The effects of an intracellular calcium antagonist HA 1077 on delayed cerebral vasospasm in dogs

Summary The effectiveness of calcium antagonists on a chronic cerebral vasospasm after an SAH is still under debate. Calcium channel blockers such as nimodipine, nefedipine etc. can dilate spastic arteries by intrathecal administration, but not by systemic (iv or po) use. HA 1077 is a novel and potent calcium antagonist vasodilator which is considered to act by employing different mechanisms from the usual calcium channel blockers since it inhibits 1. calcium ionophore A 23187 induced contraction in arterial strips and 2. phenylephrine induced contraction in calcium free media, suggesting that its site of action is in the intracellular space. HA 1077 is water soluble and relatively stable in light.In the present study, the efficacy of HA 1077 was evaluated on dogs by using the spiral arterial strips in vitro and by angiography in vivo. In the arterial strips from the control dogs, a 50% relaxation of KCl (15 mM) induced contraction was obtained by a 10^–6 M HA 1077 for the intracranial basilar and middle cerebral arteries, while a 10^–5 M was needed to obtain the same effect for the extracranial common carotid and vertebral arteries, indicating that HA 1077 is more effective for the intracranial arteries. A vasospasm was produced by the two haemorrhage model of Varsoset al. The average angiographic diameter of the basilar artery was reduced to 60% of the control on SAH day 7. Intravenous infusion of HA 1077 (0.5–3 mg/kg/30 min) significantly dilated the spastic basilar artery (up to 20–30%), for over 2 hours. A fall in the systemic BP remained less than 20% during this time. Such spasmolytic effects by intravenous administration could not have been obtained with the usual calcium channel blockers. HA 1077 may be suitable for the treatment of a vasospasm in humans as well.     

The effects of HA1077 on the cerebral circulation after subarachnoid haemorrhage in dogs

Summary We examined the effects of the recently developed calcium antagonist HA1077 on cerebral haemodynamics during the chronic stage of the two-haemorrhage canine model system of vasospasm. Regional cerebral blood flow (rCBF), regional cerebral blood velocity and regional cerebral blood volume in the canine parietal cortex were measured by Laser-doppler flowmeter. On the 7th day after the initial injection of autogenous blood, subarachnoid haemorrhage (SAH) produced a significant decrease in rCBF (59% of control, p<0.05) and Hood velocity (48% of control, p<0.05), with no remarkable change in blood volume (108% of control). Bolus intravenous administration of HA1077 (0.1–0.3 mg/kg) dose-dependently increased the rCBF and blood velocity, without significantly changing the blood volume on Day 7 after SAH. HA1077 improves haemodynamic function manifested by an increase in rCBF and velocity in this SAH model, and may be suitable for the treatment of vasospasm in patients with SAH.     

Dose escalation trial of a novel calcium antagonist,AT877, in patients with aneurysmal subarachnoid haemorrhage

Summary The initial dose-escalating clinical trial of a novel calcium antagonist, AT877, in patients with aneurysmal subarachnoid haemorrhage is reported. AT877 is characterized by its strong spasmolytic activity, its inhibition of intracellular calcium ion activity, and the inhibiton of several protein kinases.A total of 113 patients (Hunt and Hess grades I to IV) who had undergone surgery within 3 days of aneurysmal rupture entered the study. Patients were divided into 5 groups according to the total daily dose of AT877: I: 20 mg; II: 40 mg; III: 60 mg; IV: 90 mg; and V: 120–180 mg. AT877 was given by intravenous infusion over 30 min two or three times a day for 14 days after surgery.Although AT877 did not completely abolish angiographic vasospasm, severe vasospasm was seen less frequently in patients given higher doses. Vasospasm was the cause of a poor clinical outcome (Glasgow outcome scale rating 3 or greater) in 19%, 7%, 9%, 8%, and 6% of the patients in groups I to V, respectively. The results indicated a favourable clinical effect of AT877 at doses above 40 mg per day. Only mild hypotension was seen, even when 60 mg of AT877 was infused over 30 min.AT877 appears to be effective in patients with subarachnoid haemorrhage. Part of its effect may be attributable to protection of the brain from ischaemic insults due to chronic cerebral vasospasm. However, the drug still needs to be evaluated in a placebo-controlled double-blind trial (which is currently being carried out).     

