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Biomedical subjects

J J Ireland

Publications and source records attributed to J J Ireland.

At least 55 records · Page 3Linked to original sources
PubMed1985

Concentrations of luteinising hormone and progesterone in pregnant and non-pregnant heifers.

An experiment was conducted to determine if concentrations of luteinising hormone or progesterone were different in pregnant or non-pregnant heifers for seven days before and 20 days after a successful or non-successful insemination. Heifers with an oestrous cycle length of 18 to 24 days only were used and they were bled at 08.00, 16.00 and 24.00 each day for seven days before and for 20 days after insemination with thawed semen (treatment 1) or semen diluent (treatment 2). Animals allocated to treatment 3 had the embryo nonsurgically flushed from the uterus at days 10 to 12 while animals allocated to treatment 4 were inseminated with semen diluent and then had a viable embryo transferred to the uterus between days 10 and 12. All animals were slaughtered between 19 and 21 days after insemination and pregnancy rate determined. There were no differences in basal luteinising hormone levels between treatments. Blood concentrations of progesterone were not different before insemination and for 16 days after insemination for pregnant (11 out of 15) and non-pregnant heifers (14) allocated to treatments 1 and 2. Between days 17 and 20, progesterone concentrations declined in non-pregnant heifers. Transfer of an embryo to non-pregnant heifers on day 10 to 12, did not affect progesterone concentrations, but non-surgical flushing of the embryo caused a decline in blood concentrations of progesterone. It was concluded that basal blood concentrations of luteinising hormone and progesterone, in samples taken three times daily were not different in pregnant or non-pregnant heifers before and for 16 days after insemination.

Animals↗
PubMed1985

Luteal function in cows following destruction of ovarian follicles at midcycle.

Luteal function was studied in the absence of non-ovulatory ovarian follicles to determine if these follicles are involved in luteal regression in cattle. After at least one estrous cycle, cows were assigned randomly to treatment (n=5) or control (n=5). All cows were laparotomized on day 10 postestrus (Estrus = day 0). During laparotomy of treated cows, all visible follicles on both ovaries were destroyed by electrocautery, and follicular growth was prevented by ovarian x-irradiation. In controls, laparotomy and ovarian manipulation were as in treated cows but follicles were not destroyed and ovaries were not irradiated. On day 22 postestrus, ovaries of 4 treated cows contained no visible follicles and concentrations of estradiol-17beta in jugular plasma (0.4 +/- 0.1 pg/ml) were less (P<0.05) than in controls (3.2 +/- 0.4 pg/ml). Daily mean concentrations of LH from surgery to day 22 postestrus in treated cows did not differ from controls. On day 22 postestrus, progesterone in jugular plasma and weights of corpora lutea in treated cows were greater (P<0.05) than in controls. Between days 12 and 18 postestrus, concentrations of estradiol-17beta and PGF(2)alpha in utero-ovarian venous plasma of controls increased prior to detectable declines in concentrations of progesterone. Therefore, non-ovulatory ovarian follicles present during mid to late diestrus are necessary for luteal regression in non-pregnant cattle.

Journal Article↗
PubMed1985

CI628 inhibits follicle-stimulating hormone (FSH)-induced increases in FSH receptors of the rat ovary: requirement of estradiol for FSH action.

