Nutritional secondary hyperparathyroidism in rabbits

The present study was designed to document the effect of a low (0.6%) calcium-high (1.2%) phosphorus (LCaHP) diet on the development of parathyroid gland hyperplasia in rabbits and to describe the dynamics of parathyroid function (PTH–Ca²⁺ curves) in rabbits with nutritional secondary hyperparathyroidism (N2HPT). Parathyroid gland weight, parathyroid cell proliferation (measured as percentage of cells in S-phase), and parathyroid calcium (CaRmRNA) and Vitamin D (VDRmRNA) receptor expression were measured in normal rabbits and in rabbits with N2HPT. The PTH–Ca²⁺ curve was studied in normal rabbits (Group I) and in rabbits with N2HPT at two stages: 2–3 weeks (Group IIA) and 5–6 weeks (Group IIB) after being fed LCaHP diet. An increase in parathyroid gland weight and percentage of cells in S-phase was detected in the course of N2HPT. After receiving a LCaHP diet for 6 weeks rabbits had decreased levels of CaRmRNA but VDRmRNA remained unchanged. A progressive increase in the concentrations of plasma PTH (Group IIA = 167 ± 14 pg/ml and Group IIB = 377 ± 54 pg/ml, P < 0.05 versus Group I = 27 ± 3 pg/ml) was detected in the rabbits fed a LCaHP diet. This was accompanied by an increase in maximal and minimal PTH, reductions in plasma Ca²⁺ and calcitriol and elevations in plasma phosphate and creatinine. In conclusion, feeding a LCaHPD results in a rapid induction of N2HPT in rabbits. After 6 weeks on the LCaHPD rabbits develop parathyroid hyperplasia characterized by increases in PTH secretion, glandular weight and proliferation and by a decrease in CaRmRNA.     

Circadian variation of the Ca2+ -PTH curve during hypercalcaemia in dogs

To test the hypothesis that the parathyroid hormone (PTH) response to hypercalcaemia is influenced by circadian rhythms, the Ca2+ -PTH curve was studied in six dogs after infusion of CaCl2 (0.66 mEq/kg/h) at daytime (09:00 h) and at night-time (21:00 h). Plasma Ca2+ and PTH values measured before or after CaCl2 infusion were not different at day and at night. However, in the recovery from hypercalcaemia, PTH concentrations were significantly lower (P < 0.05) at 21:00 h (23 +/- 7.5 pg/ml at Ca2+ = 1.30 mm) than at 09:00 h (38.8 +/- 6.9 pg/ml at Ca2+ = 1.30 mm). In addition, the Ca2+ -PTH curve showed hysteresis at daytime (for the same Ca2+ concentration, PTH values were higher during recovery than during induction of hypercalcaemia) but not at night-time (PTH values were lower during recovery than during induction of hypercalcaemia). In conclusion, a circadian variation in the PTH secretory pattern during recovery from hypercalcaemia has been identified in dogs.     

Plasma ionized calcium and parathyroid hormone concentrations in horses after endurance rides

OBJECTIVE: To evaluate changes in plasma ionized calcium (Ca2+) and parathyroid hormone (PTH) concentrations in horses competing in endurance rides. DESIGN: Longitudinal clinical study. ANIMALS: 28 horses. PROCEDURE: Venous blood samples were obtained from horses before and after racing 80 km. Plasma pH and concentrations of Ca2+, PTH, inorganic phosphorus, albumin, lactate, and magnesium were measured. RESULTS: Overall, a significant decrease in mean (+/- SD) plasma Ca2+ concentration (from 6.44 +/- 0.42 to 5.64 +/- 0.42 mg/dl) and a significant increase in plasma PTH concentration (from 49.9 +/- 30.1 to 148.1 +/- 183.0 pg/ml) were found after exercise. Exercise also resulted in significant increases in plasma inorganic phosphorus, albumin, and lactate concentrations. No changes in plasma magnesium concentration or pH were detected after exercise. Plasma PTH concentration was not increased after exercise in 8 horses; in these horses, plasma PTH concentration decreased from 58.2 +/- 26.3 to 27.4 +/- 22.4 pg/ml, although plasma Ca2+ concentration was also decreased. CONCLUSIONS AND CLINICAL RELEVANCE: Plasma Ca2+ concentration was decreased after racing for 80 km, compared with values obtained before racing. In most horses, an increase in plasma PTH concentration that was commensurate with the decrease in plasma Ca2+ was detected; however, some horses had decreased plasma PTH concentrations.     