Interactions between vasoconstrictors in isolated human cerebral arteries

Summary This study investigates whether different endogeneous vasoconstrictors exert synergistic effects in isolated human cerebral arteries, because potentiation of contractile effects may play a role in the pathogenesis of cerebral vasospasm. Isolated human pial arteries obtained from macroscopically intact tissue during brain tumour operations were mounted onto a wire myograph. Concentration-response curves of 5-hydroxytryptamine (5-HT) were constructed in the absence and presence of threshold concentrations of the thromboxane A₂ (TXA)-analog U46619, and endothelin-1 (ET-1). Threshold concentrations of U46619 markedly enhanced the maximum contractile effect of 5-HT. The response to 5-HT Threshold concentrations of ET-1 increased the maximum response to 5-HT, and markedly shifted the dose-response curve to the left. Even after washout of ET-1, the dose-response curve of 5-HT remained shifted to the left. The increase of the contractile effect of 5-HT in the presence of U46619 did not correlate with the relaxant action of the endothelium-dependent vasodilator carbachol. Thus, synergism between contractile substances such as 5-HT, U46619, or ET-1 is seen in human cerebral arteries, and responses to 5-HT are potentiated even after washout of ET-1 and U46619. The potentiation does not depend on the endothelial function. We conclude that synergistic responses between endogeneous vasoconstrictors such as 5-HT, TXA and ET-1 may be involved in the pathogenesis of cerebral vasospasm after subarachnoid haemorrhage.     

Pathophysiology of dogs after 84% hepatectomy with emphasis on prostaglandin metabolites and the effect of a thromboxane A2 synthesis inhibitor and a prostaglandin I2 analog

The pathophysiological conditions following 84% hepatectomy were examined in terms of the changes in thromboxane A₂ (TxA₂) and prostaglandin I₂ (PGI₂) in canine model. OKY-046, TxA₂ inhibitor, and OP-2507, a PGI₂ analog, were administered to evaluate the possibility of extending hepatic resection. The 2-week survival rate following 84% hepatectomy significantly improved after the administration of OKY-046 and OP-2507, from 12.5% to 58.3% and 75.0%, respectively. Furthermore, OP-2507 significantly improved impaired hepatocyte and sinusoidal endothelial cell function after 84% hepatectomy, resulting in a satisfactory recovery to the preoperative levels. Within 24 h after 84% hepatectomy, the plasma levels of thromboxane B₂ (TxB₂) increased significantly, and the 6-keto-prostaglandin F_l (6-KF) levels became slightly elevated. OKY-046 and OP-2507 decreased TxB₂ and increased 6-KF in the plasma, resulting in the maintenance of sufficient blood flow in the portal vein and hepatic tissue and the mitigation of microcirculatory disorders. Moreover, the cytoprotective effects of the two drugs inhibited functional impairment of the residual liver. In conclusion, abnormal prostaglandin metabolites were produced after 84% hepatectomy, being involved in residual liver disorders. However, the administration of either an inhibitor of TxA₂ synthesis or PGI₂ analog ameliorated the functional impairment of the residual liver, which suggests their potential value for extending the resectability of the liver from what is presently feasible.An abstract of this study was presented at the 92nd Annual Meeting of the Japan Surgical Society held in 1992.     

Induction mechanism of small intestinal lesions caused by intravenous injection of endotoxin in rats

The pathogenesis of intestinal damage caused by bolus intravenous injection of endotoxin (ETX; 3 mg/kg) was investigated. Administration of ETX to rats induced reddish discoloration suggestive of bleeding, increased hemoglobin amounts, and leakage of plasma protein in the intestine. However, light microscopic examination of the intestine demonstrated blood congestion of the microvessels. Plasma accumulation was partially inhibited by combined pretreatment with a histamine H₁ antagonist and a serotonin (5-HT) antagonist. Neither a 5-lipoxygenase inhibitor, a soybean trypsin inhibitor, nor atropine was observed to inhibit plasma accumulation. Both the intestinal leakage of plasma and the accumulation of hemoglobin were completely inhibited by indomethacin, a selective thromboxane A synthetase inhibitor (OKY 1581), and a stable PGI₂ analogue (beraprost). Intravital microscopic observation of the microvessels of the small intestinal villi demonstrated microthrombus formation within several minutes after the injection of ETX, and pretreatment with OKY 1581 attenuated the formation of microthrombus. Platelet counts decreased significantly 10 min after ETX administration, and the decrease was not inhibited by pretreatment with either OKY 1581 or beraprost. Prothrombin time (PT) and activated partial thromboplastin time (APTT) were not prolonged. These observations thus suggest that microcirculatory disturbances by platelet thrombus, which are mediated by thromboxane A₂ at least in part, play an important role in ETX-induced intestinal damage.     

