OBJECTIVE To determine whether luteinizing hormone receptors (LHRs) are expressed in canine femoral head subchondral bone (FHSB), hip joint round ligament (RL), cranial cruciate ligament (CCL), and femorotibial joint synovium (FJS) specimens. SAMPLE 1 specimen each of the FHSB, RL, CCL, and FJS obtained from the left hind limbs of 19 fresh canine cadavers. PROCEDURES 1 section of each FHSB, RL, CCL, and FJS specimen was processed with rabbit polyclonal IgG anti-human LHR antibody, and 1 section was treated with negative control reagents. Percentage immunoexpression of LHRs in FHSB and FJS sections was analyzed by assessment of 100 bone marrow cells or synoviocytes in 3 adjacent hpf (400×). In each RL and CCL section, immunoexpression of LHRs in fibrocytes was semiquantitatively analyzed on the basis of the mean of the product of percentage staining score (from 0 [no staining] to 3 [> 50% of cells stained]) and staining intensity score (from 0 [no staining] to 2 [moderate to strong staining]) for 3 adjacent hpf. RESULTS All tissues examined had variable LHR expression. Expression of LHRs in FHSB, CCL, or FJS specimens did not differ between sexes or between sexually intact and gonadectomized dogs. However, RL specimens from female dogs had significantly greater LHR expression scores, compared with findings for male dogs. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that LHRs are expressed in structural support tissues of canine hip and femorotibial joints. Further research is required to determine the LHRs' function, mechanism of action, and potential contribution to the pathogenesis of hip dysplasia or CCL rupture in dogs.

Changes in luteinizing hormone (LH) secretion after 17beta-estradiol (E2) injection were evaluated during sexual maturation in 10 prepubertal Nelore heifers. Heifers were divided into 2 groups: intact (I) and ovariectomized (OVX). 17beta-estradiol (2 micrograms/kg) was administered to both groups at 10, 13, and 17 mo of age. Only at 10 mo of age was there a greater mean LH concentration in OVX heifers (1.33 +/- 0.29 ng/mL) compared with the I group (0.57 +/- 0.15 ng/mL). At 13 and 17 mo of age there was no significant difference between the 2 groups in any of the evaluated variables (number of peaks, total peak area, greatest peak area, and time to greatest peak occurrence). This suggests a decrease in negative E2 feedback associated with an increase in positive feedback to LH secretion during sexual maturation, and these were likely the key factors that determined the time of first ovulation in Nelore heifers.

At initiation of a 140-day postweaning weight gain test, Angus bulls were assigned in equal numbers (n = 5) to 1 of 3 treatment groups to determine effects of implantation with zeranol, an estrogenic growth promotant, on selected reproductive characteristics. The bulls, whose age (mean +/- SD) was 233 +/- 20 days at initiation of the test (day 0), were implanted with 36 mg of zeranol on day 0, on days 0 and 60, or were not implanted. At day 140, scrotal circumference and testicular consistency were unaffected by zeranol implantation. Zeranol implantation did not affect the morphologic characteristics of semen samples collected by electroejaculation on day 139. There was no effect of zeranol treatment on paired weights of testes, epididymides, or vesicular glands from bulls at slaughter 47 to 68 days after day 140. Microscopic lesions associated with estrogenic exposure were not observed in accessory sex glands or epididymides of any bull. Histopathologic changes in the seminiferous epithelium were not induced by zeranol treatment. Implantation with zeranol did not affect body weight or hip weight at day 140 or carcass weight at slaughter. Plasma concentration of luteum hormone was increased (P = 0.04), whereas testosterone concentration tended to be less (P = 0.08) in both groups of zeranol-implanted bulls after administration of gonadotropin-releasing hormone on day 140.

Existence of ultradian variation in serum progesterone concentration and the relation between progesterone and luteinizing hormone (LH) secretory patterns were investigated in nonpregnant and pregnant mares. Blood samples were taken every 15 minutes for a 24-hour period on day 8 of the estrous cycle and day 18 of pregnancy, respectively. Progesterone and LH concentrations were determined by radioimmunoassay. Progesterone was secreted in pulsatile manner in nonpregnant and pregnant mares. Luteinizing hormone also was secreted in a pulsatile manner in both groups of mares. There was little temporal relation between LH and progesterone pulses in either pregnant or nonpregnant mares.

