Biomedical subjects

M J Estienne

Publications and source records attributed to M J Estienne.

At least 19 recordsLinked to original sources

PubMed2005

The control of adenohypophysial hormone secretion by amino acids and peptides in swine.

Several different amino acids and peptides control secretion of adenohypophysial hormones and this control may be indirect, via the modulation of hypothalamic hormone secretion. Indeed, classical hypothalamic hormones (e.g., gonadotropin-releasing hormone [GnRH], growth hormone-releasing hormone [GHRH], somatostatin, etc.) may be released into the hypothalamo-hypophysial portal vasculature, travel to the adenohypophysis and there stimulate or inhibit secretion of hormones. Alternatively, some amino acids and peptides exert direct stimulatory or inhibitory effects on the adenohypophysis, thereby impacting hormone secretion. In swine, the most extensively studied modulators of adenohypophysial hormone secretion are the excitatory amino acids (ExAA), namely glutamate and aspartate, and the endogenous opioid peptides (EOP). In general, excitatory amino acids stimulate release of luteinizing hormone (LH), follicle-stimulating hormone (FSH), growth hormone (GH), and prolactin (PRL). Secretion of adenohypophysial hormones induced by ExAA is primarily, but perhaps not exclusively, a consequence of action at the central nervous system. By acting primarily at the level of the central nervous system, EOP inhibit LH secretion, stimulate GH release and depending on the animal model studied, exert either stimulatory or inhibitory influences on PRL secretion. However, the EOP also inhibited LH release by direct action on the adenohypophysis. More recently, peptides such as neuropeptide-Y (NPY), orexin-B, ghrelin, galanin, and substance P have been evaluated for possible roles in controlling adenohypophysial hormone secretion in swine. For example, NPY, orexin-B, and ghrelin increased basal GH secretion and modulated the GH response to GHRH, at least in part, by direct action on the adenohypophysis. Secretion of LH was stimulated by orexin-B, galanin, and substance P from porcine pituitary cells in vitro. Because the ExAA and various peptides modulate secretion of adenohypophysial hormones, these compounds may play an important role in regulating swine growth and reproduction.

Amino Acids↗

PubMed2005

Effect of P.G. 600 on the timing of ovulation in gilts treated with altrenogest.

We previously reported that ovulation rate, but not pregnancy rate or litter size at d 30 after mating, was enhanced by treatment with P.G. 600 (400 IU of PMSG and 200 IU of hCG, Intervet America, Inc., Millsboro, DE) in gilts fed the orally active progestin, altrenogest (Matrix, Intervet America, Inc.) to synchronize estrus. We hypothesized that in addition to increasing ovulation rate, P.G. 600 may have altered the timing of ovulation. Therefore, mating gilts 12 and 24 h after first detection of estrus, as is common in the swine industry, may not have been the optimal breeding regimen, and as a consequence, pregnancy rate and litter size were not altered. The objective of the present study was to determine the effect of P.G. 600 on the timing of ovulation in gilts treated with altrenogest. Randomly cycling, crossbred gilts (5.5 mo old, 117 kg BW, and 14.7 mm of backfat) were fed a diet containing altrenogest (15 mg/d) for 18 d. Twenty-four hours after altrenogest withdrawal, gilts received i.m. injections of P.G. 600 (n = 25) or saline (n = 25). Gilts were checked for estrus at 8-h intervals. After first detection of estrus, transrectal ultrasonography was performed at 8-h intervals to determine the time of ovulation. Gilts were killed 9 to 11 d after the onset of estrus to determine ovulation rate. All gilts displayed estrus by 7 d after treatment with P.G. 600 or saline. Compared with saline, P.G. 600 increased (P = 0.07) ovulation rate (14.8 vs. 17.5, respectively; SE = 1.1). The intervals from injection to estrus (110.9 vs. 98.4; SE = 2.7 h; P < 0.01) and injection to ovulation (141.9 vs. 128.6; SE = 3.2 h; P < 0.01) were greater in gilts treated with saline than in gilts treated with P.G. 600. Duration of estrus (54.4 vs. 53.7; SE = 2.5 h), the estrus-to-ovulation interval (30.2 vs. 31.7; SE = 2.2 h), and the time of ovulation as a percentage of estrus duration (55.8 vs. 57.5; SE = 3.0%) did not differ for the P.G. 600 and saline-injected gilts, respectively. In summary, P.G. 600 advanced the onset of estrus and ovulation following termination of altrenogest treatment and increased ovulation rate; however, treatment of gilts with P.G. 600 had no effect on the timing of ovulation relative to the onset of estrus.