Protective effects of thromboxane A2 synthetase inhibitor (OKY-046) on hepatic ischemia-reperfusion injury in rats with obstructive jaundice

The effects of OKY-046, a thromboxane A₂ synthetase inhibitor, on complete hepatic ischemia with obstructive jaundice were studied in male Wistar rats in vivo. The objective of this study was to investigate the influence of OKY-046 (i) on the hepatic microcirculation, as measured by tissue partial oxygen pressure (tPO₂), and (ii) on the release of interleukin-8 (IL-8) in hepatic tissue after reperfusion. Fourteen days after bile duct clamping, the rats were subjected to 30-min warm complete liver ischemia and then reperfusion. The rats were divided into three groups; one group received no treatment (controls, group C), one group received OKY-046 from 15 min before hepatic ischemia to the end of the experiment (group OKY), and the third group received gadolinium chloride (group Gd), injected intravenously to evaluate the contribution of the Kupffer cell to IL-8 production. Group OKY maintained significantly higher tPO₂ levels 5, 10, and 15 min after declamping compared to group C (P<0.05). The IL-8 level in liver tissue in group OKY was lower than that in group C, but the difference was not significant. Group Gd exhibited the lowest IL-8 level of the three groups (P < 0.05). These findings demonstrated that OKY-046 improved the hepatic microcirculation during the reperfusion period, influenced the Kupffer cells in terms of the avoidance of hypoxia, and depressed the concentration of IL-8 in liver tissue.     

Prevention of cerebral vasospasm with OKY-046 an imidazole derivative and a thromboxane synthetase inhibitor. A preliminary co-operative clinical study

Summary The prevention of cerebral vasospasm with OKY-046, an imidazole derivative and a thromboxane synthetase inhibitor, was studied co-operatively at ten neurosurgical services. Intravenous administrations of 2, 5 or 10 /kg/minute of OKY-046 were given continuously from the earliest possible day to the 14th SAH-day to 82 pateints with ruptured cerebral aneurysm. Sixty-eight patients (83%) showed moderate to high high-density (SAH) in their initial CTs. Angiographic vasospasms were seen in 58 patients, representing 71% of all cases or 81% of the 72 cases for which angiograms were available; the vasospasms of 45 patients (55 or 63%) were moderate to severe. Symptomatic vasospasm occurred, however, only in 27 patients (33%); in 18 of those cases, moreover, the symptoms were mild or transient. The conditions of the patients at one month after the SAH were classified into 9 grades from 0 (normal) to 8 (deceased). Fifty-two patients (63%) were classified as 0 or 1, and 64 (78%) as better than 3 (possible daily life unaided). The administration of OKY-046 was proven to decrease TXB₂ in the blood.This paper emphasizes the effectiveness of the drug for symptomatic vasospasm, and supports our previous contention that cerebral microthrombosis may play an important role in the pathogenesis of cerebral vasospasm.     

The protective effect of thromboxane A2 synthetase inhibitor against ischemic liver injury

To evaluate the role of thromboxane A₂ (TXA₂) in ischemic liver injury, the serum changes in thromboxane B₂ (TXB₂) and 6-keto-prostaglandin F₁ alpha (6-K-PGF₁) following warm ischemia of the total canine liver were examined, and the protective effect of a TXA₂ synthetase inhibitor was assessed. Total liver ischemia was performed for 60 min on two groups of dogs: a control group, in which ischemia alone was performed, and an OKY-046 group, which received a TXA₂ synthetase inhibitor. A temporary active portacaval shunt was used to eliminate the effects of splanchnic venous stasis during clamping of the hepatic pedicle. Postoperative changes in liver function, assessed by the transaminase enzyme levels, and in prostaglandins were recorded and the histologic liver findings of both groups 1 week after ischemia were compared. The levels of 6-K-PGF₁ increased after reperfusion in both groups, while those of TXB₂ increased in the control group but maintained low levels in the OKY-046 group. Liver function was better and histologic changes less marked in the OKY-046 group than in the control group, suggesting the important role of TXA₂ in ischemic liver injury and the usefulness of a TXA₂ synthetase inhibitor for protecting the liver against ischemic injury.     

