Introduction

Variations of physiological variables such as blood pressure, heart rate, hormonal secretion and glycemia (glucose concentration in the blood) have always been studied in veterinary medicine to standard physiological reference values and determine pathological conditions. The glycemia is frequently required in veterinary practice since glucose levels may indicate different pathophysiological disturbances. High levels may be secondary to some conditions such as stress and diestrus, or resulting from important diseases such as acute pancreatitis, kidney failure, hyperadrenocorticism and most frequently diabetes mellitus (Tilley & Smith Jr. 2000a). Low values may indicate hypoadrenocorticism, hepatitis or even malnourishment (Tilley & Smith Jr. 2000b). Glycemic levels can vary with many factors. Experimental studies performed in laboratory rats provided strong evidence that the hypothalamic clock controls the daily rhythm of glycemia by direct action on the liver through the sympathetic nervous system (Cailotto et al. 2005). On the other hand, Piccione et al. (2008) observed that this rhythm in dogs seems to result from their frequency of feeding, since carbohydrates are a substantial part of their diet. Guimarães et al. (2007), observed in a study that levels of glycemia are indirectly related to fasting periods before anesthesia (the longer the fasting period, the lower is the glycemia), and concluded that values never achieves hypoglycemic levels. In complement to that study, Nogueira et al. (2003) observed no difference among glycemia values obtained before and after anesthesia, as well as its relationship with the time required to complete recovery. Arrais et al. (1982) assessed glycemia levels in 7 dogs after different periods of fasting (15 and/or 19 days). Levels varied from 47.6 to 84.3 mg/dL, indicating that glucose metabolism adequate physiologically in order to maintain body regulation even after long fasting periods. Other metabolites are either regulated with the feeding rhythmicity. Total lipids, total cholesterol, phospholipids, and triglycerides, for example, vanishes when dogs are food deprived and levels of serum nonesterified fatty acids patterns are significantly higher during fasting than after food intake (Bertolucci et al. 2008, Penã et al. 2008). Despite of that, vital parameters such as blood pressure, heart rate, and body temperature are not influenced by glucose blood levels, indicating that these parameters are not driven by the digestive process (Piccione et al. 2005). The blood analysis can be performed in capillary or venous blood and varies, in healthy dogs under fasting periods of 5h (minimal), from 67 to 93 mg (mean 77.55 mg/dL and standard deviation (SD) of 7.71 in capillary samples, and from 65 to 92 mg/dL (mean 74.58 mg/dL and SD of 7.69) in venous blood samples (Aleixo et al. 2007). Physiological reference of glycemia varies from 60 to 130 mg/dL (Lassen 2004). The commonest way to perform the glycemia in veterinary practice is utilizing a portable glucometer. Besides most glucometers such as the AccuChek® Advantage (Roche diagnóstica Brasil, São Paulo, SP, Brazil) or Optium Xceed (Abbott Laboratories, Alameda, CA, USA) be projected for human patients, it is frequently utilized in Veterinary Hospitals and indicates glycemia levels with high precision (Hawkins 2005; Aleixo et al. 2007; Bluwol et al. 2007). The exam is very easily performed. As seen, many studies were already conducted to determine glycemia in healthy dogs but none was performed in dogs presenting cataracts. It's known that serum levels of glucose are involved in cataractogenesis in diabetic dogs (Barros et al. 2004; Davison & Nelms 2007; Ofri 2008). Barros et al. (1999) studied the antioxidant profile of cataractous English Cocker Spaniels and observed decreased plasma levels of vitamin C, indicating a decrease in the antioxidant capacity of the aqueous humor and the predisposition to cataract development in healthy dogs. But, in this study the blood glucose of these animals has not been evaluated. A similar study observed no correlation between the onset of cataract and ascorbic acid concentration in blood and aqueous humor in cataractous poodles, but noted decreased activity of antioxidant enzymes which may explain in part the onset of cataract in poodles (Barros et al. 2004).

