Table 1.

Percentage of proliferating cells expressing ERα or β in developing mammary gland

Stage	PCNA-positive, %	ERα-positive/ PCNA-positive, %	ERβ-positive/ PCNA- positive, %
Virgin 6-week-old	14.7  ±  1.6	1.5  ±  0.5	37.5  ±  2.8
Pregnancy day 2	14.3  ±  4.3	0.3  ±  0.2	29.7  ±  4.5
Pregnancy day 7	10.6  ±  2.2	0.2  ±  0.2	38.9  ±  7.8
Pregnancy day 14	4.3  ±  0.6	0.0  ±  0.0	46.7  ±  9.2

Results are represented as means ± SD.