Effects of injections and/or subcutaneous implants of melatonin on pituitary and plasma levels of LH, FSH and PRL in ovariectomized Syrian hamsters

Abstract

Adult female Syrian hamsters (64-82 g) were ovariectomized and thereafter maintained under light : dark cycles of 14 : 10. After 56 days of treatment the animals were killed and pituitary and plasma levels of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) were measured by radioimmunoassay. Ovariectomy caused marked rises in both the content and concentration of LH and FSH within the pituitary gland while pituitary PRL levels fell. Plasma levels of LH and FSH also rose while PRL titers remained unchanged. The daily afternoon injection of melatonin (25 ¡Lg subcutaneously) further increased the accumulation of LH and FSH within the pituitary. These responses to daily melatonin injections were prevented if animals additionally received bi-weekly subcutaneous melatonin-beeswax pellets (1 mg melatonin in 24 mg wax) which presumably released melatonin continually.