Objective

The objective of this study was to determine glycemia levels in healthy fasted dogs presenting cataracts in both eyes and in different stages of development, since our Ophthalmologic Service presents high incidence of dogs with cataracts.

Materials and Methods

Animals included in this study were attended from June/2006 to January/2009 at the University Hospital of the Veterinary College of the University of São Paulo. Dogs included 36 males and 50 females, totalizing 86 animals, with ages varying from 1 to 15 years. Animals were divided in three groups: 1 to 5 years of age (23), 6 to 10 (44) and 11 to 15 (19). Breeds included Miniature Poodles (42), Mixed breeds (15), Lhasa Apso (6), Bichon Frise (3), Maltese (3), Yorkshire Terrier (3), English Cocker Spaniel (2), Miniature Pinscher (2), Miniature Schnauzer Terrier (2), Boxer (1), Boston Terrier (1), Brazilian Terrier (1), Fox Terrier (1), Old English Sheepdog (1), Rottweiler (1), Siberian Husky (1), Teckel (1). Ophthalmic examination was performed in a dark room where both eyes were examined with a portable handheld biomicroscope (SL14, Kowa OptiMed, Inc., Torrance, CA, USA), direct (Coaxial ophthalmoscope, Welch Allyn, São Paulo, SP, Brazil) and indirect ophthalmoscopy (Binocular indirect ophthalmoscope, IOH, Neitz instruments Co., Ltd, Tokyo, Japan) after induced mydriasis with 1% tropicamide (Mydriacyl® Alcon Labs. Do Brasil Ltda, São Paulo, SP, Brazil). Dogs presenting cataracts in both eyes and no other ocular or systemic alterations were included in this study. Blood samples were obtained after at least 8 hours of food depriving and 2 hours of water depriving periods from all animals. After trimming the anatomic spot of the cephalic or saphenous veins and cleansing with antiseptic solution, samples were collected with sterile needles (20 x 5.5 mm) in 1 ml syringes. Collected samples containing approximately 0,05 ml were immediately put on the glucometer stripe. The glucometer utilized was Optium Xceed (Abbott Laboratories, Alameda, CA, USA). Glycemic levels were obtained in 20 seconds and values organized in computer data. Statistical analysis included: mean, standard deviation, median, minimum and maximum values were determined for each parameter and was accomplished by using a computer program (Excel 2003, Microsoft Corporation, USA).

Results

Every obtained value was under physiological reference standards, but varied between groups. At the younger group (23 dogs), glycemia varied from 51 to 98 mg/dL with mean value of 78 mg/dL, median of 77 mg/dL and standard deviation of 12,2. Glycemia at the 5 to 10 years old group (44 dogs) varied from 37 to 100 mg/dL with mean value of 73 mg/dL, median of 75 mg/dL and standard deviation of 15. Oldest dogs (19 animals) presented glycemia varying from 61 to 135 mg/dL with mean value of 85.7 mg/dL, median of 81 mg/dL and standard deviation of 18,9. Results indicate a statistically significant difference between the second group and the oldest group (p < 0.05).

Discussion and Conclusions

Cataracts are a very common disease in dogs and glycemia levels are frequently required in veterinary medicine. Many studies showed that the blood glucose is particularly involved in cataractogenesis in diabetic animals, but there is no relationship between this parameter and the development of cataracts in healthy dogs. Donnely et al. (1995) noted that fasting glucose levels did not differ significantly between cataractous and noncataractous human patients. In our study, since the periods of fasting remained between the range recommended by other authors (Arrais et al. 1982, Guimarães et al. 2007), thus excluding the chance of hypoglycemia occurs, we observed that there was no significant difference between the blood glucose values obtained and the physiological values of reference (Lassen 2004). Therefore, the results were similar to those evaluated in human subjects by Donnelly et al. (1995). According to Strasser (1993), there is an increase of serum glucose with age, a result also observed in our study.

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