24,25-(OH) 2 D 3 synthesis by the 0.1 mg/kg dose of estradiol at 1 hr in the androgen-primed birds. These responses in 1,25-(OH) 2 D 3 and 24,25-(OH) 2 D 3 production after a single dose of estradiol may be seen prior to a detectable rise in plasma calcium.

Acute Effects of Parathyroid Extract on Renal Vitamin D Hydroxylases in Japanese Quail

The dose- and the time-response relationships of parathyroid hormones modulation of in vitro 1,25-(OH)2D3 and 24,25-(OH)2D3 production in Japanese quail were investigated. 4-week-old female Japanese quail were injected intramuscularly with three different doses (30, 90 and 270 USP units/kg) of parathyroid extract (PTH). 4, 12 and 24 h after the in vivo administration of PTH, kidney homogenates were incubated with tritiated 25-(OH)D3. All three doses of PTH stimulated 1,25-(OH)2D3 and inhibited 24,25-(OH)2D3 production at 12 h relative to the vehicle-treated control group. The responses of the vitamin D hydroxylases were not detectable at 4 h and had returned to control levels by 24 h. Plasma calcium rose significantly at 4 h with the two higher doese of PTH (90 and 270 USP units/mg) but not with the lowest dose. By 12 h the plasma calcium had returned to control levels except at the highest dose of PTH. By 24 h all of the plasma calcium levels had returned to control values. Plasma inorganic phosphate levels were depressed at 4 h by all three PTH doses; they remained depressed at 12 h and returned to control levels by 24 h. It is concluded that the pharmacological effects of PTH on the renal vitamin D hydroxylases are slower in onset and shorter in duration when compared with those of estradiol.

Antiestrogen-induced alterations of hypothalamic dopamine and norepinephrine levels in the female rat.

The influence of antiestrogen (tamoxifen) administration in vivo on the steady state concentration of dopamine (DA) and norepinephrine (NE) in the hypothalamus-median eminence area of mature female rats was investigated. Rats were treated with tamoxifen at 3 different dose levels (0.1, 1.0 and 10.0 mg/kg, s.c.) daily for 7 or 21 days. Control groups were injected with vehicle only (10% ethanol; 1.0 ml/kg). In a separate experiment, mature female rats were ovariectomized or sham operated and killed either 7 or 21 days after operation. Dopamine and NE were estimated by high pressure liquid chromatography with electro-chemical detection. Seven days of tamoxifen treatment at 3 different dose levels did not alter DA and NE concentrations compared to the control. The chronic (21 days) tamoxifen treatment in the smallest dose (0.1 mg) significantly increased the DA concentration. The concentration of NE was reduced only at the 1.0 mg/kg dose. There was no significant difference in the NE concentration 7 or 21 days after ovariectomy or sham operation, but the DA concentration was significantly increased 21 days after ovariectomy. The uterine weights were reduced significantly after 21 days of treatment with tamoxifen in the two larger doses, but were increased with the smallest dose of tamoxifen. Uterine weight after ovariectomy both after 7 and 21 days was significantly reduced. These results suggest that chronic low-dose antiestrogen treatment may affect the hypothalamic-median eminence DA and NE concentrations. The data also suggests that antiestrogenic action (uterine growth inhibition) of tamoxifen is not related to the alterations of DA and NE in the hypothalamus-median eminence.

Regional alterations of brain catecholamines by lead ingestion in adult rats

The alterations in steady-state dopamine (DA) and norepinephrine (NE) content of hypothalamus-median eminence (HME) and striatum (STR) were measured in adult female rats fed normal calcium (1.2%) or low calcium (0.005%) diets for 4 weeks and exposed to lead via drinking water containing lead acetate (0.032, 0.32, and 3.2 mg Pb/ml) for the last 3 weeks of a 4-week diet period. Control lead-free groups of both dietary regimens received equimolar acetate as sodium acetate. The eight groups (six rats/group) were divided equally between the two diet regimens. Three weeks treatment with lead significantly reduced DA and NE in HME but DA only in STR (0.32 and 3.2 mg Pb/ml) of both dietary groups. Low dietary calcium alone reduced DA and NE in HME. In contrast with the HME low calcium diet alone had no significant effect on DA and NE in STR. No additive effect of low calcium diet and lead ingestion in catecholamine reduction was found in the brain parts studied.

Vitamin D metabolism in Japanese quail: Effects of lead exposure and dietary calcium

Abstract Four-week-old female Japanese quail were raised either on a low calcium (0.2%) or on a normal calcium (2.3 to 3.3%) diet for 15 days and at the same time they were given drinking water containing either lead acetate (0.032, 0.32, 3.2, or 16.0 mg Pb/ml) or sodium acetate (1.75 mg acetate/ml). On the 16th day, in vitro kidney production of 1,25- and 24,25-dihydroxyvitamin D 3 [1,25-(OH) 2 D 3 and 24,25-(OH) 2 D 3 ] from tritiated 25-hydroxyvitamin D 3 , plasma calcium, and phosphate, and body retention of lead (plasma, liver and femur), were determined. Under both dietary conditions, lead ingestion (0.32, 3.2 and 16.0 mg Pb/ml), when compared with sodium acetate-treated controls, resulted in the stimulation of 1,25-(OH) 2 D 3 production, but 24,25-(OH) 2 D 3 increased only under normal dietary calcium and higher doses (3.2 and 16.0 mg Pb/ml) of lead. Production of 24,25-(OH) 2 D 3 was non-detectable in all groups given low calcium diet. Lead added in vitro to kidney homogenates of untreated, age-matched quail had no significant effect on renal hydroxylases. Lead treatment also had no significant effect on plasma calcium and phosphate concentrations. The lead concentration in plasma, liver, and femur was always higher at comparable dose levels of lead under the low calcium dietary conditions. The data indicate that subacute lead ingestion results in the stimulation of renal 25-hydroxyvitamin D 3 -1-hydroxylase activity.

Estradiol-Induced Stimulation of 25-Hydroxyvitamin D3 -1-Hydroxylase in Vitamin D-Deficient Japanese Quail

The dose-response relationship of estradiol benzoate (E2B)-induced increase of in vitro 1,25-dihydroxyvitamin D3 - 1,25-(OH)2D3 - production in Japanese quail raised on a vitamin D-deficient diet was investigated. 4-week-old male and female Japanese quail, initially raised on a normal calcium and vitamin D diet, were placed on a vitamin D-deficient diet for an additional 4 weeks. At 8 weeks of age, E2B was injected intramuscularly at three different doses (0.03, 0.3 and 3.0 mg/kg) daily for 5 days. Two control groups received an equal volume of vehicle only (0.5 ml/kg, 95% ethanol). Kidney homogenates were incubated with tritiated 25-hydroxyvitamin D3 (25-OH-D3). All three doses of E2B stimulated 1,25-(OH)2D3 production beyond the basal level in both sexes but to a much greater extent in the female. Maximal stimulation was observed with the lowest dose (0.03 mg/kg) of E2B. There was no detectable 24,25-dihydroxyvitamin D3 production in any group. A rise in plasma calcium and phosphorus was seen at all three dose levels of E2B in both sexes. The femur dry weight increased significantly only at the two higher doses of E2B in both sexes. It is concluded that E2B injection in vitamin D-deficient Japanese quail can stimulate 25-OH-D3-l-hydroxylase activity beyond the already stimulated basal.