A commercially available radioimmunoassay kit for measurement of human osteocalcin was validated for use in horses. For accurate measurement of equine serum osteocalcin, blood samples may be collected at a temperature between 20 and 25 C, then centrifuged within 90 minutes; serum may be stored at - 20 C in plastic tubes for up to 26 weeks. Serum may be thawed and refrozen up to 5 times without significant change in measured equine serum osteocalcin concentration. Assay sensitivity was 0.16 ng/ ml. Recovery of bovine osteocalcin standard added to equine serum was linear. Intra-assay coefficient of variation (x 100) for 2 equine serum pools was 6.9 (mean +/- SD, 13.9 +/- 1.0 ng/ml) and 7.5 (10.6 +/- 0.8 ng/ml) %. Interassay coefficient of variation for 3 equine serum pools measured in 12 assays was 12.5 (16.1 +/- 2.0 ng/ml), 12.7 (11.5 +/- 1.5 ng/ml), and 24.6 (3.0 +/- 0.7 ng/ml) %. Dilutional parallelism was documented by assaying pooled equine serum at 4 dilutions and correcting the mean result for dilution. Significant change was not observed in equine serum osteocalcin concentration for various time-of-day blood sample collections in horses housed under continuous lighting.

Haptoglobin (HP), an acute-phase protein, is detected in serum of cows with hepatic lipidosis (fatty liver). To assess the relevance of Hp in fatty liver, induction of Hp was examined, using conditions similar to those involving development of fatty liver in cows. Induction of Hp was achieved by a combination of dexamethasone administration (0.1 mg/kg of body weight) and 2 days' starvation. Haptoglobin appearance in serum was not associated with the increase of alpha 1-acid glycoprotein (a marker for inflammation). This treatment increased serum nonesterified fatty acids concentration and decreased serum triglycerides concentration. Protein kinase C activity was decreased in the cytosolic fractions of liver and mononuclear cells. Reduction of protein kinase C-catalyzed endogenous protein phosphorylation also was observed, particularly in the cytosolic fractions of the tissue and cells. Detection of Hp in serum of cows with fatty liver appears to be explained by the fact that Hp is induced by dexamethasone administration and starvation, which are similar to the condition responsible for fatty liver development. The change of protein kinase C-catalyzed phosphorylation was suggested to be involved in the induction of Hp in cows.

We compared the plasma cortisol and immunoreactive corticotropin (IR-ACTH) responses to incremental doses (1.25, 12.5 and 125 micrograms) of synthetic ACTH (cosyntropin) administered IV to 6 clinically normal cats. Mean plasma cortisol concentration increased significantly (P < 0.0001) after administration of all 3 doses of cosyntropin. After administration of the 1.25- and 12.5-microgram doses, plasma cortisol concentration peaked at 30 minutes, then decreased to values not significantly different from baseline concentration by 90 and 120 minutes, respectively. In contrast, after administration of the 125-microgram dose, mean cortisol concentration peaked at 60 minutes and remained significantly (P < 0.05) higher than baseline values at 120 minutes. Compared with the 1.25- and 12.5-microgram doses, administration of the 125-microgram dose of cosyntropin induced significantly (P < 0.05) higher cortisol responses at 60, 90, and 120 minutes. Although individual cat's peak plasma cortisol concentration after administration of the 125-microgram dose was higher than the peak value determined after administration of the 2 lower doses of cosyntropin, these differences were not statistically significant. Mean plasma IR-ACTH concentration increased significantly (P < 0.0001) and reached a maximal value at 30 minutes after administration of all 3 doses of cosyntropin. After administration of the 1.25- and 12.5-microgram doses, plasma IR-ACTH concentration decreased to values not significantly different from baseline concentration by 60 and 120 minutes, respectively, whereas mean IR-ACTH concentration remained significantly (P < 0.05) higher than baseline values 120 minutes after administration of the 125-microgram dose. Mean peak plasma IR-ACTH concentration attained after administration of the 125-microgram dose of cosyntropin was significantly higher than that attained after administration of the 2 lower doses. Peak plasma IR-ACTH concentration attained after administration of the 12.5-microgram dose of cosyntropin was significantly higher than that attained after administration of 1.25 micrograms of cosyntropin. Results of the study indicate that IV administration of cosyntropin at doses ranging from 1.25 to 125 micrograms induces similar peak plasma cortisol responses in clinically normal cats, indicating that all of the doses may maximally stimulate the adrenal cortex. Administration of the higher cosyntropin doses did, however, result in more prolonged adrenocortical response.

