The effect of cooling on the contractility of equine digital small lamellar arteries: modulating role of the endothelium

Effect of Different Water Cooling Treatments on Changes in Rectal and Surface Body Temperature in Leisure Horses after Medium-Intensity Effort

Simple Summary

The study was performed in order to answer the question: should horses be cooled after not very intensive exercise? Thus, the efficiency of four different water cooling methods was studied in horses after medium-intensity effort for leisure horses under moderate air temperature. The water cooling methods used included spraying with cold water: (1) lower body parts, i.e., lower parts of legs; (2) upper body parts, i.e., back of the head and flanks; and (3) both lower and upper body parts. The control group was not treated with water. Water cooling was applied to 19 warmblood geldings immediately after the end of exercise and 10 and 20 min later. The internal and body surface temperatures were registered and analyzed. The water cooling methods used led to a decrease in rectal and body surface temperature. Applying cold water on lower body parts was only effective and can be recommended for practical use under the described conditions.

Abstract

Cooling a horse after intensive exercise under hot conditions is commonly recommended. The study aimed to analyze changes in the rectal and surface temperature of the horses subjected to various water cooling treatments. This followed medium-intensity exercise performed by leisure horses under moderate air temperature. The experiment involved a control group without water application, and three variants of water cooling applied to 19 warmblood geldings after medium-intensity effort. Cooling of lower, upper, and lower and upper body parts was performed. In each variant, the rectal and body surface temperatures were measured five times: before; immediately after; and 10, 20, and 30 min after effort. Using water cooling under the studied conditions did not influence a post-exercise decrease in the rectal temperature. The decrease in body surface temperature depended on the used variant of cooling down the horse. Cooling the limbs by pouring water several times changed the surface body temperature from 34.2 ± 0.37 °C to 32.0 ± 0.32 °C and was more efficient than the repeated application of cool water on both the upper and lower body parts, leading to a temperature change from 34.6 ± 0.26 °C to 33.2 ± 0.36 °C. Thus, the application of cold water on the limbs only is sufficient for cooling the horse after medium-intensity exercise under moderate air temperature (about 24 °C).

Validation of canine uterine and testicular arteries for the functional characterisation of receptor-mediated contraction as a replacement for laboratory animal tissues in teaching

Teaching practicals for receptor physiology/pharmacology in medical and veterinary schools have involved the use of in vitro experiments using tissues from laboratory animals, which have been killed for isolated vascular strip or ring preparations. However, the use of scavenged tissues has been advocated to reduce animal use. Utilising discarded tissues from routine surgical procedures, such as canine neutering, has not previously been investigated. Canine testicular and uterine tissues (discarded tissues) were obtained from routine neutering procedures performed by the veterinary team at a local animal neutering clinic for stray dogs. Rings of uterine and testicular artery were dissected and mounted on a Mulvany-Halpern wire myograph in order to characterize the adrenergic and serotonergic receptors mediating vasoconstriction. Cumulative contractile concentration-response curves were constructed for the alpha adrenoceptor agonists epinephrine (α₁ and α₂ receptors), phenylephrine (α₁ selective) and UK14304 (α₂ selective). Pre-treatment with the α₁-selective antagonist, prazosin, was also investigated. The response to serotonin (5-HT) receptor agonists were also investigated, including 5-HT (acting at both 5-HT₁ and 5-HT₂ receptors), 5-carboxamidotryptamine (5-CT; 5-HT₁ selective) and α-methyl 5-HT (5-HT₂ selective). A contractile response was observed in both canine uterine and testicular arteries to epinephrine and phenylephrine, and prazosin caused a dose-dependent parallel rightward shift in the phenylephrine dose-response curve (pA₂ values of 7.97 and 8.39, respectively). UK14304 caused a contractile response in canine testicular arteries but very little appreciable contractile response in uterine arteries. The maximum responses produced by the uterine arteries to 5-HT was significantly lower than those of the testicular arteries. In the testicular artery, the 5-HT₂ receptor selective agonist, α-methyl 5-HT, produced a similar contractile response to 5-HT but the administration of 5-CT failed to produce a response in either the testicular or uterine artery segments. These results validate the use of discarded tissue from routine canine neutering procedures as a useful source of vascular tissue for pharmacological teaching, for characterizing alpha and 5-HT receptor contractile responses.

Short communication: Changes under low ambient temperatures in the milk lipodome and metabolome of mid-lactation cows after dehorning as a calf

Horns are living tissue and cows can use their horns for thermoregulatory purposes. We investigated the effect of the presence of horns on the metabolome of milk serum and lipidome of milk fat, to assess the physiological effect of dehorning. Milk sampling took place at low ambient temperatures of -6 to 2°C. Horned and dehorned cows were kept in a mixed herd of Holstein Friesian and Brown Swiss cows. The hypothesis was that horned cows needed to increase their metabolism to compensate for additional heat loss through the presence of their horns. No differences were observed in milk yield, milk solids, and somatic cell counts between horned and dehorned cows. For the milk metabolome, horned cows showed an upregulation of several glucogenic AA that could be transformed into glucose for energy supply and a downregulation of sugar intermediates and γ-glutamylcysteine compared with dehorned cows. The fatty acid (FA) composition in horned cows showed a shift toward decreased odd medium-chain FA (C7:0, C9:0, and C11:0) and increased cis-vaccenic acid (C18:1n-7 cis-11) and stearidonic acid (C18:4n-3). The changes in milk composition related to additional heat loss in horned cows indicate a competition in C3 metabolism for glucose synthesis and de novo FA synthesis under cold stress.