Diurnal variations in the plasma concentration of parathyroid hormone in dogs

The plasma concentrations of parathyroid hormone (PTH), ionised calcium (Ca(2+)), total calcium, albumin and inorganic phosphorus, and the pH were measured in blood samples obtained from nine dogs during a period of 26 hours. The plasma pth levels fluctuated slightly during the day, by about 20 pg/ml, but there was a distinct peak (42.8 [8.8] pg/ml) at 07.00. Plasma Ca(2+) showed a diurnal pattern in which two peaks (increases of 0.03 mmol/l) were observed at 05.00 and 17.00, and the plasma concentration of inorganic phosphorus showed a similar pattern. There were no diurnal changes in total calcium or albumin.     

Serum concentrations of ionized calcium, vitamin D3, and parathyroid hormone in captive thick-billed parrots (Rhynchopsitta pachyrhyncha).

Serum collected from 68 thick-billed parrots (Rhynchopsitta pachyrhyncha) from 15 institutions was analyzed for ionized Ca (iCa), total Ca (tCa), P, total protein (TP), albumin (Alb), parathyroid hormone (PTH), and vitamin D3. Values were not distributed normally; 95% frequency intervals were as follows: iCa (0.82-1.3 mmol/L), tCa (1.37-2.09 mmol/L,), P (0.35-1.75 mmol/L), TP (21-39 g/L), Alb (9-13 g/L), PTH (0-65.68 pmol/L), and vitamin D3 (5.2-51 nmol/L). Sixty percent (+/-7.5%) of tCa was ionized. Female thick-billed parrots had significantly higher mean iCa (1.11 mmol/L, n = 22) than male thick-billed parrots (1.05 mmol/L, n = 32). tCa and iCa values in thick-billed parrots were lower than the reported values for other psittacine species. A significant positive linear relationship existed between Alb-TP and iCa-tCa ratios. A significant inverse linear relationship was also identified between the tCa-P ratio and PTH. These findings are consistent with known domestic avian Ca physiology.     

Vitamin D status in cattle with malignant catarrhal fever

The aim of the present study was to determine the vitamin D status in cattle with malignant catarrhal fever (MCF). Twelve cattle diagnosed as MCF and 6 healthy cattle (controls) were used in the study. Serum 1,25-dihydroxyvitamin D(3) (1,25-D), 25-hydroxyvitamin D(3) (25-D), calcium, phosphorus and parathyroid hormone (PTH) levels were determined as 96.83 pg/ml, 30.0 ng/ml, 2.19 mmol/l, 1.57 mmol/l and 15.21 pg/ml in MCF group and 42.33 pg/ml, 37.0 ng/ml, 2.43 mmol/l, 1.96 mmol/l and 36.08 pg/ml in controls, respectively. Although serum 1,25-D level in the MCF group was increased (P<0.01), serum calcium (P<0.01) and PTH (P<0.05) levels were decreased compared to the controls. The results suggest that there might be an interaction between vitamin D status and MCF.     

Serum concentrations of calcium, phosphorus, magnesium and calciotropic hormones in donkeys

