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PubMedDate not supplied

The effect of fetal thyroparathyroidectomy on the transport of calcium across the ovine placenta to the fetus.

The ovine fetal placenta has been perfused with autologous fetal blood under controlled conditions in eleven experiments in which the fetus was first removed. Eight of these experiments involved four pairs of twins, one lamb of which had been thyroparathyroidectomized (TXPTX) three to seven days earlier. By this time the normal placental calcium gradient from mother to fetus had either decreased or been reversed. The mean rate of transport of calcium from the mother was unchanged by previous fetal TXPTX, but the final calcium gradient achieved from the mother to the perfusing blood was significantly less than with placentae from intact fetuses. No significant alteration in fetal plasma I,25-dihydroxyvitamin D (I,25(OH)2D) concentration was observed as a result of the fetal TXPTX, indicating that hypocalcaemia can compensate for the lack of PTH in fetal production of I,25(OH)2D. Fetal thyroidectomy with replacement of thyroxine did not lead to reversal of the placental calcium gradient, indicating that calcitonin was not involved. It is suggested that in the ovine fetus, parathyroid hormone promotes the active transport of calcium from mother to fetus, so that in its absence the fetus must obtain its calcium for growth by reducing its calcaemia and thereby allow net diffusion of calcium to replace the action of the placental calcium pump. The price paid for this compensation is marked hypocalcaemia and defective calcification of osteoid.

Animals↗
PubMed1987

Thyroparathyroidectomy modifies the skeletal response to aluminum loading in the rat.

Diminished parathyroid hormone (PTH) secretion may contribute to the accumulation of aluminum (Al) in bone and to impaired bone formation in Al-related bone disease. Therefore, intact (AL, N = 9) and thyroparathyroidectomized (TPTX-AL, N = 9) rats were given intraperitoneal injections of Al, 2 mg/day, for 42 days; intact control (C, N = 11) and TPTX control (TPTX-C, N = 9) animals received i.p. injections of vehicle only. Quantitative bone histology and measurements of mineralized bone formation (Rbf) using double tetracycline labeling were done for cortical and for trabecular bone; trabecular bone aluminum content (BA) was determined by histochemical methods. BA did not differ between AL and TPTX-AL, 33 +/- 13% versus 39 +/- 14%, and Rbf decreased similarly from control values in both Al-treated groups. In contrast, osteoid production was impaired to a greater extent in TPTX-AL than in AL. Thus, osteoid area and osteoid seam width were each lower in TPTX-AL than in TPTX-C; these values did not differ between AL and C. TPTX can aggravate Al induced reductions in osteoid synthesis, and low serum PTH levels may contribute to the pathogenesis of aplastic bone. However, reductions in Rbf during Al loading are not mediated by PTH.

Aluminum↗
PubMed1985

Extrarenal handling of phosphate: effect of thyroparathyroidectomy, 1,25-dihydroxycholecalciferol, and dietary calcium.

It is known that 1,25-dihydroxycholecalciferol [1,25(OH)2D3] mobilizes inorganic phosphate (Pi) from gut and bone, thus increasing the entry of Pi into the extracellular space (ECS). In this work, we have investigated whether 1,25(OH)2D3 could also facilitate the net exit of Pi out of this pool into certain soft tissue and/or bone compartments in thyroparathyroidectomized (TPTX) rats. Sham-operated, TPTX, and TPTX rats treated with 1,25(OH)2D3 (26 pmol/day ip for 1 wk) were infused with a known amount of Pi over a given time. The amount of Pi excreted in the urine in excess of base-line values and the rise of the phosphatemia ([Pi]p) were measured. The difference between these two parameters corresponded to the net retention of infused Pi in the whole animal (RAPi) for a given rise in [Pi]p. The results show that RAPi was markedly diminished in TPTX as compared with sham-operated animals. This decrease could be corrected by 1,25(OH)2D3 treatment. Chronic reduction in the level of calcemia in TPTX 1,25(OH)2D3-supplemented rats as induced by decreasing dietary Ca intake also diminished RAPi. These effects could not be ascribed to the known actions of the experimental maneuvers on the renal excretion of Pi. Since infusions were chosen to obtain similar rises in [Pi]p and started from same levels of [Pi]p in animals of the same weight, the differences in RAPi were not due to variation of Pi retention in the ECS.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1974

Effects of dietary calcium restriction and chronic thyroparathyroidectomy on the metabolism of (3H)25-hydroxyvitamin D3 and the active transport of calcium by rat intestine.

Previous studies have shown that chronically thyroparathyroidectomized (TPTX) rats, fed a diet with restricted calcium but adequate phosphorus and vitamin D content, have higher levels of intestinal calcium absorption than controls. The results of recent acute experiments have suggested that parathyroid hormone (PTH) may be essential for regulating the renal conversion of 25-hydroxyvitamin D(3) (25-OH-D(3)) to 1,25-dihydroxyvitamin D(3) [1,25-(OH)(2)-D(3)] in response to dietary calcium deprivation. Since 1,25-(OH)(2)-D(3) is the form of the vitamin thought to be active in the intestine, increases in calcium transport mediated by this metabolite would not be expected to occur in the absence of the parathyroid glands if the preceding model is correct. The present study was undertaken to examine the chronic effects of both dietary calcium restriction and the absence of PTH on the metabolism of [(3)H]25-OH-D(3) and duodenal calcium-active transport in rats given thyroid replacement. These relatively long term studies confirm earlier observations which indicated that the adaptation of calcium absorption to a low calcium intake occurs in both sham-operated and TPTX animals. The present studies also demonstrated that despite reduced levels of 1,25-(OH)(2)-D(3) in the plasma of chronically TPTX animals fed a low calcium diet, the accumulation of this metabolite in at least one target tissue, intestinal mucosa, is identical in both the sham-operated and TPTX groups. A reduced, but continued level of 1,25-(OH)(2)-D(3) production, together with its selective accumulation by intestinal mucosa, probably explains the calcium adaptation which is observed inspite of the chronic absence of the parathyroid glands.

