Effect of adrenocorticotrophic hormone (ACTH1-24) on ovine pituitary gland responsiveness to exogenous pulsatile GnRH and oestradiol-induced LH release in vivo

Regulation of stress response on the hypothalamic-pituitary-gonadal axis via gonadotropin-inhibitory hormone

Under stressful condition, reproductive function is impaired due to the activation of various components of the hypothalamic-pituitaryadrenal (HPA) axis, which can suppress the activity of the hypothalamic-pituitary-gonadal (HPG) axis at multiple levels. A hypothalamic neuropeptide, gonadotropin-inhibitory hormone (GnIH) is a key negative regulator of reproduction that governs the HPG axis. Converging lines of evidence have suggested that different stress types and their duration, such as physical or psychological, and acute or chronic, can modulate the GnIH system. To clarify the sensitivity and reactivity of the GnIH system in response to stress, we summarize and critically review the available studies that investigated the effects of various stressors, such as restraint, nutritional/metabolic and social stress, on GnIH expression and/or its neuronal activity leading to altered HPG action. In this review, we focus on GnIH as the potential novel mediator responsible for stress-induced reproductive dysfunction.

Cattle stress and pregnancy responses when imposing different restraint methods for conducting fixed time artificial insemination

Physiological stress responses have been associated with lesser pregnancy rates in beef cattle. Alternative cattle restraint methods have been developed to reduce this negative effect. The objective was to determine if there was a difference in pregnancy rate as a result of fixed-time artificial insemination (FTAI) in Bos taurus females when using a breeding box compared with a squeeze chute for restraining cows when conducting FTAI. There were FTAI treatment regimens imposed on cows and heifers at two separate locations (Virginia Tech University, VT; and R.A. Brown Ranch, RAB) with the FTAI being conducted while animals were restrained in a squeeze chute (n = 169) or a breeding box (n = 162). There was imposing of a 7-day Co-Sync + CIDR pre-breeding treatment regimen. Females were randomly assigned to treatments just prior to breeding. Immediately following breeding, blood was collected using coccygeal venipuncture procedures for assessment of plasma cortisol concentration. Chute and exit scores (1-5) were determined at the time of FTAI. Pregnancy rate, cortisol, chute score, and exit score were analyzed. There was no difference in pregnancy rate between treatments (57 ± 26% and 69 ± 26 %, respectively P = 0.59).There were differences in chute (1.52 ± 0.05 and 1.27 ± 0.05, respectively P < 0.05) and exit (1.26 ± 0.04 and 1.08 ± 0.04, respectively P < 0.05) scores between the two treatment groups. Results from the present study are not conclusive in ascertaining effects of the two types of restraint during FTAI on reproductive efficiency.

Understanding the trade-off between the environment and fertility in cows and ewes

The environment contributes to production diseases that in turn badly affect cow performance, fertility and culling. Oestrus intensity is lower in lame cows, and in all cows 26% potential oestrus events are not expressed (to avoid getting pregnant). To understand these trade-offs, we need to know how animals react to their environment and how the environment influences hypothalamus-pituitary-adrenal axis (HPA) interactions with the hypothalamus-pituitary-ovarian axis (HPO). Neurotransmitters control secretion of GnRH into hypophyseal portal blood. GnRH/LH pulse amplitude and frequency drive oestradiol production, culminating in oestrus behaviour and a precisely-timed GnRH/LH surge, all of which are disrupted by poor environments. Responses to peripheral neuronal agents give clues about mechanisms, but do these drugs alter perception of stimuli, or suppress consequent responses? In vitro studies confirm some neuronal interactions between the HPA and HPO; and immuno-histochemistry clarifies the location and sequence of inter-neurone activity within the brain. In both species, exogenous corticoids, ACTH and/or CRH act at the pituitary (reduce LH release by GnRH), and hypothalamus (lower GnRH pulse frequency and delay surge release). This requires inter-neurones as GnRH cells do not have receptors for HPA compounds. There are two (simultaneous, therefore fail-safe?) pathways for CRH suppression of GnRH release via CRH-Receptors: one being the regulation of kisspeptin/dynorphin and other cell types in the hypothalamus, and the other being the direct contact between CRH and GnRH cell terminals in the median eminence. When we domesticate animals, we must provide the best possible environment otherwise animals trade-off with lower production, less intense oestrus behaviour, and impaired fertility. Avoiding life-time peri-parturient problems by managing persistent lactations in cows may be a worthy trade-off on both welfare and economic terms – better than the camouflage use of drugs/hormones/feed additives/intricate technologies? In the long term, getting animals and environment in a more harmonious balance is the ultimate strategy.

