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Effects of long-term oral administration of melatonin on tear production, intraocular pressure, and tear and serum melatonin concentrations in healthy dogs

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  • 1 Department of Veterinary Sciences, Polo Universitario Annunziata, University of Messina, Messina, Italy
  • | 2 Ophthalmology Section, Negah Veterinary Centre, Tehran, Iran
  • | 3 Department of Clinical Sciences, College of Veterinary Medicine, Karaj Branch, Islamic Azad University, Karaj, Iran
  • | 4 Stem Cell Preparation Unit, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran

Abstract

OBJECTIVE

To evaluate the effects of long-term (30-day) oral administration of melatonin on tear production, intraocular pressure (IOP), and concentration of melatonin in the tears and serum of healthy dogs.

ANIMALS

20 healthy sexually intact adult male dogs.

PROCEDURES

10 dogs were given melatonin (0.3 mg/kg, PO, q 24 h, administered in food at 9 am), and 10 dogs were given a placebo. Tear and serum melatonin concentrations, IOP, and tear production (determined with a Schirmer tear test) were recorded before (baseline) and 30 minutes, 3 hours, and 5 hours after administration of melatonin or the placebo on day 1 and 30 minutes after administration of melatonin or the placebo on days 8, 15, and 30.

RESULTS

Data collection time had significant effects on tear production, IOP, and tear melatonin concentration but not on serum melatonin concentration. Treatment (melatonin vs placebo) had a significant effect on tear melatonin concentration, but not on tear production, IOP, or serum melatonin concentration; however, tear melatonin concentration was significantly different between groups only 30 minutes after administration on day 1 and not at other times.

CLINICAL RELEVANCE

In healthy dogs, long-term administration of melatonin at a dosage of 0.3 mg/kg, PO, every 24 hours did not have any clinically important effects on tear production, IOP, or serum or tear melatonin concentrations.

Contributor Notes

Corresponding author: Dr. Rajaei (Mehdi_13r@hotmail.com)