OBJECTIVE: To provide reference values for serum biochemical variables that are used for evaluation of mineral metabolism in donkeys and compare values with those in horses. ANIMALS: 18 donkeys and 18 horses. PROCEDURES: Total calcium (tCa), total magnesium (tMg), and inorganic phosphorus (P) concentrations were measured in serum samples via spectrophotometry. Ionized calcium (iCa) and magnesium (iMg) concentrations were quantified with selective electrodes. By use of a micropartition system, tCa and tMg were fractionated to separate protein-bound (pCa, pMg) and ultrafiltrable fractions. Complexed calcium (cCa) and magnesium (cMg) concentrations were calculated by substracting ionized fractions from ultrafiltrable fractions. Parathyroid hormone (PTH) and calcitriol (CTR) concentrations were measured via radioimmunoassay. RESULTS: Serum tCa concentration in donkeys (3.37 +/- 0.21 mmol/L) was composed of pCa (1.59 +/- 0.21 mmol/L [47.0 +/- 4.2%]), iCa (1.69 +/- 0.04 mmol/L [50.4 +/- 3.0%]), and cCa (0.09 +/- 0.08 mmol/L [2.6 +/- 2.9%]). Serum tMg concentration (1.00 +/- 0.08 mmol/L) was fractioned in pMg (0.23 +/- 0.08 mmol/L [23.4 +/- 8.1%]), iMg (0.59 +/- 0.04 mmol/L [58.8 +/- 5.1%]), and cMg (0.18 +/- 0.08 mmol/L [17.8 +/- 7.2%]). Serum concentrations of P (1.14 +/- 0.30 mmol/L), PTH (20.4 +/- 21.2 pg/mL), and CTR (13.4 +/- 5.9 pg/mL) were determined. CONCLUSIONS AND CLINICAL RELEVANCE: Serum variables of mineral metabolism in donkeys were within reference ranges for horses. However, when compared with horses, donkeys had higher iCa, cMg, and CTR and lower pMg and PTH concentrations.     

Feline parathyroid hormone: validation of hormonal assays and dynamics of secretion

Validated assays for quantification of intact parathyroid hormone (I-PTH) are no longer available. Moreover, the third-generation PTH assay that only detects the whole PTH molecule (W-PTH) has never been tested in cats. The work presented here is aimed to validate a commercially available assay for measurement of I-PTH and W-PTH in cats and to study the dynamics of PTH secretion in healthy cats. Our results show that both assays are reliable for the measurement of feline PTH. In healthy adult cats W-PTH concentration (15.1 ± 1.6 pg/mL) was greater (P < 0.001) than I-PTH concentration (9.1 ± 0.7 pg/mL). The dynamics of PTH secretion in response to changes in extracellular calcium (Ca(2+)) were investigated in 13 cats by studying PTH-Ca(2+) curves. PTH-Ca(2+) curves were obtained by intravenous infusion of disodium ethylenediaminetetraacetic acid and CaCl(2). PTH was measured using both I-PTH and W-PTH assays. During hypocalcemia a sigmoidal curve that was similar when measured with I-PTH or W-PTH was obtained. The maximal PTH concentration in response to hypocalcemia was greater with W-PTH (179.6 ± 41.9 pg/mL) than with I-PTH (67.6 ± 10.5 pg/mL; P = 0.01). However, hypercalcemia resulted in an equivalent PTH inhibition, with both assays yielding PTH concentrations as follows: W-PTH = 4.0 ± 0.4 pg/mL and I-PTH = 4.9 ± 0.3 pg/mL (NS). Parameters of the feline PTH-Ca(2+) curve are similar to what has been previously reported in dogs.     