Animal Husbandry↗

PubMed2004

Semen characteristics and libido in boars treated repeatedly with PGF2alpha.

The objective was to determine the effects of repeated injections of PGF2alpha (Lutalyse; Pfizer) on semen and libido characteristics in terminal-line boars. Semen was collected once weekly from wk 0 to 15 and on four consecutive days during wk 16. Boars received an i.m. injection of 10 mg of PGF2alpha (n = 11) or 2 mL of vehicle (n = 11) immediately before entering the collection room. For the weekly collections, semen volume (220.3 +/- 3.2 mL; mean +/- SE), gel weight (38.7 +/- 0.7 g), total sperm cells (65.4 +/- 1.2 billion), motile sperm cells (67.4 +/- 0.6 %), and sperm velocity (125.9 +/- 1.2 microm/s), were affected by time (P < 0.01) but not by treatment (P > 0.10). Sperm concentration (0.31 +/- 0.01 billion/mL) was not affected (P > 0.10) by time or treatment. The percentage of morphologically normal sperm cells, assessed at wk 16, did not differ (P = 0.39) between groups (80.8 +/- 1.0). Libido was evaluated from wk 0 to 16. There were no effects of treatment or time (P > 0.10) on the period from injection to the start of ejaculation (225.6 +/- 9.1 s). Duration of ejaculation was affected by treatment (P < 0.01; 472.0 +/- 43.1 s and 280.4 +/- 43.1 s, for PGF2alpha-treated and control boars, respectively) and time (P < 0.01). During the intensive collection period (wk 16), semen volume (200.1 +/- 7.1 mL), gel weight (39.2 +/- 1.5 g), sperm concentration (0.19 +/- 0.01 billion/ mL), total sperm cells (39.5 +/- 3.6 billion), motile sperm cells (65.6 +/- 2.2%), and sperm velocity (117.8 +/- 3.7 microm/ s) were affected by time (P < 0.10) but not by treatment (P > 0.10). The period from injection to the start of ejaculation tended to decrease (by 44%) during the intensive collection period in PGF2alpha-treated boars, but not in controls (treatment x time, P = 0.07). Regardless, the period from injection to the start of ejaculation did not differ (P = 0.63) between groups on d 4 of the intensive collection period. Duration of ejaculation was affected by treatment (P < 0.01; 459.1 +/- 24.1 s for PGF22alpha-treated boars vs. 303.1 +/- 24.1 s for controls) but not by time (P > 0.10). Overall, there were no exceptional positive or negative effects of long-term treatment with PGF2alpha on semen characteristics and libido in boars.

Animals↗

PubMed2003

Serum and milk concentrations of leptin in gilts fed a high- or low-energy diet during gestation.

Concentrations of leptin in serum and milk were assessed in gilts fed diets during gestation that differed in energy level. Beginning at day 45 and continuing throughout pregnancy, gilts received either a high-energy (6882 kcal metabolizable energy (ME) per day) or low-energy (5221 kcal ME per day) diet (n = 9 per group). All gilts had ad libitum access to a standard lactation diet throughout a 21 day lactation. During gestation, gilts consuming the high-energy diet gained more body weight (P < 0.01) and backfat thickness (P = 0.03) than gilts fed the low-energy diet; however, serum concentrations of leptin remained similar between groups (P = 0.35). Within 24 h after farrowing, gilts fed the high-energy diet had greater levels of leptin in serum and milk than gilts that consumed the low-energy diet during gestation (P < 0.07); Across treatments, backfat thickness and leptin levels in serum were positively correlated (r(2) = 0.51; P = 0.03). At weaning, backfat thickness (P < 0.07), but not body weights or serum and milk levels of leptin (P > 0.1), were greater for gilts fed the high-energy, versus the low-energy, diet during gestation. Gilts that were fed the low-energy diet during gestation consumed more feed during week 2 of lactation (P = 0.06). Our results suggest that altering the level of energy in the diets of gestating swine can influence circulating and milk concentrations of leptin, as well as feed consumption, during lactation.

