EFFECT OF LIGHT ON THE PROLACTIN SURGES OF PSEUDOPREGNANT AND OVARIECTOMIZED, ESTROGENIZED RATS

The role of light in the regulation of the prolactin [PRL] surges of the female rat was investigated. Two model systems were utilized: one was the pseudopregnant rat which normally has 2 daily PL surges and the other was the ovariectomized (OVX) polyestradiol phosphate (PEP)-treated rat which normally has a daily afternoon PL surge. A 6 h phase advance of the 14 h:10 h photoperiod phase advanced the PL surges of pseudopregnant and OVX+PEP rats a corresponding 6 h. Blinded pseudopregnant and OVX+PEP rats had PL surges which were free running with respect to time of day, but the maximum values were similar to sighted 14 h:10 h controls. Pseudopregnant or OVX+PEP animals maintained on constant light also had free running PL rhythms, but the maximum PL values were significantly less than 14 h:10 h controls. Pinealectomy had no effect on the PL values of pseudopregnant rats maintained on constant light. The PL surges of pseudopregnant and OVX+PEP rats are endogenous circadian rhythms which can be entrained to an exogenous light-dark cycle.