Effect of ipriflavone on the response of uterus and thyroid to estrogen

Ipriflavone, 7-isopropoxy-3-phenyl-4H-1-benzopyran-4-one, was uterotropic in intact but not in ovariectomized rats. When it was administered simultaneously with estrone and estradiol-17 beta to ovariectomized rats, ipriflavone increased the uterotropic activities of both estrogens. The uterotropic activity of this compound in intact rats might be attributable to its action on the target organ of estrogen by augmenting the response to the hormone because none of the other possibilities for accelerating uterine growth such as gonadotropin-releasing, gonadotropic, and estrogen metabolism-retarding activities were demonstrated experimentally. In addition, ipriflavone increased the calcitonin releasing activity of estrone when these compounds were administered simultaneously to ovariectomized rats.     

Model for skeletal resistance to vitamin D in renal failure.

Chronic renal disease in man and animals is associated with disturbances in calcium homeostasis which are resistant to vitamin D-therapy. Partially nephrectomized and intact rats were used to evaluate the effect of uremia on the response of bone to vitamin D. Serum calcium, serum phosphorus and blood urea nitrogen levels were higher in uremic rats than in intact rats, both given vitamin D. Metaphyseal bone in uremic rats was resistant to vitamin D-induced bone resorption; osteoblasts and osteocytes appeared less active ultrastructurally and osteoclass were infrequent. Calcitonin synthesis and release evaluated electron microscopically was greater in uremic rats. It is suggested that the altered response of bone to vitamin D in uremic rats was due in part to elevated serum phosphorus and increased calcitonin release. The present model does not refute experimental and clinical data that metabolism of vitamin D is altered in renal disease. It does, however, emphasize that in chronic renal failure other parameters (phosphorus levels, calcitonin release, uremia) are operating which may influence end organ response to pharmacologic doses of vitamin D. The partially nephrectomized rat may be a useful model for evaluating end-organ resistance to vitamin D in uremia.     

Effect of ipriflavone on bone changes induced by calcium restricted, vitamin D deficient diet in rats

The preventive effect of ipriflavone, 7-isopropoxy-isoflavone, on the development of experimental osteopenia in rats was studied. Male Wistar rats (4 weeks old) on a calcium restricted, vitamin D deficient diet were given a daily oral administration of ipriflavone. The administration of ipriflavone (100 mg/kg BW/day) for 40 days significantly inhibited a decrease in the cortical thickness (14.0 +/- 1.6 vs. 17.1 +/- 2.9%, mean +/- SD, p less than 0.05) and bone calcium content (62 +/- 4 vs. 67 +/- 2 mg, p less than 0.05) in the femora of rats induced by a mild calcium restricted (0.3%), vitamin D deficient diet. This compound did not affect serum calcium levels in this condition. But a dose of 20 mg/kg BW/day of ipriflavone was insufficient to inhibit a decrease in bone calcium content. In rats fed on a more severe calcium restricted (0.03%), vitamin D deficient diet, the administration of ipriflavone (100 mg/kg BW/day) did not significantly affect the cortical thickness or calcium content. Intestinal calcium absorption measured by the in situ loop method was not significantly different between rats fed with a severe calcium restricted (0.03%), D deficient diet with or without ipriflavone (20 or 100 mg/kg BW/day) These results demonstrate that the new compound, ipriflavone, partially prevents bone calcium loss induced by a mild calcium restricted (0.3%), vitamin D deficient diet in rats. However, the precise mechanism of action of this compound remains unknown.     

Calcitonin secretion during postnatal development in the rat: beta-adrenergic agents and vitamin D3 metabolites

The possible contribution of catecholamines and vitamin D3 metabolites to the high plasma calcitonin (CT) levels in suckling baby rats is unknown. So, in vivo and in vitro (using a perifusion system) effects of beta-adrenergic agents and vitamin D3 metabolites on CT release were studied in the rat during the postnatal development. In 13-day-old rats, the increase in plasma CT levels induced by isoproterenol injection (0.1 micrograms/kg b.w.) was inhibited by a previous administration of propranolol. A significant decrease in plasma CT levels was observed after propranolol injection in baby rats (0.68 +/- 0.05 ng/ml vs. 0.93 +/- 0.01 ng/ml). A daily injection of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3; 25 pmoles/rat/day during 4 days) induced a marked rise in plasma calcium (16.1 +/- 0.2 mg/dl), and a great decrease in thyroidal CT contents (approximately 70% of control values) in 13-day-old rats while no change was noted with 24,25-dihydroxycholecalciferol (24,25-(OH)2D3). A negative correlation between plasma calcium and thyroidal CT stores was found in suckling and in weaning rats treated with different doses of 1,25-(OH)2D3, suggesting an indirect effect of 1,25-(OH)2D3 on CT secretion. The mobilization of the thyroidal CT content was greater in weaning than in suckling rats in response to a given hypercalcemia. In vitro, 5 X 10(-5) M isoproterenol induced a rapid increase in CT secretion rate while 1,25-(OH)2D3 inhibited the rise in CT release induced by 3.0 mM calcium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibitory effects of somatostatin analogs on prolactin secretion in rats pretreated with estrogen or haloperidol

