Jeffrey D. Armstrong

Effect of feed restriction on serum somatotropin, insulin-like growth factor-I-(IGF-I) and IGF binding proteins in cyclic heifers actively immunized against growth hormone releasing factor☆

Feed restriction often increases serum somatotropin (ST) and decreases insulin-like growth factor-I (IGF-I) in ruminants; however, the mechanisms responsible for this change in ST and IGF-I are not well defined. We investigated the effects of feed restriction on serum ST, IGF-I, IGF binding proteins (IGFBP), insulin and nonesterified fatty acids (NEFA) in cyclic Angus and Charolais heifers (n = 15) previously immunized against growth hormone releasing factor (GRFi) or human serum albumin (HSAi). Cows were fed a concentrate diet ad libitum (AL) or were restricted to 2 kg cotton seed hulls (R) for 4 d. Each heifer received each dietary treatment in a single reversal design. As anticipated, GRFi decreased ST, IGF-I and insulin (P < .05). In addition, GRFi decreased serum IGFBP-3 (P < .01), but increased IGFBP-2 (P < .01). Feed restriction resulted in an increase in serum ST in HSAi, but not in GRFi heifers. Regardless of immunization treatment, feed restriction decreased serum IGF-I and insulin, and increased NEFA (P < .01). In conclusion, the increase in serum ST levels observed during feed restriction was blocked by active immunization against GRF. However, feed restriction resulted in decreased serum IGF-I in GRFi heifers in spite of initial low levels of IGF-I (due to GRFi). Although GRFi decreased levels of IGFBP-3 and increased levels of IGFBP-2, feed restriction for 4 d did not alter serum IGFBP.

Aspartate and glutamate modulation of growth hormone secretion in the pig: Possible site of action

The influence of excitatory amino acids (EAA) on growth hormone (GH) secretion and the possible site of action was investigated in the pig. In Experiment (Exp) I three replicates were conducted with 30 prepuberal gilts, 130 d of age and averaging 70.6 +/- 1.3 kg body weight (BW). Six gilts each received intravenously (i.v.) 0, 50, 100, or 150 mg/kg BW of aspartate (ASP) or glutamate (GLU) in saline. Blood samples were collected every 15 min for 2 hr before and 3 hr after treatment. In Exp II, mature ovariectomized gilts (163 +/- 10 kg BW) that had been immunized against growth hormone releasing factor (GRF) conjugated to human serum albumin (GRFi; n = 4) or against human serum albumin alone (HSAi; n = 5) received 150 mg/kg BW ASP or GLU i.v. in a 2 x 2 factorial arrangement of treatments, which was then repeated in a crossover design. One week later, all animals received 10 mg/kg N-methyl-D,L-aspartate (NMA; EAA agonist) in saline i.v. Blood samples were collected as described above. In Exp III, cultures of anterior pituitary cells from market-weight (averaging 105 kg BW) gilts were studied. On Day 4 of culture, cells (10(5) seeded/well) were challenged with 10(-8), 10(-6), or 10(-4) M ASP or GLU, 10(-6) M [Ala15]-human GRF (1-29)-NH2, or the EAA antagonist, 2-amino-5-phosphonopentanoic acid (10(-4) M; AP5), alone or in combination with ASP or GLU. In Exp I, all doses of ASP and the 100- and 150-mg doses of GLU increased (P < 0.05) GH secretion when compared with Time 0. However, serum GH concentrations were higher (P < 0.01) after 150 mg/kg of ASP when compared with those after 150 mg/kg of GLU. In Exp II, serum GH concentrations increased (P < 0.05) in HSAi but not in GRFi pigs (averaging 1.2 +/- 0.2 ng/ml before and 8.2 +/- 0.7, 6.3 +/- 0.5, and 9.2 +/- 0.5 ng/ml by 15 min after ASP, GLU, and NMA, respectively). In Exp III, relative to controls (40 +/- 6 ng/ml), GH increased (P < 0.05)1.6-, 1.9-, and 1.9-fold and 1.7-, 1.8-, and 2.0-fold after 10(-8), 10(-6), and 10(-4) M ASP and GLU, respectively. The EAA receptor antagonist AP5 failed to prevent the GH response to ASP or GLU, except for 10(-8) M ASP. In summary, ASP is a more potent secretagogue of GH secretion than is GLU in vivo, whereas each is equipotent in vitro. Because no stimulation of GH by EAA was observed in GRFi pigs and no specific dose-response effect of EAA was found in vitro, it may be concluded that modulation by EAA is mediated primarily at the level of the hypothalamus or higher brain centers.

Absence of a nocturnal rise in either norepinephrine, N-acetyltransferase, hydroxyindole-O-methyltransferase or melatonin in the pineal gland of the domestic pig kept under natural environment photoperiods

Castrated male and intact female pigs were kept under natural photoperiodic and temperature conditions and were killed over a 24 h period in either May (under long days) or in December (under short days). Neither the pineal norepinephrine (NE) concentration nor the melatonin content rose at night; likewise, neither the activities of N-acetyltransferase (NAT) nor hydroxyindole-O-methyltransferase (HIOMT) increased during darkness. In May pineal melatonin content actually decreased (P less than 0.05) at night while in December NAT activity fell (P less than 0.05) at night. Daytime levels of each of these variables were equivalent to those measured in other species. The absence of a nocturnal increase in pineal melatonin production in either May or December raises the possibility that pineal melatonin may be involved in regulating seasonal breeding in the pig in a manner different from other mammals. Alternatively, pineal melatonin production may be unrelated to seasonal reproduction in the pig.

Opioid control of growth hormone in the suckled sow is primarily mediated through growth hormone releasing factor.

