Hormonal modulation of tear volume in the rat

The present study examined the influence of hormones on the tear volume of male rats. The mean tear volume in a population of 2-3-month-old intact rats equaled 4.6 +/- 0.2 microliter. This volume, however, varied depending upon the hormonal environment of the animal. Orchiectomy induced a significant, 46%, increase in the mean tear volume, compared with that of intact rats. Testosterone administration to orchiectomized rats reversed this increase and caused a significant reduction in tear volume. Of interest, this androgen action was prevented if rats were also hypophysectomized. Hypophysectomy alone decrease tear volume and this response was not influenced by later castration. Other endocrine manipulations, including thyroidectomy, adrenalectomy and estrogen treatment of orchiectomized rats had no effect on tear volume. Overall, our results indicate that tear volume may be modulated by hormones from the hypothalamic-pituitary-gonadal axis.