The effect on prolactin (PRL) secretion of acute administration of new octapeptide analogs of somatostatin (SS) with an enhanced and prolonged growth hormone inhibitory activity was investigated in rats under various pretreatment conditions with estrogen and antidopaminergic drugs. Analog D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH2 (RC-121), at a dose of 5 micrograms/100 g body wt, did not decrease basal PRL levels in thiopental-anesthetized female rats, untreated or treated with estrogen benzoate (EB) (8 micrograms/rat) for 5 days. When haloperidol was used to elevate PRL level, a single injection of RC-121 inhibited PRL release in EB-pretreated female rats or untreated female and male rats. Analog D-Phe-Cys-Trp-D-Trp-Lys-Val-Cys-Trp-NH2 (RC-160), which has a potency similar to RC-121 in the tests on inhibition of GH, in a dose of 0.2 microgram/100 g body wt, did not lower the elevated PRL level induced by alpha-methyl-p-tyrosine and/or pretreatment with EB (100 micrograms/rat, 3 and 6 days before) in pentobarbital-anesthetized male rats. However, both analogs RC-121 and RC-160, in doses of 0.2 microgram/100 g body wt, decreased the PRL levels elevated by prolonged pretreatment with EB (100 micrograms/rat, twice a week for 3 weeks) in male rats. These results indicate that acute administration of these SS analogs can induce a prolonged inhibition of PRL release when PRL is acutely elevated by haloperidol or chronically elevated by 3 weeks of estrogen administration. Future additional studies are required to investigate the effects of chronic administration of these SS analogs on PRL levels.     

Effect of the aromatase inhibitor, 4 hydroxyandrostenedione, on the endotoxin-induced changes in steroid hormones in male rats.

The increase in circulating estrogen concentrations that follows injection of Escherichia coli endotoxin (Endo) may be due to increased aromatase activity. We have therefore analysed the effect of the aromatase inhibitor, 4 hydroxyandrostenedione (4OHA) on the steroid hormone response of male rats, particularly the dramatic increase in estrogens and decrease in androgens, induced by Endo. The concentrations of corticosterone (B), progesterone (P4), 17 alpha hydroxyprogesterone (17 alpha OHP4), androstenedione (delta 4), testosterone (T), estrone (E1) and estradiol (E2) were determined 2 hours after injection of increasing doses of 4OHA with and without Endo. The increase in serum estrogen concentrations and drop in serum androgen levels in response to Endo were blocked by a single dose of 4OHA. The effect of 4OHA appeared to be dose dependent. Low doses (30 mg/kg and 50 mg/kg) induced significant changes in the estrogen and androgen responses, but the high dose (100 mg/kg) blocked all changes in sex steroids induced by Endo. 4OHA did not alter the Endo-induced changes in other steroids.     

Glucocorticoids stimulate the production of preprocalcitonin-derived secretory peptides by a rat medullary thyroid carcinoma cell line

A rat medullary thyroid carcinoma cell line, CA-77, has been established as a model system for investigating calcitonin biosynthesis and secretion. Growth of this cell line in serum-free defined medium provided suitable conditions for studying steroid hormone effects on the production of calcitonin and related peptides. After exposure for 5 days to a variety of steroids, only dexamethasone and corticosterone increased cellular content of calcitonin and a second secretory peptide (CCAP) derived from the same mRNA translation product as calcitonin. Glucocorticoids had no effect on cellular somatostatin, another secretory product of these cells. Increasing doses of dexamethasone progressively elevated cellular calcitonin and CCAP, with a maximal effect at 10(-8) M; 10(-9) M and lower doses were ineffective. On a molar basis, corticosterone was approximately 50-fold less potent than the synthetic glucocorticoid. An increase in cellular calcitonin content was observed only after 48 h of glucocorticoid treatment; a maximum increase (13-fold) occurred after 7 days. Glucocorticoids also increased basal calcitonin secretion. Similar effects were observed for cellular and secreted CCAP. Withdrawal of dexamethasone after 4 days of treatment lowered cellular calcitonin toward the level of control cultures. Dexamethasone pretreatment potentiated the acute secretory response to calcium for both calcitonin and CCAP, while no such enhancement was noted for calcium stimulation of somatostatin secretion. We conclude that the glucocorticoids specifically stimulate the production and secretion of calcitonin and CCAP, two secretory peptides derived from preprocalcitonin.     

