A comparison of canine whole and intact parathyroid hormone concentrations as measured by different assays.

OBJECTIVES: To compare an intact immunoradiometric parathyroid hormone assay with (1) a non-isotopic technique; and, (2) a whole parathyroid hormone immunoradiometric assay. MATERIALS AND METHODS: Intact parathyroid hormone concentrations were measured using immunoradiometric (Scantibodies) and chemiluminescent (Immulite 2000) assays. Whole parathyroid hormone concentration was measured using an immunoradiometric assay (Scantibodies). RESULTS: A total of 48 and 47 samples, respectively, were used to compare immunoradiometric and chemiluminescent intact parathyroid concentrations and intact and whole parathyroid hormone concentrations by immunoradiometric assays. Using chemiluminescence, 39 (81.3%) samples had intact parathyroid hormone concentrations at or below the reported limit of detection of the assay (0.3 pmol/L). Intact [6.3 (2.0 to 95.5) pmol/L] and whole [3.3 (0.8 to 125.2) pmol/L] immunoradiometric parathyroid hormone concentrations exhibited excellent correlation. CLINICAL SIGNIFICANCE: Not all parathyroid hormone assays perform similarly. The chemiluminescent assay in this study cannot be recommended for use in dogs. The immunoradiometric intact parathyroid hormone assay proved to be a more reliable method. Given the correlation between intact and whole parathyroid hormone concentrations, it remains unclear which one is superior for routine clinical decision-making.

Validation of a noninvasive diagnostic tool to verify neuter status in dogs: The urinary FSH to creatinine ratio.

Determining the presence of functional gonadal tissue in dogs can be challenging, especially in bitches during anestrus or not known to have been ovariectomized, or in male dogs with nonscrotal testes. Furthermore, in male dogs treated with deslorelin, a slow-release GnRH agonist implant for reversible chemical castration, the verification of complete downregulation of the hypothalamic-pituitary-gonadal (HPG) axis can be difficult, especially if pretreatment parameters such as the size of the testes or prostate gland are not available. The aims of this study were to validate an immunoradiometric assay for measurement of FSH in canine urine, to determine if the urinary FSH to creatinine ratio can be used to verify the neuter status in bitches and male dogs, as an alternative to the plasma FSH concentration, and to determine if downregulation of the HPG axis is achieved in male dogs during deslorelin treatment. Recovery of added canine FSH and serial dilutions of urine reported that the immunoradiometric assay measures urinary FSH concentration accurately and with high precision. Plasma FSH concentrations (the mean of two samples, taken 40 minutes apart) and the urinary FSH to creatinine ratio were determined before gonadectomy and 140 days (median, range 121-225 days) and 206 days (median, range 158-294 days) after gonadectomy of 13 bitches and five male dogs, respectively, and in 13 male dogs before and 132 days (median, range 117-174 days) after administration of a deslorelin implant. In both bitches and male dogs, the plasma FSH concentration and the urinary FSH to creatinine ratio were significantly higher after gonadectomy, with no overlapping of their ranges. Receiver operating characteristic analysis of the urinary FSH to creatinine ratio revealed a cut-off value of 2.9 in bitches and 6.5 in males to verify the presence or absence of functional gonadal tissue. In male dogs treated with deslorelin, the plasma FSH concentrations and urinary FSH to creatinine ratios were significantly lower after administration of the implant, but their ranges overlapped. We conclude that the urinary FSH to creatinine ratio can be used to verify the neuter status of bitches and male dogs. However, it cannot be used for the assessment of complete downregulation of the HPG axis after administration of a deslorelin implant. The urinary FSH to creatinine ratio is preferable over the plasma FSH concentration because it involves only one sample that can be collected relatively easy and noninvasively.

Comparison of intravenous versus intramuscular administration of corticotropin-releasing hormone in healthy cats.