The immunosuppressive effects of a leukotriene B4 receptor antagonist on liver allotransplantation in rats

The immunosuppressive effects of a leukotriene B₄ (LTB₄) receptor antagonist, ONO4057, on liver allotransplantation in rats were evaluated, and the levels of prostaglandin E₂ (PGE₂) in the liver tissue during rejection of the allografts examined. The rats were divided into four groups: group 1: Lewis rats (LEW) given a sham operation with dimethyl sulfoxide (DMSO); group 2: LEW given syngenic orthotopic liver transplantation (OLT) from LEW, with DMSO; group 3: LEW given allogenic OLT from ACI rats (ACI), with DMSO; and group 4: LEW given allogenic OLT from ACI, with ONO4057 as 10, 30, or 100 mg/kg per day dissolved in DMSO to subgroups 4a, 4b, and 4c, respectively. Histological examinations were performed, survival times monitored, and liver tissue PGE₂ levels 3, 5, 7, and 14 days after transplantation measured. The mean graft survival times in groups 4a, b, and c, at 37.5±10.4, 52.2±24.4, and 34.0±4.9 days (mean±SEM), respectively, were significantly longer than that in group 3 (at 13.0±3.2 days). Moreover, the levels of tissue PGE₂ in the liver allografts in group 4a were significantly higher than those in group 3 on days 5 and 7. These results suggest that ONO4057 has an immunosuppressive effect on liver allotransplantation since it reduces the activities of LTB₄ which augments immune responses, and also because it indirectly increases the PGE₂ level.     

Effect of intracisternal thromboxane A2 analogue on cerebral artery permeability

Summary Thromboxane, a highly vasoactive substance, is found in the cerebrospinal fluid of patients and experimental animals following subarachnoid haemorrhage. A stable synthetic analogue of thromboxane A₂ was administered intracisternally in rabbits. This resulted in an increase in endothelial permeability of the major cerebral arteries to Evans Blue dye and horseradish peroxidase. Thromboxane may be involved in the pathogenesis of cerebral vasospasm and may be related to the contrast enhancement of the arteries in the basal cisterns on CT scans of patients who are prone to develop arterial narrowing.Presented in part at the Tenth International Joint Conference on Stroke and Cerebral Circulation, New Orleans, February 21–23, 1985.     

The effect of impaired lipid metabolism on the smooth muscle cells of rabbits

Summary Our clinical data enabled us to demonstrate a correlation between impaired lipid metabolism and vasculogenic impotent men. Our aim was to evaluate the effect of an impaired lipid metabolism on the smooth muscle of the corpus cavernosum. A total of 16 rabbits were given a cholesterol-enriched diet for 3 months, and 8 of these received additional thromboxane A₂ receptor antagonist; 10 other rabbits (control) were fed a normal diet. Subsequently, cavernous tissue biopsies were taken, and tissue lipid extractions and electron microscopic evaluation were made from 3 rabbits in each group. In the untreated high-cholesterol diet group, cholesterol levels reached approx. 2.1 g/mg body weight compared with 1.07 g/mg b.wt. in the thromboxane A₂ receptor antagonist-treated group and elevated levels compared with control group. Similar results were found for the triglyceride and free fatty acid levels. Lecithin tissue levels in treated rabbits were distinctly elevated against those of other 2 groups. Ultramorphological examination of the control group disclosed normal smooth muscle cell (SMC) architecture with numerous sites of intercellular contacts. These findings contrasted with those of the high-cholesterol diet groups which showed significant SMC degeneration with loss of intercellular contacts. Our data imply that impaired lipid metabolism causes cavernous SMC degeneration which plays a major role in the pathogenesis of erectile dysfunction. The thromboxane A₂ receptor antagonist seems to produce a protective metabolic effect on the erectile tissue which may have some consequences future treatment strategies.Part of this paper was presented at the 10th Symposium of the Association for Experimental Urology of the German Urological Society, June 21–23, 1990, Munich, FRG     