Animals↗
PubMed1981

Effect of thyroparathyroidectomy and parathyroidectomy on renal function and the nephrotic syndrome in rat nephrotoxic serum nephritis.

Dietary phosphorus restriction (PR) prevents uremia in rats with nephrotoxic serum nephritis (NSN). One possible mechanism by which PR could be protective would be through the suppression of parathyroid hormone. To evaluate this possibility two separate protocols were designed. In the first rats were thyroparathyroidectomized (TPTX) before (n = 11) or 5 wk after (n = 7) NSN induction and compared to sham-operated parathyroid intact rats with NSN (n = 12). At the end of the 23-wk study, intact rats were azotemic, plasma creatinine 3.80+/-0.81 mg/100 ml vs. 0.65+/-0.07 for TPTX rats (P < 0.001). During the study 75% of intact rats died of uremia in contrast to none of the TPTX rats (P < 0.001). Renal histological damage was greatly diminished and calcification prevented in TPTX rats. The proteinuria of the heterologous phase was unaffected, but the protein excretion and hypertriglyceridemia (HTG) of the autologous phase were markedly decreased in the TPTX rats. The degree of HTG and proteinuria had a high positive correlation (P < 0.001). Late TPTX also produced significant decreases in proteinuria and HTG regardless of the degree of azotemia, and prevented azotemia if the plasma creatinine at the time of TPTX was </=0.85 mg/100 ml. In additional studies selective parathyroidectomy (PTX) was performed. The adequacy of this procedure was documented by showing a similar fall in plasma Ca and urinary cyclic AMP in PTX animals as found in TPTX animals. However, selective PTX had no effect on proteinuria, histologic damage, or functional deterioration. These studies further showed that early, histologic damage and functional deterioration preceeded renal parenchymal calcification. Because animals were pair fed and both groups were given 1,25-dihydroxycholecalciferol to normalize serum Ca and P levels these studies exclude alterations in plasma Ca and P levels, dietary intake, urinary P excretion, and vitamin D administration in promoting the protective effect of TPTX on renal function. We conclude that TPTX is equally effective in preventing functional deterioration and more effective in reducing proteinuria in NSN than PR. The mechanism of this protective effect remains to be elucidated, since it does not primarily involve either the elimination of parathyroid hormone or the prevention of renal parenchymal calcification.

Animals↗
PubMed1980

Movement of subcellular calcium in bile pool of hepatocyte in rats: effect of thyroparathyroidectomy.

The movement of subcellular calcium in the bile pool of hepatocyte was investigated after a single intraperitoneal administration of calcium chloride in rats. The administration of calcium (4.0 mg/100 g BW) produced a remarkable elevation of serum calcium and a corresponding increase in liver calcium. The calcium taken by the liver cells at 10 min after calcium administration was markedly located into the nuclei, mitochondria and microsomes, and this distribution was not accompanied by a significant elevation in the cytosol level. At 20 min after calcium administration, the calcium increase above the subcellular structure was clearly reduced. On the other hand, serum calcium was markedly increased by calcium administration in both intact and thyroparathyroidectomized rats. However, the liver calcium increase induced in intact rats by calcium administration was much more than that in thyroparathyroidectomized rats. Also, the bile calcium level was markedly elevated in thyroparathyroidectomized rats. The present results suggest that the calcium taken by the liver cells is bound to the nuclei, mitochondria and microsomes, and then transported into the biliary duct.

Animals↗
PubMedDate not supplied

Postpneumonectomy lung growth following thyroparathyroidectomy.

Hormonal regulation of compensatory lung growth is not well understood, but it may be similar to that during compensatory growth of other organs. Liver regeneration is blocked by hypocalcemia in thyroparathyroidectomized (TPX) animals. Although calcium status is an important regulator of growth in many biological systems, the effect of TPX on compensatory lung growth is unknown. In male Sprague-Dawley rats, TPX lowered blood ionized calcium by 42% (p < .01) within two days; it remained depressed for at least one additional week. Thyroid-intact and TPX animals were therefore subjected either to sham thoracotomy or to left pneumonectomy on post-TPX day 2. Growth of the right lung was assessed on day 9 when, in pneumonectomized animals, lung mass had increased 23% (p < .01). TPX had no effect on right lung mass in sham animals. Similarly, TPX had no effect on the postpneumonectomy increase in right lung mass, which reached 118% (p < .01) of that in TPX controls. Analysis of right lung DNA, RNA, and protein concentrations on day 9 revealed that tissue macromolecule content increased postoperatively in both PNX and TPX/PNX rats in proportion to lung growth. These results demonstrate that postpneumonectomy compensatory growth of the lung is not blocked in the thyroparathyroprivic hypocalcemic rat.

Animals↗