Adipose Tissue↗

PubMed2001

Effects of P.G. 600 on the onset of estrus and ovulation rate in gilts treated with Regu-mate.

Three experiments assessed the onset of estrus and ovulation rate in gilts treated with gonadotropins after the withdrawal of an orally active progestin. In Exp. 1, all cycling gilts received the progestin (Regu-mate; Intervet America Inc., Millsboro, DE) at a rate of 15 mg/d for 18 d. Twenty-four hours after the last feeding of Regu-mate, 32 gilts received an i.m. injection of 400 I.U. PMSG and 200 I.U. hCG (P.G. 600, Intervet America, Inc.), and 32 gilts received an i.m. injection of deionized water. The percentage of gilts displaying estrus < or = 7 d (P = 0.64) and the injection-to-estrus interval (P = 0.37) were similar for P.G. 600-treated gilts (93.8% and 4.1 +/- 0.1 d) and controls (90.6% and 4.3 +/- 0.1 d). Ovulation rate was greater (P < 0.01) in P.G. 600-treated gilts (28.8 +/- 1.1) compared with controls (17.4 +/- 1.1). In Exp. 2, 58 cycling gilts received Regu-mate (15 mg/d) for 18 d. Twenty-four hours after Regu-mate withdrawal, gilts received i.m. P.G. 600 or water (n = 29/treatment). Gilts were bred via AI 12 and 24 h after first detection of estrus. The percentage of gilts displaying estrus < or = 7 d (P = 0.45) and the injection-to-estrus interval (P = 0.27) were similar for P.G. 600-treated gilts (82.7% and 4.0 +/- 0.1 d) and controls (89.7% and 4.2 +/- 0.1 d). Ovulation rate was greater (P < 0.01) in P.G. 600-treated gilts (26.2 +/- 1.8) compared with controls (18.1 +/- 1.7). Pregnancy rate (P = 0.71) and the number of live embryos at d 30 postmating (P = 0.40) were similar for P.G. 600-treated gilts (91.7% and 15.6 +/- 1.2) and controls (88.5% and 14.1 +/- 1.2). In Exp. 3, prepubertal gilts (142.6 +/- 0.7 d of age) received Regumate (15 mg/d) (n = 20) or a control diet not including Regu-mate (n = 20) for 18 d. Twenty-four hours after Regu-mate withdrawal, all gilts received i.m. P.G. 600. The percentage of gilts displaying estrus < or = 7 d (P = 0.49) and the P.G. 600-to-estrus interval (P = 0.69) were similar for Regu-mate-fed gilts (95% and 4.3 +/- 0.2 d) and controls (88.9% and 4.2 +/- 0.2 d). Ovulation rate was similar (P = 0.38) for Regu-mate fed gilts (16.6 +/-1.6) and controls (14.4 +/- 1.8). In cycling gilts, administration of P.G. 600 after withdrawal of Regu-mate increased ovulation rate, but not litter size at d 30 postmating. There was no beneficial effect of Regu-mate pretreatment on the response to P.G. 600 in prepubertal gilts.

Animals↗

PubMed2000

Effect of testosterone on n-methyl-d, l-aspartate-induced growth hormone secretion in male swine.

