Investor Relations

Effect of ovarian follicles on luteal regression in heifers

Description
Our objectives were to determine whether or not ovarian follicles contribute to spontaneous luteal regression in heifers and, if so, when during diestrus do follicles exert their effect. Thirty-one Holstein heifers having displayed at least one
Published
of 9
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Related Documents
Share
Transcript
  EFFECT OF OVARIAN FOLLICLES ON LUTEAL REGRESSION IN HEIFERS 1 2 A. Villa-Godoy 3, J. J. Ireland 3, J. A, Wortman 4, N. K. Ames s, T. L. Hughes 3 and R. L, FogweU 3 6 Michigan State University, East Lansing 48824 Summary Our objectives were to determine whether or not ovarian follicles contribute to spontaneous luteal regression in heifers and, if so, when during diestrus do follicles exert their effect. Thirty-one Holstein heifers having displayed at least one estrous cycle (19 to 21 d) were assigned, as available, to randomized blocks for a factorial experiment. Reproductive organs were exposed through a midventral incision on d 9, 12 or 15 postestrus (estrus = d 0). Visible follicles were electrocauterized and both ovaries were x-irradiated (1,500 fads) in treated heifers, whereas ovaries of controls were exteriorized but follicles were not destroyed and ovaries were not x-irradiated. In two additional heifers, the ovary containing the corpus luteum was exteriorized and x-irradiated on d 15 postestrus, but follicles were not electrocauterized. Jugular blood was collected before and every 8 h after surgery until d 24 postestrus. All heifers were ovariectomized on d 24 postestrus to inventory follicles and to weigh corpora lutea. No follicles 1This article is published as Michigan Agr. Exp. Sta. Journal article 10731. 2 We thank Dr. J. L. Gill and L. T. Chapin for their assistance in the experimental design and computer analysis; Drs. E. M. Convey, J. S. Kesner and K. Leung for their suggestions and critical evaluation of this project. Financial support to A. Villa-Godoy was provided by CONACYT (Consejo Nacional de Ciencia y Tecnologia, Ciudad Universitaria, Mexico City, Mexico). 3 Anim. Reprod. Laboratory, Dept. of Anim. Sci. 4present address: School of Vet. Med., 3850 Spruce St., Univ. of Pennsylvania, Philadelphia, PA 19104. s Dept. of Large Anim. Clin. Sci. 6Correspondence: R. L. Fogwell, Anim. Reprod. Lab., Dept. of Anim. ScL, Michigan State Univ., East Lansing, MI 48824--1225. Received January 25, 1984. Accepted October 18, 1984. (> 1 mm diameter) were observed in ovaries from treated animals and concentrations of estradiol-173 did not change over time, whereas different numbers of follicles were observed in ovaries from controls and concentrations of estradiol-173 increased (P<.05) during proes- trus. Hence, treatment destroyed follicles and prevented follicular development. On d 24 postestrus, corpora lutea from treated heifers (5.5 -+ .5 g) were heavier (P<.001) than corpora lutea from controls (1.1 + .1 g), independent of day when follicles were destroyed. From surgery to d 24 postestrus concentrations of progesterone in serum were sustained in treated heifers but declined (P<.01) in controls on d 16 to 17 postestrus. In treated heifers, concentra- tions of luteinizing hormone (LH) increased (P<.01) after surgery, confirming that follicular products exert a negative influence on secretion of LH in presence of functional corpora lutea. In control animals, mean concentrations of LH did not change over time, which indi- cates that reduced secretion of LH is not required for luteolysis. In animals in which the ovary bearing a corpus luteum was selectively x-irradiated, luteal weights (1.3 -+ .3 g) and profiles of progesterone did not differ from the controls. Thus, x-rays did not have a direct effect on the corpus luteum. Luteal func- tion was extended after destruction of ovarian