Effects of H2-receptor antagonist and selective muscarinic receptor antagonist on early gastric stagnation after pylorus-preserving pancreaticoduodenectomy: Results of a randomized controlled study

The suppressive effects of an H₂-receptor antagonist, ranitidine, and a selective muscarinic receptor antagonist, pirenzepine, in improving gastric stasis during the early postoperative period after pylorus-preserving pancreaticoduodenectomy (PPPD) were assessed. Thirty-two PPPD patients were divided into four groups of 8 patients each. Group 1 served as controls and were given no medication. Group 2 received i.v. ranitidine alone, group 3 received i.v. pirenzepine alone, and group 4 received i.v. ranitidine and pirenzepine combined. The daily volume and the total acidity of the gastric juice, aspirated via a nasogastric tube, were measured on post-PPPD days 1–13. One patient in group 1 was withdrawn from this study due to severe gastric bleeding. The mean daily aspirated volume of gastric juice in group 1 (n=7) was 1043±362 ml on the 3rd postoperative day, and it gradually fell after the 5th postoperative day, but still exceeded 500 ml on day 13. In group 2 (n=8), the mean maximum volume, 614±251ml, was reached on the 4th postoperative day, and in group 3 (n=8), the mean maximum volume, 680 + 391 ml, was reached on the 3rd postoperative day. In contrast, in group 4 (n=8), the gastric juice output appeared to be suppressed and the mean maximum volume was 380±218 ml, this being reached on the 6th postoperative day. Gastric juice secretion was significantly higher in group 1 than in the other three groups (P<0.01). The total acidity was significantly lower in groups 3 and 4 than in group 1 (P<0.01). These results indicate that the postoperative administration of the combination of ranitidine and pirenzepine suppresses the volume and acidity of the gastric juice after a PPPD.     

The effects of a thromboxane A2 receptor antagonist on neurologic recovery after 15 min complete global brain ischemia in dogs

The effects of a thromboxane A₂ receptor antagonist (anti-TXA₂; ONO-3708) on the neurologic recovery after 15min complete cerebral ischemia were investigated in dogs. Complete cerebral ischemia was achieved by occlusion of the trunk of the aorta, the superior and the inferior caval vein. Seventeen dogs were divided into 2 groups; 1) control group (no drug, n = 9), 2) Anti-TXA₂ group (anti-TXA₂ 200mcg·kg^–1 in iv bolus soon after recirculation followed by continuous infusion at a rate of 10mcg·kg^–1·min^–1 for 3 days, n = 8). EEG, auditory brainstem response (ABR), middle latency response (MLR), and somatosensory evoked potential (SEP) recordings were obtained before ischemia, 120min after re-circulation and on the 7th day after ischemia. The neurologic recovery score (NRS) were determined on the 3rd and the 7th day. Impaired EEG score was significantly higher in the anti-TXA₂ group on 7th day after ischemia (P < 0.05). Anti-TXA₂ increased the reappearance rates of the ABR-Vth (P < 0.05) and the SEP-N₃ waves (P < 0.01) at 120min after ischemia. The survival rate tended to be higher in the anti-TXA₂ group. However, NRS did not significantly differ in the groups.(Takahashi M, Iwatsuki N, Ono K, et al.: The effects of a thromboxane A₂ receptor antagonist on neurologic recovery after 15min complete global brain ischemia in dogs. J Anesth 5: 73–78, 1991)     

Differential expression of adenosine A1 and A2A receptors after upper cervical (C2) spinal cord hemisection in adult rats