Previous research from our laboratory demonstrated that n-methyl-d, l-aspartate (NMA), a potent agonist of glutamate, increased growth hormone (GH) secretion in barrows and boars. To determine if testosterone modulates NMA-induced GH secretion, Poland China x Yorkshire swine were challenged with NMA in a model that compared GH responses in boars with those of barrows or barrows treated with testosterone propionate (TP). Boars and barrows weighing 112.6+/-1.4 kg (mean +/- SE) were fitted with indwelling jugular vein catheters. Barrows (n = 16) were given i.m. injections of TP (25 mg in corn oil) twice daily from d 0 to d 6. Boars (n = 16) and control barrows (n = 15) received twice daily injections of corn oil. On d 6, blood was sampled every 15 min for 4 h. Two h after sampling began, all animals received an i.v. injection of NMA at a dose of 2.5 mg/kg body weight. Mean testosterone concentrations (ng/ml serum) were similar (P > .1) for boars (8.1+/-0.8) and barrows receiving TP (7.3+/-0.3), but were greater in both cases (P < .05) than for barrows receiving corn oil (.2+/-.01). Prior to NMA injections, mean GH concentrations were similar (P > .1) among groups and averaged 2.7+/-.2 ng/ml serum across treatments. Serum concentrations of GH after NMA increased (P < .05) similarly among groups and averaged 6.3+/-0.3 ng/ml across treatments during the 2-h period after injection. These results were not supportive of a role for testosterone as a modulator of NMA-induced GH secretion in male swine.

Animals↗

PubMed2000

PGF2alpha facilitates the training of sexually active boars for semen collection.

The objective was to determine the effects of PGF2alpha on the training of sexually active boars (i.e., boars experienced with natural mating) to mount an artificial sow for semen collection. Boars were moved to a semen collection pen twice weekly for 4 wk. After entering the pen, boars received im treatment with 10 mg PGF2alpha (n = 7) or 2 mL deionized water (n = 7). Boars were classified as trained when after a successful collection, the animals mounted the artificial sow and allowed semen collection on the next scheduled day without first receiving an injection of PGF2alpha or deionized water. The semen from 6 of 7 PGF2alpha-treated boars and 2 of 7 control boars was collected during the first exposure to the artificial sow (P < .03). After 4 training sessions, 7 of 7 PGF2alpha-treated boars and 4 of 7 controls were successfully trained (P < .05). The number of false mounts (mounting artificial sow but not allowing semen collection) per session was lower (P < .07) for PGF2alpha-treated boars (.6 +/- 1.0), compared to boars receiving deionized water (3.9 +/- 1.0) or trained boars receiving no treatment (3.4 +/- .7). Reaction time (elapsed time after entering collection pen until the start of ejaculation) was lower (P < .04) for PGF2alpha-treated boars (267.4 +/- 63.4 sec), compared to boars treated with deionized water (628.4 +/- 98.3 sec) or boars receiving no treatment (440.4 +/- 46.4 sec). In summary, use of PGF2alpha facilitated the training of sexually active boars to mount an artificial sow for semen collection.

Animals↗

PubMed2000

Concentrations of leptin in serum and milk collected from lactating sows differing in body condition.

Leptin concentrations in the circulation and milk were determined in sows that differed in body condition at farrowing, and in feed consumption during lactation. Serum concentrations of leptin at farrowing and weaning were highest in sows exhibiting the greatest amount of backfat. Leptin was detected in both skim and whole milk throughout lactation, but levels were not correlated with backfat thickness or circulating leptin concentrations. This report provides the first evidence for the presence of leptin in sow milk; its function in the physiology of suckling pigs remains to be determined.

Adipose Tissue↗

PubMed2000

Growth performance and adipose tissue deposition in barrows fed n-methyl-D,L-aspartate.