Bisphenol A influences the plasma calcium level and inhibits calcitonin secretion in goldfish

In teleosts, it is well known that plasma calcium levels increase as a result of treatment with estrogen for at least during 2 weeks and that calcitonin secretion is induced by estrogen. The present study examined the influence of bisphenol A on calcium homeostasis in goldfish and compared the above known estrogenic action. In goldfish kept in water containing bisphenol A (10(-6) M), the plasma calcium concentration increased significantly (P<0.001) at 4 days but decreased significantly (P<0.05) at 8 days. By the treatment of bisphenol A, calcitonin secretion was not induced until 4 days. At 8 days, however, plasma calcitonin, as well as calcium, decreased significantly (P<0.05), although vitellogenin was detected in the plasma. Therefore, bisphenol A influences plasma calcium levels, but its action is different from that of estrogen, which indicates that bisphenol A affects the calcium homeostasis and might bring about abnormal conditions in teleosts.     

A transient increase in renal clearance of phosphate in response to continuous infusion of salmon calcitonin in rats.

The effects of intravenous carrier-free salmon calcitonin on renal clearances of phosphate, calcium, magnesium, sodium and potassium were studied in male parathyroid-ectomized (PTX) and intact rats. Both natural and synthetic hormone, when infused at constant rates (0.005 approximately 0.5 MRC U/hr), produced a rapid increase (peaking at about 60-90 min) in phosphate clearance. However, the maximal increase was transient in nature in PTX rats. In intact rats, the phosphaturic response was somewhat more pronounced and the decline after the peak was rather modest. When a large amount (4 MRC U) of calcitonin was given in divided doses, the second dose produced a lesser extent of phosphaturia in both intact and PTX rats. The phosphaturic response was accompanied by an increase in sodium and potassium clearances in PTX rats and by an increase in potassium clearance in intact rats. A fall in the apparent clearance values for calcium and magnesium occurred and was maintained throughout the infusion period of hormone in both intact and PTX rats. In conclusion, PTX rats respond to the intravenous administration of salmon calcitonin with a transient phosphaturic response which is accompanied by parallel diuresis of sodium and potassium along with sustained retention of calcium and magnesium by the kidney.     

Gap junction modulation in rat uterus. III. Structure-activity relationships of estrogen receptor-binding ligands on myometrial and serosal cells

A number of steroidal and nonsteroidal estrogen receptor-binding ligands were tested for their ability to affect the formation and internalization of gap junctions in hypophysectomized rat uterine myometrial and serosal cells. Potent estrogen, including diethylstilbestrol, estradiol benzoate (EB), estradiol-17 beta, and the weak estrogens, estriol and estrone, stimulate formation of macular and annular gap junctions in myometrium in a dose-dependent fashion when administered in daily injections over 5 days. Induction of annular gap junctions in the uterine serosal epithelium follows a similar dose-dependent pattern of estrogen stimulation but requires lower levels of hormone to initiate the response. In myometrium, differential stimulation of circular and longitudinal myometrial cell layers was observed, with 3 to 5 times more gap junctions detected in the circular than in the longitudinal layer. Progesterone, estriol, or estrone suppress the myometrial gap junction response to EB when administered concurrently with EB. However, the EB-stimulated appearance of myometrial cell gap junctions was blocked when the progesterone-to-estrogen ratio exceeded 100:1. The estrogen receptor-binding androgens, 5 alpha-androstane-3 beta,17 beta-diol (Adiol) and delta 5-androstene-3 beta,17 beta-diol failed to induce myometrial gap junctions at doses up to 5 mg/day for 5 days, whereas Adiol did induce annular gap junctions in the serosal cells at the highest dosage tested. Of the triphenylethylene derivatives and related compounds evaluated, including mixed isomers of tamoxifen and CI 628, the cis (zuclomiphene, ZUC) and trans (enclomiphene) isomers of clomiphene citrate, and a fixed-ring antiestrogen, nafoxidine, only ZUC was able to induce gap junctions in myometrial and serosal cells. These studies indicate that induction of gap junctions in rat uterine myometrial cells is an estrogen-dependent response that requires higher levels of estrogen than other estrogen-dependent target cell responses in the rodent uterus.     