The effect of metoclopramide (MC), a dopamine antagonist on luteinizing hormone (LH), was examined in anestrous primaparous cows. Metoclopramide has been found to be beneficial in overcoming fescue toxicosis; increasing LH secretion stimulates return to ovulatory function after parturition. Consequently, if MC had negative effect on LH secretion, it would indicate that administration of MC to reproducing animals might be limited. Of 14 postpartum (47 to 66 days) cows, 7 were given MC (4 mg/kg of body weight, IV), and 7 served as controls. Blood was obtained via jugular cannulas at 15-minute intervals for 8 hours; MC was given at the end of the first hour, and gonadotropin-releasing hormone (GnRH, 7 mg/kg), was given IV at the end of hour 7 as a challenge stimulus for LH secretion. Prior to GnRH administration, MC did not have significant effect on LH secretion, as judged by mean serum LH concentration, LH pulse frequency, and LH pulse amplitude. Administration of MC resulted in greater (P < 0.05) LH response to GnRH, indicating enhanced secretory ability when the pituitary gland was challenged. Serum prolactin concentration was increased (P < 0.01) by MC administration. Therefore, MC did not have adverse effect on LH secretion in postpartum cows.

Luteinizing hormone (LH) and ACTH concentrations were measured in plasma from 7 cows to determine whether ACTH secretion changes with the phase of the estrous cycle, and to determine whether any ACTH peaks are associated with LH peaks. Blood was collected every 5 minutes for 190 minutes during the luteal and follicular phases of the estrous cycle. Radioimmunoassays were used to measure ACTH and LH in plasma. Mean concentration of ACTH in all cows did not differ significantly between luteal (35.1 +/- 8.0 pg/ml) and follicular (37.5 +/- 9.4 pg/ml) phases of the estrous cycle. Mean concentration of luteal-phase LH of all cows (2.0 +/- 1.1 ng/ml) was significantly (P < 0.01) lower than mean concentration of follicular-phase LH (5.4 +/- 1.6 ng/ml). Frequency of peaks in ACTH concentration was low during the sampling period. Mean number of luteal-phase ACTH peaks (0.29 +/- 0.49) was not significantly different from that of follicular-phase samples (0.43 +/- 0.53). Unlike ACTH, mean frequency of LH peaks was significantly (P < 0.05) higher in plasma from cows in the follicular phase of the estrous cycle (2.9 +/- 0.7), compared with that from cows in the luteal phase (0.29 +/- 0.49).

The effect of glucocorticoids on early follicular growth in sows undergoing normal estrous cycles was evaluated by administration of dexamethasone during the middle of the luteal phase. Plasma specimens were obtained for measurement of luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone, and estradiol-17 beta concentrations. Fifteen sows were used. Control sows (n = 5) were given physiologic saline solution twice daily from day 9 to day 14 of the estrous cycle. Sows of the second group (n = 5) were given dexamethasone (30 microgram/kg of body weight, IM) similarly, and those of the third group (n = 5) were given dexamethasone plus gonadotropin-releasing hormone (GnRH+ 50 microgram at 6-hour intervals, IV). Plasma specimens, obtained twice daily from day 8 through day 26, indicated that progesterone production and luteal regression were not inhibited by any of the 3 treatment regimens. Although preovulatory plasma estradiol concentration increased in control sows, such was not observed in the sows treated with dexamethasone or dexamethasone plus GnRH (P less than 0.01). Ovulation, with formation of corpora lutea, occurred in gilts given saline solution. Dexamethasone administration resulted in persistence of 19 to 41 follicles/ovary (2 to 4 mm in diameter), and dexamethasone-plus-GnRH treatment resulted in 6 to 18 follicles/ovary (5 to 6 mm in diameter). Plasma was obtained at 15-minute intervals for 12 hours to compare the effect of treatmenton hormone concentrations on day 12 of the estrous cycle with the values on day 8. Glucocorticoid administration had no significant effect on mean concentration, final concentration excluding those hormone concentrations that constituted part of a pulse (referred to as base line), number of pulses, pulse amplitude, and area under the pulse for either gonadotropin. Addition of GnRH to dexamethasone treatment significantly (P less than 0.01) increased all plasma LH values, but only base-line concentration of FSH. For estradiol, pulse amplitude and mean pulse area were increased (P less than 0.05), and although the frequency of pulses was not significantly altered, base-line concentration in glucocorticoid-treated sows was significantly reduced, compared with that of control sows. In sows treated with GnRH plus dexamethasone, the pulse frequency of estradiol was significantly (P less than 0.01) increased, but pulse area and amplitude were similar to those of sows given saline solution. Dexamethasone treatment was associated with an increase in mean and base-line concentrations of progesterone. The results suggest that high midcycle glucocorticoid concentrations (1) do not inhibit luteal function or regression, (2) have little influence on LH and FSH secretion during the middle of the luteal phase, (3) alter the pattern of estradiol secretion, (4) are associated with the persistence of small ovarian follicles, and (5) result in the development of fewer but larger follicular structures when GnRH is administered concurrently.