Although estradiol (E2) alone does not increase receptors for FSH in granulosa cells, E2 priming before administration of FSH increases numbers of FSH receptors significantly compared with FSH alone. We hypothesized that if E2 is required for FSH to increase its own receptor, blocking estrogen action should prevent FSH-induced increases in FSH receptors. Five groups of hypophysectomized rats were injected sc with: saline at 0 h; the antiestrogen CI628 (1 mg) at -6 h; human FSH (hFSH, 2 micrograms) at 0 h; CI628 at -6 h, then hFSH at 0 h; and CI628 plus E2 (2 mg) at -6 h, then FSH at 0 h. Animals were decapitated at 0, 6, 12, or 24 h, and granulosa membrane receptors for FSH, LH, and nuclear receptors for E2 were measured. LH receptor levels increased only after administration of E2 before hFSH. Treatment with hFSH for 6 h increased numbers of FSH receptors 3-fold (P less than 0.01) without any increase in numbers of E2 receptors. At 12 and 24 h, hFSH increased numbers of FSH and E2 receptors 6- and 7-fold (P less than 0.01) over controls. CI628 prevented the hFSH-induced increases in FSH receptors at 6, 12, and 24 h. Administration of E2 concomitant with CI628 before hFSH significantly reversed the inhibitory effects of CI628 on hFSH-induced increases in FSH receptors. There were no changes in affinity of FSH or E2 receptors from 0 to 24 h. To determine whether E2 was acting on the adenylate cyclase system, the ability of hFSH to increase the content of cAMP in granulosa cells in each treatment group was determined. After an iv injection of hFSH, cAMP levels were similar in CI628- and saline-treated rats but had increased 6-fold (P less than 0.01) in hFSH or CI628 plus hFSH-treated animals. Thus, blocking hFSH-induced increases in FSH and E2 receptor appeared to have no effect on FSH stimulation of cAMP. In conclusion E2 appears to be required for FSH action, perhaps by acting within granulosa cells distal to the cAMP-adenylate cyclase system.

Animals↗
PubMed1985

Effect of ovarian follicles on luteal regression in heifers.

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 rads) 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 (greater than or equal to 1 mm diameter) were observed in ovaries from treated animals and concentrations of estradiol-17 beta did not change over time, whereas different numbers of follicles were observed in ovaries from controls and concentrations of estradiol-17 beta increased (P less than .05) during proestrus. Hence, treatment destroyed follicles and prevented follicular development. On d 24 postestrus, corpora lutea from treated heifers (5.5 +/- .5 g) were heavier (P less than .001) than corpora lutea from controls (1.1 +/- .1 g), independent of day when follicles were destroyed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Decrease of various luteal enzyme activities during prostaglandin F2 alpha-induced luteal regression in bovine.

Luteal gonadotropin receptors decrease in cows, sheep and rats within 24 h following an injection of a luteolytic dose of prostaglandin (PG) F2 alpha. But it is not known whether this decrease is the specific event, or a reflection of general decline in luteal cell structure, function and metabolism. In order to investigate this possibility, 15 of 21 heifers were given on day 9 of the estrous cycle, a single 500 micrograms injection of Cloprostenol (CO), a synthetic PGF2 alpha analog. These heifers were ovariectomized in groups of 5 at 12, 24 and 36 h after CO. For controls, a group of 6 heifers were ovariectomized just prior to injection of the others. Serum progesterone levels decreased whereas LH levels increased (P less than 0.05) by 12 h with no additional changes observed at 24 or 36 h. The luteal plasma membranes [125I]hCG specific binding, as well as 5'-nucleotidase (5'-NE) activity, decreased by 12 h and continued to decline (P less than 0.05) until 24 h (binding) or 36 h (5'-NE). Scatchard analysis showed that the decrease in [125I]hCG binding was due to a decrease in receptor number rather than a decrease in receptor affinity. The activities of cytochrome c oxidase in mitochondria, NADH cytochrome c reductase in rough endoplasmic reticulum and galactosyl transferase in Golgi decreased while NAD pyrophosphorylase in nuclei virtually disappeared following the injection of CO. The beta-N-acetyl-D-glucosaminidase (a lysosomal hydrolase) activity in the homogenate increased by 12 h and continued to increase up to 36 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Effect of cyanoketone on follicle-stimulating hormone (FSH) induction of receptors for FSH in granulosa cells of the rat.

Follicle-stimulating hormone (FSH) enhances the conversion of testosterone or androstenedione into estradiol by stimulating the aromatase enzyme system. Estradiol also enhances FSH action. Thus, a synergistic action of FSH and estradiol may be required for maturation of ovarian follicles. We hypothesized that estradiol may be required for FSH action. Thus, blocking estrogen synthesis should prevent FSH-induced increases in FSH receptors. Hypophysectomized rats were divided into five groups and injected subcutaneously with: 1) saline, 2) cyanoketone (0.05 mg, blocks the conversion of pregnenolone to progesterone), 3) ovine FSH (oFSH, 200 micrograms), 4) cyanoketone then oFSH 24 h later, or 5) cyanoketone plus estradiol [or progesterone, testosterone, promegestrone (R5020), dihydrotestosterone (DHT), 2 mg], then FSH 24 h later. Animals were decapitated at 0, 12 or 24 h after an injection of oFSH, and membrane receptors for FSH and luteinizing hormone (LH), plus nuclear receptors for estradiol from granulosa cells, were measured. LH receptor levels were increased only after administration of FSH and estradiol. At 0 and 24 h, numbers of FSH or estradiol receptors were similar in saline- and cyanoketone-treated animals. FSH alone increased (P less than 0.01) FSH and estradiol receptors 3-fold and 4-fold, respectively, over controls by 12 and 24 h. Cyanoketone prevented these increases in FSH and estradiol receptors. Estradiol replacement fully reversed the effects of cyanoketone on FSH action. Replacement with progesterone and testosterone was able to only partially restore levels of FSH receptors; however, estradiol receptor numbers were also increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Androstenols↗
PubMed1984