Rabbit model of primary hyperparathyroidism induced by high-phosphate diet

The objective of this study is to establish a new rabbit model of primary hyperparathyroidism (PHPT) induced by high-phosphate diet. One hundred twenty rabbits were divided into two groups of 60 each. The treatment group was fed a high-phosphate diet (Ca:P = 1:7) and the control group was given a normal animal diet (Ca:P = 1:0.7) for 1 to 6 mo. Serologic examinations, including parathyroid hormone (PTH), calcium and phosphorus levels, blood urea nitrogen, creatinine, and uric acid, and the histologic examination, including parathyroid, kidney, and bones, were performed at the end of each month for 6 mo. Compared with the control, serum PTH levels in the treatment groups were elevated at all six time points, whereas serum calcium levels were reduced, and serum phosphorus levels remain unchanged over the course of the first 3 mo. Serum calcium levels were increased, whereas serum phosphorus levels were reduced at 4, 5, and 6 mo. Parathyroid histopathological examination showed no change during the first month, whereas 60% of the animals exhibited mild hyperplasia starting at 2 mo, and 90% of the animals in the treatment group exhibited mild-to-moderate hyperplasia with gland enlargement starting from 3 mo through the end of the study. Histopathological examination of the kidneys showed no change at 1 mo, but focal parenchymal inflammation with calcium deposition was observed in the treatment groups at 2 to 6 mo. Fibrous tissue of the bone extended toward the cortex, and fibrosis was evident at the third month. The fibrous cells were found to be concentrated mainly on the inner and outer membranes of the bone cortex, and the amount of fibrous tissue increased as the disease progressed. We conclude that a new rabbit animal model of PHPT can be successfully created by the administration of a high-phosphate diet. This animal model can be used in various future studies related to PHPT.     

Alterations in serum parathyroid hormone and electrolyte concentrations and urinary excretion of electrolytes in horses with induced endotoxemia

Hypocalcemia and hypomagnesemia are common in horses with sepsis and endotoxemia. We hypothesize that endotoxemia triggers a systemic inflammatory response that results in hypocalcemia and hypomagnesemia. The goal of this study was to determine the effect of endotoxin (lipopolysaccharide [LPS]) administration to healthy horses on serum parathyroid hormone (PTH), ionized calcium (Ca2+) and total calcium (tCa), ionized magnesium (Mg2+) and total magnesium (tMg), phosphate (Pi), potassium (K+), sodium (Na+), chloride (Cl-), and insulin concentrations, and on the urinary excretion of these electrolytes. Twelve mares were infused with Escherichia coli LPS (30 ng/kg/h i.v.) for 1 hour. Six mares were infused with saline (controls). In LPS-infused horses, heart rate increased significantly from (mean +/- SD) 40.0 +/- 1.3 to 70.0 +/- 9.0 beats/min, respiratory rate from 12.7 +/- 1.0 to 21.1 +/- 3.0 breaths/min, body temperature from 37.4 +/- 0.3 to 38.9 +/- 0.6 degrees C, and tumor necrosis factor-alpha concentrations from 6.6 +/- 3.5 to 507 +/- 260 pg/mL (P < .05). White blood cell count decreased significantly from 7570 +/- 600 to 1960 +/- 560 cells/ microL. Serum concentrations of Ca2+ decreased from 6.5 +/- 0.3 to 6.0 +/- 0.3 mg/dL, of Mg2+ from 0.53 +/- 0.06 to 0.43 +/- 0.04 mM, of tMg from 0.78 +/- 0.05 to 0.62 +/- 0.08 mM, of K+ from 4.3 +/- 0.4 to 3.0 +/- 0.5 mEq/L, and of Pi from 3.4 +/- 0.5 to 1.7 +/- 0.5 mg/dL (all P < .05). PTH increased significantly from 1.3 +/- 0.4 to 6.0 +/- 5.2 pM; however, in some horses (n=2), PTH did not increase despite hypocalcemia. Insulin increased significantly from 9.4 +/- 3.6 to 50.5 +/- 9.6 microIU/mL (n=3). Urinary fractional excretion of Ca2+ decreased significantly from 4.7 +/- 1.4 to 1.7 +/- 1.2%, of Mg2+ from 36.6 +/- 6.5 to 11.7 +/- 7.3%, and of K+ from 37.9 +/- 11.3 to 17.7 +/- 6.2%. Fractional excretion of Pi increased from 0.02 +/- 0.02 to 0.14 +/- 0.07% and of Na+ from 0.26 +/- 0.13% to 1.2 +/- 0.5%. No changes were found in serum tCa, Na+, and Cl- concentrations. In conclusion, endotoxemia in horses resulted in electrolyte abnormalities that included hypocalcemia, hypomagnesemia, hypokalemia, hypophosphatemia, and increased serum PTH and insulin concentrations.     