follicles and inhibition of follicular growth on d 9, 12 or 15 postestrus, demonstrating that secretions of ovarian follicles are required for spontaneous luteal regression. Furthermore, it was determined that the luteolytic effect of follicles is exerted within a short interval after d 15 postestrus. (Key Words: Heifers, Luteal Function, Follicles, X-Irradiation.) ntroduction There is evidence that estrogens are involved in the luteolytic process in cattle and sheep. In 519 JOURNAL OF ANIMAL SCIENCE, Vol. 60, No. 2, 1985  520 VILLA GODOV ET AL. cattle, exogenous estrogen at midcycle induced premature luteal regression Wiltbank et al., 1961) and reduced luteal weight Brunner et al., 1969). Similarly, estradiol has a luteolytic effect when given at midcycle to sheep Hawk and Bolt, 1970; Kahn and Denamur, 1973). Physiological significance of luteal regression induced by exogenous estradiol is enhanced by the observations that concentration of estro- gens in jugular blood increased between d 10 and 15 postestrus in cattle Hansel and Ecktern- kamp, 1972; Shemesh et al., 1972; Kanchev et al., 1976). Coinciding with increases in concen- trations of estrogens in blood, numbers of nonatretic ovarian follicles in heifers are greater between d 12 and 14 postestrus than at other intervals of diestrus Rajakoski, 1960). The series of events listed above occur before detectable decreases in concentrations of progesterone in peripheral blood in cattle Chenauh et al., 1975). Interestingly, destruc- tion of ovarian follicles at midcycle extended luteal function in sheep Karsch et al., 1970). Thus, follicles present after midcycle have physiological significance in spontaneous luteal regression in sheep and possibly in cattle. The present experiment was designed: 1) to deter- mine whether or not presence of ovarian follicles is required for normal luteolysis in heifers and, if so, 2) to identify the interval during diestrus when ovarian follicles contrib- ute to the luteolytic process. aterials and ethods Thirty-one nulliparous Holstein Heifers that had experienced at least one estrous cycle 19 to 21 d; estrus = d 0) were assigned to random- ized blocks within a 2 x 3 factorial experiment. The main effects were: 1) follicular destruction, sham vs electrocautery plus x-irradiation and 2) day postestrus 9, 12 or 15) when surgery occurred. Heifers were anesthetized with thiamylal sodium followed by endotracheal intubation and administration of halothane to sustain anesthesia. Reproductive organs were exposed through a midventral incision. Struc- tures visible on ovarian surfaces were inven- toried and corpora lutea were marked with India ink for subsequent identification. In treated animals, all follicles visible on the ovarian surface were electrocauterized and development of nonvisible follicles was prevent- ed by x-irradiation of ovaries. The total dose of x-irradiation 1,500 rads, 15 gray, at a depth of 1.0 cm) was delivered in 10 to 13 min using a peak of 300 kv x-ray beam having one-half value layer of 2 mm Cu. Each ovary was x- irradiated independently while suspended in a lead shield 4 mm thickness) designed to protect all nonovarian tissues from x-irradiation. Sham-irradiated heifers experienced anesthesia, laparotomy and suspension of ovaries in lead shields as treated heifers, but follicles were not cauterized and ovaries were not x-irradiated. Electrocanterization of ovarian stroma did not interfere with follicular growth, ovulation, luteal development or luteolysis in ewes Gin- ther, 1971). Therefore electrocauterization of ovarian stroma was not considered a necessary control procedure in this experiment. To determine if x-rays had a direct effect on luteal function only the ovary bearing a corpus luteum was x-irradiated in two heifers that were 15 d postestrus. All surgically related proce- dures for these animals were