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ABSTRACT
In pregnant ewes bearing twin fetuses and fed an adequate Ca diet, the consequences of calcitonin (CT) deficiency (induced by thyroidectomy performed on day 30 of gestation, associated with daily thyroxine supplementation) differed according to the time of pregnancy. Such a deficiency had no significant effect either on fetal total body Ca content or on placental transfer of Ca in 77-day-old fetuses. On the contrary, CT deficiency for 110 days (on day 140 of pregnancy) was associated with an increased Ca concentration in fetal total body and increased placental transfer of Ca from the dam to its fetus, which did not occur in five thyroidectomized ewes supplemented with thyroxine and CT. This indicates that CT might protect the skeleton of the pregnant female against excessive demineralization by modulating placental transfer of Ca, when such a transfer becomes important, during periods of intense mineralization of the fetal skeleton.
J. Endocr. (1985) 104, 17–21
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SUMMARY
The influence of injections of calcitonin on the hypercalcaemia and hyperphosphataemia induced by 1α-hydroxycholecalciferol (1α-OHD3) and 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) was studied in growing lambs and lactating cows respectively.
In lambs, the hypercalcaemic and hyperphosphataemic effect of 0·1 μg 1α-OHD3/kg body weight (i.v.) was completely inhibited by 20 units calcitonin/kg body weight, injected subcutaneously in four equal doses at intervals of 12 h, the first injection of calcitonin occurring immediately after injection of 1α-OHD3. Moreover, the same dose of calcitonin partly inhibited the hypercalcaemia and hyperphosphataemia observed after injection of 0·25 μg 1α-OHD3/kg body weight.
In lactating cows, four injections of calcitonin (5 u./kg body weight each, at intervals of 12 h) prevented the rise of plasma calcium and phosphate levels occurring after injection of 1,25-(OH)2D3 (0·01 μg/kg body weight).
The results indicated that high plasma calcitonin levels can inhibit the hypercalcaemic and hyperphosphataemic effects of 1,25-(OH)2D3 in ruminants. Thus, hypocalcaemia might occur in parturient cows in spite of raised concentrations of 1,25-(OH)2D3 in plasma.
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ABSTRACT
The influence of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) on salivary inorganic phosphorus (Pi) concentration and secretion was studied in two groups of four heifers, the right parotid ducts of which were chronically fitted with a re-entrant cannula.
In four heifers i.v. Pi loading (5 mmol/min for 2 h) induced hyperphosphataemia associated with a decrease in plasma 1,25-(OH)2D concentration and an increase in salivary Pi concentration and secretion. In four other heifers, daily 1α-hydroxycholecalciferol injections (1 μg/kg body wt per day for 3 days) induced hyperphosphataemia associated with an increase in plasma 1,25-(OH)2D concentration and a decrease in salivary Pi concentration and secretion. These treatments had no significant effect on salivary calcium concentration and secretion.
Our results indicate that plasma 1,25-(OH)2D concentrations rather than phosphataemia regulate salivary Pi concentration and secretion in cattle.
J. Endocr. (1987) 112, 427–430
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ABSTRACT
Plasma concentrations of atrial natriuretic peptide (ANP), plasma renin activity (PRA), plasma concentrations of aldosterone, urine flow rate and sodium and potassium excretion were studied in two groups of four conscious 3-day-old male calves, infused with hypertonic saline or vehicle. Hypertonic saline infusion (20 mmol NaCl/kg body weight) was accompanied by a progressive rise in plasma concentrations of ANP (from 16·5 ± 0·2 pmol/l at time 0 to 29·3 ± 3·0 pmol/l at 30 min; P< 0·05) and by a gradual decrease in PRA (from 1·61±0·23 nmol angiotensin I/1 per h at time 0 to 0·54± 15 nmol angiotensin I/1 per h at 90 min; P<0·05); there was no change in the plasma concentration of aldosterone. Within the first 2 h of the 24-h urine collection period there was a marked rise in urine flow rate and sodium excretion in treated calves when compared with control animals (66·0 ± 8·3 vs 15·9±1·2 ml/kg body weight per 2 h (P<0·05) and 6·7±1·3 vs 0·4±0·02 mmol/kg body weight per 2 h (P<0·01) respectively). During the following 22 h, urinary water and sodium excretion remained at significantly high levels.
Thus, in the conscious newborn calf, changes in plasma ANP levels and urinary water and sodium excretion during hypertonic saline infusion are compatible with the hypothesis that endogenous ANP participates, at least in part, in the immediate diuretic and natriuretic renal response induced by the sodium overload.
J. Endocr. (1988) 119, 23–29
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ABSTRACT
Plasma concentrations of atrial natriuretic peptide (ANP) were studied in eight adult non-pregnant cows and in two groups of six chronically catheterized bovine fetuses and their mothers in the eighth month of pregnancy. The first group of fetuses was used for studying the effect of an acute i.v. sodium load (240 mmol NaCl/fetus) on fetal ANP; the second group acted as controls. The mean basal ANP levels in the third-trimester bovine fetus were three to four times higher than maternal values (39·5 ± 5·5 and 9·4 ± 0·6 pmol/l respectively; P<0·01). Basal maternal plasma ANP levels were twice as high in pregnant cows in the third trimester of pregnancy than in non-pregnant cows (9·4 ± 0·6 and 4·3 ± 0·7 pmol/l respectively; P<0·05).