Changes in inhibin-like bioactivity in ovulatory and atretic follicles and utero-ovarian venous blood after prostaglandin-induced luteolysis in heifers.

The objectives of this study were to develop a bioassay for measuring inhibin bioactivity in untreated samples of bovine follicular fluid (BFF) and then examine changes in inhibin bioactivity in ovulatory and atretic follicles and utero-ovarian venous blood during the periovulatory period in heifers. A rat pituitary cell culture system was used to bioassay inhibin-like activity. Addition of 0.005 to 1 microliter untreated (whole), unfiltered charcoal-stripped, or filtered whole BFF to pituitary cultures caused a linear suppression of LHRH-induced FSH release but had no effect on LH secretion. Steroids in BFF did not suppress FSH secretion, since removal of steroids from BFF with charcoal did not remove the FSH-suppressive activity in BFF. Addition of ether extracts of BFF caused a slight but nonparallel suppression of FSH secretion; however, heating these extracts removed most of this suppressive activity. Removal of BFF from pituitary cultures completely restored the capacity of pituitary cultures to respond to LHRH. It was concluded that the inhibin bioassay was specific for detecting inhibin-like activity in fluids from individual follicles without interference of steroids. Within 12 h after a prostaglandin (PG) injection during the luteal phase of heifers, LH levels in serum increased 2- to 4-fold and remained at this level until the occurrence of the preovulatory gonadotropin surge. In contrast, FSH did not change before the gonadotropin surge. Inhibin bioactivity was measured in all follicles (greater than or equal to 6 mm) 0, 12, 24, 36, 48, 60, and 72 h after and in utero-ovarian venous serum 0, 24, and 36 h after PG-induced luteolysis. From 0-36 h after PG administration, inhibin-like activity increased linearly in presumed ovulatory follicles and utero-ovarian venous serum. Then, from 48-72 h after PG treatment, before the preovulatory LH surge, inhibin activity decreased in ovulatory follicles. After the surge but before ovulation, inhibin-like activity increased in ovulatory follicles. Inhibin-like activity in atretic follicles did not change after PG treatment and was lower in atretic than ovulatory follicles. Since a single hypothalamic releasing factor, LHRH, may control the secretion of LH and FSH, increased secretion of inhibin from preovulatory follicles before the preovulatory LH and FSH surges could account for the absence of a presurge rise in FSH in blood, as was observed for LH during this time in heifers. Diminished follicular production of inhibin during the gonadotropin surge could explain the preovulatory release of FSH along with LH during this time.

Animals↗
PubMed1984

Production of estradiol by each ovary during the estrous cycle of cows.

The objective of our experiment was to examine changes in serum concentrations of estradiol in each utero-ovarian vein before, during and after gonadotropin surges. Four cows were given prostaglandin F2 alpha (PGF2 alpha) during diestrus and three cows were allowed to cycle spontaneously. All cows had a cannula in each utero-ovarian vein and in one jugular vein. Most cows had two transient rises in estradiol, primarily coming from a single ovary, preceding and after luteinizing hormone (LH) surges. The first rise in estradiol began after luteal regression and was sustained from 48 h before a pre-ovulatory LH surge to the end of the LH surge. The second rise in estradiol was sustained from 72 to 168 h after the end of an LH surge. To determine how rapidly asymmetrical production of estradiol began during luteolysis, several cows were injected with PGF2 alpha during the luteal phase. Blood samples were taken from a jugular and both utero-ovarian veins at hourly intervals before and after PGF2 alpha. Asymmetrical production of estradiol began within 3 h after an injection of PGF2 alpha. We concluded: (1) that a single ovary was responsible for the sustained increases in concentration of estradiol that occur during proestrus to estrus and early diestrus in cows and (2) that cows may have at least one follicle capable of producing estradiol during most days of an estrous cycle, thus little delay in selection of which follicle eventually ovulates occurs after luteal regression.