Moderate hypothermia attenuates α1-adrenoceptor-mediated contraction in human varicose spermatic vein: The role of nitric oxide(Short communication)

The effects of moderate hypothermia (28 °C) on the response of human varicose spermatic vein to α₁-adrenoceptor agonist phenylephrine and the role of endothelial nitric oxide (NO) in these effects were studied. Concentration-response curves for phenylephrine (10^-9 to 3 × 10^-4 M) were recorded in rings with and without endothelium at 37 and 28 °C. To further analyze the role of NO, in the response to phenylephrine during hypothermia, the effects of this agonist in the presence of N^G-nitro-L-arginine methyl ester (10^-4 M) were also determined. Under every condition tested, phenylephrine produced a marked, concentration-dependent contraction. Sensitivity of intact veins to the agonist was consistently lower at 28 °C than at 37 °C. There was no significant difference in phenylephrine response at 28 and 37 °C in vessels without endothelium but at 28 °C veins without endothelium showed a higher sensitivity than intact veins to phenylephrine. The sensitivity of veins with and without endothelium to nitroprusside (10^-9 to 3 × 10^-3 M) was significantly decreased during hypothermia, and endothelium removal did not affect the relaxation to this nitrovasodilator. These results suggest that moderate hypothermia decreases the sensitivity of human varicose spermatic vein to phenylephrine probably by increasing the availability of endothelial NO.

Measurement of digital laminar and venous temperatures as a means of comparing three methods of topically applied cold treatment for digits of horses

OBJECTIVE

To compare effects of 3 methods of topically applied cold treatment (cryotherapy) on digital laminar and venous temperatures in horses.

ANIMALS

9 healthy adult Thoroughbreds.

PROCEDURES

Thermocouples were placed in palmar digital veins and digital laminae of both forelimbs of horses. Three methods of cryotherapy were applied to the distal aspects of the limbs: wader boot (63-cm-tall vinyl boot filled with ice and water [ice slurry]), ice bag (5-L fluid bag filled with ice slurry), and a gel pack boot (boot containing frozen gel packs). Gel packs and ice slurries were replenished every hour during cryotherapy. The forelimb that received the first treatment was randomly assigned; thereafter, control and treated forelimbs were alternated for each treatment. For each treatment, temperatures were recorded every minute during 15-minute pretreatment, 2-hour treatment, and ≥ 30 minute rewarming periods. Once temperatures had returned to within 3°C below pretreatment values, the experiment was repeated in a similar manner for other cryotherapy methods.

RESULTS

Digital venous temperatures were similar to laminar temperatures during each treatment. Ice bag and wader boot treatments caused similar cooling of digits. Gel boot treatment did not cause substantial cooling of digits.

CONCLUSIONS AND CLINICAL RELEVANCE

Ice bag treatment caused laminar and digital venous cooling equivalent to that of wader boot treatment. Cryotherapy by use of 5-L fluid bags with an ice slurry may be a readily available, practical, and efficient method for prevention of laminitis in horses. Digital laminar and venous temperatures were similar in forelimbs of horses before and during cryotherapy.

Contractile responses of isolated equine digital arteries under hypoxic or hyperoxic conditions in vitro: role of reactive oxygen species and Rho kinase

The underlying pathophysiological triggers for equine acute laminitis are unknown, although digital vasoconstriction, ischaemia, hypoxia and reperfusion injury may be involved. The contractile responses of isolated equine digital arteries (EDAs), harvested from the hindlimbs of normal horses postmortem at an abattoir, were studied acutely (up to 3 h) under hyperoxic (95% oxygen, 5% CO2 ) and hypoxic (95% nitrogen, 5% CO2 ) conditions in organ baths. Phenylephrine (PHE; 10(-6) m), 5-hydroxytryptamine (5-HT; 10(-7) m) and high potassium (K(+) ; 118 mm) caused contraction in EDAs which was significantly (P<0.0001) enhanced under hypoxic conditions. In contrast, contraction stimulated by 9,11-dideoxy-9α,11α-epoxymethanoprostaglandin F2α (U44069; 3 × 10(-8) m) was not significantly enhanced by hypoxia (P=0.75). Hypoxia-enhanced contraction in response to K(+) was greater (P<0.03) in vessels with a functional endothelium than in vessels in which the endothelium was removed by rubbing. Fasudil (10(-6) to 10(-5) m), a Rho kinase inhibitor, and apocynin (10(-3) to 3 × 10(-3) m), an NADPH oxidase inhibitor, significantly (P ≤ 0.05) inhibited hypoxia-enhanced contraction in response to PHE and 5-HT. In conclusion, hypoxia-enhanced contraction occurred in EDAs. This appears to be partially mediated by reactive oxygen species produced by NAPDH oxidase, which activate Rho kinase to increase calcium sensitisation and enhance smooth muscle contraction.