Evidence that melatonin binding sites in the pars tuberalis do not mediate the photoperiodic actions of melatonin on LH and prolactin secretion in ewes

An experiment was designed to determine whether the pars tuberalis is the site of action of melatonin involved in the photoperiodic control of LH and prolactin secretion in sheep. In an attempt to produce a «short-day» effect on these hormones (i.e. stimulation of LH secretion and inhibition of prolactin release), microimplants of melatonin were placed either around the pituitary stalk (n=6) or in the third ventricle (n=5) as a control for the efficacy of the microimplant. Two sham-operated groups were treated with empty microimplants around the pituitary stalk (n=4) or in the third ventricle (n=3)