Short-term treatment of rats with high dose 1,25-dihydroxyvitamin D3 stimulates bone formation and increases the number of osteoblast precursor cells in bone marrow.

Using an experimental rat model, this study was undertaken to assess the effects of a short-term application of high dose 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] on calcium homeostasis, cancellous bone formation, and numbers of osteoblast precursors in ex vivo bone marrow cultures. For Exp 1 and 2, 6-month-old female rats were sc injected with either 0.2 microg 1,25-(OH)2D3/kg x day or vehicle on days 1, 2, and 3 of the studies. Serum calcium and urinary excretion of calcium were monitored for 12 days in Exp 1. In Exp 2, the rats were ip labeled with five different fluorochromes on days 0, 5, 10, 15, and 20, respectively. Half of the rats in each group were killed on day 7, the rest of the rats were killed on day 24, and the first lumbar vertebrae were processed for histomorphometry. In Exp 3, 0.2 microg 1,25-(OH)2D3/kg BW or vehicle was sc administered to 6-month-old male rats on days 1, 2, and 3, and the number of colony-forming units with the ability to express alkaline phosphatase, to calcify, and/or to synthesize collagen were enumerated sequentially on days 4, 6, 8, 10, 12, and 14 in bone marrow cultures. Short-term 1,25-(OH)2D3 treatment resulted in increased values for serum and urinary calcium during the treatment phase in Exp 1, depressed osteoclast numbers and strongly elevated osteoblast perimeter by day 7, and stimulated mineral apposition rate and bone formation rate in the interval between days 5-15 of Exp 2. Moreover, 1,25-(OH)2D3 administration to rats significantly enhanced the number of mesenchymal precursor cells in bone marrow with the ability to differentiate into an osteoblastic phenotype in ex vivo bone marrow cultures on day 4 of Exp 3. These studies provide evidence that short-term 1,25-(OH)2D3 treatment creates new bone remodeling units and augments osteoblast recruitment and osteoblast team performance in rat cancellous bone.

Synthesis and biological activities of a new series of secosteroids: vitamin D phosphonate hybrids.

By a structural combination of phosphonate and bisphosphonate moieties with the vitamin D skeleton a series of new vitamin D analogs was synthesized. Derivatives with 24beta-hydroxy- or 24-keto groups exerted considerable vitamin D activities in vitro while the hypercalcemic potentials were significantly reduced as compared to 1alpha,25-dihydroxyvitamin D(3) (calcitriol). Whereas the 24-hydroxy analogs did not influence bone formation in vivo in dosages below the hypercalcemic threshold, the 24-ketones were found to induce synthesis of new bone matrix in non-hypercalcemic doses. Vitamin D bisphosphonate hybrids, on the other hand, which did not elicit substantial vitamin D activities in vitro and tend to decrease serum calcium levels in vivo clearly induced osteoid formation in rats, indicating a mechanism of action different to calcitriol.

Synthesis and biological activities of 8(14)a-homocalcitriol.

8(14)a-Homocalcitriol was synthesized and tested for its biologic activities. It exhibited a vitamin D agonist activity profile. The compound was bound to the pig intestinal receptor with an affinity slightly less than calcitriol, showed the same potency in inducing HL 60 cell differentiation and inhibition of keratinocyte proliferation as calcitriol, and was found to be approximately 10-fold less potent in inducing hypercalcemia and hypercalciuria after a single injection in normal rats.

Cardiovascular effects of iohexol in the rat and the isolated rabbit heart.

The haemodynamic and cardiac side effects of the new non-ionic contrast medium, iohexol, were investigated anaesthetized rats and isolated perfused rabbit hearts. Iohexol, caused a positive inotropic response in both models, elevated coronary flow and in high doses had an inhibitory influence on the cardiac conducting system. From a comparison with Amipaque and Urografin 76 it was concluded that with respect to cardiac side effects iohexol can be ranked between these media.

Centrifugal isolation of bone marrow from bone: an improved method for the recovery and quantitation of bone marrow osteoprogenitor cells from rat tibiae and femurae.

