The influence of exogenous steroid hormones on steroid receptors, uterine histological structure and the bacterial flora of the normal bitch

Oestrogen (ER) and progesterone (PR) receptors have been shown to vary in b oth concentration and distribution during the oestrous cycle of the bitch, influenced by the normal changes in endogenous reproductive hormones. The i nfluence of exogenous steroid hormones on steroid receptors and the histolo gical structure of the uterus was studied in two groups of parous Beagle bi tches. Group A (n = 6) were treated with progesterone (P-4) in oil i.m. (3 mg/kg) in late metoestrus on the day that peripheral plasma P-4 concentrati ons were first identified as < 10 ng/ml, and subsequently once weekly on th ree other occasions. Group B (n = 6) were treated with a single i.m. inject ion of MPA (50 mg, 4.2-5.6 mg/kg) following the same protocol. Full-thickne ss uterine wall biopsies were obtained from the mid part of one horn 2-7 da ys after the last (fourth) injection of P-4 or MPA. During the subsequent o estrus, when peripheral plasma P-4 concentrations were between 8 and 10 ng/ ml, each bitch in both groups (n = 12) received a single injection of oestr adiol benzoate (ODB) in oil i.m (7.5 mg, 0.63-0.84 mg/kg). All bitches had an ovariohysterectomy 7 days later. Full-thickness uterine wall samples wer e obtained from the mid part of the intact horn and other parts of the uter us. Swabs were tal;en from the uterine lumen for bacteriological examinatio n; all were sterile. Tissue samples were sectioned and examined for evidenc e of lesions, and stained for ER and PR receptors using an immunocytochemic al method. The immunoreactivity was scored semiquantitatively, incorporatin g both the intensity and distribution of specific staining of the receptors using a simplified histoscore (H-score). At the time of ovariohysterectomy , fluid had accumulated in the isolated section of the uterine horn distal to the point of biopsy; the volume was greater in the MPA-treated bitches. There was also evidence in some sections of histological changes in the end ometrium. Variations in the expression of both ER and PR were seen between bitches, which may have been due to some not bring in mid-metoestrus at the time of treatment. In general, ER scores were low after P-4, and MPA treat ment, but following ODB there was a significant (P < 0.05) increase in ER e xpression in all parts of the endometrium. PR scores were zero in the gland ular epithelium of all 12 bitches after P-4, MPA and ODB treatment, whereas in the other parts of the endometrium they were generally moderate to high . Following treatment with ODB, PR generally increased in the three regions of the endometrium where PR were present. The study shows that ER and PR d istribution and expression in the endometrium of bitches can be modified by P-4, MPA and ODB, with evidence of individual variation. (C) 1999 Elsevier Science B.V. All rights reserved.