We previously reported that broilers fed n-methyl-D,L-aspartate (NMA) exhibited enhanced feed conversion efficiency and decreased percentage of fat in carcasses. In this experiment, growth performance and backfat thickness were evaluated in barrows fed NMA. Poland China x Yorkshire barrows weighing 68.8 +/- 1.7 kg (mean +/- SE) were allowed ad libitum access to feed containing NMA at levels of either 0 (n = 7), 100 (n = 6), 200 (n = 8), or 300 (n = 8) mg/kg for 36 d. Barrows were slaughtered at 99.5 +/- 2.3 kg BW. There was no effect (P > 0.1) of NMA on ADG or feed consumption. Gain:feed ratio decreased (P < 0.03) in a linear fashion with increasing level of NMA. There was a cubic effect (P < 0.05) of NMA treatment on first-rib backfat thickness. In response to graded levels of NMA, backfat thickness at the 10th rib (P < 0.08) and last rib (P < 0.03) increased in a linear fashion. The NMA had no effect (P > 0.1) on backfat thickness measured at the lumbar vertebra or longissimus muscle area measured at the 10th rib interface. The percentage of lean in the carcass decreased in a linear fashion (P < 0.05) in response to increasing levels of NMA in the diet. In summary, NMA had an overall negative effect on growth performance and carcass yield characteristics in barrows. The dichotomous effects of NMA on feed efficiency and body composition in poultry and swine warrants further scrutiny.

Adipose Tissue↗

PubMed2000

Serum concentrations of luteinizing hormone, growth hormone, testosterone, estradiol, and leptin in boars treated with n-methyl-D,L-aspartate.

Three experiments were conducted to determine the effects of n-methyl-D,L-aspartate (NMA), an agonist of the excitatory amino acid glutamate, on secretion of hormones in boars. In Exp. 1, boars (185.0+/-.3 d of age; mean +/- SE) received i.v. injections of either 0, 1.25, 2.5, 5, or 10 mg of NMA/kg BW. There were no effects of NMA (P>.1) on secretion of LH and testosterone. Treatment with NMA, however, increased (P<.01) circulating GH concentrations in a dose-dependent manner. In Exp. 2, boars (401 d of age) received an i.v. challenge of NMA at a dose of 10 mg/kg BW or .9% saline. Treatment with NMA, but not saline (P>.1), increased serum concentrations of LH (P<.01), GH (P <.01), and testosterone (P<.06). In Exp. 3, boars that were 152, 221, or 336 d of age were treated i.v. with NMA (10 mg/kg BW). Across ages, treatment with NMA increased circulating concentrations of LH (P<.07) and testosterone (P<.01). However, NMA increased (P<.01) mean GH concentrations in only the oldest boars. Treatment with NMA had no effect (P>.1) on circulating concentrations of estradiol or leptin; however, estradiol concentrations increased (P<.03) with age. In summary, NMA increased secretion of LH, GH, and testosterone in boars. However, endocrine responses to treatment with NMA may be influenced by age of the animal. Finally, NMA did not influence circulating concentrations of estradiol or leptin.

Age Factors↗

PubMed1999

Effect of cysteamine hydrochloride on secretion of growth hormone in male swine.

The objective of this study was to determine the effect of cysteamine hydrochloride (CSH) on growth hormone (GH) secretion in male swine. Twelve Poland China x Yorkshire boars, weighing 103.4 +/- 3.0 kg and fitted with indwelling jugular vein catheters, were individually penned in an environmentally controlled room. Boars received i.v. injections of either 0, 25, 50, or 75 mg CSH/kg body weight (BW) at h 0 (n = 3/treatment). Blood samples were collected every 15 min from h 0 to h 4. Serum concentrations of GH were determined by radioimmunoassay. There was an effect of treatment (P < .05) on mean GH concentrations. Mean GH concentrations (ng/ml) were 1.97 +/- .46, 2.24 +/- .59, .91 +/- .06, and .62 +/- .08 for boars receiving 0, 25, 50, and 75 mg CSH/kg BW, respectively. The dose of CSH-mean GH response had a linear (P < .01) component. Cysteamine hydrochloride at the 75 mg/kg BW dose decreased mean GH concentrations (P < .05) compared to the 0 and 25 mg/kg BW groups. The frequency and amplitude of GH pulses were similar (P > .1) among treatments. Overall, GH pulse amplitude was 2.35 +/- .58 ng/ml and GH pulse frequency was .75 +/- .07 pulses/h. Results from this experiment indicate that CSH suppresses circulating GH concentrations in a dose dependent fashion in boars.