Animals↗
PubMed1983

Identification of estrogen receptors in granulosa cells of immature rats.

Nuclear and cytoplasmic binding sites for estradiol (E2-17 beta) in granulosa cells of immature rats were characterized. These binding sites for estrogen were high affinity, low capacity with an affinity constant (Kd) of 1.9 X 10(-10)M (binding capacity, Ro = 80 pM) for nuclear sites and a Kd = 3.5 X 10(-10) M (Ro = 45 pM) for cytosol sites. Binding was specific for biologically active estrogens. The estrogen receptor in granulosa cells is a protein and heat-labile as treatment with protease or pre-incubation at 37 degrees C for 1 h significantly diminished binding. RNase and DNase had no effect on estrogen binding. Sedimentation coefficients for nuclear and cytosol binding components were 5S and 8S respectively, similar to values obtained with uteri. Finally, translocation was demonstrated after a s.c. injection of E2-17 beta. Forty-five minutes post-injection, cytosol binding sites for estradiol were depleted concomitant with accumulation of nuclear binding sites. We concluded that granulosa cells of immature rats have binding sites specific for estradiol which have characteristics similar to the classical estrogen receptor in uteri.

Animals↗
PubMed1983

Development of nonovulatory antral follicles in heifers: changes in steroids in follicular fluid and receptors for gonadotropins.

The objective of this study was to examine changes in steroid concentrations in follicular fluid (FF) and in gonadotropin receptors in nonovulatory follicles that develop after ovulation in heifers. Six groups of six to seven heifers were ovariectomized on days 3, 5, 7, 9, 11, and 13 of an estrous cycle. Follicles 6 mm or more in diameter were separated into two classes, estrogen-active (E-A) and estrogen-inactive (E-I). E-A follicles had higher concentrations of estradiol than progesterone and androgens in FF and a low incidence of atresia. E-I follicles had higher concentrations of progesterone or androgens than estradiol in FF and a high incidence of atresia. Diameters, numbers of granulosa cells, and capacities of granulosa cells and thecal tissue to bind [125I]iodo-hCG increased in E-A follicles from days 3-7. During this time, diameters, numbers of granulosa cells, concentrations of estradiol, and capacities of granulosa cells and thecal tissue to bind gonadotropins were greater in E-A than E-I follicles. On days 9, 11, and 13, each heifer had only a single E-I follicle. Compared with E-A follicles on day 7, E-I follicles on days 9, 11, and 13 were smaller and had less granulosa cells, less estradiol in FF, and a lower capacity to bind [125I]iodo-hCG. After day 7, E-A follicles were not observed until day 13. We conclude that at least two periods of growth and atresia of follicles occur between days 3-13 of an estrous cycle in heifers. One is during days 3-7 when a single E-A follicle 6 mm or more in diameter develops and all other E-I follicles regress. The other is between days 7 and 13 when the E-A follicle from day 7 becomes an E-I follicle and regresses, and another E-A follicle develops.

Androgens↗
PubMed1983

Growth and differentiation of large antral follicles after spontaneous luteolysis in heifers: changes in concentration of hormones in follicular fluid and specific binding of gonadotropins to follicles.

