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A study has been made of changes in the amount and concentration of some chemical constituents of the rat uterus during the latter part of pregnancy and post-partum involution in both lactating and non-lactating animals. Dry, defatted, uterine tissue was analysed for hexose, hexosamine, uronic acid, nucleic acid and collagen. Samples of serum were analysed for free hydroxyproline and serum mucoprotein.

Up to the 3rd day post partum the rate of uterine involution (by weight) was similar in both lactating and non-lactating rats. During this period the overall rate of tissue loss was found to be a first order process kinetically, the fraction of tissue lost per day being about one-third. Thereafter there was a marked divergence in the two groups; hyperinvolution occurred in the lactating group but not in the non-lactating animals.

The disappearance of collagen showed a distinct lag during the first 24 hr post partum in both groups. At 5 to 8 days post partum, uteri from nonlactating animals contained 12% more collagen than non-pregnant controls and about 100% more than uteri from lactating rats.

The total hexose content showed the largest relative decrease post partum of all the chemical components studied; the hexose concentration fell sharply during involution to about half the value found on the 20th day of pregnancy. Hexosamine and uronic acid concentrations, however, showed only slight decreases while the collagen concentration varied considerably during the involution period. The serum hydroxyproline showed a slight increase post partum in contrast to the serum mucoprotein level which was markedly elevated during the latter part of pregnancy and the whole of the involution period studied.

Administration of oestrone prevented hyperinvolution in lactating rats.

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M. G. Hunter, S. A. Grant and G. R. Foxcroft

Summary. Ovaries were collected from naturally cycling gilts during the preovulatory period and the stage relative to the LH surge estimated by measurement of oestradiol and progesterone concentrations in follicular fluid. Many of the follicles recovered had become flaccid with an associated increase in follicular fluid viscosity. Marked infolding of both the granulosa and theca tissue in some follicles suggested early luteinization. However, these morphological changes did not necessarily occur simultaneously in the same follicle, or in all follicles within an ovary. Moreover, they were not consistently related to characteristic differences in the concentration of follicular fluid steroids, suggesting either that the morphological and biochemical aspects of the luteinization of follicles may be independently controlled, or may respond at different rates to the same signal.

Keywords: pig; follicle; histology; heterogeneity

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S. A. Grant, M. G. Hunter and G. R. Foxcroft

Summary. Ovaries were recovered from groups of naturally cyclic pigs (N = 5) on each of Days 16, 18, 20 and 21 of the oestrous cycle. Follicular diameter, follicular fluid volume and concentrations of oestradiol, testosterone and progesterone, and granulosa cell number were determined in all follicles ⩾2 mm in diameter (n = 511). In alternate follicles either granulosa cell aromatase activity and theca testosterone content or 125I-labelled hCG binding to granulosa and theca were determined. The mean total number of follicles recovered per animal decreased as the follicular phase progressed and a strong positive relationship (P < 0·001) existed between follicular diameter and volume on all days. The number of granulosa cells recovered per follicle was variable, and not related to oestrogenic activity of the follicles. Mean follicular fluid oestradiol, testosterone and 125I-labelled hCG binding all increased until Day 20 and decreased on Day 21, whereas mean theca testosterone content, 125I-labelled hCG binding to theca tissue and aromatase were all maximal on Day 21. On Days 20 and 21 a subset of 14–16 large follicles was readily distinguishable from the remaining smaller, less oestrogenically active population in each animal. Yet, consistently within these subsets there was a difference in follicular diameter of ∼ 2·0 mm and also a considerable range of biochemical development even among follicles of equal size. These results indicate asynchrony at the time of recruitment and selection among follicles destined to ovulate and suggest that heterogeneity continues into the immediate preovulatory period.

Keywords: follicle; development; pig; heterogeneity