BACKGROUND: Because of the lack of a current validated assay for feline endogenous adrenocorticotropic hormone (ACTH) in response to administration of currently available ovine corticotropin-releasing hormone (oCRH) preparations, a complete evaluation of the hypothalamic-pituitary-adrenal axis in cats has not been possible. OBJECTIVE: This study was undertaken to (1) determine the pituitary (ACTH) and adrenal (cortisol) response to both IV and IM administration of a currently available oCRH product in healthy cats, and (2) validate an endogenous ACTH assay for use in cats. ANIMALS: Seventeen healthy cats receiving oCRH (n = 11) or placebo (n = 6). METHODS: Prospective, randomized, placebo-controlled study. oCRH at 1 µg/kg or placebo was given either IM or IV. Endogenous cortisol and ACTH concentrations were evaluated after the injection. A comparison of IM versus IV and placebo versus treatment was made. RESULTS: The DiaSorin immunoradiometric assay (IRMA) assay for ACTH performed well, showing both parallelism and acceptable intra- and interassay coefficients of variation. There was a significant difference between groups (P = .025) and a significant difference between times (P = .025) when endogenous ACTH concentrations were compared after oCRH IV or IM. No significant differences were observed in cortisol concentrations comparing IV to IM oCRH. CONCLUSIONS: IM administration of oCRH results in significantly greater ACTH concentrations but not cortisol concentrations when compared with IV administration. Samples should be drawn before and at 60 minutes after the injection. The Diasorin IRMA is valid for feline endogenous ACTH measurements.

Development of a feline proinsulin immunoradiometric assay and a feline proinsulin enzyme-linked immunosorbent assay (ELISA): a novel application to examine beta cell function in cats.

The prevalence of feline diabetes mellitus has increased several-fold over the last three decades. In humans, progression from obesity to diabetes is marked by changes in the release of proinsulin. A specific proinsulin (FPI) assay has not been available to examine similar changes in cats. The goal of this study was to develop a proinsulin assay for the analysis of beta cell function in cats. Monoclonal antibodies were developed against recombinant FPI and used in a two-site sandwich immunoradiometric assay (IRMA) and enzyme-linked immunosorbent Assay (ELISA). The antibody pair had negligible cross-reactivity with bovine insulin and feline C-peptide. The working range was 11-667pmol/L for the IRMA and 11-1111pmol/L for the ELISA. An intravenous glucose tolerance test was performed in six long-term obese and six lean adult healthy cats and serum glucose, insulin, and FPI concentrations were determined. The proinsulin and insulin secretion pattern in response to glucose was significantly different between lean and obese cats but the pattern was similar within a group. Both groups had similar baseline proinsulin/insulin ratios; however, obese cats showed a significantly higher proinsulin/insulin ratio during the first 15min of the IVGTT and a much lower ratio during the last 30min suggesting a time-delayed adjustment to the increased insulin demand. In conclusion, we report the development and validation of an IRMA and an ELISA for FPI. This novel assay is useful to elucidate FPI secretion and can be used similar to a C-petide assay to evaluate residual beta cell function in cats.

Basal and GnRH-induced secretion of FSH and LH in anestrous versus ovariectomized bitches.

The basal and gonadotropin releasing hormone (GnRH)-induced plasma concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH) were studied in four anestrous and four ovariectomized (OVX) bitches. Blood samples were obtained via jugular venipuncture 40min before and 0, 10, 20, 30, 60, 90, and 120min after the i.v. administration of synthetic GnRH in a dose of 10microg/kg body weight. The basal plasma FSH and LH concentrations were significantly higher in the OVX bitches than in the anestrous bitches. In the anestrous bitches, the plasma FSH concentration was significantly higher than the pretreatment level at 10, 20, and 30min, whereas the plasma LH concentration was significantly elevated at 10 and 20min. The maximal GnRH-induced plasma FSH concentration in the anestrous bitches did not surpass the lowest plasma FSH concentration in the OVX bitches, whereas the GnRH-induced plasma LH concentrations in the anestrous bitches overlapped with the basal plasma LH concentrations in the OVX bitches. In the OVX bitches, GnRH administration did not induce a significant change in the plasma FSH concentration, whereas the plasma LH concentration increased significantly at 10 and 20min. In conclusion, the results of the present study indicate that in anestrous bitches GnRH challenge results in increased plasma levels of both FSH and LH, whereas in the OVX bitches, in which the basal plasma FSH and LH concentrations are higher, only a rise in the plasma LH concentration is present after GnRH stimulation. The results also suggest that a test to measure plasma concentration of FSH in single samples appears to have potential in verification of neuter status in bitches.

