Steroid diffusion into the navicular bursa occurs in horses affected by palmar foot pain

Palmar foot pain is frequently treated by steroid injections into the distal interphalangeal joint (DIPJ) in the anticipation that the steroid will diffuse to the navicular bursa and palmar foot structures. The object of this study was to determine if triamcinolone acetonide (TA) would in fact be able to locally diffuse from the DIPJ into the navicular bursa in horses affected by palmar foot pain. Both forelimb DIPJs (nine horses) were injected with 10 mg of TA. Navicular bursa fluid samples, both forelimb and one hind limb (systemic control), were analysed for TA with high-performance liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) six hours later. Foot radiographs were graded (0-4) on severity of changes. Forelimb navicular bursa TA concentrations (mean±sd log(10), 3.20±0.56) were significantly higher than systemic control concentrations (mean±sd log(10), 1.89±0.3) (P<0.0001). Horses with a radiographic grade of >2 were four times as likely to have TA log(10) concentrations less than 3.2 (158.49 ng/ml). TA locally diffused from the DIPJ into the navicular bursa in horses affected by palmar foot pain; TA concentrations decreased as radiographic severity increased.

Effects of intestinal ischemia on in vitro activity of adjacent jejunum in samples obtained from ponies

OBJECTIVE

To determine whether intestinal ischemia would alter activity of the jejunum in vitro or alter staining characteristics for certain types of enteric neurotransmitters.

SAMPLE POPULATION

Jejunal samples obtained from 10 ponies.

PROCEDURE

Jejunal samples were obtained from locations proximal and distal to an area of small intestine made ischemic for 60 minutes. A portion of each sample was stained to detect substance P-like immunoreactivity, cholinergic and adrenergic neurons, and nitric oxide synthase. Portions of the remaining samples were suspended in muscle baths. General activity patterns (frequency and amplitude of contraction), responses to neuronal depolarization induced by electrical field stimulation (EFS), and responses to 1 microM norepinephrine (NE) were compared with responses of a normal section of small intestine obtained prior to ischemic insult.

RESULTS

Staining patterns were not altered. Proximal and distal sections had evidence of decreased contractility, compared with the normal section. Contraction frequency also was decreased, and distal sections had lower contraction frequency than proximal sections. Relaxation responses were decreased in distal sections. Responses to NE differed significantly for distal and proximal sections, compared with normal sections.

CONCLUSIONS AND CLINICAL RELEVANCE

Short-term ischemia can significantly affect adjacent bowel. Contractile and relaxation responses are impaired. Discrepancies in intestinal motility patterns and alterations in response to NE for sections proximal and distal to ischemic intestine could lead to clinical ileus or slowed transit of ingesta.

Thoracoscopic-assisted diaphragmatic hernia repair using a thoracic rib resection

OBJECTIVE

To describe the surgical treatment of a dorsal diaphragmatic hernia in an adult horse using thoracic rib resection aided by thoracoscopy and a flank incision.

STUDY DESIGN

Case report.

ANIMAL POPULATION

One client-owned horse.

RESULTS

A six-year-old Dutch warmblood gelding was admitted for colic-associated colonic incarceration in a diaphragmatic hernia. Seven weeks after the initial colic surgery, the gelding underwent surgery to repair the defect. Thoracoscopy and a flank incision were used to identify the location of the hernia and the subsequent site of rib resection. The stomach was adhered to the edges of the defect, leaving only a small residual hole. Resection of the 14th rib provided excellent exposure of the defect and closure of the remaining hernia.

CONCLUSION AND CLINICAL RELEVANCE

Thoracic rib resection can provide access to diaphragmatic hernias in adult horses. Thoracoscopy or a flank incision, or both, may aid in determining which rib is best resected.

Evaluation of substance P as a neurotransmitter in equine jejunum

OBJECTIVE

To determine whether substance P (SP) functions as a neurotransmitter in equine jejunum.

SAMPLE POPULATION

Samples of jejunum obtained from horses that did not have lesions in the gastrointestinal tract.

PROCEDURE

Jejunal smooth muscle strips, oriented in the plane of the circular or longitudinal muscle, were suspended isometrically in muscle baths. Neurotransmitter release was induced by electrical field stimulation (EFS) delivered at 2 intensities (30 and 70 V) and various frequencies on muscle strips that were maintained at low tension or were under contraction. A neurokinin-1 receptor blocker (CP-96,345) was added to baths prior to EFS to interrupt SP neurotransmission. Additionally, direct effects of SP on muscle strips were evaluated, and SP-like immunoreactivity was localized in intestinal tissues, using indirect immunofluorescence testing.