The objective of the present study was to characterize changes in growth, concentrations of steroids in follicular fluid (FF) and gonadotropin receptors of individual antral follicles after spontaneous luteolysis in heifers and to reexamine our hormonal method of classifying healthy and atretic follicles. Groups of heifers were ovariectomized (OVX) before regression of corpora lutea on d 17, 18 and 19 of an estrous cycle and after regression of corpora lutea at time periods before, during and after preovulatory gonadotropin surges. Each follicle greater than or equal to 6 mm in diameter was examined for concentration of progesterone, androstenedione, testosterone and estradiol-17 beta in FF and capacities of granulosal and thecal cells to specifically bind 125I-bovine follicle stimulating hormone (bFSH) or 125I-human chorionic gonadotropin (hCG). Follicles were separated into two classes, estrogen-active (E-A) or estrogen-inactive (E-I). Concentrations of estradiol in FF were higher than both progesterone and androgens in E-A follicles, whereas either androgens or progesterone was higher than estradiol in E-I follicles. Diameters, volumes of FF and numbers of granulosal cells in E-A follicles increased from d 17 through the end of the preovulatory gonadotropin surges. During this time, concentrations of progesterone, androstenedione and estradiol in FF and specific binding of 125I-hCG to granulosal and thecal cells increased, whereas specific binding of 125I-bFSH to granulosal cells decreased. In E-I follicles, progesterone in FF decreased and androstenedione increased from d 17 through end of gonadotropin surges. The E-I follicles had a higher incidence of granulosal cells with pycnosis than E-A follicles. We concluded that changes in growth, concentration of steroids in FF and gonadotropin receptors in E-A follicles after spontaneous luteolysis were similar to changes we previously reported for E-A follicles after prostaglandin-induced luteolysis, and that ratio of concentration of estradiol in FF to both progesterone and androgens could be used to separate potential ovulatory (E-A) from atretic (E-I) follicles in heifers.

Androstenedione↗
PubMed1983

Effect of charcoal-treated bovine follicular fluid on secretion of LH and FSH in ovariectomized heifers.

The objective of the experiment was to determine whether pools of charcoal-treated bovine follicular fluid (bFF) removed from large (greater than 10 mm) follicles during the preovulatory (d 18 to 1), postovulatory (d 2 to 6) or mid-cycle (d 7 to 17) stages of the bovine estrous cycle altered secretion of luteinizing hormone (LH) or follicle-stimulating hormone (FSH) in ovariectomized heifers. After a 20-ml injection of bFF given at three consecutive 6-h intervals, secretion of FSH was depressed from approximately 116 to 53 ng/ml by each pool of bFF. In contrast, bFF did not affect secretion of LH. Serum from an ovariectomized cow (control) had no effect on secretion of LH or FSH. We concluded that bFF contained a nonsteroidal component (perhaps inhibin) that suppressed FSH secretion in heifers.

Animals↗
PubMed1982

Development of antral follicles in cattle after prostaglandin-induced luteolysis: changes in serum hormones, steroids in follicular fluid, and gonadotropin receptors.

Changes in growth, concentrations of steroids in follicular fluid, and numbers of gonadotropin receptors in follicles 6 mm or more in diameter were examined 12, 24, 36, 48, 60, and 72 h after prostaglandin (PG)-induced luteolysis in heifers. Follicles with higher concentrations of estradiol than progesterone and androgens in follicular fluid (FF) were classified as estrogen active (E-A). Follicles with higher concentrations of progesterone or androgens than estradiol in follicular fluid were classified as estrogen inactive (E-I). Although E-A and E-I follicles were similar in size 12-72 h after PG treatment, before the preovulatory surge of LH, numbers of granulosa cells, estradiol concentrations, and capacities of follicles to specifically bind gonadotropins were markedly lower in E-I follicles. Most E-I follicles had histological signs of atresia, whereas E-A follicles did not. Sizes, concentrations of steroids in FF, and specific binding of gonadotropins to follicle cells did not change in E-A or E-I follicles 12-72 h after PG treatment but before the preovulatory surge of LH. However, diameters of E-A follicles were highly correlated with concentrations of estradiol and progesterone in FF and with capacities of granulosa and thecal cells to specifically bind [125I] iodo-hCG. In contrast, diameters of E-A follicles were highly negatively correlated with concentrations of testosterone in FF and with capacities of granulosa cells to specifically bind [125I] iodobovine FSH. We conclude that E-I follicles are atretic and E-A follicles are potentially ovulatory follicles. In addition, after a single injection of PG during an estrous cycle in heifers, the growth the differentiation of ovulatory follicles were not synchronized.

Animals↗
PubMed1982

Effect of progesterone on basal LH and episodic LH and FSH secretion in heifers.

