Ultrasonographic appearance of the bovine uterus during the estrous cycle

The uteri of 22 Holstein heifers were monitored during 58 interovulatory intervals by transrectal ultrasonographic imaging. The ultrasonographic appearance of the uterus was influenced by the stage of the estrous cycle. Profound changes in characteristics visualized by ultrasonography included thickness of the uterine body, ultrasonographic evidence of edema, and accumulation of intravaginal and intrauterine fluids. Scores representing intravaginal fluid, intrauterine fluid, ultrasonographic texture, and number of gray-scale zones (comprising the image of the uterus) increased before ovulation, then decreased until approximately day 3 to day 6 (ovulation = day 0). The scores for uterine shape and number of cross sections of a uterine horn in one 5-MHz field began to increase before ovulation, reached a high plateau during the period associated with maximal progesterone production, and decreased before the time associated with estrus and ovulation.     

Plasma gonadotropins and ovarian hormones during the estrous cycle in high compared to low ovulation rate gilts

Mature gilts classified by low (12 to 16 corpora lutea [CL], n = 6) or high (17 to 26 CL, n = 5) ovulation rate (OR) were compared for plasma follicle-stimulating hormone (FSH), luteinizing hormone (LH), progesterone, estradiol-17beta, and inhibin during an estrous cycle. Gilts were checked for estrus at 8-h intervals beginning on d 18. Blood samples were collected at 8-h intervals beginning on d 18 of the third estrous cycle and continued for one complete estrous cycle. Analysis for FSH and LH was performed on samples collected at 8-h intervals and for ovarian hormones on samples collected at 24-h intervals. The data were standardized to the peak of LH at fourth (d 0) and fifth estrus for the follicular phase and analyzed in discrete periods during the periovulatory (-1, 0, +1 d relative to LH peak), early-luteal (d 1 to 5), mid-luteal (d 6 to 10), late-luteal (11 to 15), periluteolytic (-1, 0, +1 d relative to progesterone decline), and follicular (5 d prior to fifth estrus) phases of the estrous cycle. The number of CL during the sampling estrous cycle was greater (P < 0.005) for the high vs low OR gilts (18.8 vs 14.3) and again (P < 0.001) in the cycle subsequent to hormone measurement (20.9 vs 14.7). For high-OR gilts, FSH was greater during the ovulatory period (P = 0.002), the mid- (P < 0.05) and late-luteal phases (P = 0.01), and tended to be elevated during the early-luteal (P = 0.06), but not the luteolytic or follicular periods. LH was greater in high-OR gilts during the ovulatory period (P < 0.005), but not at other periods during the cycle. In high-OR gilts, progesterone was greater in the mid, late, and ovulatory phases (P < 0.005), but not in the follicular, ovulatory, and early-luteal phases. Concentrations of estradiol-17beta were not different between OR groups during the cycle. Inhibin was greater for the high OR group (P < 0.005) during the early, mid, late, luteolytic, and follicular phases (P < 0.001). The duration of the follicular phase (from last baseline estrogen value to the LH peak) was 6.5 +/- 0.5 d and was not affected by OR group. These results indicate that elevated concentrations of both FSH and LH are associated with increased ovulation rate during the ovulatory phase, but that only elevated FSH during much of the luteal phase is associated with increased ovulation rate. Of the ovarian hormones, both inhibin and progesterone are highly related to greater ovulation rates. These findings could aid in understanding how ovulation rate is controlled in pigs.     

Ovine luteinizing hormone: isoforms in the pituitary during the follicular and luteal phases of the estrous cycle and during anestrus.

Pituitaries were collected from late follicular phase (n = 5), mid-luteal phase (n = 5), and anestrous ewes (n = 4) to assess changes in intrapituitary LH heterogeneity at selected reproductive states. After homogenization, an aliquot of each pituitary extract was desalted by flow dialysis against water and chromtofocused on a pH 10.5 to 4.0 gradient. Concentrations of LH in pituitary extracts and chromatofocusing fractions were determined by RIA. The LH in pituitary extracts resolved into 13 isoforms during chromatofocusing, which were coded with letters beginning with the most basic isoform. Follicular and mid-luteal phase ewes exhibited similar distributions of intrapituitary LH among its isoforms. Relative to follicular and luteal phase ewes, anestrous ewes had lower percentages of isoforms D and E as well as higher percentages of isoforms G, H, J and K. Isoform F, the predominant molecular form of LH, constituted a similar percentage in all treatment groups (P > .05). Thus, the distribution of intrapituitary LH among its isoforms did not change significantly between the mid-luteal and follicular phases of the estrous cycle, but higher percentages of the weakly basic and acidic forms of LH were present during anestrus. These observations suggest that intrapituitary LH heterogeneity changes minimally throughout the estrous cycle of ewes during the breeding season.     