Duration of antiestrogenecity of compound CDRI-85/287: a new orally active nonsteroidal antiimplantation agent.

Duration of antiestrogenic and antiimplantation action of CDRI-85/287, (2-(4-(2-N-piperidino)ethoxy phenyl)-3-phenyl(2H)benzo(2)pyran), was studied in rat. Pretreatment of ovariectomized immature rats with this compound caused translocation of cytoplasmic estrogen receptor (ER) to the nucleus and a marked depletion of cytoplasmic ER pool resulting in a nonresponsive state of the uterus to subsequent estrogen administration until day 4. While in rats pretreated with estradiol, increased cytoplasmic ER level made the uterus responsive to a second injection of estrogen. In the delayed implantation model, 85/287 pretreated rats were given estrone on days 4, 5 or 6 post-antiestrogen treatment. No implantations were observed after estrone administration on day 4, but were present when estrone was given on days 5 or 6. Summation of these results suggests the duration of action of 85/287 to be 3-4 days in rat.     

Biphasic stimulatory effects of estrogen on gonadotropin surges induced by continuous administration of gonadotropin-releasing hormone in women

The present experiments were performed to study the effects of preovulatory levels of estrogen on GnRH-induced gonadotropin release. Twelve female volunteers in various phases of the menstrual cycle received estradiol infusion for 66 h at a constant rate of 500 micrograms/24 h which is grossly equivalent to its production rate during the preovulatory follicular phase. In 8 of the women, GnRH was administered concomitantly from 6 h after the initiation of estradiol infusion. The administered doses of GnRH were 2.5 and 5 micrograms/h. Blood samples obtained throughout the infusion were analysed for LH, FSH, estradiol and progesterone. The sole administration of estradiol failed to induce the positive feedback effect on gonadotropin release within the experimental period in the early follicular phase (days 3-7) in 4 women. In 5 women treated during the follicular phase, remarkable LH releases were induced after a lag period by the infusion of both GnRH and estradiol. The induced LH surge formed a prolonged biphasic pattern. Although a similar pattern of FSH was observed in some cases, its response was minimal compared with that of LH. In 3 women during the luteal phase, however, a combined administration of estradiol and GnRH induced only a short term release of LH which was terminated in only 12 h. The present data indicate that 1) Preovulatory levels of estrogen affect the late part of the LH surge which is induced by constant administration of low doses of GnRH resulting in a prolonged biphasic release of LH, and 2) These effects of both hormones are not manifest in the presence of high levels of progesterone. These results indicate the possibility of a role of GnRH and estrogen in the mechanism of the prolonged elevation of a gonadotropin surge at mid-cycle.     

Pressor doses of vasopressin result in only transient elevations in plasma peptide levels

We recently reported that neuronostatin, a novel neuropeptide, biphasically increased mean arterial pressure, first through the activation of the sympathetic nervous system followed by the release of vasopressin. In those experiments, we found that centrally administered neuronostatin increased plasma vasopressin levels only 2-3 times greater than levels observed in saline-treated controls, and that the increase in mean arterial pressure (approximately 15 mm Hg) could be blocked by pretreatment with a V1-vasopressin antagonist. Here we report the relationship between two to three fold elevations in plasma vasopressin levels and concomitant changes in mean arterial pressure in conscious, unrestrained male rats. We injected increasing doses of vasopressin (5, 20, and 100 ng/kg, intra-arterially) and measured both changes in plasma vasopressin levels and the elevation in mean arterial pressure achieved. At 5-min post injection, plasma levels of vasopressin and mean arterial pressures were similar to those observed following central neuronostatin administration in our earlier study. Thus we conclude that small increases in circulating vasopressin levels can result in significant elevations in mean arterial pressure at least in the conscious rat.     