Labor and delivery stimulate increased release of catecholamines and endogenous opioid peptides in neonates. Catecholamines promote adaptation to the extrauterine environment after birth. Enkephalins are stored together with catecholamines in the adrenal medulla and have an inhibitory effect on catecholamine release. We investigated the influence of labor and neonatal hypoxia on epinephrine, norepinephrine, and met-enkephalin release in calves. Blood samples were taken from the umbilical artery before rupture of the umbilical cord and from the jugular vein repeatedly after birth. Highest plasma norepinephrine concentration was found in calves delivered at the end of gestation (term calves) before umbilical cord rupture. In calves delivered before the physiologic end of gestation (preterm calves), norepinephrine values increased after cord rupture, but remained lower than values in term calves. Epinephrine release followed a similar pattern, but norepinephrine was clearly predominant. In term calves, met-enkephalin values were significantly higher than values in preterm calves. In calves of both groups, met-enkephalin release increased after cord rupture. During birth, the increase in catecholamine release seems to take place earlier than that of enkephalins. Norepinephrine-dominated stimulation during expulsion of the calf might be followed by increasing enkephalinergic inhibition after cord rupture and onset of respiration. Reduced release of catecholamines and enkephalins in preterm calves may be connected with delayed adaptation to the extrauterine environment.

Plasma cortisol and corticosterone responses of 8 clinically normal adult ferrets to synthetic ACTH (cosyntropin) were evaluated. Cosyntropin was administered iv at 4 dosages (0.5, 1.0, 5.0, and 10 micrograms/kg of body weight) at 2- to 4-week intervals, with blood samples collected 60 and 120 minutes after injection. After completion of the studies, an additional ACTH stimulation test was performed by administering cosyntropin (1.0 micrograms/kg) IM. The baseline plasma cortisol concentrations from all studies ranged from 25.9 to 235 nmol/L (mean +/- SEM = 73.8 +/- 7.0 nmol/L), and plasma corticosterone values ranged from 1.7 to 47 nmol/L (mean +/- SEM = 8.3 +/- 1.1 nmol/L). After iv administration of cosyntropin, plasma concentrations of cortisol and corticosterone increased significantly (P < 0.05) and reached peak values at 60 minutes; however, there were no significant differences between plasma cortisol or corticosterone responses to the 4 dosages of cosyntropin. Intramuscular administration of 1.0 Kg of cosyntropin/kg induced increases in plasma cortisol and corticosterone concentrations that were similar to the responses induced by iv administration of cosyntropin. The mean molar ratio of cortisol to corticosterone, calculated from the resting plasma concentrations, was approximately 9:1, whereas the ACTH-stimulated cortisol to corticosterone ratio was approximately 4:1. Results of this study indicated that administration of cosyntropin to clinically normal ferrets, at dosages ranging from 0.5 to 10 micrograms/kg, increased plasma concentrations of cortisol and corticosterone. Although cosyntropin stimulates the adrenocortical secretion of cortisol and corticosterone, cortisol appears to be the predominate circulating glucocorticoid in ferrets.

Twelve mature (5 sexually intact males, 4 castrated males, and 3 females) mixed-breed dogs were surgically thyroidectomized and used in a Latin-square design pharmacokinetic study of orally administered L-thyroxine. The dogs were treated with 44, 22, and 11 Kg of L-thyroxine/kg as a single morning dose or in divided doses, morning and evening. Serum concentration of thyroxine (T4) was evaluated to determine a number of pharmacokinetic variables for comparison. Mean steady-state concentrations (C(SS)) were determined from the area under the curve. Variables were analyzed for comparisons between dosages by use of ANOVA. Concentration at steady state was highest for dogs of the 44-micrograms/kg of body weight once-daily group and was lowest for dogs of the group given 11 micrograms/kg in 2 daily doses. Single daily administration resulted in higher C(SS), except at the 22-micrograms/kg/d dosage. Clearance was faster for the 22- and 44-micrograms/kg/d dosages than for the 11-micrograms/kg/d dosage. The half-life (t(1/2)) and mean residence time (MRT) also were shorter for the 44-micrograms/kg/d dosage, possibly indicating more rapid elimination of the drug at higher doses and dose-dependent kinetics. Perhaps, as the dogs' metabolism increased with higher iodothyronine concentrations, hormone degradation was accelerated. Interval (divided vs single dose) caused some expected changes: maximal concentration was higher and minimal concentration was lower when single administration was used. These undulations resulted in iodothyronine concentrations above the physiologic range for a number of hours, whereas concentration closer to physiologic ranges was achieved by use of divided doses. Delayed absorption (lag time) was seen in 37 of the 72 data sets, but was generally short, about 0.25 hour. Mean time to maximal concentration was 3 to 4 hours. At the higher dosages, serum total T4 concentration was high normal or above normal during most of the time after L-thyroxine administration, but serum concentration of total 3,5,3'-triiodothyronine did not remain within the normal range until the 44-micrograms/kg/d dosage was used. The customary dosage of 22 micrograms/kg/d (0.1 mg/10 lb/d) may not be adequate for most dogs. Pharmacokinetic variables appear to be highly dependent on the individual dog. Those with rapid absorption and higher concentration tended to have these characteristics at each dosage in this study. The pharmacokinetic variables, therefore, appear to be highly individualized, and dosages recommended for treatment of hypothyroidism should be considered to be only a starting point for the average dog. To avoid underdosing or overdosing, monitoring of treatment to adjust dose for individual dog kinetic variables seems to be imperative.