Effects of blinding or afternoon melatonin injections on plasma cholesterol, triglycerides, glucose, TSH and thyroid hormone levels in male and female Syrian hamsters.

Adult male and female hamsters (Mesocricetus auratus) were divided into 3 treatment groups: intact, blinded, and intact hamsters which received daily sc injections of 25 microgram melatonin (MEL) at 1700 h. After 10 weeks of treatment, thyroxine (T4), triiodothyronine (T3) and cholesterol levels in both male and female blinded or MEL-treated animals were depressed compared to plasma titers of their respective intact control groups. Plasma thyrotropin (TSH) levels were depressed by MEL treatment but unaffected by blinding in male hamsters; in contrast, blinded or MEL-treated female hamsters had significantly higher TSH levels than the control group. Plasma triglyceride levels were depressed by both blinding and MEL-treatment in males but were unaffected in females.