Zebrafish: A Versatile Animal Model for Fertility Research

The utilization of zebrafish in biomedical research is very common in the research world nowadays. Today, it has emerged as a favored vertebrate organism for the research in science of reproduction. There is a significant growth in amount numbers of scientific literature pertaining to research discoveries in reproductive sciences in zebrafish. It has implied the importance of zebrafish in this particular field of research. In essence, the current available literature has covered from the very specific brain region or neurons of zebrafish, which are responsible for reproductive regulation, until the gonadal level of the animal. The discoveries and findings have proven that this small animal is sharing a very close/similar reproductive system with mammals. More interestingly, the behavioral characteristics and along with the establishment of animal courtship behavior categorization in zebrafish have laid an even stronger foundation and firmer reason on the suitability of zebrafish utilization in research of reproductive sciences. In view of the immense importance of this small animal for the development of reproductive sciences, this review aimed at compiling and describing the proximate close similarity of reproductive regulation on zebrafish and human along with factors contributing to the infertility, showing its versatility and its potential usage for fertility research.

Direct actions of ACTH on ovarian function of pseudopregnant rabbits

The present study sought to assess whether the receptors for adrenocorticotropic hormone (ACTH), MC2R, and for glucocorticoid (GR) are expressed in corpora lutea (CL) of pseudopregnant rabbits and whether ACTH and cortisol exert any direct action on luteal function. By immunohistochemistry, positive reaction for MC2R and GR was detectable within luteal cells of CL. The MC2R mRNA levels were five-fold less abundant in day 9 than in day 4 CL (P<0.01). At both stages, ACTH agonist (ACTH 1-24) increased progesterone and prostaglandin (PG) E(2) (PGE(2)) (P<0.01), but reduced PGF(2α) releases (P<0.01) in vitro. ACTH 1-24 injection increased plasma cortisol levels within 4h (P<0.01), but decreased (P<0.01) progesterone 24h later and for the following two days. ACTH administration to estrous rabbits caused a transitory increase in blood progesterone concentrations (P<0.01). Daily injections of ACTH did not modify progesterone profile following ovulation. In conclusion, ACTH directly up-regulates CL progesterone production in vitro via MC2R, but indirectly hampers luteal function via cortisol-GR associated mechanism.

Role of urocortin 2 secreted by the pituitary in the stress-induced suppression of luteinizing hormone secretion in rats

We have previously shown that urocortin 2 (Ucn 2), a member of the corticotropin-releasing factor (CRF) peptide family that binds to CRF type 2 receptor, is expressed in proopiomelanocortin (POMC) cells of rat pituitary and that its secretion and expression are increased by CRF in both the anterior and intermediate lobes and suppressed by glucocorticoids in the anterior lobe. We have also shown that Ucn 2 secreted by POMC cells acts on gonadotrophs expressing CRF type 2 receptors and inhibits the expression and secretion of gonadotropins. In the present study, we examined whether pituitary Ucn 2 is involved in stress-induced inhibition of gonadotropin secretion. A 90-min period of immobilization stress increased POMC mRNA expression without influencing Ucn 2 mRNA expression and suppressed luteinizing hormone (LH) β-subunit mRNA expression in the anterior lobe and plasma LH levels, while it increased both POMC and Ucn 2 mRNA expression in the intermediate lobe of the pituitary. Pretreatment with anti-CRF IgG blocked immobilization-induced increases in plasma ACTH and corticosterone and in POMC mRNA expression in both pituitary lobes and Ucn 2 mRNA expression in the intermediate pituitary. It also blocked immobilization-induced suppression of plasma LH and LH β-subunit mRNA expression. Pretreatment with anti-Ucn 2 IgG blocked immobilization-induced suppression of plasma LH and LH β-subunit expression without affecting immobilization-induced ACTH and corticosterone release and POMC or Ucn 2 mRNA expression. These results suggest that CRF suppresses the secretion and expression of LH probably through pituitary Ucn 2 in stress.

Sexual motivation in relation to social rank in pair-housed sows

The influence of social subordination on sexual motivation during oestrus was studied using 36 sows of which 24 treatment sows were housed in pairs and 12 control sows were housed individually in 12 and 6 m(2) pens, respectively. Video recordings were made from 07:00 h to 19:00 h during the first 2 days after grouping, which took place 3 days after weaning of the piglets. Based on the aggressive interactions between the pair-housed sows, their rank was determined. From day 4 after weaning, a test for sexual proceptive behaviour was carried out twice daily and back-pressure test was carried out four times daily in order to detect standing oestrus. When standing oestrus had occurred, transrectal ultrasonographical scans were also carried out in order to determine if ovulation took place. The proceptivity test took place in a T-maze with a 2 m x 10 m runway ending in two 1.5 m x 1.5 m goal boxes each adjacent to a stimulus compartment. One compartment contained an adult sexually experienced boar and the other was empty. Latency to and duration of time spent close to the boar and time spent presenting were recorded during the 10-min test period. On the first day that standing oestrus had been detected, a test for sexual receptivity was also carried out by introducing the sow to a mature boar in his home pen (9 m(2)). Sexual- and fear-related behaviour of sow and boar were recorded until mating was terminated or the sow had spent 5 min in the pen without mating being initiated. During oestrus the proceptivity test showed a significant increase (P < 0.05) in the time spent standing close to the boar and in presenting for single-housed sows and for pair-housed dominant sows, but not for subordinate sows. During oestrus subordinate sows spent significantly less time standing close to the boar than the dominant sows (P = 0.01) and the same tended to be the case for presenting (P = 0.07). In the receptivity test more subordinate sows than dominant sows fled (40% versus 0%, P = 0.001) and more subordinate sows than dominant sows squealed (58% versus 15%, P = 0.02) as a response to boar stimulation. In both tests, the single-housed sows differed neither from the dominant nor the subordinate sows. There was however no difference between the groups in the weaning to oestrous interval, duration of oestrus and number of piglet born. In addition, all the sows ovulated. The results indicate that social subordination can have significant consequences for sexual motivation in sows. Subordinate sows showed fear-related behaviour in response to boar stimulation even when they were in standing oestrus. Thus, both heat detection and mating may be impaired in subordinate sows. The results emphasise the importance to alleviate the social stress experienced by subordinates as well as the need for stock people to pay special attention to these animals when they are to be mated or inseminated.

