Micro-organisms and the appearance of leucocytes in the vaginal wall of cyclic female rats at metoestrus

Sexual responses of male rats to odours from female rats in oestrus are not affected by female germ-free status

Rats detect and use odorant molecules as a source of information about their environment. Some of these molecules come from conspecifics, and many arise as by-products from microbial activity. Thus, compared to conventionally housed rats, germ-free rats are raised in an environment with fewer odorants, but this reduction is rarely quantified. Using gas chromatography-mass spectrometry, we found that germ-free rat faeces samples contained half as many volatile molecules than conventional rat faeces (52 vs 109 (±2.4) molecules; P < 0.001) and overall these were only 12% as abundant. We then investigated if odours from female germ-free rats in oestrus would have pro-erectile effects in conventional male rats. For this aim, conventionally housed Brown Norway (BN) rats (n = 16) with sexual experience with either Fischer or BN females, were exposed to four different odour types: faeces from germ-free Fischer rat in oestrus, faeces from conventional rats in oestrus and di-oestrus (either from Fischer or BN), and a control (either 1-hexanol or male rat faeces). The number of penile erections per test as well as the duration of freezing behaviour was significantly higher with the oestrous odours (germ-free and conventional) compared to the control, with intermediate responses to the di-oestrous faeces. The findings indicate that, despite a significantly reduced composition in terms of volatiles compared to conventionally housed rats, the faeces of germ-free rats contain sufficient odorants to evoke sexual responses in conventional male rats. Oestrous odours of rats thus appear not to be of microbial origin.

Hormonal modulation of the vaginal bacterial flora in experimental polycystic ovarian disease

Rats exposed to constant light develop polycystic ovarian (PCO) disease with persistent estrus, representing an estrogen-dominant condition. Herein, we report that fluctuations seen in the vaginal microflora in cyclic rats were not observed in PCO rats with persistent estrus. The vaginal-cervical mucosa of PCO rats showed numerous adherent bacteria by scanning electron microscopy, similar to that seen in proestrus and estrus rats, but unlike the diestrus rats in which fewer organisms adhered to the mucosa. Administration of human chorionic gonadotropin induced ovulation in PCO rats, which was associated with a significant decrease in serum estradiol, an increase in progesterone, and a significant decrease in the estradiol/progesterone ratio compared with baseline values (P < 0.01). This also resulted in an influx of leukocytes in the vagina with a significant decrease in vaginal anaerobic as well as aerobic bacterial flora. These data demonstrate that loss of cyclic ovarian activity in PCO rats with persistent estrus causes increased bacterial colonization of the vaginal-cervical mucosa, and the ovarian hormones appear to modulate the colonization of bacteria in the lower genital tract.

Regulation of the bacterial microflora of the vagina in cyclic female rats

The bacterial microflora was examined in the vagina of cyclic female rats kept under normal laboratory conditions. Large variations occurred during the cycle with high numbers of bacteria (10(5)-10(8) per vagina) during proestrus and estrus and low numbers (10(1)-10(4) per vagina) during the diestrus period. Histological analysis of in situ vaginal tissue and transplanted vaginal tissue revealed an association of high bacterial numbers with the presence of large amounts of cellular debris in the vaginal lumen during the period of epithelial keratinization. Absence of phagocytosis in leucocytes at mestestrus suggested that leucocytes did not play an active role in reduction of bacterial numbers between estrus and metestrus. Accurate measurement of the pH in the vaginal lumen failed to reveal differences which could explain the reduction in bacterial numbers between estrus and metestrus. The cyclic changes in the bacterial population-consisting of species which are normally present in the intestinal flora-- seem to be controlled by cyclic changes in the amounts of cellular debris in the vaginal lumen.