Tachykinin neurokinin 3 receptor signaling in cholecystokinin-elicited release of oxytocin and vasopressin

Neurokinin 3 receptor (NK3R) signaling has an integral role in the stimulated oxytocin (OT) and vasopressin (VP) release in response to hyperosmolarity and hypotension. Peripheral injections of cholecystokinin (CCK) receptor agonists for the CCK-A (sulfated CCK-8) and CCK-B (nonsulfated CCK-8) receptors elicit an OT release in rat. It is unknown whether NK3R contributes to this endocrine response. Freely behaving male rats were administered an intraventricular pretreatment of 250 or 500 pmol of SB-222200, a specific NK3R antagonist, or 0.15 M NaCl before an intraperitoneal or intravenous injection of CCK-8 (nonsulfated or sulfated) or 0.15 M NaCl. Blood samples were taken before intraventricular treatment and 15 min after intraperitoneal or intravenous injection, and plasma samples were assayed for OT and VP concentration. Intraperitoneal injection of both nonsulfated and sulfated CCK-8 significantly increased plasma OT levels and had no effect on plasma VP levels. Intravenous injection of sulfated CCK-8 stimulated an increase in plasma OT levels and did not alter plasma VP levels. However, intravenous injection of nonsulfated CCK-8 stimulated a significant increase in plasma levels of both OT and VP. No other studies have demonstrated CCK-8-stimulated release of VP in rat. NK3R antagonist did not alter baseline levels of either hormone. However, pretreatment of NK3R antagonist significantly blocked the CCK-stimulated release of OT in all CCK treatment groups and blocked VP release in response to intravenous injection of nonsulfated CCK-8. Therefore, central NK3R signaling is required for OT and VP release in response to CCK administration.     

Effect of ipriflavone on glucocorticoid-induced osteoporosis in rats

Ipriflavone, 7-isopropoxy-3-phenyl-4H-1-benzopyran-4-one, was administered orally for 12 weeks to male rats with prednisolone-induced osteoporosis. Microdensitometric analysis of a roentgenograph of the femurs revealed that ipriflavone increased the density of the distal metaphysis dose-dependently and tended to increase the density of the diaphysis. It also inhibited dose-dependently the decrease in the mechanical strength of the tibia, breaking strain and breaking energy, and the fractional content of ash in femurs. These results indicate that ipriflavone markedly suppresses bone resorption at the metaphysis where the content of trabecular bone with a rapid turnover rate is high, and possibly inhibits bone reduction at the diaphysis.     

Effect of parathyroid hormone on the increase in serum glucose and insulin levels after a glucose load to thyroparathyroidectomized rats.

Thyroparathyroidectomy (TPTX) caused a significant increase in serum glucose and a corresponding fall in serum calcium in both fed and fasted rats. The increase in serum glucose, induced by TPTX, was markedly potentiated by a single intraperitoneal administration of calcium (2 mg/100 g BW) which caused a significant elevation of serum calcium in thyroparathyroidectomized rats. Parathyroid hormone (PTH; 20 U/100 g BW) administered subcutaneously to thyroparathyroidectomized rats, caused a significant decrease in serum glucose (0.1 g/100 g BW) to sham-operated rats significantly increased both serum glucose and insulin. The rise of serum glucose produced by a glucose load was markedly potentiated by TPTX, but the increase in serum insulin was not promoted significantly. The administration of PTH decreased both serum glucose and insulin levels increased by a glucose load to thyroparathyroidectomized rats, in a dose-dependent manner. The administration of calcitonin (80 MRC mU/100 g BW) significantly prevented the effect of PTH to decrease serum glucose after a glucose load to thyroparathyroidectomized rats, and calcitonin increased serum insulin. These results suggest that the effect of PTH on serum glucose does not involve insulin secretion.     

The effects of fasting and refeeding on serum parathormone and calcitonin concentrations in young and old male rats.

Although fasting and refeeding reveal the existence of age-related changes in carbohydrate and lipid metabolism, the effects of aging on mineral metabolism in refed animals are unknown. We therefore investigated hormonal regulation of calcium metabolism in young (4 months) and old (26 months) male rats fasted for 48 hours and then refed for 4 or 24 hours. Serum concentrations of total and ionized calcium and parathormone were similar in control young and old rats. Serum calcitonin level was higher, and the concentrations of albumin and inorganic phosphate and alkaline phosphatase activity were lower in fed old rats. In young fasted rats, the serum ionized and total calcium was decreased, and phosphate concentration was increased. In old rats, fasting resulted in the increase of serum parathormone level. Fasting reduced serum alkaline phosphatase activity to a similar extent in both age groups. In young rats, refeeding for 24h normalized serum calcium and phosphate levels and alkaline phosphatase activity, and decreased serum concentrations of PTH and calcitonin. In old refed rats, serum calcitonin concentration was raised by 77% compared to fed or fasted animals, whereas parathormone levels were normalized. Our results indicate that old fasted or refed rats maintain normal serum calcium concentration in a different way than young animals, possibly through the increase in serum levels of parathormone and/or calcitonin. Thus, dietary manipulations such as fasting and refeeding constitute an interesting model for the investigation of the effects of aging on the hormonal regulation of serum calcium level.     

