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Biomedical subjects

N Horiuchi

Publications and source records attributed to N Horiuchi.

At least 127 records · Page 7Linked to original sources
PubMed1979

Salmon calcitonin-induced stimulation of 1 alpha,25-dihydroxycholecalciferol synthesis in rats involving a mechanism independent of adenosine 3':5'-cyclic monophosphate.

The effect of natural salmon calcitonin on accumulation in plasma of 1 alpha,25-dihydroxy-[3H]cholecalciferol from 25-hydroxy[3H]cholecalciferol in vivo was investigated in vitamin D-deficient thyroparathyroidectomized rats into which graded doses of the hormone were continuously infused by use of a balance study system. A dose-dependent increase in plasma concentrations of 1 alpha,25-dihydroxy[3H]cholecalciferol was observed with calcitonin infusion for 6--30h at a rate greater than 20 M.R.C. m-units/h. Infusion of parathyrin or cyclic AMP produced a similar stimulation [Horiuchi, Suda, Takahashi, Shimazawa & Ogata (1977) Endocrinoly 101, 969--974], but the maximal effect of calcitonin was additive to that of either parathyrin or cyclic AMP. Furthermore concurrent infusion of theophylline (0.5 mumol/h) did not potentiate the effect of submaximal doses (3 and 20 M.R.C. m-units/h) of calcitonin. Plasma concentrations of calcium showed a decrease with calcitonin infusion for 30h, but those of Pi remained unchanged. These results strongly suggest that the rat kidney is endowed with a calcitonin-sensitive 1 alpha-hydroxylase system that is separate from the parathyrin/cyclic AMP system and is independent of changes in plasma Pi.

Animals↗
PubMed1979

Failure to demonstrate stimulatory effect of prolactin on vitamin D metabolism in vitamin-D-deficient rats.

The effect of administration of bovine prolactin in vivo on renal 1 alpha-hydroxylase (1 alpha-OHase) activity was investigated using thyroparathyroidectomized and sham-operated vitamin-D-deficient male rats. A high dose (1.5 IU/hr) and a low dose (0.3 IU/hr) of bovine prolactin was constantly infused into the cannulated femoral vein for 6 hr or 30 hr. The accumulation of 1 alpha, 25-hydroxyvitamin D3 [1 alpha, 25-(OH)2-D3] in plasma produced from 25-hydroxy-vitamin D3 (25-OH-D3) was calculated from the 6-hr conversion of intravenously injected [3H]-25-OH-D3 to [3H]-1 alpha, 25-(OH)2-D3. Both high dose and low dose of prolactin administration caused no significant stimulatory effect on 1 alpha-OHase activity in TPTX animals. Also, in sham-operated rats the prolactin treatment produced no significant change in the 1 alpha-OHase activity. Plasma calcium concentrations showed a tendency to increase slightly. These results suggest that prolactin has no direct stimulatory role on renal 1 alpha-OHase activity in rats. Its effect on calcium metabolism may be mediated by a different mechanism(s).

Animals↗
PubMed1978

An estimation of the parathyroid hormone secretion rate in vitamin D deficient rats.

In an attempt to define the rate of endogenous secretion of parathyroid hormone in vitamin D deficiency, graded amounts of hormone were infused constantly into vitamin D deficient and vitamin D fed acutely thyroparathyroidectomized rats in a perfusion balance study. The dose of hormone needed to compensate for acute thyroparathyroidectomy was estimated. Serum levels of calcium and phosphorus, renal clearances of phosphorus and urinary excretion of cyclic AMP, each determined 16 hr after the surgery, were employed as parameters of the hormone effect. It was concluded that, in the condition of the perfusion balance study, the secretion rate of parathyroid hormone was 5.1-8.6 USP u/hr in the vitamin D deficient animals compared with 0.81-0.84 USP u/hr in the control.

Animals↗
PubMed1977

In vivo evidence for the intermediary role of 3',5'-cyclic AMP in parathyroid hormone-induced stimulation of 1alpha,25-dihydroxyvitamin D3 synthesis in rats.

Teh stimulatory effect of parathyroid hormone (PTH) on renal 1alpha-hydroxylation of 25-hydroxyvitamin D3 (25-OH-D3) was studied in thyro-parathyroidectomized (TPTX), vitamin D-deficient rats into which bovine PTH, theophylline, cAMP or dibutyryl cAMP (dbcAMP) was constantly infused. The accumulation in plasma of 1alpha,25-dihydroxy-vitamin D3 [1alpha,25-(OH)2-D3], produced from 25-OH-D3, was enhanced by infusion of either cAMP (0.9 MUMOL/H) OR DBCAMP (1 mumol/h) to a level similar to the maximum obtained by PTH (i95--7.5 U/h) infusion. A submaximal dose (1 U/h) of PTH caused a similar extent of stimulation, when infused with theophylline. When either 2 mumol/h of cAMP or 7.5 U/h of bovine PTH was infused starting 18 h after TPTX, the accumulation of 1alpha,25-(OH)2-D3 in plasma was similarly restored withing 6 h to the level found in the sham-operated animals. These results strongly support the concept that cAMP plays an important intermediary role in the stimulation of 1alpha,25-(OH)2-D3 production induced by both exogenous and endogenous PTH.

Animals↗