Pituitary receptors for GnRH and estradiol, and pituitary content of gonadotropins in beef cows. I. Changes during the estrous cycle

To further characterize the endocrinological changes in the hypothalamo-hypophyseal axis thoughout the bovine estrous cycle, cycling beef heifers (n = 24) were randomly assigned to six groups. These heifers were slaughtered 6, 12, 18, 19, 20 or 21 days following their previous estrus (day 0). Anterior pituitaries and hypothalami were collected. Hypothalami were divided into the preoptic area and medial basal hypothalamus, and content of gonadotropin-releasing hormone (GnRH) was quantified by radioimmunoassay. Contents of luteinizing hormone (LH) and follicle stimulating hormone (FSH) in the anterior pituitary gland were quantified by radioimmunoassay. Membrane receptors for GnRH were quantified by a standard curve technique and receptors for estradiol in anterior pituitary cytosol were quantified by saturation analysis. There was no significant change in content of GnRH in the hypothalamus or content of FSH in the anterior pituitary on any of the days examined; however, content of GnRH in the preoptic area was lower (P less than .1) on day 19 postestrus. Cytosolic receptors for estradiol increased (P less than .05) on day 18 post-estrus and returned to baseline by day 19. Content of LH and the number of receptors for GnRH in the anterior pituitary gland decreased (P less than .01) on day 19 postestrus, and the number of receptors for GnRH remained low through day 21 postestrus. The reduction in anterior pituitary content of LH was transient indicating that synthesis of LH restores pituitary content to preovulatory levels before the number of receptors for GnRH returns to normal.     

Follicle stimulating hormone pattern and luteal function in ewes receiving bovine follicular fluid during three stages of the estrous cycle

The objectives of this study were to determine 1) the ability of charcoal-extracted bovine follicular fluid (bFF) to suppress endogenous follicle stimulating hormone (FSH) at various stages of the estrous cycle and 2) the effects of suppression of FSH on luteal function and lengths of the current and subsequent estrous cycles. Twenty-six mature ewes were assigned randomly to receive 5 ml of either bFF or saline, subcutaneously, at 8-h intervals on d 1 through 5 (bFF n = 6; saline n = 3), d 6 through 10 (bFF n = 6; saline n = 3) or d 11 through 15 (bFF n = 6; saline n = 2) of the estrous cycle (d 0 = estrus). Blood was collected daily beginning at estrus and continued until the third estrus (two estrous cycles) or 40 d; more frequent samples were collected 2 h prior to initiation of treatment (0600), hourly for the first 8 h of treatment, then every 4 h until 0800 on the first day after treatment, and finally at 1600 and 2400 on that day. Plasma concentrations of FSH were lower (P less than .001) in bFF-treated than in saline-treated ewes. Treatment with bFF reduced (P less than .05) plasma concentrations of progesterone during the current but not during the subsequent estrous cycle. Treatment with bFF did not affect plasma concentrations of estradiol-17 beta. Administration of bFF on d 11 through 15 of the estrous cycle lengthened the interval from the decline in progesterone to estrus and the inter-estrous interval by approximately 3 and 4 d, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

In vitro metabolism of glucose by bovine reproductive tissues obtained during the estrous cycle and after calving.