SUMMARY. The high variation often observed in the ex vivo fibroblastic-colony forming unit (CFU-f) assay is likely to be due to both biological and experimental variation. To determine whether we could improve experimental methods we developed an alternative method of bone marrow cell (BMC) isolation employing a centrifugation step. The osteogenic capacity of centrifugally isolated BMC was compared to that of BMC that were isolated using the standard "flushing" technique using the CFU-f assay. The centrifugation method was found to be both quick and simple to perform and allowed simultaneous preparation of all samples. Centrifugally isolated BMC gave rise to approximately 100% more cfu-ap and cfu-f in cultures from both tibiae and femurae. The proportion of alkaline phosphatase positive colonies remained the same and colony morphologies were similar for both isolation methods. Histological comparison of the flushed and spun bones showed that after the flushing procedure many cells remained in the marrow cavity especially in the trabecular area. In contrast, centrifugation completely emptied the marrow space of all cells except bone lining cells and osteoblasts. Thus the osteogenic capacity of the bone marrow can be expressed as the number of CFU-f per bone instead of the frequency as is the norm. Using these methods to isolate BMC for ex vivo investigations should lead to a reduction in CFU-f number variation due to the isolation method. http://link.springer-ny. com/link/service/journals/00223/bibs/65n5p411.html

Pharmacological profile of a novel carbacyclin derivative with high metabolic stability and oral activity in the rat.

A novel carbacyclin derivative (16S)-13,14-dehydro-16,20-dimethyl-3-oxa-18,18,19,19-tetradehydro- 6a- carbaprostaglandin-I2 (3-oxa-analogue) has been synthesized in order to find chemically and metabolically stable prostacyclin-mimetics with a potency equal or even superior to PGI2. The 3-oxa-analogue was found to be stabilized against beta-oxidation, a main metabolic degradation step also for chemically stable PGI2-analogues. The compound is orally available and displays a long duration of 4.5-48 h of antiaggregatory and hypotensive action. The 3-oxa-analogue inhibits ADP-induced platelet aggregation with an IC50 of 3.0 nM. Following intravenous application the 3-oxa-analogue lowers diastolic blood pressure in a dose dependent manner, the ED20 being 0.1-0.2 micrograms/kg after injection and less than or equal to 0.05 micrograms/kg/min after infusion respectively. In vivo platelet aggregation is inhibited after i.v. infusion of the 3-oxa-analogue with an IC50 of 0.037 micrograms/kg/min. As compared to Iloprost, the 3-oxa-analogue is 5-12 fold more potent with respect to in vivo hypotensive and anti-aggregatory effects. The results of the present studies indicate that the 3-oxa-analogue has a pharmacological profile comparable to prostacyclin (PGI2) and Iloprost. Due to the fact that the 3-oxa-analogue is chemically and metabolically stable, long term oral treatment can be achieved in clinical conditions in which PGI2 and Iloprost have already been shown to be therapeutically useful principles.

Mespirenone and other 15,16-methylene-17-spirolactones, a new type of steroidal aldosterone antagonists.

The ability of a series of 15,16-methylene-spirolactones in comparison to known antimineralocorticoids to inhibit the renal actions of aldosterone was tested in adrenalectomized, glucocorticoid-treated rats. The standard procedure involved continuous i.v. infusion with an isotonic solution of low sodium content (0.05% NaCl + 5.2% glucose, 3 ml/rat/h) supplemented with d-aldosterone [1 micrograms/(kg X h)] resulting in a long-lasting reduction of renal sodium excretion, increase of renal potassium excretion and hence decrease of the urinary Na/K-ratio. In some experiments sodium input was increased (0.2% NaCl + 4.3% glucose or 0.9% NaCl, respectively). The test drugs either were administered orally 1 h before start of the infusion or were added to the infused solution. With the exception of two steroids which could only be tested at single doses, all compounds were administered at three doses ranging from 2.2 to 40 mg/kg (p.o.) or from 0.83 to 6.7 mg/kg/h (i.v.). Spironolactone or spirorenone (oral administration) and potassium canrenoate (i.v. infusion) served as reference compounds. The antimineralocorticoid activity of the steroids was judged by the increase in the aldosterone-lowered Na/K-ratio in urine which was collected at hourly intervals for 15 or 21 h, respectively. Adrenalectomized, glucocorticoid-treated rats receiving an i.v. infusion without aldosterone were used as controls. To obtain preliminary information on potential antiandrogenic and progestogenic (side-)effects, binding of the test-compounds to androgen receptors (rat prostate cytosol) and progestogen receptors (rabbit uterus cytosol) was measured in vitro using 3H-dihydrotestosterone (DHT) and 3H-progesterone (prog.) as tracer and unlabelled DHT and prog. as references. All steroids tested exhibited antimineralocorticoid activity. For compounds tested at three doses levels the potency relative to the standard used was evaluated using regression analysis based on the Na/K-ratio or the log (Na X 100)/K-ratio. The relative potency of the other compounds was estimated by comparing the biological effect of single doses of test drug and standard drug, respectively, using nonparametric statistical tests.(ABSTRACT TRUNCATED AT 400 WORDS)