the same as for treated and controls, except no follicles were cauterized on either ovary. Jugular blood was collected through poly- vinyl cannulae approximately 30 min before and every 8 h 0600, 1400 and 2200 h) after surgery until 24 d postestrus. Concentrations of progesterone and luteinizing hormone LH) in serum were determined in all samples according to methods described by Louis et al. 1973) and Convey et al. 1976), respectively. From 20 assays, mean concentrations of progesterone in serum from cows in estrus were .6 • .03 ng/ml and were 11.2 + .02 ng/ml in serum from pregnant cows. From a single radioimmuno- assay, mean concentrations of LH were 1.38 -+ .24 ng/ml in serum from cows in diestrus and 9.86 -+ 1.7 in serum from cows in which secre- tion of LH was induced by exogenous gonado- tropin releasing hormone. Because luteolysis occurred in some control heifers as early as the evening of d 16 postestrus, concentrations of LH during intervals from surgery to d 16 postestrus will be reported and discussed. Concentrations of estradiol-173 were deter- mined as reported previously Carruthers and Hafs, 1980) in serum collected before surgery and at 0600 h each day after surgery until d 24 postestrus. From 20 assays, mean concentra- tions of estradiol-173 in serum from ovari- ectomized cows were 2.1 • .40 pg/ml and were 6.4 • .20 and 11.3 • .10 pg/ml when 5 or 10 pg, respectively, of estradiol-173 were added to this serum.  OVARIAN FOLLICLES AND LUTEOLYSIS IN HEIFERS 521 Ovaries were removed supravaginally from all heifers 24 d postestrus. Corpora lutea marked previously with India ink were dissect- ed from ovaries and weighed. Ovaries were sliced into sections of approximately 1 mm to inventory follicles. Concentrations of proges- terone, LH and estradiol-17~3 in serum were analyzed by split-plot analysis of variance for repeated sampling over time (Gill and Hafs, 1971). To analyze the data from animals in which only the ovary bearing the corpus luteum was x-irradiated, all data were rearranged as a 2 x 3 + 1 split-plot factorial experiment. In x-irra- diated heifers, there were no differences (P<.05) in concentrations of progesterone among samples within day during the experimental period. In sham-irradiated animals, differences in concentrations of progesterone (P<.05) occurred only on the day when luteolysis was first detectable. Thus, concentrations of proges- terone in serum are expressed as daily means. Dunnett s test was utilized to detect significant changes in concentrations of progesterone over time. Comparisons were between the highest mean concentration of progesterone and the subsequent daily means within the same treat- ment (Gill, 1978). Due to heterogeneity of variance in concentrations of LH among groups of animals, data were transformed to logl0 (Y + 10). According to Bartlett s procedure (Gill, 1978), transformation of concentrations of LH as described, removed (P>.2) heterogeneity of variance. Thus, all statistical analyses related to concentrations of LH were performed on transformed data. Because variance of concen- trations of estradiol-17/3 was heterogeneous among groups of heifers and homogeneous variance was not achieved by transformation of data, concentrations of estradiol-17/3 were contrasted with the minimum-norm-quadratic- unbiased-estimator in linear regression (Rao and Subrahmaniam, 1971). One-way analysis of variance was utilized to contrast weights of corpora lutea. Follicles inventoried in all animals at surgery and in sham-irradiated heifers on d 24 postestrus were categorized according to size as small (< 5 mm), medium (5 to 10 ram) or large (> 10 mm). These data were analyzed by one-way analysis of variance. Chi- square procedures (Gill, 1978) were used to compare numbers of corpora hemorrhagica and new corpora lutea recorded on d 24 postestrus in ovaries from sham-irradiated