Tear level of nerve growth factor in normal dogs

Purpose To evaluate tear level of nerve growth factor (NGF) in normal dogs. Methods In the present study we investigated the presence and the level of NGF in the tear of 12 normal dogs (24 eyes) with different sex (5 males and 7 females) and age (ranging from 2 to 12 years old). Tears were collected by washing the eye surface 150 microliter of physiological salt after clinical examinations. Tear samples were stored at -20°C until tested for presence of NGF performed with a commercially available immunoenzymatic assay and expressed as pg/ml of sample. Results All samples examined showed presence of NGF, suggesting that this growth factor is a constitutive biological mediator of the ocular surface. It was also found that the level of NGF in the right eye is different from the left eye. Thus, the average concentration in the tear of the right was 7,97 (ranging from 5.0 to 38.3 pg/ml), whereas the average in the left eyes was 15,79 (ranging from 5.0 to 67.5 pg/ml). Conclusion Tear fluid is a secretion of lacrimal gland that lubrificates the eye surface and plays a critical role in response to eye irritation, by improving optical performance and the deficit induced by keratoconjuntivitis sicca. The observation that NGF is present in tear of dogs in a physiological relevant amount suggests that this molecule may be involved in the regulation of corneal homeostasis. Moreover, as NGF is known to play a role in emotional and anxiety-like behaviour, and tear secretion is a widespread phenomena among vertebrates, the possibility exists that NGF might be also involved in these behaviour responses. Because cats rarely suffer from emotional behavioural and keratoconjuntivitis sicca further studies may help to understand the role of NGF in tear secretion.