Infusion of a pineal gland-derived antigonadotropic decapeptide into the lateral ventricle depresses prolactin levels in male rats.

The primary structure of a pineal gland-derived antigonadotropic decapeptide (AGD) was determined recently, and a synthetic analog prepared by solid state methods. Adult male Harlan SD rats were maintained under controlled photoperiods. Each was fitted stereotaxically with a stainless steel cannula for infusion into a right lateral ventricle. Each cannula was attached to a subcutaneous osmotic minipump filled either with artificial cerebrospinal fluid (CSF) or the AGD in CSF (0.5 micrograms/microliters). Additional Tygon microbore cannulae were inserted through the femoral artery and placed in the abdominal aorta for blood sampling and the determination of prolactin (PRL) levels by radioimmunoassay. CSF (1.0 microliter/hr) or the AGD (0.5 microgram/hr) was infused into the right lateral ventricle over a period of seven days. Circulating PRL concentrations were significantly depressed by AGD infusion both in the morning and late afternoon; adenohypophysial concentrations were concomitantly elevated on infusion day seven. These results confirm previous observations of inhibitory effects of the AGD on PRL secretion, and further support its postulated central mechanism of action.