Changes in the Collagen of the Uterine Cervix of the Mouse During the Oestrous Cycle

Abstract

The uterine cervix of the mouse consists of dense connective tissue with smooth muscle and has a small and relatively inextensible lumen in the non-pregnant state (Leppi, 1964). However, the cyclic variation of ovarian hormones results in small changes in cervical dilatability (Crelin, 1958). The present study was undertaken as, unlike the rat, there is a lack of information on the actual collagen content of the mouse cervix throughout the oestrous cycle. It was also felt to be a useful basis for an investigation currently in progress into cervical collagen changes during pregnancy in this species.Albino, virgin mice aged 3-6 months from a closed but not inbred colony were used. Animals with a regular cycle were selected after taking vaginal smears for at least two cycles. Allen's (1922) definitions were used to designate smears as prooestrus, oestrus, metoestrus and dioestrus. On the day of experiment smears were taken from the selected animals just before death, which was caused by chloroform inhalation. After removal of the reproductive tract, the cervical region was dissected away at the bifurcation of the uterine horns and the vagina trimmed off to expose the caudal projection of the cervix. The tissue was weighed immediately and again after overnight drying at 65°C. Collagen was estimated by hydroxyproline assay according to the method of Prockop & Udenfriend (1960).The means and standard errors of wet and dry weights, total collagen, collagen concentration ana percentage water content of cervical tissue at different stages of the oestrous cycle are shown in Table 1. The total collagen and the weight (wet and dry) of the cervix were greatest at oestrus and least at dioestrus. In contrast the collagen concentration (compared with wet or dry weight) was lowest during prooestrus and oestrus and highest at dioestrus. The water content varied only slightly but was marginally higher in the oestrogen-dominated part of the cycle than in metoestrus or dioestrus.Disregarding the slight variation in water content, it appears that the increase in cervical weight at oestrus is due, in only a small proportion, to increased collagen content, and in a much greater proportion to other tissue components, and this results in the overall fall in collagen concentration. This growth differential under the influence of oestrogen has previously been demonstrated in intact rats

The Effect of Pregnancy on the Collagen of the Uterine Cervix of the Mouse

“…These findings coincide with the marked degree of cervical softening which occurs 4-5 days before delivery (Leppi, 1964). The preparturient changes reported here are similar to those found in the oestrogen-domi¬ nated non-pregnant mouse (Rimmer, 1972) but are much greater. This is likely to be due to the enhancing effect of relaxin upon the other ovarian hormones before delivery (Steinetz et al 1957;Kroc et al 1959).…”

“…In the present investigation the lowest weight and highest collagen concen¬ tration were found on day 9 with the lowest water and total collagen content on days 8 and 10 respectively. This combination of conditions corresponds with that at dioestrus but exceeds the values recorded during theoestrous cycle (Rimmer, 1972). It may be significant that the plasma progesterone reaches a peak at this stage of pregnancy in the mouse (Forbes & Hooker, 1957).…”

“…Graphs of wet weight and total and percentage collagen content are shown in Fig. 2, together with, for comparison, the equivalent findings for the oestrous cycle (calculated from the results of Rimmer, 1972 In the first half of pregnancy, the weight and total collagen content of the cervix fell to a minimum on days 9 and 10 respectively while the collagen concentration rose to a maximum at 9 days. The decline in total collagen was interrupted by a transient increase on day 5.…”

“…However, there is a lack of information on the actual collagen content and concentration throughout pregnancy. The uterine cervix of the rat has been investigated in this respect (Harkness & Harkness, 1954), but in view of certain species differences (for example, in the mouse there is a fluctuation in total collagen of the cervix during the oestrous cycle (Rimmer, 1972) and the formation of an interpubic ligament during pregnancy (Hall, 1947)) it may be unwise to extrapolate from rat to mouse. It'^was therefore decided to study the uterine cervix of the mouse in pregnancy by recording daily the weight and total collagen and thence the water content and collagen concentration of samples of cervical tissue both during gestation and on the day after parturition.…”