In response to an i.v. hypertonic saline injection, fetal plasma ANP levels increased significantly (P<0·01) to a maximum of 86·7± 17·6 pmol/l 10 min after the injection, and returned to baseline within 60 min after the treatment; during the 20 min following the i.v. sodium load, fetal plasma ANP correlated significantly with fetal plasma sodium concentrations (r 0·96; n=12) and with fetal plasma osmolality (r =0·94; n=12). No significant changes in maternal ANP values were observed in the two groups of animals.
These results suggest that ANP secretion is stimulated during pregnancy in cows, and that, in the bovine fetus, a hypertonic sodium load appears to be a potent stimulus for ANP release.
Journal of Endocrinology (1989) 121, 5–9
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ABSTRACT
Intravenous infusion of aldosterone (10 μg/kg body wt per h for 5 h) in four 2-month-old calves decreased salivary and urinary sodium (Na+) concentration and increased salivary potassium (K+) concentration without modifying salivary flow or urinary K+ concentration. Intravenous angiotensin II infusion (0·3 μg/kg body wt per min for 1 h) in four Na+-replete 16-month-old bulls decreased salivary Na+ concentration and increased that of K+. It also increased plasma cortisol and plasma aldosterone concentrations, and decreased plasma renin activity (PRA). In four 16-month-old bulls Na+ deficiency (induced by chronic cannulation of the righ parotid duct and loss of saliva for 5 days) had similar effects to those observed following aldosterone infusion in calves: a decrease in salivary Na+/K+ ratio. This decrease was associated with an increase in PRA and an increase in plasma aldosterone concentration. In these animals a close positive relationship was observed between PRA and plasma aldosterone concentration (r = 0·91; n = 20; P < 0·01). Thus in cattle, during Na+ deficiency, the effect of aldosterone on parotid glands participates in the regulation of Na+ metabolism.
J. Endocr. (1986) 108, 405–411
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I.N.R.A., Theix, 63110 Beaumont, France and Groupe Hospitalier de la Timone, 13385 Marseille, France
(Received 31 May 1978)
Very little information is available concerning interrelationships between maternal and foetal concentrations of 25-hydroxy vitamin D3 (25-OHD3; Hillman & Haddad, 1974; Ross, Care, Pickard, Peacock & Robinson, 1976; Weisman, Sapir, Harell & Edelstein, 1976). This paper describes the concentrations of 25-OHD3 in the plasma of pregnant and lactating ewes and their foetal and newborn lambs.
Five ewes bearing single lambs were selected by radiography performed on day 100 of gestation in winter. The daily intakes of calcium, phosphate and magnesium for each animal were respectively, 11, 7 and 2 g. From day 26 pre partum until day 4 post partum, blood samples were collected through catheters implanted on day 115 of gestation in the left foetal and maternal carotid arteries (Mellor & Matheson, 1975). Plasma concentrations of 25-OHD3
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ABSTRACT
Parathyroid hormone-related peptide (PTHrP) has been shown to stimulate the placental calcium pump in pregnant ewes. Recent studies also suggest a physiological role for this peptide during lactation. In the present work, we have studied the possible role of synthetic human PTHrP(1–34), (1–86) and (140–173) fragments on calcium, inorganic phosphorus and magnesium secretion into milk of four adult goats in early lactation. This was done by measuring differences in calcium, inorganic phosphorus and magnesium concentrations in the carotid artery and superficial epigastric vein, the concentration of these minerals in milk and milk production. Both PTHrP(1–34) and (1–86) fragments stimulated calcium, inorganic phosphorus and magnesium uptake by the mammary gland and secretion into milk, without any significant effect on milk production. Therefore PTHrP might have important physiological roles in the pregnant and/or lactating female, by regulating calcium transport through the placenta and mammary gland.
Journal of Endocrinology (1992) 132, 353–359
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Amylin (AMY), a peptide co-secreted with insulin by pancreatic beta-cells, inhibits bone resorption and stimulates osteoblastic activity. The ovariectomized (OVX) rat is an established animal model for human osteoporosis. Thus, the present experiment was performed to study the effects of AMY on estrogen deficiency-induced bone loss in rats. Thirty-one 6-month-old Wistar rats were randomized by body weight (BW) into two groups. The first underwent surgical OVX (n=21). The second was sham-operated (SH; n=10). Sixty days after surgery, 11 OVX rats were s.c. injected with rat AMY (3 microg/100 g BW/day, for 30 days; OVX+AMY), and 10 with solvent alone in the same way (0.15 ml/100 g BW; OVX). Each rat, housed in an individual cage, was fed daily the mean quantity of diet consumed the day before by SH rats. This diet contained 0.24% calcium and 0. 16% phosphorus. The 31 animals were killed on day 90. No difference in daily weight gain and BW was observed between groups. Neither AMY treatment nor OVX had any significant effect upon femoral morphology, femoral failure load, diaphyseal femoral density (representative of cortical bone) and total femoral calcium content. Nevertheless, both distal metaphyseal (representative of cancellous bone) and total femoral bone densities were higher in SH and OVX+AMY than in OVX rats. The highest plasma osteocalcin concentration was measured in OVX+AMY rats. Simultaneously, urinary deoxypyridinoline excretion was lower in OVX+AMY than in OVX rats. These results indicate that in OVX rats, AMY treatment inhibited trabecular bone loss both by inhibiting resorption and by stimulating osteoblastic activity.
