Effect of neonatal pineal ablation on estradiol receptors in mammary glands of rats housed under varying photoperiods.

Estradiol receptors (ER) in mammary glands of female Holtzman rats, either intact or neonatally pinealectomised and housed in 10:14 or 24:0 L:D (light:dark) schedule were studied at 30, 40, 50 +/- 5 and 65 +/- 5 days of age. Whereas ER were detectable only at the age of 60-65 days in intact rats housed in 10:14 L:D, they were present as early as 30 days onwards in the pineal ablated group. In the 24:0 L:D pinealectomised group, though mammary gland ER were maximum around 40 days of age and temporarily undetectable around day 50, they had stabilized around the age of 60-65 days. The data demonstrates for the first time, the modulation of ER in rat mammary glands in response to varying photoperiods as well as pineal ablation. Earlier reports on incidence of chemically induced mammary tumours have been compared to the receptor modulation.