Objective To determine whether tetanus antitoxin, equine serum, and acetylcysteine, which are currently used in the treatment of equine corneal ulcer, inhibit the digestion of equine corneal collagen when exposed to collagenase in vitro. Animals studied Corneas from 40 adult horses. Procedures Sections of equine corneas were incubated with saline, a solution of bacterial collagenase in saline, bacterial collagenase in saline plus equine tetanus antitoxin, bacterial collagenase in saline plus equine serum, or bacterial collagenase in saline plus acetylcysteine. Each one of the collagenase inhibitors was tested at different concentrations. The degree of corneal collagen digestion was determined by concentrations of hydroxyproline released into the incubation media and/or by weight loss of the cornea. Results Corneas exposed to collagenase released a significant (0.05 level) large amount of hydroxyproline (43.1 ± 2.3 µg/mL/100 mg cornea/5 h) and decreased cornea weight by up to 89%. Blood serum (200 µL/mL), purified albumin or globulin fractions of serum, tetanus antitoxin (120 units/mL), and acetylcysteine (20 mg/mL) when used at the highest concentrations blocked collagenase digestive activity by approximately 50%. Dilution of inhibitors decreased corneal protection and linearly increased corneal weight loss. Purified equine serum albumin and globulin fractions were equally effective in protecting corneas. Conclusions This experiment indicates that tetanus antitoxin, serum and acetylcysteine equally protected corneas from collagenase digestion, in vitro. However, a clinical trial is needed to establish relative therapeutic value.

Cerebral microvascular endothelial cells form a barrier between the blood and brain, which is critical for normal neuronal functions. These endothelial cells can be challenged by metabolic and respiratory acidosis, especially in newborn babies. We investigated mechanism(s) by which cerebral endothelial cells recover intracellular pH (pHi) when challenged with an intracellular acid load. pHi in piglet cerebral microvascular endothelial cells in primary culture was monitored using the pH-sensitive fluorescent dye BCECF (2',7'-bis-2-carboxyethyl-5(6)-carboxy-fluorescein acetoxymethyl ester), with dual wavelength fluorescence spectroscopy. Endothelial cells attached to coverslips and continuously superfused with HCO3-/CO2 containing medium (25 mM HCO3-, 5% CO2; pH 7.40) have a steady state of pHi of 7.18 +/- 0.02. Under basal conditions, amiloride (100 microMol) and H2DIDS (0.5 mM) decreased pHi 0.12 +/- 0.01 and 0.05 +/- 0.01 pH units, respectively. Removal of external Na+ lowered pHi 0.18 +/- 0.02pH units, while Cl- free medium decreased pHi 0.16 +/- 0.03pH units. These data suggest the presence of an amiloride-sensitive Na+-H+ exchanger and a Na+-dependent HCO3- -Cl- anion exchanger in endothelial cells. Propionate and high PCO2 cause rapid intracellular acidification at constant pH. The cells recover to control pHi over 10 min. Recovery from propionate was largely inhibited by amiloride, slightly inhibited by H2DIDS, and completely prevented by the combination. pHi recovery during elevated PCO2 was blocked by amiloride, H2DIDS, or Na+-free media. These results indicate that recovery from intracellular acidosis can involve amiloride-sensitive Na+-H+ exchange and a Na+-dependent HCO3-/Cl- anion exchange. Relative contributions of pumps and their independence appears to depend on the nature of the acid load.

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Sustained dexamethasone administration to horses results in insulin resistance, which may predispose them to laminitis. A single dose of dexamethasone is commonly used as a diagnostic aid, yet the effect of a single dose of dexamethasone on glucose homeostasis in horses is not well defined. The objective of this study was to characterize the change in glucose dynamics over time in response to a single dose of dexamethasone. A combined glucose-insulin tolerance test (CGIT) was performed on 6 adult geldings before and at 2, 24, and 72 h postdexamethasone (40 microg/kg of BW, i.v.); a minimum of 1 wk of rest was allowed between treatments. Before any treatment, the CGIT resulted in a hyperglycemic phase followed by a hypoglycemic phase. Dexamethasone affected glucose dynamics in 3 ways: 1) at 2 h, dexamethasone shortened the ascending branch of the negative phase (P < 0.001) of the test, indicating moderate insulin resistance; 2) at 24 h, dexamethasone impaired glucose clearance by extending the positive phase and eliminating the negative phase while insulin was elevated before the CGIT, indicating a decreased response to insulin; and 3) at 72 h, dexamethasone caused a deeper nadir value (P < 0.001) compared with predexamethasone, indicating an increased response to insulin. It was concluded that dexamethasone decreased the response to insulin as early as 2 h and maximally at 24 h. At 72 h, dexamethasone caused an increased response to insulin, which was unexpected.