Heifers between Days 6 and 10 of the cycle were allocated at random to groups of 8 and treated with (i) a 4% progesterone-releasing intravaginal device (PRID) + oestrogen capsule for 12 days; (ii) 4% PRID for 12 days; (iii) 20% PRID for 12 days; (iv) 4% for 14 days; or (v) 20% PRID for 14 days. Blood was obtained daily during treatment and at 2- or 4-h intervals for 72 h after removal of PRIDs. Some animals were sampled every 20 min for 4.676 h on the 3rd day after PRID insertion, and 1 day before and 36 h after removal of the PRID insertion, and 1 day before and 36 h after removal of the PRID. During progesterone treatment there was: (i) no correlation between concentrations of progesterone and LH within days; (ii) a significant negative correlation between progesterone and days (P less than 0.01) and also between progesterone and LH over days (P less than 0.01); (iii) the overall correlation co-efficient between LH and days was positive (P less than 0.05). The amplitude of LH or FSH episodes was not affected as progesterone concentrations declined during PRID treatment, but the number of LH (but not FSH) episodes was increased (p less than 0.01). After PRID removal, the amplitude of both LH and FSH episodes increased (P less than 0.01). We suggest that progesterone is part of a negative feedback complex on LH secretion in cattle and that this effect is apparently mediated through frequency of episodic LH release.

Animals↗
PubMed1982

Serum luteinizing hormone, follicle stimulating hormone and prolactin response to photoperiod during the estrous cycle of Holstein heifers.

The objectives were to determine if photoperiods of 8 h light:16 h dark (8L:16D) and 16L:8D affect time of day when preovulatory surges of luteinizing hormone (LH) and follicle stimulating hormone (FSH) occur and if photoperiods affect diestrus and estrous concentrations of LH, FSH and prolactin (PRL). Postpubertal Holstein heifers were assigned to receive either 8L:16D (n - 9) or 16L:8D (n = 9) from September 21 through January 31. Hormone concentrations were determined in serum collected at 2-h intervals during diestrus and estrus of a single estrous cycle in autumn and again 4 mo later, during a single estrous cycle in winter. Neither photoperiod nor season affected time of day at which preovulatory LH and FSH surges occurred in heifers. The LH surges did not differ in amplitude and duration within and between photoperiods and within individual animals. In 29 of 33 surges, peak concentrations of FSH coincided with peaks of LH. Peak concentrations of FSH were greater during the winter than during autumn in heifers exposed to 8L:16D, but were not different between autumn and winter in heifers exposed to 16L:8D. Between autumn and winter, surges of FSH were similar in magnitude and duration within individual animals. In comparison with 8L:16D, PRL was increased in heifers that received 16L:8D in autumn, but photoperiod had no effect on PRL during winter. Concentrations of PRL were increased at estrus relative to diestrus in autumn and winter. It is concluded that photoperiods of 8 and 16 h do not affect the timing, amplitude or pattern of preovulatory surges of LH or FSH, the rise in PRL associated with estrus, or length of estrous cycles in postpubertal Holstein heifers.

Animals↗
PubMed1981

The differential effect of progesterone on concentrations of luteinizing hormone and follicle-stimulating hormone in heifers.

The effects of progesterone on LH and FSH concentrations in cattle are not clearly understood. The objective of this experiment was to determine the effect of various concentrations of progesterone on serum concentrations of LH and FSH in heifers. After estrous synchrony, animals were assigned to four different treatment groups (n = 10/group). Heifers received vaginal coils containing either 2% or 6.75% progesterone between days 8-10 (luteal phase) or days 17-18 (follicular phase) after estrus. Coils remained in place for 7 days. One day before removal of coils, all animals received an injection of prostaglandin-F2 alpha to cause regression of existing corpora lutea. Both the stage of the cycle and the percentage of progesterone in the coil affected serum concentrations of progesterone while the coils were in the vagina. Concentrations of FSH during progesterone treatment were not different for animals on different treatments. While coils were in the vagina, there was a significant increase in serum LH concentrations in heifers in the follicular phase given 2% progesterone coils, but no increase in LH was observed in the other three treatment groups. After removal of the progesterone coils, but before the preovulatory gonadotropin surges, LH increased but not FSH. The LH and FSH surges occurred synchronously. After the surges, FSH concentrations increased at a faster rate than LH. These data suggest that differential feedback mechanisms exist for LH and FSH in heifers. (Endocrinology 108: 568, 1981)

Animals↗