BACKGROUND: In an animal model of spinal cord injury, a latent respiratory motor pathway can be pharmacologically activated via adenosine receptors to restore respiratory function after cervical (C2) spinal cord hemisection that paralyzes the hemidiaphragm ipsilateral to injury. Although spinal phrenic motoneurons immunopositive for adenosine receptors have been demonstrated (C3-C5), it is unclear if adenosine receptor protein levels are altered after C2 hemisection and theophylline administration. OBJECTIVE: To assess the effects of C2 spinal cord hemisection and theophylline administration on the expression of adenosine receptor proteins. METHODS: Adenosine A1 and A2A receptor protein levels were assessed in adult rats classified as (a) noninjured and theophylline treated, (b) C2 hemisected, (c) C2 hemisected and administered theophylline orally (3x daily) for 3 days only, and (d) C2 hemisected and administered theophylline (3x daily for 3 days) and assessed 12 days after drug administration. Assessment of A1 protein levels was carried out via immunohistochemistry and A2A protein levels by densitometry. RESULTS: Adenosine A1 protein levels decreased significantly (both ipsilateral and contralateral to injury) after C2 hemisection; however, the decrease was attenuated in hemisected and theophylline-treated animals. Attenuation in adenosine A1 receptor protein levels persisted when theophylline administration was stopped for 12 days prior to assessment. Adenosine A2A protein levels were unchanged by C2 hemisection; however, theophylline reduced the levels within the phrenic motoneurons. Furthermore, the decrease in A2A levels persisted 12 days after theophylline was withdrawn. CONCLUSION: Our findings suggest that theophylline mitigates the effects of C2 hemisection by attenuating the C2 hemisection-induced decrease in A1 protein levels. Furthermore, A2A protein levels are unaltered by C2 hemisection but decrease after continuous or interrupted theophylline administration. The effects on protein levels may underlie the stimulant actions of theophylline.     

Comparison of the effects of 1,25-dihydroxycholecalciferol,prostaglandin E2, and osteoclast-activating factor with parathyroid hormone on the ultrastructure of osteoclasts in cultured long bones of fetal rats

Summary The effects of 1,25-dihydroxy vitamin D₃ [1,25(OH)₂D₃], prostaglandin (PGE₂), and osteoclast-activating factor (OAF) on the size of osteoclasts, nuclei, ruffled borders, and clear zones in cultured long bones of fetal rats were quantitated. In addition, the number of osteoclasts in the bones was counted and the release of calcium from the bone into the culture medium was determined. These data were compared with the corresponding effects of parathyroid hormone (PTH). All agents tested increased the size of the ruffled borders significantly after 3 h, the size of the clear zones after 12 h, and the size of the cells after 12–24 h. No important differences in sizes were noticed between the agents tested or between the agents and PTH. The number of osteoclasts was increased after 24 h of treatment with PTH, but not after the other agents. Calcium release was significantly increased for all agents between 12 and 24 h. It is concluded that bone resorption by 1,25(OH)₂D₃, OAF, and PGE₂ is mediated primarily by increased activity of existing osteoclasts similar to PTH activation.     

Effects of vitamin D and parathyroid hormone on cyclic AMP production by bone cells isolated from rat calvariae

Summary Studies presented here were designed to investigate further the basis for an impaired cAMP response to parathyroid hormone (PTH) in osteoblastlike calvarial bone cells isolated from vitamin D-deficient rat pups. The goal was to perturb Ca, PTH, and vitamin Din vivo in order to see which factors might be responsible for the impairedin vitro bone cell cAMP response. Pups either were parathyroidectomized (PTX) 3–5 days, implanted with osmotic minipumps delivering high doses of PTH, given repeated, high doses of 1,25(OH)₂D₃, or were D-deficient (-D, i.e., born and suckled by D-deficient mothers). Osteoblastlike bone cells, isolated by sequential enzyme digestion and centrifugation, were exposed to PTH for 5 min in the presence of a phosphodiesterase inhibitor. In bone cells isolated from -D rat pups, both basal and PTH-induced cAMP accumulation were significantly lower than in +D bone cells. Earlier, we had shown that two daily injections of -D pups with 50 ng 1,25(OH)₂D₃ restores this reduced bone cAMP response of -D pups toward normal. In the present study, neither basal nor PTH-induced bone cell cAMP accumulation was affected by subjecting D-replete pups to PTX, PTH infusion, or repeated high doses of 1,25(OH)₂D₃ despite the fact that each treatment markedly changed serum Ca or serum immunoreactive PTH. The results indicate that the impaired bone cell cAMP response seen in -D pups is not a direct result of chronic hypocalcemia and that the “heterologous desensitization” seenin vitro with added 1,25(OH)₂D₃ could not be duplicated byin vivo treatment of +D pups with supraphysiologic doses of 1,25(OH)₂D₃. Finally the lack of alteration in the bone cell cAMP response to PTHin vitro after chronic PTH infusionin vivo fails to support the notion that the impaired response in -D bone cells can be explained entirely by “homologous desensitization” induced by high circulating levels of PTH in the hypocalcemic, -D rat pup.     