Intraoperative parathyroid hormone concentration to confirm removal of hypersecretory parathyroid tissue and time to postoperative normocalcaemia in nine dogs with primary hyperparathyroidism

Objective To determine (1) whether the intraoperative parathyroid hormone concentration ([PTH]) during parathyroidectomy (PTX) can be used to indicate cure in dogs with primary hyperparathyroidism and (2) the time taken for postoperative serum calcium concentration to normalise. Design Retrospective study (2005–10) from a private referral hospital in Sydney, New South Wales, Australia. Procedure Nine client‐owned dogs underwent surgical PTX for naturally occurring primary hyperparathyroidism. [PTH] was measured from serum samples taken immediately post‐induction (pre‐PTX]) and at least 20 min after adenoma removal (post‐PTX) for all dogs, and during parathyroid gland manipulation (intra‐PTX) for six dogs. The concentration of ionised calcium (iCa) was measured at various time points postoperatively until it normalised, then stabilised or decreased below reference ranges. Statistical analysis compared the mean pre‐, intra‐ and post‐PTX [PTH] and the average rate of decline of iCa concentration postoperatively. Results All dogs demonstrated a significant decrease from mean pre‐PTX [PTH] (168.51 pg/mL) to mean post‐PTX [PTH] (29.20 pg/mL). There was a significant increase in mean intra‐PTX [PTH] (279.78 pg/mL). The average rate of decline of iCa concentration postoperatively to within the reference range (1.12–1.40 mmol/L) occurred after 24 h. Conclusion Intraoperative measurements of [PTH] can be used clinically to determine cure of primary hyperparathyroidism. Parathyroid hormone increases significantly during parathyroid gland manipulation. Plasma iCa concentration returns to within the reference range on average 24 h after successful PTX. Not all dogs require vitamin D or calcium supplementation pre‐ or postoperatively.     

Interaction between the levels of hormones and minerals in sera of healthy and sick cows

An interaction between blood levels of parathyroid hormone, calcitonin, 1.25-dihydroxycholecalciferol and levels of calcium, phosphorus and magnesium was examined in 85 cows, which included healthy cows and cows with ostemalacia, mastitis and paresis. Levels of parathyroid hormone (PTH) and calcitonin were determined in vitro using IMMULITE analyser (Diagnostic Products Corporation, USA), by means of immunometric assay. Levels of vitamin D were measured using the enzyme linked immunosorbent assay (ELISA). Levels of calcium, phosphorus and magnesium were determined using the automated Eos-Bravo analyser (Hospitex Diagnostics, Italy) with HOSPITEX reagents. The lowest blood levels of calcium (1.38 +/- 0.18 mmol/L) and phosphorus (0.65 +/- 0.12 mmol/L) were found in cows with parturient paresis. Decreased blood levels of phosphorus and magnesium were also determined in cows with osteomalacia. For cows with parturient paresis, which received a mineral supplement, the average serum level of calcium was by 20.7% higher than the level found in those which did not receive a supplement, and the level of phosphorus was by 23.6% higher, however, these levels remained low. The blood level of parathyroid hormone ranged from 3.47 to 5.20 pmol/L in healthy cows and from 3.95 to 15.21 pmol/L in sick cows. The highest and statistically significant increase in blood PTH level (up to 18.31 +/- 1.88 pmol/L) was found in cows with parturient paresis. The blood level of PTH correlated inversely with the level of calcium in cows with osteomaliacia (r = -0.89) and in cows with parturient paresis (r = -0.49 and r = -0.61, respectively). The serum level of calcitonin ranged from 1.46 pmol/L to 2.40 pmol/L in healthy and sick cows and the difference was not statistically significant. Lower serum levels of vitamin D were found in heifers-in-calf and in cows with mastitis. A clear correlation between levels of calcitonin, vitamin D and macronutrients was not found.     