Animals↗

PubMed1999

Effects of N-methyl-D, L-aspartate on secretion of growth hormone-releasing hormone from the boar hypothalamic-preoptic area and median eminence in vitro.

N-methyl-D, L-aspartate (NMA) elicited secretion of growth hormone (GH)-releasing hormone from both the hypothalamic-preoptic area and the median eminence that were collected from boars. We suggest that the previously described increase in GH secretion that follows peripheral treatment of swine with NMA is attributable, at least in part, to NMA-stimulated secretion of GH-releasing hormone from the central nervous system.

Animals↗

PubMed1998

Effect of exogenous gonadotropins on the weaning-to-estrus interval in sows.

The efficacy of PG 600 (400 IU PMSG and 200 IU hCG) for accelerating the onset of estrus was determined for sows weaned during the summer. Yorkshire sows (average parity = 4.6), nursing 8.6 +/- 0.2 pigs (mean +/- SEM) were weaned after 27.7 +/- 0.4 d of lactation and were treated intramuscularly with either PG 600 (n = 35) or with 0.9% saline (n = 35). Sows were checked for estrus once daily in the presence of a mature boar. Treatment with PG 600 increased (P < 0.05) the percentage of sows in estrus within 7 d after weaning (97.1 vs 82.9%). Relative to controls, sows given PG 600 expressed estrus sooner (3.8 +/- 0.1 d vs 4.5 +/- 0.1 d; P < 0.01). Sows exhibiting estrus within 7 d after treatments were artificially inseminated 0 and 24 h after first exhibiting estrus. The percentage of inseminated sows that farrowed tended to be higher (P < 0.07) for control than for PG 600-treated sows (96.6 vs 82.3%). The number of pigs born live was similar (P > 0.1) for sows treated with PG 600 and with saline, and was 12.7 +/- 0.6 and 11.7 +/- 0.7, respectively. Pigs farrowed by saline-treated sows, however, tended to be heavier (P < 0.09) than pigs farrowed by sows treated with PG 600 (1.49 +/- 0.06 kg vs 1.34 +/- 0.06 kg). In summary, PG 600 accelerated the onset of estrus in sows weaned during the summer. Sows mated during the induced estrus, however, tended to have a lower farrowing rate and farrowed lighter pigs than control sows inseminated during a natural estrus occurring within 7 d after weaning.

Animals↗

PubMed1998

Serum concentrations of luteinizing hormone, growth hormone, and cortisol in gilts treated with N-methyl-D,L-aspartate during the estrous cycle or after ovariectomy.

The objective of this experiment was to determine the effects of n-methyl-d,l-aspartate (NMA), an agonist of the neurotransmitter glutamate, on circulating concentrations of LH, GH, and cortisol in gilts treated during the luteal (n = 4) or follicular (n = 4) phase of the estrous cycle, or after ovariectomy (n = 4). Blood was sampled every 15 min for 10 h on each of two consecutive days. On the 1st d, two gilts from each group received i.v. injections of NMA (10 mg/kg BW) at h 4 and 6, and the remaining gilts received .9% saline (vehicle). The following day, gilts that had received NMA on the 1st d received vehicle, and gilts that had received vehicle on d 1 received NMA. All gilts received an i.v. challenge of GnRH (.1 microg/kg BW) at h 8 on each day. The NMA treatment increased (P < .01) LH pulse frequency in luteal-phase gilts by 125%. In contrast, NMA decreased (P < .05) mean concentrations of LH by 48% and suppressed (P < .01) LH pulse frequency by 33% in ovariectomized gilts. No characteristics of LH secretion were affected (P > .05) by NMA in follicular phase gilts. Serum LH concentrations for the 2-h period following GnRH were lower (P < .05) in follicular-phase gilts than in ovariectomized gilts and were 1.15 +/- .09 (mean +/- SE), .81 +/- .05, and .51 +/- .17 ng/mL for ovariectomized, luteal-phase, and follicular-phase gilts, respectively. Treatment with NMA increased circulating concentrations of GH by 334% (P < .01) and cortisol by 77% (P < .03) in all gilts. We suggest that the effects of NMA on LH release in gilts depend on the circulating steroidal milieu. In contrast, NMA evokes secretion of GH and cortisol irrespective of the reproductive status of treated gilts.

