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In order to test the in vivo effect of prolactin on estrogen receptor (ER) binding capacity in tumors induced by 7,12 dimethylbenz(a)anthrancene (DMBA-tumor), growth of the tumors from changes in prolactin and estrogen levels was compared retrospectively with cytoplasmic ER levels. It was demonstrated that some tumors required prolactin, some needed prolactin-estrogen during their growth period anda small number were not influenced by hormonal milieu. ER was present in hormonally dependent tumors but was low or absent in hormonaly-independent tumors. Deletion of hormones by endocrine ablation in the host rat resulted in tumor regression loss of ER. Replenishment of ER and subsequent tumor growth were accomplished by injection of prolactin or prolactin-estrogen in endocrine ablated rats but were not achieved in rats bearing tumors exposed to prolactin-nafoxidine. Our results demonstrate that both estrogen and prolactin were essential for growth of hormonally dependent DMBA-tumors. Tumor growth was also prevented when cytoplasmic ER was not replenished , indicating that ER may be an indispensable prerequisite for growth. Prolactin, independently of or cooperatively with estrogen, stimulated ER binding capacity. These results support the hypothesis that there may exist a prolactin regulatory mechanism of estrogen action at the tumor site. The interactions of estrogen and prolactin in situ in modulating hormonal receptor binding capacities may contribute to the overall stimulatory effect of these two hormones on DMBA-tumors.

The cytoplasmic content of estrogen and progesterone receptors (ERc and PRc) was measured in the rat uterine and mammary tissues during the period from late pregnancy through lactation. Uterine ERc and PRc, which sedimented at the 8S and 4S regions, respectively, of a 5-20% sucrose gradient, showed similar rise and decline patterns before and after parturition. Following a decline from the 15th day (114 +/- 13.7 fmol/mg protein) to the 20th day of pregnancy (57.7 +/- 10.2 fmol/mg protein), ERc levels increased almost 2.5-fold at the time of parturition. A decrease to the predelivery level by 24 h post-delivery was followed by a steady increase to 270.6 +/- 46 fmol/mg protein by 15 days of lactation. Uterine PRc levels also showed a peak similar to that of ERc at the time of parturition (24.3 +/- 1.1 fmol/mg protein). The level of ERc in mammary gland 6 h postpartum was the lowest (1.5 +/- 0.3 fmol/mg protein) and during the first 10 days of lactation ERc levels were maintained at about 10 fmol per mg of cytosol protein. Results herein suggest that levels of these steroid receptors may be hormonally regulated and that the uterus and mammary gland may have a different sensitivity to these regulatory control mechanisms. The physiological significance in the variation of these receptors in conjunction with the onset of parturition is discussed.

Cytosolic progesterone receptors (PRcs) from the reproductive tract of the female turkey were analyzed by high-performance liquid chromatography using a diethylaminoethyl (DEAE) ion-exchange column. PRcs from oviduct tissue of laying, incubating, photorefractory and short-day turkey hens were compared. In general, three types of PRcs were identified: Receptor I, a partially displaceable species that was eluted at a 0.13 M salt concentration; and Receptors II and III, which were two specific binding species eluting at 0.23 M and 0.26 M, respectively. In the subdivided tissue from the laying hen oviduct, Receptor I was the major PRc species of the isthmus and Receptor III was the only receptor present in the uterus. The infundibulum and magnum each contained a small amount of Receptor II and a substantial amount of Receptor III. The whole oviduct of incubating hens contained a greater proportion of Receptor I than Receptor II or III, and these last two receptor types were present in equal quantity. The whole oviduct of the short-day hens had an equal distribution of the three receptor types. In the presence of sodium molybdate, an inhibitor of phosphatase and protease, only one sharp Receptor II species was seen in the magnum and uterus of the laying hen oviduct and in the whole oviducts of incubating and short-day hens. The transformation of Receptor II to Receptor III in the absence of sodium molybdate was facilitated by the aging of cytosol at 0-4 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)