Effect of cation–anion balance in feed on urine pH in rabbits in comparison with other species

In the present investigation, the impact of diet composition on urine pH in rabbits was compared with previous studies on rabbits, cats, dogs, pigs and horses. A total of 13 dwarf rabbits were fed six different diets with a cation–anion balance (CAB) between ?39 and +320 mmol/kg dry matter (DM) using ammonium chloride (NH₄Cl) as an acidifier. CAB was calculated as follows: CAB (mmol/kg DM) = 49.9*Ca + 82.3*Mg +43.5*Na + 25.6*K ? 59*P ? 62.4*S ? 28.2*Cl; minerals in g/kg DM. Urine, faeces and blood were collected. Urine pH ranged from 5.26 ± 0.22 at a CAB of ?39 mmol/kg DM to 8.56 ± 0.24 at a CAB of +320 mmol/kg DM. A low CAB in the feed reduced blood pH and blood base excess significantly. Renal excretion of Ca, P, Na and Mg and water was significantly higher in rabbits eating acidifying diets. In comparison with other species, rabbits reacted to acidifying diets in a similar way as cats, dogs and pigs. Rabbits on a mildly alkalizing diet, however, had a trend to higher urine pH than other monogastric species on such diets (cats, dogs, pigs, horses).     

Radioimmunoassay of parathyroid hormone in cats

A radioimmunoassay for measurement of midmolecule parathyroid hormone (PTH) concentration in serum from dogs was validated for use on serum from cats. The assay detected an increase in serum concentration of PTH after IV infusion of Na2 EDTA in healthy cats. Infusion of calcium chloride caused a decrease in measured PTH. Accuracy of the assay was demonstrated by quantitative recovery of a feline parathyroid gland extract added to pooled feline sera. Mean interassay and intra-assay coefficients of variation were 0.13 and 0.07, respectively. Sensitivity of the assay was 0.1 ng of PTH/ml. The median PTH concentration measured in 40 adult cats was 3.5 ng/ml, with a range of 1.16 to 11.0 ng/ml.     

Hormonal calcium regulation and calcium setpoint in offspring of bitches with different calcium intakes during pregnancy

High maternal calcium (Ca) intake may lead to alterations in development and differentiation of fetal tissues and may result in altered 'programming' of Ca homeostasis, with eventual effects on Ca handling and skeletal development in the offspring during later life. In bitches fed a diet with a Ca intake three times above recommendations (3.27 g/100 g vs 1.14 g/100 g dry matter) during the second half of pregnancy, the plasma concentration of 1,25 dihydroxy cholecalciferol (1,25 (OH)₂ vit D) appeared to decrease, while plasma Ca, phosphorus (P), parathyroid hormone (PTH) and calcitonin (CT) concentrations remained unchanged. High maternal Ca intake did not result in altered basal or stimulated plasma concentrations of Ca, P, PTH, CT and 1,25 (OH)₂ vit D in the offspring (n = 7) when compared with pups from bitches fed a normal Ca diet during the entire pregnancy (controls, n = 7). The Ca setpoint for PTH secretion (^Ca S_for PTH) was therefore not different from controls. From this pilot study it may be concluded that excessive Ca intake during late pregnancy in the bitch has no deleterious effects on hormonal Ca homeostasis in the offspring.     

Effects of sample handling on adrenocorticotropin concentration measured in canine plasma, using a commercially available radioimmunoassay kit.

A commercially available radioimmunoassay (RIA) kit for measurement of human adrenocorticotropin (hACTH) was validated for use in dogs. Assay sensitivity was 3 pg/ml. Intra-assay coefficient of variation (x 100; CV) for 3 canine plasma pools was 3.0 (mean +/- SD, 33 +/- 0.99 pg/ml), 4.2 (71 +/- 2.4 pg/ml) and 3.7 (145 +/- 3.7 pg/ml) %. Interassay CV for 2 plasma pools measured in 6 assays was 9.8 (37 +/- 3.6 pg/ml) and 4.4 (76 +/- 3.4 pg/ml) %, respectively. Dilutional parallelism was documented by assaying 2 pools of canine plasma at 3 dilutions and correcting the measured result for dilution. Corrected mean concentrations for the first pool were 33 (+/- 0.99), 36 (+/- 4.3), and 33 (+/- 6.8) pg/ml; corrected mean concentrations for the second pool were 145 (+/- 5.4), 141 (+/- 10.8) and 125 (+/- 3.4) pg/ml. Recovery of 1-39hACTH added to canine plasma (6.25, 12.5, 25.0, 50.0, and 100.0 pg/ml) was linear and quantitative (slope = 0.890, R2 = 0.961). To test whether anticoagulant or the protease inhibitor, aprotinin, influences ACTH concentration in canine plasma, ACTH was measured in canine blood collected in 4 tubes containing anticoagulant: heparin (H), heparin + 500 kallikrein inhibitor units (KIU) of aprotinin/ml (HA), EDTA (E), and EDTA + aprotinin (EA). Plasma ACTH concentration was the same when samples containing H and HA, or HA and E were compared, and was significantly (P less than 0.01) lower in samples containing EA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of diet on calcium metabolism, tissue calcification and urinary sludge in rabbits (Oryctolagus cuniculus)