Animals↗

PubMed1997

Role of neuropeptides and amino acids in controlling secretion of hormones from the anterior pituitary gland in pigs.

All reproductive processes involve one or more of the protein hormones secreted from the anterior pituitary gland: LH, FSH, prolactin, growth hormone, ACTH and thyroid-stimulating hormone (TSH). Primary hormones of reproduction, such as LH and FSH, directly regulate a reproductive activity. For example, LH and FSH stimulate follicular growth and the associated secretion of oestradiol in sows. In contrast, secondary hormones of reproduction such as TSH are permissive and regulate other physiological systems that indirectly, but profoundly, influence reproduction. Reproduction in pigs can be enhanced by developing strategies to alter and control secretion of hormones from the anterior pituitary gland. However, the successful manipulation of adenohypophysial hormone secretion will require a sound understanding of the mechanisms controlling the function of the hypothalamic-pituitary axis. Hypothalamic hormones including GnRH, dopamine, growth hormone-releasing hormone (GHRH), somatostatin, corticotrophin-releasing hormone (CRH) and thyrotrophin-releasing hormone (TRH) are synthesized in perikarya that possess axons that terminate at the median eminence. These hormones are released into the hypothalamo-hypophysial portal vasculature, travel to the anterior pituitary gland and stimulate or inhibit secretion of adenohypophysial hormones. Secretion of hypothalamic hormones is ultimately controlled by a variety of neurotransmitters and neuropeptides, the most studied in swine being the endogenous opioid peptides (EOP) and more recently, the excitatory amino acids (ExAA). In general, EOP inhibit GnRH and hence LH secretion, and this effect involves the central catecholaminergic system. A definitive role for EOP in the modulation of FSH release remains to be determined. EOP stimulate secretion of GHRH and thus growth hormone release, and depending on the animal model studied, EOP exert either stimulatory or inhibitory influences on prolactin secretion. ExAA, working via N-methyl-D-aspartate (NMDA) receptors at the central nervous system, stimulate secretion of LH, FSH, growth hormone and prolactin in appropriate animal models. However, in certain situations, an inhibitory effect of ExAA on LH secretion has been demonstrated. The modulation of growth hormone and prolactin secretion by ExAA involves EOP. Research investigating the function of ExAA and EOP in the physiological control of swine reproduction warrants further scrutiny.

Animals↗

PubMed1996

N-methyl-D,L-aspartate-induced growth hormone secretion in barrows: possible mechanisms of action.

