Estrogen and progesterone receptors in the fetal and newborn vagina of guinea pig: biological, morphological, and ultrastructural responses to tamoxifen and estradiol.

Estrogen and progesterone receptors were characterized in the fetal and newborn vagina of guinea pig. The concentrations of estrogen receptor (total sites, cytosol plus nuclei) which were very high [7090 +/- 1700 (+/- SD) fmol/mg DNA] in the fetal vagina (62-64 days gestation) decreased significantly after birth and increased slightly at 2 weeks of age. Tamoxifen (TAM) and estradiol (E2) or the combined treatment (TAM + E2) induced a great increase in weight and DNA content in both the fetal and newborn vagina. After a 12-day treatment to pregnant or newborn guinea pigs, the fetal vagina wet weights (milligrams +/- SD) were as follows: control animals, 87 +/- 14; +TAM, 254 +/- 38; +E2, 177 +/- 19; +(TAM+E2), 218 +/- 41. The values in newborn vaginas were: 155 +/- 40, 434 +/- 75, 477 +/- 49, and 512 +/- 76, respectively. The DNA contents per vagina (in micrograms per +/- SD) in the fetal tissues were as follows: control, 187 +/- 64; +TAM, 563 +/- 74; +E2, 650 +/- 100; and +(TAM+E2), 776 +/- 113; in the newborn vagina these values were: 592 +/- 75, 880 +/- 113; 781 +/- 75, and 901 +/- 15, respectively. Histological studies showed drastic morphological alterations after each of the treatments, particularly in the epithelial cells. Similarly, the ultrastructural examination with transmission electron microscopy showed the alteration of mitochondria, the development of the rough endoplasmic reticulum, and the formation of numerous vacuoles and secretory granules. TAM stimulated the number of specific sites for progesterone, but less intensely than did E2. However, in the combined experiment (TAM+E2), TAM did not block the action of E2. It is concluded that TAM acts in the fetal and newborn vagina of guinea pigs as a real estrogen agonist.