heifers. esults At surgery, numbers of small (6.2 + 1.2/ heifer), medium (3.2 + .6) and large (1.7 +- .2) follicles on the ovarian surface did not differ between treatments within day postestrus or within follicular size among day postestrus (P>.05). No differences were detected in any of the categories of follicles between the ovary containing the corpus luteum and the contra- lateral ovary (P>.05). On d 24 postestrus, macroscopic examina- tions of ovaries from sham-irradiated heifers revealed variable numbers of follicles (21.1 -+ 2.6 follicles/heifer + SE), but numbers of follicles and corpora hemorrhagica did not differ among heifers sham-irradiated on d 9, 12 or 15 postestrus. In contrast, no follicles larger than 1 mm in diameter were observed in ovaries from heifers treated on d 12 and 15 postestrus. Two follicles of approximately 3 mm in diam- eter each were present in one heifer that was treated on d 9 postestrus. All data from this animal were eliminated from analysis and discussion. Eleven of 16 control heifers had a corpus hemorragicum or a corpus luteum different than that marked at surgery, indicat- ing that those animals ovulated before d 24 postestrus. There was no evidence of recent ovulation on ovaries from treated heifers. Slopes for regression of concentrations of estradiol-17~ in peripheral blood were contrast- ed with zero-slope. Significant increases in concentrations of estradiol-17/3 were indicated by positive slopes. Negative slopes indicated decreases in concentrations of estradiol-17~. In sham-irradiated heifers, concentrations of estra- dio1-17/3 increased (P<.001) during proestrus (figure 1). However, concentrations of estradiol- 17/3 remained unchanged in heifers x-irradiated on d 9 or 12 postestrus and declined (P<.05) in animals x-irradiated on d 15 postestrus. When slopes for regression of concentrations of estradiol-17/~ in x-irradiated heifers on d 9, 12 or 15 were contrasted with those from the corresponding controls, they were not parallel (P<.001). Between surgery and d 16 postestrus, mean concentrations of LH in sera from heifers x-irradiated on d 9, 12 or 15 postestrus were higher (P<.01) than in contemporary controls (figure 2). As indicated by positive slopes (P<.01), concentrations of LH increased from surgery to d 16 postestrus in all x-irradiated  522 VILLA-GODOY ET AL. E t ~ c~ zK I LU [[ 0----'0 SHAM //~ 91... DAY 9 A--. X-IRRAD / / I t I I J 1 I '~ u I I I I I I I 9 12 1,5 18 21 24 DAY 12 I 1 i I I l I 1 I I I I | I I 9 12 15 18 21 24 l 9 I I I I I I I I I I I I I I [ 12 15 18 21 24 DAYS POSTESTRUS Figure 1. Profiles of concentrations of estradiol- 17 in jugular serum from sham and x-irradiated heif- ers on d 9 n = 3 or 4), 12 n = 6) or 15 n = 6) postes- trus. Each point represents mean values • standard error. heifers. In contrast, concentrations of LH in sham-irradiated animals remained unchanged (P> .05). Independent of day when follicles were destroyed, concentrations of progesterone in x-irradiated heifers did not parallel (P<.01) concentrations of progesterone of the corre- sponding control animals (figure 3). The first detectable decline in concentrations of proges- terone (P<.01) occurred between d 16 and 17 postestrus in heifers sham-irradiated on d 9, 12 or 15 postestrus. In contrast, concentrations of progesterone in x-irradiated heifers on d 9 and 15 were sustained until d 24 postestrus. Mean concentrations of progesterone declined (P<.01) by d 23 or 24 in heifers treated on d 12 postestrus (figure 3). However, in three of six heifers x-irradiated on d 12, concentra- tions of progesterone were sustained until d 24 postestrus (figure 4, A), whereas in the other three animals of the same group, concentrations of progesterone declined (P<.01) on d 23 or 24 after estrus (figure 4, B). Thus, heifers treated on d 12 after estrus were partitioned into two subgroups