title: Daily rhythm of tear production in normal dog maintained under different Light/Dark cycles.
abstract: This study was conduced to assess the daily rhythm of tear production in clinically healthy dog. For our study eight female purebred Beagles were subjected to three different Light/Dark schedules: 12/12L/D, 24/0L/D and 0/24L/D cycles. In all subjects Schirmer tear test I was performed at 4h intervals over a 24h period. A statistical significant effect of photoperiod was observed comparing the three different L/D schedules, and a statistical significant difference was observed comparing left and right eye during the 12/12L/D schedule. We demonstrated daily variation of tear production in dogs maintained under an L/D cycle. We also provided strong evidence that the rhythm of tear production is endogenously generated because it persisted in constant darkness. Although the range of excursion of the daily/circadian oscillation in STT I (about 2mm/min) is likely too narrow to be of clinical significance, it is statistically significant and may have physiological implications not yet appreciated.
authors.affiliation: Department of Experimental Sciences and Applied Biotechnology, Laboratory of Veterinary Chronophysiology, Faculty of Veterinary Medicine, University of Messina, 98168 Messina, Italy. giuseppe.piccione@unime.it
authors.forename: G
authors.initials: G
authors.lastname: Piccione
authors.forename: C
authors.initials: C
authors.lastname: Giannetto
authors.forename: F
authors.initials: F
authors.lastname: Fazio
authors.forename: A
authors.initials: A
authors.lastname: Assenza
authors.forename: G
authors.initials: G
authors.lastname: Caola
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D003624:Darkness; D004285:Dogs; D005260:Female; D007839:Functional Laterality; D008027:Light; D010507:Periodicity; D012016:Reference Values; D013666:Tears / Q000378:metabolism*