Total parenteral nutrition using continuous intravenous infusion via the posterior vena cava in rats

The Optimal Duration of PTH(1-34) Infusion Is One Hour per Day to Increase Bone Mass in Rats

Parathyroid hormone (PTH) is a potential medicine for osteoporosis, and subcutaneous (s.c.) PTH treatment enhances bone mass; however, continuous infusion of PTH elicits bone resorption and induces bone loss. To clarify this contradictory phenomenon, we examined bone markers and bone mass in rats to assess the optimal duration of PTH(1-34) infusion. Continuous infusion of PTH at 1 µg/kg/h (Css, steady-state concentration ca. 300 pg/mL) for 1-4 h clearly stimulated the expression both of bone formation-related genes (c-fos, Wnt4, EphrinB2) and of bone resorption-related genes (tnfsf11, tnfsf11b, encoding receptor activator of nuclear factor-kappaB ligand (RANKL), osteoprotegerin (OPG)), but s.c. treatment stimulated these genes only 1-h after the injection. Rats were treated with 1-, 2-, or 4-h infusions of PTH daily using a totally implanted catheter system, and the femoral bone mineral density (BMD) was measured at 4 weeks. The 1-h infusion of PTH significantly stimulated serum bone formation markers (procollagen I N-terminal propeptide (PINP) and osteocalcin) on day 14 and femoral BMD at 2 and 4 weeks, but the 4-h infusion of PTH did not enhance BMD. Since the 4-h infusion increased the levels of both the bone formation markers and a bone resorption marker (urinary C-terminal telopeptide of type 1 collagen (CTx)), the increased bone resorption may predominate over bone formation. The intermittent elevation of plasma PTH to 300 pg/mL for 1-h each day is optimal for increasing bone mass in rats. In osteoporosis therapy in human, using the optimal duration for the clinical dose of PTH may selectively stimulate bone formation.

Stimulation of adrenal chromaffin cell proliferation by hypercalcemia induced by intravenous infusion of calcium gluconate in rats

Increased incidence of adrenal pheochromocytoma is frequently encountered in rat carcinogenicity studies. In some of the studies, the finding is judged to be due to a rat-specific mechanism of carcinogenesis caused by a disturbance of calcium homeostasis. However, direct evidence that the proliferation of chromaffin cells in the adrenal medulla is induced solely by hypercalcemia is not available. In this study, calcium gluconate was intravenously infused for 7 days to rat chromaffin cells by a tail cuff method, and cumulative labeling with bromodeoxyuridine (BrdU) was carried out to evaluate the proliferative activity. The serum calcium concentration was dose-dependently increased, and a high calcium concentration was stably sustained from day 2 to 7. In the adrenal medulla, BrdU-positive chromaffin cells increased in the calcium gluconate-treated animals, and the BrdU-labeling index increased in a dose-dependent manner. In addition, an increased BrdU-labeling index of chromaffin cells was shown to correlate with the serum calcium concentration. Our results demonstrate that hypercalcemia directly enhances the proliferative activity of chromaffin cells and that the proliferative activity is correlated with the serum calcium concentration.

CONTRIBUTION OF INTESTINAL CALCIUM ABSORPTION TO 1,25-DIHYDROXYVITAMIN D3-INDUCED CALCIUM ACTION IN THE TOTAL PARENTERAL NUTRITION RAT

To investigate the contribution of intestinal calcium (Ca) absorption to 1,25-dihydroxyvitamin D(3) (1,25(OH) (2)D(3))-induced Ca action, we assessed parameters related to Ca metabolism after a single dosing of 1,25(OH)(2)D (3) in the total parenteral nutrition (TPN) solution or 5% D-mannitol (MAN) solution treatment with rats. Animals were divided into 6 groups (vehicle, 100 microg/kg p.o. and 25 microg/kg i.v.; n=8) in Experiment 1 and 8 groups (vehicle, 1, 10 and 100 microg/kg p.o.; n=6) in Experiment 2 at TPN or MAN solution treatment. In both experiments, the parameters related to Ca metabolisms, urinary Ca and urinary deoxypyridinoline on 0-24 hr or serum Ca, osteocalcin and parathyroid hormone at 24 hr were measured after 1,25(OH)(2)D (3) dosing. 1,25(OH)(2)D(3)-related increased urinary Ca or serum Ca were observed in both experiments. Decrease rates in change of urinary Ca in TPN solution treatment rats were 36.3% (100 microg/kg p.o.) or 47.1% (25 microg/kg i.v.) of MAN solution treatment rats in Experiment 1, and 29.0% (1 microg/kg), 56.2% (10 microg/kg) or 35.3% (100 microg/kg) of MAN solution treatment rats in Experiment 2. Decrease rates in change of serum Ca at 72 hr in TPN solution treatment rats were 57.3% (100 microg/kg p.o.) or 44.5% (25 microg/kg i.v.) of MAN solution treatment rats in Experiment 1, and were 57.0% (100 microg/kg) of MAN solution treatment rats in Experiment 2. There were no differences in the change of serum Ca in the 1,25(OH)(2)D(3) 1 or 10-microg/kg group in Experiment 2. Our results suggest that differences in urinary Ca or serum Ca between MAN solution treatment rats and TPN solution treatment rats express the contribution of intestinal Ca absorption to 1,25(OH)(2)D(3)-induced Ca action in the conditions of the study.