Rabbits absorb more calcium (Ca) from their diet than they require, and excrete surplus via urine, which therefore contains a typical 'sludge'. This makes rabbits susceptible to Ca-containing uroliths. But given the Ca content of diets of free-ranging specimens, and the limited reports of urinary sludge and Ca contents in free-ranging lagomorphs, we can suspect that rabbits are naturally adapted to high urinary Ca loads. We fed four groups of New Zealand hybrid rabbits [n = 28, age at start 5-6 weeks) pelleted diets consisting of lucerne hay only (L, Ca 2.32% dry matter (DM)], lucerne:oats 1:1 (LG, Ca 1.36%), grass hay only (G, Ca 1.04%), or grass:oats 1:1 (GG, 0.83%) for 25 weeks, with water available ad libitum. Diets were not supplemented with Ca, phosphorus, or vitamin D. Rabbits on diets LG and GG had lower food and water intakes, lower faeces and urine output, grew faster and had higher body mass at slaughter (mainly attributable to adipose tissue). Apparent Ca digestibility decreased in the order L-LG-G/GG. Rabbits on L had larger and heavier kidneys, more urinary sediment at sonography, and a higher urinary Ca content than the other groups. No animal showed signs of urolithiasis/calcinosis at X-ray, sonography, or gross pathology. Kidney/aorta histology only sporadically indicated Ca deposits, with no systematic difference between groups. Under the conditions of the experiment, dietary Ca loads in legume hay do not appear problematic for rabbits, and other factors, such as water supply and level of activity may be important contributors to urolithiasis development in veterinary patients. However, due to the lower Ca content of grass hay, the significantly lower degree of urinary sludge formation, and the significantly higher water intake related with grass hay feeding, grass hay-dominated diets are to be recommended for rabbits in which urolithiasis prevention is an issue.     

Effects of phosphorus/calcium-restricted and phosphorus/calcium-replete 32% protein diets in dogs with chronic renal failure.

Twenty-four dogs with induced, severe chronic renal failure were allotted to 2 groups of 12 each. Group-A dogs were fed a 0.4% phosphorus (P)/0.6% calcium, 32% protein diet, and group-B dogs were fed a 1.4% P/1.9% calcium, 32% protein diet. Dogs were studied over 24 months to determine clinical status, survival, blood biochemical alterations, glomerular filtration rate (GFR), urinary excretion of P and protein, renal morphologic changes, and renal tissue concentrations of calcium, P, and magnesium. Group-A dogs developed statistically significant differences from group-B dogs in several blood biochemical values (PCV and total solids, calcium, P, potassium, sodium, chloride, total CO2 (TCO2), anion gap, and parathyroid hormone concentrations) and in urinary P excretion. Mean (+/- SEM) GFR values in group-A and group-B dogs were nearly identical when diets were initiated (group A = 0.73 +/- 0.05 ml/min/kg of body weight; group B = 0.72 +/- 0.08 ml/min/kg), but significantly (P = 0.0346) lower GFR developed in group-B than in group-A dogs over time. At 24 months, GFR in survivors was 0.83 +/- 0.08 and 0.63 +/- 0.15 ml/min/kg for dogs of groups A and B, respectively. Other measurements favored the hypothesis that P/calcium restriction was beneficial, but values failed to reach statistical significance. Survival was greater at 24 months in group-A than in group-B (7 vs 5) dogs, and renal tissue concentrations of calcium and P were higher in group-B than in group-A dogs. Differences were not detected between groups in urinary excretion of protein and in the type or severity of renal lesions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Human-parathormone assay for use in dogs: validation, sample handling studies, and parathyroid function testing