The effect of 1 alpha, 25-dihydroxycholecalciferol on iron metabolism

Chronic administration of hypercalcemic doses of 1 alpha, 25-dihydroxycholecalciferol to intact, vitamin-D repleted rats for 4 weeks, enhanced net intestinal absorption of iron and liver iron stores. Daily net iron and calcium absorptions were found to be significantly correlated in both control and treated rats. In duodenal loop experiments, pretreatment with 1 alpha, 25-dihydroxycholecalciferol reversed the adverse effect of high Ca/Fe ratio on iron absorption. The increased intestinal absorption of iron did not result in a change of serum iron levels nor of total iron binding capacity due to the enhanced incorporation of absorbed iron into liver ferritin. The curve of uptake of 59Fe into circulating red cells of treated rats suggested retarded release of the isotope from stores. The hypothesis is advanced that the systemic metabolic defect (tissue hypoxia, raised erythropoietin levels) produced by 1 alpha, 25-dihydroxycholecalciferol is responsible for the disruption of the physiological coordination between iron stores and intestinal absorption.     

Effects of oral estrone on rat energy balance

Oral doses of estrone from 10 nmol/(kg day) to 10 micromol/(kg day) were given to adult Wistar male rats for 10 days. Body composition, energy balance, total body estrone balance and plasma metabolites and hormones were measured at the end of the treatment. Body weight (as well as food intake, body energy, fat and water accrual) increased at doses in the 10--100 nmol/(kg day) range, but decreased at higher doses. Energy expenditure decreased with increasing doses of estrone. Plasma metabolite changes suggested the maintenance of energy homeostasis, and lipid parameters indicated that lipid mobilization increased with the increasing doses of estrone. Plasma estrone, acyl-estrone and estradiol levels decreased at low doses and increased at high doses of estrone. We conclude that: (a) repeated estrone gavages, even at very high doses, do not result in the accrual of estrone in the body; (b) low doses of estrone promote growth and high doses decrease body mass and fat accretion; (c) administration of estrone at low doses decreases its circulating levels and the levels of estradiol and acyl-estrone, a situation reverted at higher doses and (d) estrone administration induces a dose-dependent shift towards lower energy expenditure.     

Characterization of calcium accumulation in the brain of rats administered orally calcium: The significance of energy-dependent mechanism

The characterization of calcium accumulation in the brain of rats administered orally calcium chloride solution was investigated. Rats received a single oral administration of calcium (15–50 mg/100 g body weight), and they were sacrificed by bleeding-between 15 and 120 min after the administration. The administration of calcium (50 mg/100 g) produced a significant increase in serum calcium concentration and a corresponding elevation of brain calcium content, indicating that the transport of calcium into the brain is associated with the elevation of serum calcium levels. The increase in brain calcium content by calcium administration was not appreciably altered by the pretreatment with Ca²⁺ channel blockers (verapamil or diltiazem with the doses of 1.5 and 3.0 mg/100 g). In thyroparathyroidectomized rats, the administration of calcium (50 mg/100 g) caused a significant increase in brain calcium content, indicating that calcium-regulating hormones do not participate in the brain calcium transport. Now, brain calcium content was clearly elevated by fasting (overnight), although serum calcium level was not significantly altered. Calcium administration to fasted rats induced a further elevation of brain calcium content as compared with that of control (fasted) rats. The fasting-induced increase in brain calcium content was appreciably restored by refeeding. This restoration was also seen by the oral administration of glucose (0.4 g/100 g) to fasted rats. The present study demonstrates that serum calcium is transported to brain, and that the increased brain calcium is released promptly. The release of calcium from brain may be involved in energy metabolism, and this release may be weakened by the reduction of glucose supply into brain. The finding suggests a physiological significance of energy-dependent mechanism in the regulation of brain calcium.