Prolactin release induced by histamine in maturing male and female rats

It has been previously shown that histamine (HA) increases PRL release in adult rats. The purpose of the present work was to determine the ontogeny of the HA-induced PRL response in male and female rats. Animals from day 1 to day 40 after birth were injected, under ether anesthesia, into the lateral brain ventricles with 9.0 micrograms HA (free base) per rat. Fifteen minutes later a sample of blood was taken from the jugular vein and plasma PRL levels were determined by RIA. Results obtained indicate that HA is able to induce increased PRL release in developing rats. Sex differences were observed. In male rats, the earliest PRL response was observed at day 10 whereas female rats showed clearcut responses at day 1. During development, males showed a quite regular pattern of responses but in female rats there were highly irregular; positive responses did present a 5-day periodicity. In general terms, the magnitude of the PRL responses in developing rats was lower than observed in adult rats. However, in 20-day old male and female rats and 40-day old female rats, a marked increase of PRL took place after the HA injection.