The role of LH pulse frequency in ACTH-induced ovarian follicular cysts in heifers

The aim of the present study was to induce ovarian cysts experimentally in cattle using ACTH and to closely examine the role of LH pulse frequency in ovarian cyst formation. Five regularly cycling Holstein-Friesian heifers (15-18-month-old) were used. Ovaries were scanned daily using an ultrasound scanner with a 7.5 MHz rectal transducer. Daily blood samples were obtained via tail venepuncture for hormone analyses. Additional blood samples (for FSH and LH pulses) were obtained through an indwelling jugular vein catheters every 15 min for 8 h on Days 2 (early luteal phase; ELP), 12 (mid-luteal phase; MLP) and 19 (follicular phase; FP) of control estrous cycle and on alternate days during follicular cyst (FC) formation and persistence. Cysts were induced using subcutaneous injections of ACTH (Cortrosyn) Z; 1 mg) every 12 h for 7 days beginning on Day 15 of the subsequent estrous cycle. Plasma concentrations of progesterone (P4), estradiol-17beta, FSH and LH were determined by double antibody radioimmunoassay while cortisol concentration was determined by enzyme immunoassay (EIA). Ovarian follicular and endocrine dynamics were normal during the control estrous cycles. Ovarian follicular cysts were induced in four of the five heifers. Mean maximum size of cysts was larger (P<0.05) than that of ovulatory follicles (26.78+/-3.65 versus 14.1+/-0.90 mm), respectively. Cortisol levels were increased during ACTH treatment. High concentrations of estradiol and low progesterone were observed after cyst formation. LH pulse frequency was significantly reduced (P<0.05) during cyst formation and persistence compared to ELP (7.5+/-0.75) and FP (6.5+/-0.58), but was not significantly (P=0.23) different from MLP (2.8+/-0.29) pulses. Mean LH pulse amplitude and concentrations were not different. Similarly, the mean pulse frequency, amplitude and concentration of FSH were not different between control study and cystic heifers. These results suggest that the LH pulse frequency observed following ACTH treatment may interact with high estradiol concentration to induce ovarian cyst formation in heifers.

What is stress, and how does it affect reproduction?

Stress is revealed by the inability of an animal to cope with its environment, a phenomenon that is often reflected in a failure to achieve genetic potential. Field data from dairy cows show that stressors such as milk fever or lameness increase the calving to conception interval by 13-14 days, and an extra 0.5 inseminations are required per conception. We suggest that a variety of endocrine regulatory points exist whereby stress limits the efficiency of reproduction. Transport produces an immediate constant increase in arginine vasopressin (AVP) and corticotrophin-releasing hormone (CRH) secretion in ewes, but adrenocorticotrophic hormone (ACTH) reaches a maximum in the first hour while cortisol is highest during the second hour. In contrast, after an insulin injection, the hypothalamo-pituitary-adrenal (HPA) response is delayed occurring only after glucose decreases below a threshold. Changes in AVP, CRH and ACTH each follow a similar time course, but eventually the secretion of AVP and CRH decreases while glucose is still at a nadir. Negative feedback effects appear to operate mainly at the pituitary level during transport but at the hypothalamus during hypoglycaemia. We also have endocrine evidence to show that stressors interfere with precise timings of reproductive hormone release within the follicular phase. Transport, or insulin, reduce the frequency and amplitude of gonadotrophin-releasing hormone and LH pulses, suggesting that these stressors exert effects at the hypothalamus or higher centres in the brain. Both stressors also delay the onset of the luteinising hormone (LH) surge. Preliminary results suggest that opioids mediate these effects but progesterone/glucocorticoid receptors are not involved because the antagonist, RU486, is unable to reverse insulin-induced delays in the LH surge. There is also evidence to support effects at pituitary level because exogenous ACTH, or transport, reduce the amount of LH released by challenges with GnRH. The reduction in endogenous GnRH/LH secretion ultimately deprives the ovarian follicle of adequate gonadotrophin support leading to reduced oestradiol production by slower growing follicles. Thus, there is a level of interference by stressors at the ovary. Reproduction is such an important physiological system that animals have to ensure that they can respond to their surroundings; thus, it is advantageous to have several protein mechanisms, i.e. at higher brain, hypothalamus, pituitary and target gland levels. However, when pushed too far, subfertility occurs.