Effects of sulfamethoxazole-trimethoprim on thyroid function in dogs.

OBJECTIVE: To evaluate effects of trimethoprim-sulfamethoxazole (T/SMX) on thyroid function in dogs. ANIMALS: 6 healthy euthyroid dogs. PROCEDURE: Dogs were administered T/SMX (14.1 to 16 mg/kg, PO, q 12 h) for 3 weeks. Blood was collected weekly for 6 weeks for determination of total thyroxine (TT4), free thyroxine (fT4), and canine thyroid-stimulating hormone (cTSH) concentrations. Schirmer tear tests were performed weekly. Blood was collected for CBC prior to antimicrobial treatment and at 3 and 6 weeks. RESULTS: 5 dogs had serum TT4 concentrations equal to or less than the lower reference limit, and 4 dogs had serum fT4 less than the lower reference limit after 3 weeks of T/SMX administration; cTSH concentrations were greater than the upper reference limit in 4 dogs. All dogs had TT4 and fT4 concentrations greater than the lower reference limit after T/SMX administration was discontinued for 1 week, and cTSH concentrations were less than reference range after T/SMX administration was discontinued for 2 weeks. Two dogs developed decreased tear production, which returned to normal after discontinuing administration. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that administration of T/SMX at a dosage of 14.1 to 16 mg/kg, PO, every 12 hours for 3 weeks caused decreased TT4 and fT4 concentrations and increased cTSH concentration, conditions that would be compatible with a diagnosis of hypothyroidism. Therefore, dogs should not have thyroid function evaluated while receiving this dosage of T/SMX for >2 weeks. These results are in contrast to those of a previous study of trimethoprim-sulfadiazine.

Effects of dietary supplementation with sodium chloride on urinary relative supersaturation with calcium oxalate in healthy dogs.

OBJECTIVE: To evaluate the effect of dietary supplementation with sodium chloride (NaCl) on urinary calcium excretion, urine calcium concentration, and urinary relative supersaturation (RSS) with calcium oxalate (CaOx). ANIMALS: 6 adult female healthy Beagles. PROCEDURE: By use of a crossover study design, a canned diet designed to decrease CaOx urolith recurrence with and without supplemental NaCl (i.e., 1.2% and 0.24% sodium on a dry-matter basis, respectively) was fed to dogs for 6 weeks. Every 14 days, 24-hour urine samples were collected. Concentrations of lithogenic substances and urine pH were used to calculate values of urinary RSS with CaOx. RESULTS: When dogs consumed a diet supplemented with NaCl, 24-hour urine volume and 24-hour urine calcium excretion increased. Dietary supplementation with NaCl was not associated with a change in urine calcium concentration. However, urine oxalate acid concentrations and values of urinary RSS with CaOx were significantly lower after feeding the NaCI-supplemented diet for 28 days. CONCLUSIONS AND CLINICAL RELEVANCE: Dietary supplementation with NaCl in a urolith-prevention diet decreased the propensity for CaOx crystallization in the urine of healthy adult Beagles. However, until long-term studies evaluating the efficacy and safety of dietary supplementation with NaCl in dogs with CaOx urolithiasis are preformed, we suggest that dietary supplementation with NaCl be used cautiously.

Validation and clinical utility of a novel immunoradiometric assay exclusively for biologically active whole parathyroid hormone in the horse.

