Neural regulation of adenohypophysial prolactin secretion in tetrapods: Indications from in vitro studies

Abstract

AbstractThe in vitro prolactin‐secreting capacities of adenohypophyses of Columba livia (pigeon) and Necturus maculosus (salamander) were compared with those of living and dead rat adenohypophyses over an eight‐day culture period. The living rat adenohypophysis produced prolactin at a constantly high rate. The dead rat tissue showed no evidence of active prolactin secretion. The secretion rate of prolactin by the pigeon adenohypophysis decreased rapidly with time in vitro and closely resembled the performance of dead rat adenohypophysis. Necturus adenohypophysis showed a slight initial decrease in prolactin secretion rate, which then plateaued at a constantly low level. The effects of acid extracts of cerebral and hypothalamic tissues of Agelaius tricolor (blackbird) on prolactin secretion in vitro by Agelaius adenohypophysis were examined. The extract of cerebral tissue had no effect, but the hypothalamic extract increased prolactin secretion, indicating that the blackbird hypothalamus contains a stimulator of prolactin secretion. These results indicate that the neural mechanism which controls prolactin secretion in Columba and Agelaius is different from that which exists in rats and other laboratory mammals. No definite conclusions can be drawn regarding neural regulation of prolactin secretion in Necturus.