Four experiments were conducted to determine mechanisms by which n-methyl-d,l-aspartate (NMA) increases serum concentrations of growth hormone (GH). Blood samples were collected from barrows every 15 min for 2 h (Exp. 1, 2, and 3) or 3 h (Exp. 4) immediately before and immediately after i.v. treatments. In Exp. 1, barrows (n = 4/treatment) received either .9% saline or 1.25, 2.5, or 5 mg of NMA/kg of BW. The change in circulating GH concentrations was greater (P < .05) for barrows receiving 2.5 mg (by 883%) or 5.0 mg of NMA/kg of BW (by 1,095%) than for those injected with saline. In Exp. 2, barrows (n = 4/treatment) received NMA (2.5 mg/kg of BW) or injections of 1.25 mg of the pure d or pure 1 isomers of NMA/kg of BW. Growth hormone concentrations increased by 177% (P < .025) after NMA treatment and by 245% (P < .01) after injection of the pure d isomer of NMA. The pure 1 isomer of NMA had no effect (P > .1) on GH concentrations. In Exp. 3, barrows received NMA (2.5 mg/kg of BW) 10 min after i.m. injection of saline (n = 7) or ketamine hydrochloride ( n = 8; 19.9 mg/kg of BW), an n-methyl-d-aspartate (NMDA) receptor antagonist. The NMA increased (P < .01) GH concentrations by 289% in saline-pretreated barrows but had no effect (P > .1) on barrows pretreated with ketamine hydrochloride. In Exp. 4, barrows (n = 4/treatment) received NMA 3 h after i.v. pretreatment with antisera to GH-releasing factor (GRF; 154 mL) or no pretreatment. Serum GH concentrations increased by 166% (P < .05) after injection of NMA in barrows receiving no pretreatment. The NMA had no effect (P > .1) on GH concentrations in barrows receiving antisera to GRF. Our results support the concept that NMDA stimulates GRF, and hence GH secretion, by activating an NMDA receptor.

Animals↗

PubMed1996

The role of excitatory amino acids in pulsatile secretion of luteinizing hormone in gilts and barrows.

The relationship of excitatory amino acid (EAA) activity to LH secretion was investigated in ovariectomized crossbred prepuberal gilts (93 +/- 1 kg BW) and Yorkshire barrows (94 +/- 2 kg BW) in two experiments. In Exp. 1, eight gilts received, i.m., saline (S) or 20 mg of Ketamine (K)/kg BW, a noncompetitive EAA receptor antagonist. Within these groups, four then received 10 mg of N-methyl-DL-aspartate (NMA)/kg BW, an EAA agonist, or S i.v. Mean serum LH concentrations were similar among groups before treatment, did not change after S+S, but decreased (P < .05) by 1 h after S+NMA, 3 h after K+S, and 2 h after K+NMA. Serum cortisol concentrations did not change after S+S, but were increased (P < .05) from 30 to 90 min after S+NMA, at 120 min after K+S, and from 30 to 120 min after K+NMA. In Exp. 2, barrows received 2.5 mg of NMA/kg BW i.v. immediately after i.m. injection of S (n = 7) or 19.9 mg of K/kg BW (n = 8). Mean serum LH concentrations for the 2 h before treatment were similar among barrows, but decreased (P < .05) by 2 h after K+NMA and was not altered after S+NMA. Serum cortisol concentrations were increased at 30 min after S+NMA and from 60 to 90 min after K+NMA. We suggest that EAA both inhibit and stimulate LH secretion, with the inhibitory effects lying within the basal hypothalamus and the stimulatory effects lying within higher brain centers.

Animals↗

PubMed1995

Luteinizing hormone and growth hormone concentrations in serum of prepubertal gilts treated with N-methyl-D,L-aspartate.

Prepubertal Yorkshire gilts, 189 d of age and 96 kg body weight (BW), were used to determine the effects of intravenous injections of N-methyl-D,L-aspartate (NMA) on circulating concentrations of luteinizing hormone (LH) and growth hormone (GH). In Experiment 1, blood was sampled from four gilts every 15 min for 2 hr on four consecutive days. One hour after the initiation of sampling on each day, gilts received either vehicle (0.9% saline solution) or 1.25, 2.5, or 5 mg of NMA/kg BW as per a 4 x 4 latin square arrangement of treatments. There was no effect of treatment (P > 0.1) on concentrations of LH in serum. However, relative to vehicle-treated animals, gilts administered 2.5 mg of NMA/kg BW had elevated (1,120%; P < 0.05) circulating levels of GH. In Experiment 2, samples were collected from 15 gilts at 15-min intervals for 1 hr before and 1 hr after NMA (10 mg/kg BW; n = 8) or vehicle (n = 7). NMA increased serum concentrations of both LH (by 80%; P < 0.05) and GH (by 700%; P < 0.01). We suggest that LH and GH secretion in gilts was enhanced by treatment with NMA.

Animals↗