REDUCED POSTNATAL LACTOTROPIC ACTIVITY IN THE RAT - POSSIBLE IMPLICATION OF VIP, ENDOGENOUS OPIOIDS, DOPAMINE AND GLUCOCORTICOIDS

In this study, the possible intervention of VIP (Vasoactive Intestinal Peptide), beta-endorphine, glycocorticoids and dopamine, in postnatal lactotrophs hypoactivity at the rat, was investigated. Our results sh ow that the injection of VIP (40 mu g/kg), beta-endorphine (125 mu g/k g) or its antagonist, naloxone (2 mg/kg), does not provide a change in serum PRL before or after ether stress at 6-day-old rats. However, af ter adrenalectomy, 6 day-old neonates became sensitive to ether stress as do adults, while acute treatment wish dexamethasone (2 mg/kg) or d opamine (1 mg/kg), abolished this response completely. Sulpiride injec tion (1 mg/kg), on the contrary potentialized response. This lactotrop h insensitiveness to ether stress, TRH, VIP, and beta-endorphine, duri ng the beginning of postnatal life in the rat, might be explained, par tially, by the failure of stimulatory factors ''PRF'' (Prolactin Relea sing Factors), together with strength of inhibitory factors ''PIF'' (P rolactin Inhibitory Factors), such as dopamine and glycocorticoids.