relative to duration of luteal func- tion, to examine numbers of follicles present at surgery and concentrations of estradiol-1713. For heifers in which concentrations of proges- terone declined, there were more (P<.001) medium size follicles (9.7 + 2.3) at surgery than in heifers with sustained concentrations of progesterone (.7 + .7). The regression line of concentrations of estradiol-17~ over time in heifers from both subgroups (figure 4, A and B) were parallel and did not differ from zero-slope (P>.05). However, the srcin of the slope (4.8 + 1.1 pg estradiol-173/ml) in heifers with reduced concentrations of progesterone was higher (P<.001) than the srcin observed in heifers with sustained concentrations of progesterone (2.7 -+ .7 pg estradiol-17~/ml). Thus, initial 2.8 2.2 1.6 1.0 .4 2.8 E 2.2 s 1 6 T d 1.0 .4 2.8 2.2 1.6 1.0 .4 T 9 12 15 DAY 12 9 12 15 DAY 15 / I I I,, I I I I t 15 DAYS POSTESTRUS Figure 2. Profiles of concentrations of LH in jugu- lar serum from sham and x-irradiated heifers on d 9 (n = 3 or 4), 12 (n = 6) or 15 (n = 6) postestrus. Each point represents mean values • standard error.  OVARIAN FOLLICLES AND LUTEOLYSIS IN HEIFERS 523 E E v W z 0 rr w up w L9 0 0~ 0_ 0--- -0 SHAM ~ ~_~DAY A A X-IRRAD. I I I I I I I , I XT)' (T) '(~) ~ 9 12 15 18 21 24 I 9 DAY 2 I L I I I I I I I I I "~"-0-~ 12 15 18 21 24 3 I I 9 5. l i i i J i i i I ~O--t'-.-..~ 12 15 18 21 24 DAYS POSTESTRUS Figure 3. Profiles of concentrations of progester- one in jugular serum from sham and x-irradiated heif- ers on d 9 n = 3 or 4), 12 n = 6) or 15 n = 6) postes- trus. Each point represents mean values + standard error concentrations of estradiol-17fl were sustained during the experimental period in both sub- groups. However, concentrations of estradiol- 17fl at the beginning of the experiment were higher in heifers with reduced concentrations of progesterone than in heifers with maintained concentrations of progesterone. Concentrations of LH were similar P>.05) in both subgroups of heifers x-irradiated on d 12 postestrus figure 5) and were different P<.01) from concentra- tions of LH in sham-irradiated animals on d 12 postestrus. On d 24, corpora lutea from heifers treated on d 9, 12 or 15 were heavier P<.001) than corpora lutea from contemporary control heifers table 1). Concentrations of progesterone, estradiol- 17/3 figure 6) and LH, weights of corpora lutea 1.3 + .3 g) and numbers of follicles on d 24 postestrus 14 + 1.4) in heifers in which only the ovary bearing the corpus luteum was x-irradiated, did not differ from values observed in sham-irradiated heifers on d 15 postestrus. Discussion Weights of corpora lutea on d 24 postestrus and concentrations of progesterone in serum from heifers in which the ovary bearing the corpus luteum was selectively irradiated, indicate that there were no detectable direct effects of x-rays on corpora lutea. This agrees with previous reports in rats MacDonald et al., 969; Christiansen et al., 1970) and ewes I T ; I LvL 2.8 - ~- ....... 2--_ -- 2.1 ;'',2 5 ,8 2 24 T 1 6 9 ..0 4 .............. ~ I I I I I I 9 12 15 18 21 24 DAYS POSTESTRUS Figure 4. Profiles of concentrations of estradiol- 17/3 and progesterone in jugular serum from heifers x-irradiated on d 12 postestrus. Panel A: heifers n = 3) with luteal function sustained to d 24 postes- trus and Panel B: heifers n = 3) with luteal regression by d 24 postestrus. Each point represents mean values -+ standard error. 12 15 DAYS POSTESTRUS Figure S. Profiles of concentrations of LH in jugu- lar serum from heifers x-irradiated on d 12 postes- trus. A: heifers n = 3) with luteal function sustained to d 24 postestrus and B: heifers n = 3) with luteal regression by d 24 postestrus. Each point represents mean values + standard error.
Search
Similar documents
View more...
Tags
Related Search
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks