LH In Ewes Research Articles

Effect of cerebroventricular infusion of insulin and (or) glucose on hypothalamic expression of leptin receptor and pituitary secretion of LH in diet-restricted ewes☆

The objective was to determine the effect of central infusion of insulin and (or) glucose on hypothalamic expression of leptin receptor and pituitary secretion of LH in the ewe. Twenty-two ovariectomized ewes (32 wk of age) were fitted with two lateral cerebroventricular (LCV) cannulae and fed 33% of NRC requirements for 8 wk. Ewes ( n ≥ 5/group) were then infused, via LCV cannulae, with artificial cerebrospinal fluid (aCSF) or aCSF containing physiological concentrations of insulin (INS), glucose (GLU), or INS + GLU; the mass of each increasing linearly from Day 0 (mass = 0 units/h) to Day 8 (mass of INS = 80 mIU/hr and GLU = 10 mg/hr). Jugular serum was collected every 12 min for 4 hr on Days 0, 2, and 4. Ewes treated with INS or INS + GLU had greater (P < 0.06) mean concentrations of LH than aCSF treated ewes on Day 2 (13.8 ± 1.8 and 12.5 ± 1.3 > 8.0 ± 3.3 ng/ml). Furthermore, on Day 4, concentrations of LH in INS treated ewes exceeded that (P < 0.07) of aCSF treated ewes (14.8 ± 2.0 > 7.4 ± 3.0 ng/ml). Expression of NPY mRNA did not differ between treatments (P = 0.87). Leptin receptor mRNA expression was dramatically reduced (P < 0.0002) in INS+GLU versus aCSF treated ewes. These data provide evidence to suggest that insulin may be an important component of hypothalamic mechanisms regulating secretion of LH and expression of leptin receptors in undernourished ruminants.

Effect of transport on pulsatile and surge secretion of LH in ewes in the breeding season.

The aim of this study was to elucidate the mechanism(s) involved in stress-induced subfertility by examining the effect of 4 h transport on surge and pulsatile LH secretion in intact ewes and ovariectomized ewes treated with steroids to induce an artificial follicular phase (model ewes). Transport caused a greater delay in the onset of the LH surge in nine intact ewes than it did in ten ovariectomized ewes (intact: 41.0 +/- 0.9 h versus 48.3 +/- 0.8 h, P < 0.02; ovariectomized model: 40.8 +/- 0.6 h versus 42.6 +/- 0.5 h, P < 0.02). Disruption of the hypothalamus-pituitary endocrine balance in intact ewes may have reduced gonadotrophin stimulation of follicular oestradiol production which had an additional effect on the LH surge mechanism. In the ovariectomized model ewes, this effect was masked by the exogenous supply of oestradiol. However, in these model ewes, there was a greater suppression of maximum LH surge concentrations (intact controls: 29 +/- 4 ng ml-1 versus intact transported 22 +/- 5 ng ml-1, P < 0.02; ovariectomized model controls: 35 +/- 7 ng ml-1 versus model transported 15 +/- 2 ng ml-1, P < 0.02). Subsequent exposure to progesterone for 12 days resulted in the resumption of a normal LH profile in the next follicular phase, indicating that acute stress leads to a temporary endocrine lesion. In four intact ewes transported in the mid-follicular phase, there was a suppression of LH pulse amplitude (0.9 +/- 0.3 versus 0.3 +/- 0.02 ng ml-1, P < 0.05) but a statistically significant effect on pulse frequency was not observed (2.0 +/- 0.4 versus 1.7 +/- 0.6 pulses per 2 h). In conclusion, activation of the hypothalamus-pituitary-adrenal axis by transport in the follicular phase of intact ewes interrupts surge secretion of LH, possibly by interference with LH pulsatility and, hence, follicular oestradiol production. This disruption of gonadotrophin secretion will have a major impact on fertility.

Attenuation of the estradiol-induced surge release of luteinizing hormone by antihistamine in ovariectomized ewes

Ovariectomized ewes received intramuscular (i.m.) injections of an H 1-histamine receptor antagonist, diphenhydramine, or saline during the anestrous and breeding seasons to determine if histamine may regulate the estradiol-induced surge release of LH in ewes. In addition, concentrations of histamine and GnRH in hypothalamic regions and histamine and LH in the pituitary gland were determined during the estradiol-induced surge of LH. Pretreatment mean, basal, and estradiol-induced secretion of LH did not differ ( P > 0.05) among seasons. However, the quantity of LH (ng) measured during the estradiol-induced surge of LH was less ( P < 0.05) in ewes treated with diphenhydramine (411 ± 104) than saline (747 ± 133). Treatment with diphenhydramine did not ( P > 0.05) influence steady-state concentrations of histamine in hypothalamic or pituitary gland tissues, hypothalamic concentrations of GnRH, or anterior pituitary concentrations of LH during the estradiol-induced surge of LH. It is concluded that histamine may modulate the estradiol-induced surge release of LH in ewes by affecting the secretion of GnRH.

Ovarian secretion rates and peripheral concentrations of inhibin in normal and androstenedione-immune ewes with an autotransplanted ovary

Active immunization of sheep against androstenedione results in an increase in ovulation rate that is associated with increased plasma levels of LH and progesterone, but not FSH. Although immunized ewes have more activated follicles the secretion rate of oestradiol is not increased. An experiment was conducted to examine the effect of androstenedione immunity on the ovarian secretion and peripheral plasma concentrations of inhibin. Merino ewes in which the left ovary had been autotransplanted to a site in the neck were divided into control (n = 5) and androstenedione-immune (n = 6) groups. Ovarian and jugular venous blood was collected every 10 min at two stages of the follicular phase, 21-27 h and 38-42 h after a luteolytic dose of an analogue of prostaglandin F2 alpha (PG), and every 15 min for 6 h on day 10 of the subsequent luteal phase. The ewes were monitored regularly for luteal function by measurement of the concentration of progesterone and preovulatory LH surges. The concentration of inhibin in jugular and ovarian venous plasma was determined by radioimmunoassay and ovarian secretion rates and peripheral concentrations are expressed as pg of 1-26 peptide fragment of the alpha chain. The ovarian secretion rate of inhibin tended to be greater in androstenedione-immune ewes at all stages of the oestrous cycle measured, with this difference being statistically significant (P less than 0.05) during the luteal phase (100 +/- 40 and 260 +/- 80 (S.E.M.) pg/min for control and immune groups respectively). The pattern of ovarian inhibin secretion exhibited pulsatile-like fluctuations which were not associated with LH pulses. Peripheral concentrations of inhibin were generally higher in immunized than in control ewes with this difference being significant (P less than 0.01) from day 4 to 14 of the luteal phase (59 +/- 5 and 110 +/- 7 ng/l for control and immune respectively). The ovarian secretion rate of immunoactive inhibin was greater (P less than 0.01) during the follicular phase than during the luteal phase in both groups of ewes, and peripheral concentrations of inhibin increased (P less than 0.001) following injection of PG in ewes from both treatment groups. We concluded that androstenedione immunity results in an increase in ovarian inhibin secretion, an effect that can probably be attributed to the greater number of large oestrogenic follicles present in the ovaries of these ewes.(ABSTRACT TRUNCATED AT 400 WORDS)

Luteinizing hormone in nutrient-restricted ovariectomized ewes2

This study was designed to evaluate profiles of serum concentrations of LH, pituitary content of LH and GnRH receptors, and hypothalamic content of GnRH in undernourished, ovariectomized ewes. In earlier studies, pulsatile secretion of LH diminished as duration of undernutrition progressed in prepubertal or adult ovariectomized ewes. Ewes having similar body condition scores (CS) of 5 to 9 (1 = extremely thin, 5 = moderate, 9 = obese) were fed maintenance or low-energy diets (100% and 60% of NRC requirements, respectively). Blood samples for analysis of LH were collected at 15-min intervals for 4 h at initiation of the project and immediately prior to slaughter. Serum concentrations of LH did not differ (P greater than .05) among groups at the initial sampling period. At slaughter, ewes with CS less than or equal to 2 (n = 7) had lost 26.8 kg (42% of initial weight). Ewes with CS greater than or equal to 3 (n = 12) had lost an average of 13.7 kg (18% of initial weight). Concentrations of LH in ewes with final CS greater than or equal to 3 was similar (P greater than .05) to that observed during the initial sampling period. However, release of LH was reduced (P less than .01) in ewes with CS less than or equal to 2 compared with ewes with CS greater than or equal to 3 (2.6 vs 9.5 and 3.2 vs 10.5 ng/ml for basal and mean concentrations, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of immunization against recombinant bovine inhibin α subunit on circulating concentrations of gonadotrophins in ewes

Immunization of ewes against a pure recombinant preparation of the alpha subunit of bovine inhibin (alpha-bI) resulted in a three- to fourfold increase in ovulation rate, associated with antibodies in plasma recognizing pure native 31 kDa inhibin. The aim of this study was to examine the effects of this immunization on basal and GnRH-stimulated plasma concentrations of FSH and LH in ewes during the anoestrous and breeding seasons. The groups were untreated control ewes (n = 5), control ewes treated with keyhole limpet haemocyanin (KLH alone, n = 4), ewes treated with alpha-bI alone (n = 4) and alpha-bI-KLH conjugate-treated ewes (n = 3). There were no effects of immunization on basal FSH or LH in anoestrous ewes, despite the presence of antibodies recognizing 31 kDa inhibin. In the breeding season, immunization against alpha-bI resulted in increased basal (follicular phase, P less than 0.1; luteal phase P less than 0.05) and GnRH-stimulated (follicular phase only, P less than 0.001) release of FSH, but not LH. The data are compatible with the hypotheses that the increase in ovulation rate in immunized ewes is due to an increase in circulating FSH concentrations and that inhibin may only have a major peripheral influence on FSH in sheep during the breeding season.

Effects of domperidone and thyrotropin-releasing hormone on secretion of luteinizing hormone and prolactin during the luteal phase and following induction of luteal regression in sheep

Effects of domperidone, a peripheral dopamine receptor antagonist, on secretion of LH and prolactin were studied during the luteal phase and following administration of PGF 2α. Since hyperprolactinemia has been reported to inhibit secretion of LH in ewes, effects of thyrotropin-releasing hormone (TRH) also were examined. Ewes 8–10 days post-estrus were assigned to be treated with: 1) vehicle (n=5); 2) 0.3 mg domperidone (n=6); 3) 1.0 mg domperidone (n=6); 4) 3 μg TRH (n=6); or 5) 10μg TRH (n=6) every 4 hours for 60 hr. Luteal regression was induced with PGF 2α at 12 hr after initiation of treatments. During the luteal phase, pulses of LH were more frequent (P<.05) and the amplitudes of these were higher (P<.05) in ewes treated with domperidone or TRH than in control ewes. These changes in LH occured even though each treatment elevated markedly concentrations of prolactin in plasma. After induction of luteal regression, mean of LH and frequency of LH discharges were similar in all groups. However, in ewes treated with the 1.0 mg/4 hr dose of domperidone the pulse amplitude was greater than in the other groups (2.3 vs 1.1 ng/ml). Dose-response relationships and the magnitude of the prolactin release following domperidone or TRH varied with time. Treatments did not affect the timing of the LH surge or the increase in progesterone associated with the subsequent cycle. Based on these data we conclude that: 1) endogenous hypothalamic dopamine mediates some of the inhibitory effects of progesterone on secretion of LH and prolactin; 2) dopamine limits the extent of the usual follicular phase increase in prolactin; 3) acute hyperprolactinemia does not inhibit the secretion of LH; and 4) administration of TRH can increase the frequency and amplitude of LH pulse frequency and amplitude in sheep in the luteal phase of LH in sheep.

Pituitary content of gonadotropins and receptors for gonadotropin-releasing hormone (GnRH) and hypothalamic content of GnRH during the periovulatory period of the ewe.

Studies were undertaken to determine if the number of hypophyseal receptors for GnRH changes at the time of the preovulatory surge of LH in ewes. Concentrations of LH, FSH, progesterone, and estradiol in serum and concentrations of LH and FSH in pituitary were measured. The content of GnRH in the hypothalamus was also determined. Estrus was synchronized in 35 cross-bred ewes by injecting prostaglandin F2 alpha (PGF2 alpha) at 0 and 4 h (7.5 mg each, im) on day 14 of a naturally occurring estrous cycle, followed 30 h later by the injection of estradiol (25 micrograms in safflower oil, im). Five ewes were killed at each of the following times relative to the first injection of PGF2 alpha: 0, 24, 32, 44, 50, 56 and 96 h. Blood samples were collected throughout the course of the experiment. Concentrations of progesterone in serum decreased markedly by 8 h after PGF2 alpha and were uniformly undetectable (less than 300 pg/ml) by 34 h. Concentrations of estradiol in serum increased after the injection of estradiol and returned to basal values 10 h later. Surges of LH, which were usually coincident with surges of FSH, occurred between 43 and 53 h. Concentrations of both LH and FSH in the pituitary declined after the LH surge. There were no significant changes in the amount of GnRH contained in the preoptic area, the median eminence, or the hypothalamus. The number of receptors for GnRH increased at 24 and 32 h compared to the 0 h value and remained elevated at 44 and 50 h. After the LH surge (56 h), the number of GnRH receptors declined and at 96 h was not different from the number measured at 0 h. Since an increase in the number of receptors will result in the formation of more receptor-hormone complex and may lead to an augmented response, these data suggest that an increase in the number of hypophyseal receptors for GnRH may contribute to the preovulatory LH surge in ewes.

Ovarian feedback control of follicle-stimulating hormone in the ewe: evidence for selective suppression.

The role of estradiol and progesterone in the feedback control of FSH secretion during the ovine estrous cycle was examined in three experiments. In the first, FSH was monitored in serum obtained every 4 h throughout the normal cycle. Although there was considerable variability among animals, the mean FSH concentration was elevated 1-2 days after estrus, then declined gradually to a midluteal phase nadir, and remained there until the preovulatory FSH surge on estrus. In the second study, the contribution of estradiol and progesterone to the determination of this pattern was analyzed. Ewes were ovariectomized 2 days after estrus, and the physiological pattern and level of each steroid were reproduced, alone or in combination, by sequential additions and removals of Silastic implants. None of the treatments maintained physiological concentrations of FSH, although some suppression by steroids was evident. In contrast, the time course of LH in ewes receiving estradiol plus progesterone was virtually identical to that in intact ewes. In the last study, the feedback actions of the preovulatory estradiol rise were examined by producing a variety of physiological estradiol increments under conditions which simulated the follicular phase of the cycle. Again, the estradiol rise could not account for the low basal level of FSH typical of the follicular phase, whereas basal LH was normal. A normal FSH surge, however, was reliably induced by estradiol. These results support the hypothesis that an ovarian hormone other than estradiol or progesterone contributes to the feedback control of tonic FSH secretion during the ovine estrous cycle. Further, since these two steroids can account for secretion of LH, this putative hormone most likely selectively suppress FSH.

Dynamics of luteinizing hormone release after intravenous administration of crude stalk-median eminence extract or synthetic gonadotropin-releasing hormone.

SummaryThe comparative ability of crude acidic extracts of stalk-median eminence (SME) and of synthetic Gn-RH to induce the release of LH in ewes was examined. Intravenous injections of 4 SME equiv...

Effect of continuous infusion of gonadotrophin-releasing hormone in ewes at different times of the year

Gn-RH (3 mug/hr for 8 hr) evoked a surge of LH in ewes during the anoestrous season which was of similar peak height to that found at oestrus but of shorter duration. When Gn-RH was given on 3 consecutive days, the response was considerably reduced on the 2nd and 3rd day. Follicles grew as a result of Gn-RH infusion but peripheral plasma oestrogen concentration did not increase. During the anoestrous season 9/18 ewes ovulated but only 1/6 did so at mid-anoestrus. Mature follicles or a CL were found in 15/18 ewes that had increased peripheral plasma progesterone concentrations for 1-5 days (11 ewes) or 9-14 days (4 ewes). The concentrations of progesterone found were always lower than those observed during the normal cycle. In the breeding season 10/11 ewes ovulated but there was no evidence that the induced CL were maintained.

Influence of the presence of rams on the timing of ovulation and discharge of LH in ewes.

The influence of the presence of the male on the ovulation process was investigated in ewes after oestrus control by progestagens (intravaginal fluorogestone acetate) and PMSG. Permanent contact with the rams throughout oestrus accelerates the ovulation and the appearance of the LH surge. The results suggest that the action of the presence of the male on ovulation is mediated by way of the ovulatory surge of LH.

Influence of the presence of rams on the timing of ovulation and discharge of LH in ewes

The influence of the presence of the male on the ovulation process was investigated in ewes after oestrus control by progestagens (intravaginal fluorogestone acetate) and PMSG. Permanent contact with the rams throughout oestrus accelerates the ovulation and the appearance of the LH surge. The results suggest that the action of the presence of the male on ovulation is mediated by way of the ovulatory surge of LH.

Serum LH in ewes following sequential removal of ovarian follicles, corpora lutea and stroma.

The ovary exerts a dominant influence on the secretion of gonadotrophins from the pituitary gland (Nalbandov, 1964). Ovariectomy of ewes caused an increase in serum LH and FSH (Arendarčik & Maraček, 1968; Roche, Foster, Karsch & Dziuk, 1970). The purpose of this experiment was to determine which compartments of the ovary (follicles, CL or stroma) normally maintain the basal level of LH in serum during the luteal phase of the oestrous cycle and throughout anoestrus (Roche, Foster, Karsch, Cook & Dziuk, 1970; Denamur, 1972). Twenty Grade Columbia ewes of 4 to 8 years of age were penned outdoors with `painted' vasectomized rams. Ewes were checked twice daily for marks and the day of oestrus was designated Day 0 of the oestrous cycle. The ovaries were exposed at

Serum LH in Ewes Treated with Synthetic Luteinizing Hormone-Releasing Hormone/Follicle Stimulating Hormone-Releasing Hormone (LH-RH/FSH-RH) at Three Periods of Anestrus2

Serum LH in Ewes Treated with Synthetic Luteinizing Hormone-Releasing Hormone/Follicle Stimulating Hormone-Releasing Hormone (LH-RH/FSH-RH) at Three Periods of Anestrus2