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M. Lorber; Circadian Variation in Rat Exorbital Lacrimal Gland Dimensions . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2504.
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Purpose: Circadian variations for eye-related parameters such as anterior chamber dimensions and intraocular pressure are known. Others related to the anterior surface of the eye include corneal epithelium mitoses, tear glycoproteins and their turnover rate, lacrimal fluid peroxidase, and particular endocrine secretions such as prolactin. Consequently, the size of the rat exorbital lacrimal gland has been investigated in regard to possible circadian variation. Methods: Sixteen adult female rats were anesthetized with i.p. sodium pentobarbital. Eight, b.w. 207 + 12 g (SD), were studied about 10 AM and eight, b.w. 215 + 6 g, about 3 PM. All procedures were done during a two week period in December to avoid seasonal variations. The left exorbital lacrimal gland was exposed by removal of skin and overlying fascia and the organ’s attachments removed. Its width (W) and length (L) were measured with a dividers whose points were placed in the jaws of a digital micrometer. Dimensions were read to 0.1 mm. Results: Initial dimensions (mm) in situ were: AMW 9.16 + 0.88 (SD), PMW 8.37 + 0.60; AML 12.61 + 0.29, PML 12.39 + 0.53. After ligation and transection of the duct and vessels: AMW 8.85 + 0.81, PMW 7.99 + 0.40; AML 11.60 + 0.47; PML 11.50 + 0.93. After dorsal fascia separation: AMW 8.96 + 0.85, PMW 8.05 + 0.64; AML 11.44 + 0.82, PML 11.69 + 0.75. After excision: AMW 7.97 + 0.91, PMW 7.20 + 0.61; AML 11.88 + 0.83, PML 11.88 + 1.13. Statistical analysis: ANOVA: AMW (F < 0.001), PMW (F < 0.001); AML & PML (F = NS). All corresponding AM and PM width measurements were significantly different by independent t-tests (P < 0.05). About 25% of the overall reduction in AM width occurred when the duct and vessels were ligated and severed but about 75% took place on excision. Corresponding figures for the PM rats were similar, 30% and 70%. There was no circadian variation in excised organ weight, AM 0.1227 + 0.0218 g, PM 0.1187 + 0.0232 g or excised organ thickness, AM 2.60 + 0.26 mm, PM 2.75 + 0.19 mm. Conclusions: There is circadian variation in in situ exorbital lacrimal gland width, but not length, being about 9-10% wider in the AM than PM. At both times organ width further decreased by about 25-30% on ligating and severing its duct and vessels. This indicates that altogether they exerted a slight transverse force on the exorbital lacrimal gland, causing the organ to tend to narrow when they were detached. Narrowing was even greater after excision, by about 70-75% of the overall dimensional change, indicating that while in situ its organ bed had firmly stabilized gland dimensions despite its duct, vascular and fascial attachments having been removed.
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