REASONS FOR PERFORMING STUDY: Parathyroid hormone (PTH) plays a critical role in the regulation of mineral metabolism in mammals. Until recently, the standard method for PTH measurement has been the 2nd generation intact-PTH (I-PTH) assay. Current evidence indicates that the I-PTH assay binds to the PTH molecule and to an inactive N-terminally truncated PTH fragment that tends to accumulate in the blood of uraemic patients. Therefore, a new 3rd generation PTH assay that detects only the whole PTH molecule (W-PTH; cyclase-activating PTH [CAP]) has been developed. OBJECTIVES: To validate this more specific W-PTH assay for measurement of equine PTH and evaluate its clinical utility. METHODS: W-PTH and I-PTH were measured in plasma samples from normal horses (adults and foals) and horses with nutritional secondary hyperparathyroidism (N2HPT) and with chronic renal failure (CRF). Replicate measurements and dilutional paralellism were used for assay validation. Changes in blood ionized calcium were induced by EDTA and CaCl2 administration. RESULTS: Performance of the W-PTH assay (accuracy, sensitivity, specificity and ability to detect changes in PTH in response to changes in calcium) was similar to that of the I-PTH assay. Surprisingly, the relative W-PTH concentration in normal horses and foals was higher than the relative I-PTH concentration. W-PTH values remained higher than I-PTH during acute hypo- and hypercalcaemia. An increase in both W-PTH and I-PTH concentrations was found in horses with N2HPT. In horses with CRF, W-PTH and I-PTH values were very low and no increase in I-PTH was observed. CONCLUSIONS: The W-PTH assay can be used for measurement of equine PTH. POTENTIAL RELEVANCE: The use of W-PTH assay is likely to improve the diagnosis of mineral metabolism in horses.

Detection of parathyroid hormone-related protein in cats with humoral hypercalcemia of malignancy.

BACKGROUND: Increased serum parathyroid hormone-related peptide (PTHrP) concentration is used to diagnose humoral hypercalcemia of malignancy (HHM) in humans and animals. A commercially available assay for human PTHrP has diagnostic utility in the dog, but has not been assessed in cats. OBJECTIVE: The goals of this study were to determine serum or plasma levels of PTHrP in a population of hypercalcemic cats and to determine whether increased PTHrP concentration was associated with malignancy. In addition, we validated immunoradiometric assays (IRMAs) for intact parathormone (iPTH) and PTHrP for use with feline samples. METHODS: A retrospective analysis of iPTH and PTHrP results from 322 hypercalcemic cats (ionized calcium concentration > 1.4 mmol/L) was performed. Immunoassays for human iPTH and PTHrP (residues 1-84) were validated using standard methods, and reference intervals were calculated using values from 31 healthy adult cats. Hypercalcemic cats were classified as parathyroid-independent (iPTH < 2.3 pmol/L), equivocal (iPTH 2.3-4.6 pmol/L), or parathyroid-dependent (iPTH > 4.6 pmol/L). Seven cats with detectable or increased PTHrP concentrations were evaluated further for underlying disease. Formalin-fixed neoplastic tissues were immunohistochemically stained using rabbit antibody to human midregion PTHrP. RESULTS: Assays for iPTH and PTHrP showed acceptable precision for feline samples. The reference interval for iPTH was 0.8-4.6 pmol/L and for PTHrP was < 1.5 pmol/L. The majority of hypercalcemic cats (263/322, 81.7%) were parathyroid-independent, with fewer cats in the equivocal (32/322, 9.9%) and parathyroid-dependent (27/322, 8.4%) groups. In 31 (9.6%) cats, PTHrP concentration was > 1.5 pmol/L (range 1.5-26.6 pmol/L). All 7 cats for which follow-up information was available had HHM; 6 had carcinomas (4 lung carcinomas, 1 undifferentiated carcinoma, 1 thyroid carcinoma) and 1 had lymphoma. All tumors had mild to moderate positive staining for PTHrP; however, lung carcinomas from normocalcemic cats also stained positive. CONCLUSIONS: Human IRMA for PTHrP (1-84) can be used to measure PTHrP in cats. Malignancies, particularly carcinomas, appear to secrete PTHrP and induce HHM in this species. Immunohistochemistry alone cannot predict the occurrence of HHM in cats.

