Twenty-Eight-Day Toxicity Study of Melatonin Infused Subcutaneously in Rats Via an Osmotic Pump

Abstract

This 28-day study in rats evaluated the safety of melatonin delivered continuously subcutaneously by an ALZET Osmotic Pump. ALZET Osmotic Pumps 2ML4 continuously delivered 60 μ1/day of vehicle (polyethylene glycol 400), 0.03%, 0.3%, or 3% melatonin subcutaneously for 28 days to Sprague-Dawley rats (19/sex/group). The dose of melatonin delivered based on weekly group mean body weights (n = 10) was approximately 0.050,0.50, and 4.8 mg/kg day for the male groups and 0.074, 0.75, and 7.3 mg/kg day for the female groups. An additional group (19/sex) underwent surgery, but no osmotic pumps were implanted (sham control). No deaths or changes in clinical observations occurred that were attributed to melatonin. No drug effect occurred in body weights, hematology, clinical chemistry, urinalyses, or gross pathology. A dose-related trend of increasing serum melatonin concentrations occurred in males and females. In males, there was a trend toward decreasing serum prolactin concentrations with time at all levels of melatonin treatment. No difference in serum follicle-stimulating hormone (FSH) concentrations occurred between treated groups. Most of the samples were at the limit of detection for the serum luteinizing hormone (LH) assay (0.157 ng/ml). A dose-related increase occurred in urine 6-sulphatoxymelatonin (the primary metabolite) concentrations in melatonin-treated male and female groups. No treatment-related organ weight or histopathology changes were present in rats infused with 0.03% or 0.3% melatonin. Two of 10 males administered 3.0% melatonin had decreased testes weights and testicular degenerative changes composed of reduced or absent spermatogenesis, spermatidic giant cells, and edema. The cause of the observed testicular degenerative changes in the high-dose group and possible reversibility should be investigated in follow-up studies of longer duration.

Long‐term postinfarction melatonin administration alters the expression of DHPR, RyR2, SERCA2, and MT2 and elevates the ANP level in the rat left ventricle

“…However, in their toxicity study of melatonin, Prevo et al. [25] also used subcutaneous osmotic pumps with melatonin dissolved in PEG 400, and they reported a corresponding serum melatonin level (112 pg/mL) 2 wk after the operation. There are no studies providing information about the possible effect of PEG 400 on the levels of melatonin, but the observed, relatively high melatonin concentrations in sham rats might still be due to the effect of the vehicle used (PEG 400) and/or the subcutaneous pumps.…”

“…Of note is that the melatonin concentrations in the plasma and LV of the sham-operated animals were surprisingly high compared, for example, with our earlier results concerning the levels of melatonin in sham rats 2 wk after MI [23] (about 100 pg/mL versus 15 pg/mL and about 250 pg/g versus 30 pg/g, respectively). However, in their toxicity study of melatonin, Prevo et al [25] also used subcutaneous osmotic pumps with melatonin dissolved in PEG 400, and they reported a corresponding serum melatonin level (112 pg/mL) 2 wk after the operation. There are no studies providing information about the possible effect of PEG 400 on the levels of melatonin, but the observed, relatively high melatonin concentrations in sham rats might still be due to the effect of the vehicle used (PEG 400) and/or the subcutaneous pumps.…”

“…Furthermore, Prevo et al. [25] showed that 28‐day subcutaneous infusion of melatonin in rats had no obvious toxicity or side effects. All the experiments in this study were approved by the Animal Use and Care Committee of the University of Oulu and Oulu County Government.…”

“…This regimen was chosen based on an earlier study that shows the suitability of 60% PEG 400 as a vehicle for lipophilic compounds when using osmotic pumps [24]. Furthermore, Prevo et al [25] showed that 28-day subcutaneous infusion of melatonin in rats had no obvious toxicity or side effects.…”

Melatonin Administration Methods for Research in Mammals and Birds

“…Furthermore, the release rates in vivo and in vitro are not significantly different (Theeuwus, 1987). Prevo et al (2000) used ALZET osmotic pumps to administer increasing concentrations of melatonin (0.03%, 0.3%, and 3%) to Sprague-Dawley rats and observed a dose-dependent change in plasma melatonin and 6-sulphatoxymelatonin, a melatonin metabolite, in urine. The constant mass and volumetric delivery of osmotic pumps ensured a controlled release of the same concentration throughout the duration of the experiment, which is not guaranteed with any other method described in this review.…”