Ten commercially available parathormone (PTH) assays were competitively validated, using dilutional parallelism, intra-assay and interassay coefficients of variation, and sensitivity and measured responses of 2 dogs to calcium and EDTA infusions. A 2-site immunoradiometric assay for intact human-PTH was superior to the others for estimating canine-PTH, met the criteria for validity, and was further investigated. A series of sample-handling studies was performed. Serum and plasma samples stored at 24 C lost 15% (n = 5; P less than 0.05) of PTH between 2 and 24 hours. This did not occur at 6 C. The mean PTH concentration of sera from blood samples clotted at 24 C was 6% (P less than 0.05) higher than equivalent EDTA samples. Serum samples stored at 6 and 37 C deteriorated 35% and 100% (n = 5; P less than 0.05), respectively, after 1 week, whereas samples stored at -20 and -70 C for 4 weeks did not deteriorate. There was no significant deterioration of PTH in samples frozen (-40 C) and thawed up to 7 times (n = 5). Parathyroid function testing was investigated by use of 2-hour infusions of disodium EDTA (25 mg/kg/h), 10-minute infusions of calcium gluconate (3 mg of elemental calcium/kg/10 min), and physiologic saline controls (n = 8). Renal function was monitored before and after EDTA infusion by exogenous creatinine clearance. Infusion of disodium EDTA increased mean PTH concentration from 67 (time 0) to 317 and 235 pg/ml at 90 and 180 minutes, respectively (P less than 0.001). Infusion of calcium gluconate decreased mean PTH concentration from 84 (time 0) to 14 and 12 pg/ml at 15 and 60 minutes, respectively (P less than 0.005). There were no observable side effects of the infusions in normal conscious dogs and no differences in exogenous creatinine clearance after EDTA infusion.     

Comparison of serum parathyroid hormone and ionized calcium and magnesium concentrations and fractional urinary clearance of calcium and phosphorus in healthy horses and horses with enterocolitis

OBJECTIVE: To evaluate calcium balance and parathyroid gland function in healthy horses and horses with enterocolitis and compare results of an immunochemiluminometric assay (ICMA) with those of an immunoradiometric assay (IRMA) for determination of serum intact parathyroid hormone (PTH) concentrations in horses. ANIMALS: 64 horses with enterocolitis and 62 healthy horses. PROCEDURES: Blood and urine samples were collected for determination of serum total calcium, ionized calcium (Ca2+) and magnesium (Mg2+), phosphorus, BUN, total protein, creatinine, albumin, and PTH concentrations, venous blood gases, and fractional urinary clearance of calcium (FCa) and phosphorus (FP). Serum concentrations of PTH were measured in 40 horses by use of both the IRMA and ICMA. RESULTS: Most (48/64; 75%) horses with enterocolitis had decreased serum total calcium, Ca2+, and Mg2+ concentrations and increased phosphorus concentrations, compared with healthy horses. Serum PTH concentration was increased in most (36/51; 70.6%) horses with hypocalcemia. In addition, FCa was significantly decreased and FP significantly increased in horses with enterocolitis, compared with healthy horses. Results of ICMA were in agreement with results of IRMA. CONCLUSIONS AND CLINICAL RELEVANCE: Enterocolitis in horses is often associated with hypocalcemia; 79.7% of affected horses had ionized hypocalcemia. Because FCa was low, it is unlikely that renal calcium loss was the cause of hypocalcemia. Serum PTH concentrations varied in horses with enterocolitis and concomitant hypocalcemia. However, we believe low PTH concentration in some hypocalcemic horses may be the result of impaired parathyroid gland function.