Effects of 5-Hydroxytryptophan and Melatonin on Plasma Prolactin Concentration in Intact and Cervical Ganglionectomized Goats

Abstract

One or 3mg of 5-hydroxytryptophan (5-HTP) per kg of body weight were injected in 3 non-lactating female Saanen goats via the external jugular vein at a light hour of a day (14 hours of lighting per day, 350 lux at goat's head, room temperature 20±2°C). The plasma prolactin (PRL) concentrations began to increase from 5 to 15 minutes after administration and rose to a peak within 40 minutes. When 10μg of melatonin per kg of body weight were administered in 2 of these 3 goats, the plasma PRL concentration increased markedly within 5 minutes. We then confirmed the following in 4 other goats under the same lighting conditions: 1) the normal level of the plasma PRL concentration, and 2) the releasing responses to both 1mg of 5-HTP and 10 and 20μg of melatonin per kg of body weight. Thereafter we dissected the ganglion cervicale craniale of these goats (GCCX). After GCCX, the plasma PRL concentrations were decreased during the light hours in 2 of the goats but showed almost no changes in the 2 others. The plasma PRL concentrations in all 4 of these goats did not increase during the dark hours. When 5-HTP was administered after GCCX, the plasma PRL concentrations increased slightly. The peak in plasma PRL concentration induced by melatonin after GCCX was diminished to 10-20% of that in the intact animals.