During the breeding season, the effect of constant administration of an agonist analog of gonadotropin-releasing hormone (GnRH; goserelin acetate) on reproductive activity of mares was determined. Twenty-four mares undergoing estrous cycles were allocated at random to 6 groups (n = 4/group) and, on May 29 (day 0), received no treatment (group 1, controls), 120 micrograms (group 2), 360 micrograms (group 3), 600 micrograms (group 4), or 1,200 micrograms (group 5) of GnRH agonist/d for 28 days via a depot implanted subcutaneously. The final group of mares (group 6) was treated with 120 miocrograms of GnRH agonist/d for 84 days (3 occasions at 28-day intervals). During a pretreatment period (April 19 to May 29) and for 90 days after initiation of GnRH agonist treatment, follicular development and ovulation were monitored by transrectal ultrasonography of the reproductive tract at 2- to 3-day intervals. On each occasion a blood sample was collected for determination of luteinizing hormone (LH) and progesterone. Estrous behavior was monitored by teasing of mares with a stallion. Initiation of agonist treatment was random, relative to the stage of the estrous cycle, and all mares ovulated within 11 days before or after implantation. in 3 of 4 nontreated control mares, estrous cycles were observed throughout the study, with interovulatory intervals ranging from 18 to 26 days. In the remaining mare, concentration of progesterone was high after asynchronous double ovulation during the pretreatment period, suggestive of persistent corpus luteum. In group-2 mares, ovulation occurred in all mares 7 days before and 2 days after initiation of treatment; however, the next anticipated ovulation was delayed in 3 of 4 mares (interovulatory interval, 33 to 70 days). Estrous cycles were not disrupted in the remaining mare. At higher doses (groups 3-5), 1 mare each from groups 3 and 5 ovulated between days 0 and 2 of treatment initiation, but faded to ovulate during the remainder of the study (anovulatory for > 88 days). Similarly, an additional 2 mares of groups 2 and 3 ovulated within 2 days of GnRH agonist treatment. A second ovulation occurred in these mares 32 to 35 days later, thereafter, both mares were anovulatory for the remainder of the study. In the remaining 8 mares, interovulatory intervals were either lengthened (n = 6 mares, range, 32 to 82 days) or were unaffected (n = 2) by treatment. One group-6 mare had a lengthened interovulatory interval, 1 was anovulatory for > 90 days, and the remaining 2 mares were unaffected by treatment. During the 28-day treatment period, serum concentration of LH decreased (P < 0.05) only in mares of groups 3-5. In group-6 mares, concentration of LH was unchanged during each 28-day period after depot GnRH agonist administration. Thus, constant administration of a GnRH agonist to mares during the breeding season disrupted their estrous cycles. Anovulation or lengthening of the interovulatory interval by GnRH agonist treatment was associated with persistence of a corpus luteum or an extended follicular phase.

The potential of a gonadotropin-releasing hormone (GnRH) agonist (goserelin acetate), delivered constantly for 28 days via a subcutaneous depot, to induce ovulation in seasonally anestrous mares, was investigated. Two experiments were conducted, in which a range of doses (30 to 240 micrograms/mare/d) was examined. Mares were selected on the basis of lack of substantial follicular development (follicle diameter < 20 mm determined ultrasonically) and low serum concentrations of luteinizing hormone (LH) and progesterone. Constant administration of the GnRH agonist-induced ovulation in anestrous mares, but a dose-response relation was not observed. Furthermore, with identical doses tested in consecutive or alternate years, considerable variation was observed in the ovulatory response. In general, ovulation in all treated mares was accompanied by increased circulating concentrations of LH and a decrease in follicle-stimulating hormone values. Ovulation was preceded by an increase in estradiol and LH concentrations. In mares in which ovulation did not occur, concentration of LH increased during agonist treatment, whereas that of follicle-stimulating hormone either increased or did not change. It was concluded that constant administration of GnRH agonists may induce ovulation in mares during seasonal anestrus; however, percentage of mares ovulating and the lack of reproducibility of effect indicate that this approach is inappropriate for use as a reliable method to manipulate breeding activity in commercial broodmares.