Effects of vitamin D3 metabolites on bone cell calcium transport

Summary The vitamin D₃ metabolite, 25-hydroxycholecalciferol, at concentrations of 0.01 to 10.0 g/ml, decreased calcium uptake by isolated bone cells. The effect occurred within 1 min after the simultaneous addition of metabolite and⁴⁵Ca. Lactic acid and ATP production by the cells was not affected. 24(R), 25-dihydroxycholecalciferol produced a similar decrease in calcium uptake. Vitamin D₃ had no effect at concentrations from 0.01 to 10.0 g/ml. No effect of 1,25-dihydroxycholecalciferol on calcium uptake was observed with concentrations from 0.1 to 100 ng/ml and various preincubation periods extending to 2 h. None of the agents had any effect on calcium efflux. The effects of 25-hydroxycholecalciferol and 24(R), 25-dihydroxycholecalciferol on calcium uptake were not seen in isolated fetal rat skin cell preparations.     

Effects of weight loss on serum 1,25-(OH)2-vitamin D concentrations in adults: A preliminary report

Summary During a review of 42 metabolic studies in healthy women and men we observed that serum 1,25-(OH)₂-D concentrations were directly correlated to the observed daily changes in body weight (r=0.68;P<0.001) and to caloric intake/kg/day (r=0.39;P=0.01). These relationships could not be accounted for by related and physiologically expected changes in serum Ca or iPTH concentrations. However, serum 1,25-(OH)₂-D concentrations were observed to be inversely correlated to serum PO₄ levels (r=−0.44;P=0.004). In addition, serum PO₄ levels were inversely correlated to the daily changes in body weight (r=−0.40;P=0.009). Since dietary sodium intake averaged 142 mmol/day, it is unlikely that the observed changes in weight were the result of changes in salt and water balance. Thus it seems reasonable to speculate that serum 1,25-(OH)₂-D concentrations may vary directly with energy balance, as reflected by changes in body weight. This effect may be mediated by alterations in PO₄ metabolism. The accurate assessment of serum 1,25-(OH)₂-D levels thus appears to require several measurements over time periods during which body weight is stable.     

Effects of age and sex on the regulation of plasma 1,25-(OH)2-D by phosphorus in the rat

Summary Dietary phosphate deprivation in women, but not men, is accompanied by a fall in plasma PO₄ and a rise in plasma 1,25-(OH)₂-vitamin D concentrations. In contrast, young male rats exhibit a fall in plasma PO₄ and a rise in plasma 1,25-(OH)₂-D concentrations in response to PO₄ deprivation. To evaluate whether age and sex influence basal plasma 1,25-(OH)₂-D levels and their regulation by PO₄ deprivation, plasma 1,25-(OH)₂-D, PO₄, and Ca levels were measured in male and female rats ranging in age from 6 weeks to 6 months while they were eating normal or low PO₄ diets for 1 to 16 days. Similar observations were also made in 6-week-old castrated male and female rats, males replaced with testosterone, and females replaced with estradiol. Basal plasma 1,25-(OH)₂-D levels were higher in 6-week-old males (228±76 pmol/l) than in 6-week-old females (148±62 pmol/l;P<0.01) and declined by age 11 weeks to stable levels averaging about 100 pmol/l without sex difference. Dietary PO₄ deprivation resulted in a three-to fourfold increase in plasma 1,25-(OH)₂-D concentrations regardless of age and sex, accompanied by a correlated rise in serum Ca concentrations. Castration of 6-week-old males and females eliminated the sex difference in basal plasma 1,25-(OH)₂-D levels and appeared to enhance the elevation of plasma 1,25-(OH)₂-D concentrations in response to PO₄ deprivation in females. Although gonadal hormones may modify basal plasma 1,25-(OH)₂-D levels, they are not required for the augmentation of plasma 1,25-(OH)₂-D levels in response to PO₄ deprivation.