Development of a sensitive immunoradiometric assay for detection of platelet surface-associated immunoglobulins in thrombocytopenic dogs.

OBJECTIVE: To develop a direct assay to measure platelet surface-associated immunoglobulins (PSAIg) in dogs and to determine whether the assay is useful in the diagnosis of immune-mediated thrombocytopenia (IMT). ANIMALS: 20 healthy dogs were used to develop reference intervals, and 23 dogs with IMT and 17 with non-IMT were used to evaluate the clinical use of this assay. PROCEDURE: After optimization of platelet collection and assay conditions, concentrations of PSAIg were measured, using radiolabeled staphylococcal protein A (SpA) and polyclonal antibodies against canine IgG (anti-gamma) and IgM (anti-micro). Concentrations of PSAIg were expressed as the percentage of radiolabeled immunoglobulin detector bound. RESULTS: Cut-off values (mean + 3 SD) were as follows: SpA, 1.1%; anti-gamma, 1.3%; and anti-micro, 3.5%. Values greater than these cut-off values were considered positive. Values determined by use of radiolabeled SpA for all dogs with IMT were greater than the cut-off value; values were considered high positives (> 5 times cut-off value) for 22 of these 23 dogs. Although 9 of 17 dogs with non-IMT also had PSAIg concentrations greater than the cut-off value, values were considered high positives for only 3 of these 9 dogs. CONCLUSIONS AND CLINICAL RELEVANCE: The immunoradiometric assay developed is a reliable and sensitive method to detect PSAIg in dogs. However, to obtain accurate results, optimum temperature, time, and storage conditions must be used. Detection of increased concentrations of PSAIg in dogs presumed to have non-IMT should alert clinicians to reconsider an immune-mediated basis for the thrombocytopenia.

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.

Evaluation of canine serum thyrotropin (TSH) concentration: comparison of three analytical procedures.

A comparative study of 3 analytical methods (immunoradiometric assay, enzyme immunometric assay, and chemiluminescent immunometric assay) for canine serum thyrotropin (TSH) was performed. Ninety-six dogs were included in the study. The within- and between-run precision was evaluated for each method, and correlations for the results obtained with each method were examined. The best within- and between-run precision was obtained with the chemiluminescent immunometric assay. Satisfactory correlations for the 3 analytical procedures were obtained but varied in relation to serum TSH concentration.

Biochemical indicators of bone metabolic activity in buffalo (Bubalus bubalis) during late pregnancy and early lactation.

Blood levels of calcium, inorganic phosphorus, magnesium, osteocalcin, intact parathyroid hormone, calcitonin, alkaline phosphatase activity, creatinine and thyroid hormones were estimated in 10 healthy buffalo during late pregnancy (30, 15 days and 7 days before calving), within 12 h after calving and 7-15-30-45 and 60 days after calving. The almost constant serum levels of calcium, phosphorus, intact parathyroid hormone, and the low calcitonin concentration indicate that these buffalo need to utilize only a little of their endogenous mineral resources. Bone-turnover could be demonstrated by variations in the serum levels of osteocalcin and alkaline phosphatase activity. A study of these bone markers could be useful for other research purposes and for future clinical application in pathological conditions.

cDNA cloning of canine common alpha gene and its co-expression with canine thyrotropin beta gene in baculovirus expression system.

