CHANGES IN ESTROGEN, PROGESTERONE AND EPIDERMAL GROWTH-FACTOR RECEPTOR CONCENTRATIONS AND AFFINITIES DURING THE ESTROUS-CYCLE IN THE NORMALMAMMARY-GLAND AND UTERUS OF DOGS

Changes in the concentrations and affinities of receptors for oestroge n (ER),progesterone (PR) and epidermal growth factor (EGF-R) were stud ied in mammary glands of healthy bitches with regard to age, the locat ion in the mammary chain and the stage of the oestrous cycle. Uterus w as used as the reference tissue for the evaluation of steroid receptor s. Mammary and uterine samples from 7 healthy bitches were taken at fi ve stages of the oestrous cycle in such a way that all the locations i n the mammary chain were represented at each stage of the cycle (10 sa mples/dog). ER, PR and EGF-R were detected by biochemical assays using increasing concentrations of tritiated (steroids) or iodinated (EGF) ligands. A significant direct correlation was found between the ER and PR concentrations for mammary and uterine samples. No significant cor relation was found between the steroid receptors and EGF-R concentrati ons. Mammary ER concentrations were significantly higher in bitches of 5 years of age or older than in younger ones; in posterior glands (4t h and 5th pairs) than in anterior glands; and in the mid-luteal phase. Mammary PR did not vary significantly with age or location but: was s ignificantly lower in the early luteal phase than in other phases. A s imilar decrease in PR concentrations was observed in the uterus during the early luteal phase and uterine ER and PR concentrations were very low in the mid-luteal phase. Mammary EGF-R were not significantly hig her in the early or mid-luteal phase than in pro-oestrus or anoestrus. The differences observed between the uterine and mammary steroid rece ptor concentrations during the oestrous cycle could be due to differen t mechanisms for regulating steroid receptor expression in the two tis sues. Mammary EGF-R concentrations may be linked, as in other species, to cellular proliferation and/or to the serum progesterone concentrat ions.