RESULTS

Substance P contracted circularly and longitudinally oriented muscle strips. Prior treatment with CP-96,345 altered muscle responses to SP and EFS, suggesting that SP was released from depolarized myenteric neurons. Depending on orientation of muscle strips and stimulation variables used, CP-96,345 increased or decreased the contractile response to EFS. Substance P-like immunoreactivity was detected in the myenteric plexus and circular muscle layers.

CONCLUSIONS AND CLINICAL RELEVANCE

Substance P appears to function as a neurotransmitter in equine jejunum. It apparently modulates smooth muscle contractility, depending on preexisting conditions. Effects of SP may be altered in some forms of intestinal dysfunction. Altering SP neurotransmission in the jejunum may provide a therapeutic option for motility disorders of horses that are unresponsive to adrenergic and cholinergic drugs.

Adrenergic, cholinergic, and nonadrenergic-noncholinergic intrinsic innervation of the jejunum in horses

OBJECTIVE

To determine the major neurotransmitters that regulate contractile activity in the jejunum of horses.

SAMPLE POPULATION

Jejunal specimens from 65 horses without gastrointestinal tract lesions.

PROCEDURE

Jejunal smooth muscle strips, oriented in the plane of the circular or longitudinal muscular layer, were suspended isometrically in muscle baths. Neurotransmitter release was induced by electrical field stimulation (EFS) delivered at 30 and 70 V intensities and at various frequencies on muscle strips maintained at low or high muscle tone. To detect residual nonadrenergic-noncholinergic neurotransmission, the response of muscle to EFS in the presence of adrenergic and cholinergic blockade was compared with the response in the presence of tetrodotoxin.

RESULTS

Atropine (ATR) decreased the contractile response of muscle strips to EFS under most conditions. However, ATR increased the contractile response of high-tone circular muscle. Adrenergic blockade generally increased the muscle responses to 30 V EFS and in high-tone longitudinal muscle but decreased contractile responses in high-tone circular muscle. Tetrodotoxin significantly altered the responses to EFS, compared with adrenergic and cholinergic receptor blockade.

CONCLUSIONS

Acetylcholine and norepinephrine appear to be important neurotransmitters regulating smooth muscle contractility in the equine jejunum. They induce contraction and relaxation, respectively, in most muscle preparations, although they may cause opposite effects under certain conditions. In addition, nonadrenergic-noncholinergic excitatory and inhibitory influences were detected.

CLINICAL RELEVANCE

Acetylcholine or norepinephrine release within the myenteric plexus of horses may alter gastrointestinal motility.

Influence of adrenergic and cholinergic mediators on the equine jejunum in vitro

OBJECTIVE

To characterize the response of equine jejunal smooth muscle to adrenergic and cholinergic mediators.

DESIGN

Evaluation of myogenic responses, using an in vitro model.

SAMPLE POPULATION

Intestinal tissues were obtained from horses without gastrointestinal tract disorders or systemic disease.

PROCEDURE

Baseline myogenic tone and amplitude and frequency of contraction were determined for suspended jejunal muscle strips. The level of adrenergic and cholinergic regulation was assessed, using atropine and adrenoceptor antagonists. The response of the muscles to norepinephrine was characterized, using adrenergic blockade and alpha- and beta-agonists.

RESULTS

Adrenergic and cholinergic blockade had minimal effect on baseline myogenic activity. However, alpha 1- and beta 2-agonists induced significant (P < 0.05) decreases in the amplitude and frequency of contraction. Surprisingly, alpha 2-agonists caused an increase in the contraction amplitude of longitudinal muscle fibers (neurogenic in origin). Change in circular muscle activity was not induced by alpha 2-agonists. Norepinephrine induced a similar selective response and was inhibited by yohimbine.

CONCLUSIONS

Baseline jejunal activity appears to be myogenic in origin and can function independently of sympathetic and parasympathetic input. However, intestinal smooth muscle can be affected by adrenergic agonists and potentially by increased concentrations of circulating catecholamines. Norepinephrine may act by altering the activity of other neurotransmitters. Differing responses between circular and longitudinal muscle fibers indicates a need to evaluate both components.

CLINICAL RELEVANCE

Selective alpha 2-agonists may be potentially useful for motility modification of the equine jejunum. Therapeutic use of adrenergic blockade will be effective only in cases of increased adrenergic stimulation.