The common alpha gene of the canine glycoprotein hormones was cloned, sequenced and co-expressed with the canine thyrotropin beta (TSH beta) gene in the baculovirus expression system, and a bioactive recombinant canine TSH was purified. The canine common alpha gene was cloned from the total RNA extracted from the canine pituitary gland by the reverse transcription polymerase chain reaction (RT-PCR) using primers that were designed based on the consensus sequences from other species. The resulting 476 bp PCR product is consisted of the full coding sequence for the 96 amino acid mature alpha subunit, and a sequence encoding a 24 amino acid signal peptide. Homology analysis with other species revealed that the canine common alpha subunit potentially contains five disulfide bonds and two oligosaccharide chains N-linked to Asn residues located at positions 56 and 82. For expression in the baculovirus expression system, the common alpha gene was cloned downstream of the p10 promoter of the pAcUW51 transfer vector, and the previously cloned canine TSH beta gene was inserted under the polyhedrin promoter of the same vector. The recombinant virus containing both alpha and beta genes was generated and propagated before being used to transfect the Sf9 insect cells for expression. The medium from the Sf9 cultures, presumably containing canine TSH alpha and beta in native heterodimer confirmation, exhibited TSH bioactivity as indicated in the cAMP stimulation assay in FRTL-5 cells. The expressed recombinant protein was purified from the culture medium with an affinity column that was coupled with IgG purified from the polyclonal antibodies generated against the partially purified native canine TSH.

Pituitary-adrenocortical responses to the first dyadic encounters in male rhesus monkeys: effect of dominance relationship.

Male rhesus monkeys unfamiliar with each other were paired in a cage, and blood samples were collected before and a few hours after pair formation. Adrenocorticotrophic hormone (ACTH) and cortisol levels in each blood sample were measured. Dominant-subordinate status was ascertained through two rank tests, the food competition test and the agonistic behavior test, which were performed immediately after pair formation. As a result, the dominance relationship was determined in seven pairs formed from five animals, and the differences in ACTH and cortisol values between the dominant and subordinate animal in these pairs were compared statistically. The day after the first encounter, a second encounter was conducted in randomly selected pairs of monkeys. In the first encounters, higher levels of both ACTH and cortisol were detected in dominant animals in comparison to subordinate animals. Changing the animal's partner altered the stress responses whenever the animal's dominant-subordinate status changed. The elevated levels of ACTH and cortisol in dominant animals disappeared on the day after the first encounter. In dominant animals, the pituitary-adrenocortical stress response reacts sharply to situational demands, whereas subordinate animals have a weaker response. This acute stress response is different from a chronic stress response. When the subordinate animal cannot escape, its hypothalamic-pituitary-adrenocortical axis appears to be suppressed.

Abnormalities of hypothalamic-pituitary-adrenal and hypothalamic-somatotrophic axes in Fawn-Hooded rats.

Fawn-Hooded (FH) rats show central and peripheral abnormalities in serotoninergic functions and have attracted attention as an animal model of some pathologies, including depression and hypertension. In addition, these rats show a reduced growth rate. As the hypothalamic-pituitary-adrenal (HPA) axis has been implicated in both depression and hypertension, and the hypothalamic-somatotrophic (HSM) axis has a major role in growth, these two endocrine axes were characterised in FH rats as compared with outbred Sprague-Dawley (SD) rats in basal conditions. FH rats showed normal serum ACTH and corticosterone concentrations, but reduced serum corticosterone binding capacity. At a central level, normal expression of mRNA for glucocorticoid type II receptors in the hippocampal formation and mRNA for corticotrophin-releasing factor (CRF) in the paraventricular nucleus of the hypothalamus were observed in FH rats, whereas expression of mRNA for CRF in the central nucleus of the amygdala was enhanced compared with the expression in SD rats. Serum GH concentrations were normal in FH rats, IGF-I tended to be lower, and mRNA for somatostatin (SRIF) in the periventricular nucleus of the hypothalamus was significantly lower in FH rats than in SD rats. The reduced SRIF gene expression in rats with normal or slightly reduced GH and IGF-I, respectively, might be secondary to a defective central and peripheral response to IGF-I, compatible with the reduced growth of FH rats. The present results suggest that FH rats have abnormalities in both HPA and HSM axes that might be related to some of their physiopathological characteristics.

Measurement of parathyroid hormone in horses.

