Suckling-Induced Serum Prolactin Levels Are Modified by Interference with Milk Ejection in Lactating Rats¹

^a Instituto de Neurobiología, Buenos Aires, Argentina ^b Laboratorio de Investigaciones en Neuroendocrinología de la Reproducción Humana (LINERH), Hospital Carlos G. Durand, Buenos Aires, Argentina

The aim of this study was to determine whether suckling-induced prolactin (PRL) levels were modified when milk ejection was impaired. Milk ejection impairment was achieved in two experimental models: a) depriving the dam of sleep during suckling and b) increasing the nonsuckling intervals in lactating dams.

Sleep deprivation blocked milk ejection and enhanced suckling-induced PRL levels in dams that had been previously separated from their pups. When milk ejection is blocked in litter-deprived dams, mammary glands are not evacuated and they remain engorged. Suckling stimuli were not the cause of the difference in suckling-induced serum PRL levels in control and sleep-deprived dams.

The engorgement of the mammary glands may play a role, as a maximum suckling-induced PRL increase was not observed in nonseparated SD dams with nonengorged mammary glands. Moreover, suckling-induced PRL levels were decreased when engorged mammary glands of SD dams were evacuated through an oxytocin injection.

A parallel increase between suckling-induced PRL levels and mammary gland weight was observed in the experiments in which milk ejection was impaired through an increase in the intervals of nonsuckling, providing additional support for a relationship between mammary gland engorgement and the regulation of suckling-induced PRL levels.

¹ This work has been supported by the Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) and by Fundacion Instituto de Neurobiologia, Buenos Aires, Argentina.

² Correspondence: Serrano 669, (1414) Buenos Aires, Argentina. FAX: 54–1–856–7108; fuacta{at}ssdnet.com.ar