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  • Author or Editor: Johannes van der Kolk x
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Objective—To compare the effects of IV administration of various doses of ovine corticotrophin–releasing hormone (oCRH) on plasma and saliva cortisol concentrations in healthy horses and determine whether an oCRH challenge test protocol is valid for use in adult horses.

Animals—24 healthy Warmblood horses.

Procedures—Each horse received oCRH in saline (0.9% NaCl) via IV administration at a dose of 0 (control treatment), 0.01, 0.1, or 1.0 Mg/kg (6 horses/group). Jugular blood and saliva samples were collected simultaneously 15 minutes before and immediately prior to injection (baseline); data from these samples were pooled to provide basal values. Subsequently, 14 postinjection blood and saliva samples were both collected within a 210-minute period. Cortisol concentrations in all samples were assessed via a solid-phase radioimmunoassay.

Results—All doses of oCRH induced significant increases from baseline in both plasma and salivary cortisol concentrations. Compared with the smaller doses of oCRH, the 1.0 Mg/kg dose of oCRH induced significantly greater plasma cortisol concentrations. A relationship (r = 0.518) between basal cortisol concentrations in plasma and saliva was detected.

Conclusions and Clinical Relevance—For use as a CRH challenge test in adult horses, a protocol involving IV administration of a dose of at least 0.01 Mg of oCRH/kg and postinjection collection of blood samples from 10 to 180 minutes and saliva samples from 20 to 50 minutes for assessment of plasma and saliva cortisol concentrations should be sufficient. Application of such a test might be helpful to detect states of chronic activation of the hypothalamo-pituitary-adrenocortical axis at the hypothalamic level.

Full access
in American Journal of Veterinary Research


Objective—To determine the influence of intensified training and subsequent reduced training on glucose metabolism rate and peripheral insulin sensitivity in horses and identify potential markers indicative of early overtraining.

Animals—12 Standardbred geldings.

Procedures—Horses underwent 4 phases of treadmill-based training. In phase 1, horses were habituated to the treadmill. In phase 2, endurance training was alternated with high-intensity exercise training. In phase 3, horses were divided into control and intensified training groups. In the intensified training group, training intensity, duration, and frequency were further increased via a protocol to induce overtraining; in the control group, these factors remained unaltered. In phase 4, training intensity was reduced. Standardized exercise tests were performed after each phase and hyperinsulinemic euglycemic clamp (HEC) tests were performed after phases 2, 3, and 4.

Results—10 of 12 horses completed the study. Dissociation between mean glucose metabolism rate and mean glucose metabolism rate-to-plasma insulin concentration ratio (M:I) was evident in the intensified training group during steady state of HEC testing after phases 3 and 4. After phase 4, mean glucose metabolism rate was significantly decreased (from 31.1 ± 6.8 μmol/kg/min to 18.1 ± 3.4 μmol/kg/min), as was M:I (from 1.05 ± 0.31 to 0.62 ± 0.17) during steady state in the intensified training group, compared with phase 3 values for the same horses.

Conclusions and Clinical Relevance—Dissociation between the glucose metabolism rate and M:I in horses that underwent intensified training may reflect non-insulin–dependent increases in glucose metabolism.

Full access
in American Journal of Veterinary Research


OBJECTIVE To determine effects of anesthesia on plasma concentrations and pulsatility of ACTH in samples obtained from the cavernous sinus and jugular vein of horses.

ANIMALS 6 clinically normal adult horses.

PROCEDURES Catheters were placed in a jugular vein and into the cavernous sinus via a superficial facial vein. The following morning (day 1), cavernous sinus blood samples were collected every 5 minutes for 1 hour (collection of first sample = time 0) and jugular venous blood samples were collected at 0, 30, and 60 minutes. On day 2, horses were sedated with xylazine hydrochloride and anesthesia was induced with propofol mixed with ketamine hydrochloride. Horses were positioned in dorsal recumbency. Anesthesia was maintained with isoflurane in oxygen and a continuous rate infusion of butorphanol tartrate. One hour after anesthesia was induced, the blood sample protocol was repeated. Plasma ACTH concentrations were quantified by use of a commercially available sandwich assay. Generalized estimating equations that controlled for horse and an expressly automated deconvolution algorithm were used to determine effects of anesthesia on plasma ACTH concentrations and pulsatility, respectively.

RESULTS Anesthesia significantly reduced the plasma ACTH concentration in blood samples collected from the cavernous sinus.

CONCLUSIONS AND CLINICAL RELEVANCE Mean plasma ACTH concentrations in samples collected from the cavernous sinus of anesthetized horses were reduced. Determining the success of partial ablation of the pituitary gland in situ for treatment of pituitary pars intermedia dysfunction may require that effects of anesthesia be included in interpretation of plasma ACTH concentrations in cavernous sinus blood.

Full access
in American Journal of Veterinary Research