Measurement of parathyroid hormone (PTH) in horses was performed on plasma samples using 2 immunoradiometric assays: a human intact PTH assay and a rat amino-terminal PTH assay. The assays were validated by assessment of their precision, sensitivity and specificity, and also by evaluating PTH changes in the horse in response to variation in blood ionised calcium. Intra- and inter-assay variance, precision and sensitivity were similar for both human and rat assays; however, the rat assay was slightly more precise and sensitive than the human assay. Both assays detected an increase in PTH levels in the horse when blood ionised calcium was decreased and a decline in PTH concentration with hypercalcaemia. Measurement of PTH concentration in samples from healthy horses with the human assay yielded a mean (+/-s.e.) value of 31.3+/-4.1 pg/ml. When using the rat assay, PTH values were 44.1+/-5.3 pg/ml. Plasma samples held for up to 3 months at -20 degrees C did not show a significant change in PTH concentration. In conclusion, the human intact PTH and the rat amino-terminal assays detected equine PTH and can be used for measurement of this hormone in horses. Quantification of equine PTH using these assays will allow more precise diagnosis of a variety of disorders affecting mineral metabolism in horses.

Influence of type and breed of horse on serum osteocalcin concentration, and evaluation of the applicability of a bovine radioimmunoassay and a human immunoradiometric assay [corrected].

OBJECTIVES: To evaluate applicability of a human osteocalcin (OC) immunoradiometric assay (IRMA) for use with equine serum and compare it with a bovine radioimmunoassay (RIA) previously proven valid for such samples, and to describe the effect of type and breed of horses on serum OC concentration. ANIMALS: 100 healthy horses of either sex, classified as type I or II (draught or warmblood, respectively). Each type was represented by 2 breed groups, each comprising 25 horses. PROCEDURE: Blood samples were collected in the morning, and the serum was separated. Osteocalcin was measured, using commercially available RIA and IRMA kits, according to the manufacturer's instructions. All samples were evaluated in duplicate. RESULTS: The human IRMA did not recognize equine OC. Significant variations in the bovine RIA results were observed between types of horses. Draught horses had lower OC concentration, compared with warmblood horses. Significant difference was not observed between breeds for type of horse. Sex had no influence on serum OC values, but age was a significant covariable for both types of horses. CONCLUSIONS: No crossreactivity exists between the equine and human amino- and/or carboxy-terminus of OC, using this particular human IRMA kit. Difference in blood OC concentration exists between draught and warmblood types of horses. CLINICAL RELEVANCE: Use of this human IRMA kit is not valid for equine serum. Horse type must be taken into account when evaluating OC concentration in research or clinical situations, especially if small variations in OC concentration are expected.

Neonatal alloimmune thrombocytopenia in a quarter horse foal.

Neonatal alloimmune thrombocytopenia is recognized as a spontaneous disease of human infants, piglets, and possibly mules, but it has not been previously reported in horses. A 1-day-old Quarter Horse foal presented to Michigan State University Large Animal Clinic with severe thrombocytopenia of unknown origin. Immunoglobulins that bound to the foal's platelets were identified in the mare's plasma, serum, and milk by indirect assays. The immunoglobulins were further shown to recognize platelets from the foal's full brother, born 1 year earlier. These findings, coupled with the clinical course of the foal during its period of hospitalization, strongly suggest that neonatal alloimmune thrombocytopenia can spontaneously occur in neonatal horses. This diagnosis should be considered for foals with severe thrombocytopenia when other causes can be excluded, and platelet antibody assays should be used to support this diagnosis.

Evaluation of an immunoradiometric assay for thyrotropin in serum and plasma samples of dogs with primary hypothyroidism.

A commercially available immunoradiometric assay was used to measure the thyrotropin (TSH; thyroid-stimulating hormone) concentration in the serum and plasma of 23 dogs. The basal concentration in five dogs with histologically confirmed primary hypothyroidism (median 0.18 microg/l, range 0.16-0.72 microg/l) was slightly, but not significantly, higher than that in 13 clinically healthy dogs (median 0.09 microg/l, range 0.06-0.34 microg/l). The TSH values in 11 euthyroid dogs with various dermatological diseases (median 0.09 microg/l, range 0.05-0.53 microg/l) were significantly lower than in the hypothyroid dogs, but there was considerable overlap. The assay alone was therefore not capable of giving a firm diagnosis.