Two experiments were conducted to determine the effect of physiological state (stage of the estrous cycle or time after calving) on the in vitro metabolism of glucose by reproductive tissues. In Exp. 1, the corpus luteum and ipsilateral uterine horn were collected at surgery from 15 cows at early (d 6 to 7), middle (d 10 to 13), or late (d 17 to 19) stages of the estrous cycle. Luteal or endometrial tissues (45 mg) were incubated (4 h, 37 degrees C) in metabolic flasks containing Nutrient Mixture F-10 (3 mL), increasing concentrations of glucose (1, 2, 5, 10, or 15 mM), and 1 microCi of [U-14C]glucose. Luteal tissue collected at the middle stage of the estrous cycle had greater (P less than .04) rates of glucose uptake (17.8 vs 12.1 ng/mg of wet tissue per min) and oxidation (138.6 vs 67.7 pg/mg of wet tissue per min) and a lower (P less than .02) rate of metabolism of glucose to lactate (10.5 vs 13.3 ng/mg of wet tissue per min) than tissue collected at the late stage. Compared to tissue collected at early and late stages, endometrial tissue collected at the middle stage of the estrous cycle had a similar (P greater than .5) rate of glucose uptake (29.6 vs 27.8 and 26.1 ng/mg of wet tissue per min), a lower (P less than .02) rate of metabolism of glucose to lactate (13.8 vs 16.6 and 16.4 ng/mg of wet tissue per min), and a greater (P less than .1) rate of oxidation of glucose (84.1 vs 65.8 and 72.3 pg/mg of wet tissue per min). In Exp. 2, the previously gravid uterine horn was collected at surgery on d 20 (n = 8) or 30 (n = 7) after calving, or the uterine horn ipsilateral to the preovulatory follicle was collected at first observed estrus after calving (n = 8). Uterine tissue obtained at first estrus after calving had a greater (P less than .003) rate of glucose uptake and oxidation (88.8 vs 77.3 and 75.5 pg/mg of tissue per min) than d-20 or d-30 endometrium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Beta-carotene uptake and changes in ovarian steroids and uterine proteins during the estrous cycle in the canine

The uptake of beta-carotene by reproductive tissues and the effects of beta-carotene on reproductive function in the dog are unknown. We studied the uptake of beta-carotene by blood, corpus luteum, and uterine endometrium and the role of dietary beta-carotene in influencing ovarian steroid and uterine protein production during the estrous cycle in the dog. Mature female Beagle dogs (n = 56) were fed diets containing 0, 2, 20, or 50 mg of beta-carotene daily for approximately 6 wk before estrus detection. Blood was sampled at regular intervals from estrus through d 45 after ovulation (d 0 = ovulation), when laparotomy was performed. The ovaries were obtained for the isolation of corpus luteum. The uterus was flushed with phosphate-buffered saline and the endometrium obtained by scraping. Beta-carotene was not detectable in plasma, corpus luteum, or endometrium of unsupplemented dogs. However, beta-carotene and alpha-carotene in plasma, corpus luteum, and uterine endometrium increased in a dose-dependent manner. Alpha-carotene made up a high percentage of total carotenoids even though the alpha-carotene content in the dietary source was very low. Dogs fed 50 mg of beta-carotene had significantly higher concentrations of plasma progesterone between d 12 and 26 compared with unsupplemented dogs. Dietary beta-carotene did not influence plasma estradiol-17beta and total uterine proteins. Therefore, beta-carotene is absorbed into plasma, corpus luteum, and uterine endometrium of dogs. Furthermore, dietary beta-carotene increased plasma progesterone concentrations during the estrous cycle. It is possible that dietary beta-carotene may improve reproductive function in the canine.     

Ovarian follicular populations and in vitro steroidogenesis on three different days of the bovine estrous cycle

This study was undertaken to determine changes in follicular populations on ovaries of dairy cows during three stages of the estrous cycle and their steroidogenic capacity in vitro. Numbers of small (2.0 to 5.0 mm), intermediate (5.1 to 10 mm) and large (greater than 10 mm) antral follicles on ovaries of multiparous cows and heifers (n = 31) in the early luteal (d 4), mid-luteal (d 12) and follicular phase (d 19) of the estrous cycle were determined (d 0 = estrus), and steroidogenic capacity of intermediate and large follicles was measured in vitro. Total number of follicles and number of small follicles were greatest (P less than .05) on d 19 compared with d 12, with numbers on d 4 not different from either d 12 or 19. Intermediate follicles were fewer (P less than .05) on d 19 compared with d 4 or 12. Numbers of large follicles did not change. The proportion of estrogen active (EA) follicles was greater (P less than .05) on d 19 compared with d 4 or 12. Accumulation of estradiol-17 beta (E) into culture medium by intermediate follicles decreased (P less than .05) with increasing days of the estrous cycle, while accumulation of progesterone (P) was greater on d 19. In large follicles, accumulation of E into culture medium was greatest (P less than .05) on d 19 and the lowest on d 12 (P less than .05). In summary, the proportion of EA follicles increases during the preovulatory period, and E production increases in large EA follicles.(ABSTRACT TRUNCATED AT 250 WORDS)