Endogenous opioid peptides mediate the effect of suckling on LH and PRL in the domestic pig. However, the role of opioids in modulating GH during lactation in swine is not known. Primiparous sows that had been immunized against GRF(1-29) conjugated to human serum albumin (GRF-HSA, n = 5) or HSA (n = 4) were used to determine changes in GH after naloxone. Treatments were imposed in all sows on day 21 of lactation when antibody titers were 9100 +/- 1629. All sows received (i.v.) naloxone (0.25 mg/kg) or saline (0.0125 ml/kg) at 15 min intervals for 165 min. Active immunization against GRF-HSA during lactation decreased (P less than 0.05) mean concentration (4.8 +/- 0.2 vs 2.6 +/- 0.1 ng/ml) and frequency (1.5 +/- 0.3 vs 0.4 +/- 0.2 peaks/4 hr). Concentrations of LH and PRL were similar in GRF-HSA and HSA immunized sows. Naloxone suppressed (P less than 0.05) GH in all sows. In HSA sows, naloxone abolished episodic release of GH and decreased average, but not basal, concentrations of GH. In sows immunized against GRF-HSA, naloxone decreased (P less than 0.05) average and basal GH but failed to decrease frequency of GH release. Naloxone failed to alter frequency of LH release. Concentrations of PRL decreased (P less than 0.05) after naloxone in all sows. In conclusion, immunization against GRF-HSA blocked most of the effect of lactation on GH. Blocking opioid receptors with naloxone decreased GH and PRL in all sows. In contrast to previous findings naloxone had no effect on LH. Opioids alter concentrations of GH through a GRF dependent and GRF independent pathway.

Effect of active immunization against growth hormone releasing factor on concentrations of somatotropin and insulin-like growth factor I in lactating beef cows.

Two experiments were conducted to determine the effects of immunoneutralization of growth hormone-releasing factor [GRF(1-29)-NH2] on concentrations of somatotropin (ST) and insulin-like growth factor I (IGF-I) in lactating beef cows. In Experiment 1, multiparous Hereford cows were immunized against 2 mg GRF(1-29)-(Gly)4-Cys-NH2 conjugated to human serum albumin (GRFi, n = 3) or 2 mg human serum albumin (HSAi, n = 3) at 52 +/- 1 d prior to parturition. Boosters (1 mg) were administered on days 12, 40 and 114 postpartum (pp). Serum samples were collected at 15-min intervals for 5 hr on days 18, 46 and 120 pp, followed by administration (IV) of an opioid agonist (FK33-824; 10 micrograms/kg) and an antagonist (naloxone; .5 mg/kg) at hours 5 and 7, respectively. A GRF-analog ([desamino-Tyr1, D-Ala2, Ala15] GRF (1-29)-NH2; 3.5 micrograms/kg) and arginine (.5 g/kg) were administered at hour 10 on days 47 and 121, respectively. Percentage binding of [125I]GRF (1:100 dilution of serum) 28 d after primary immunization was greater in GRFi (14.3 +/- 4.9) than in HSAi (.7 +/- .3) cows. Binding increased to 29.3 +/- 6.5% after first booster in GRFi cows. Episodic release of ST was abolished by immunization against GRF; concentration and frequency of release of ST were lower (P less than .05) in GRFi than in HSAi cows on all days pp. Concentrations of IGF-I were lower in GRFi than in HSAi cows throughout lactation. Serum ST failed to increase following FK33-824 or arginine in GRFi; however, ST increased after both compounds in HSAi cows. Concentrations of ST following GRF-analog were greater (P less than .05) in HSAi than in GRFi cows. Experiment 2 was conducted to determine if a lower dose of antigen and a single booster would be sufficient to lower ST and IGF-I in lactating cows. Multiparous Hereford and Angus cows were assigned to GRFi (n = 6) or HSAi (n = 6). Primary (1.2 mg) and booster (.5 mg) immunizations were administered -14 and 8 d from calving, respectively. Cows were restricted to 60% of recommended intake of energy during lactation in order to elevate concentrations of ST. Serum samples were collected at 15-min intervals for 6 hr on days 26, 50, 73, 90 and 109 pp. Two of six GRFi cows had binding less than 10% (1:1,000 dilution of serum) and were omitted from further analyses.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in the hypothalamic-hypophyseal-ovarian axis of primiparous sows following weaning or pulsatile gonadotropin releasing homrone administration and weaning

Lactating primiparous sows were used to examine relationships among hypothalamic gonadotropin releasing hormone (GnRH), serum, and anterior pituitary gonadotropins and follicular development after weaning or after administering GnRH pulses (1.5 ug) once hourly for 72 h before weaning. Control sows were either slaughtered at 0 or 72 h after weaning or were cannulated for collection of blood samples until 24 h after estrus. Sows pulsed with GnRH were either slaughtered 72 h after beginning of GnRH treatment or were cannulated for collection of blood samples until 24 h after estrus. Exogenous GnRH pulsed hourly during 72 h prior to weaning stimulated follicular growth as demonstrated by an increase in number of surface follicles >5 mm in diameter and a decrease in number of follicles <5 mm in diameter. Interval (h) from weaning to an increase in estradiol (>16 pg/ml) was less in GnRH-pulsed than in control sows (P < 0.05), but hours from weaning to estrus were similar between groups. Amounts of GnRH in the medial basal hypothalamus (MBH), stalk median eminence (SME), and hypophyseal portal area (HPA) were similar among control sows killed at 0 or 72 h and sows pulsed with GnRH. Serum concentrations of luteinizing hormone (LH) and frequency of release of LH were similar between GnRH-pulsed and control sows, but concentrations of LH and follicle stimulating hormone (FSH) in anterior pituitary were lower in GnRH-pulsed sows than control sows. Administration of GnRH for 72 h prior to weaning in primiparous sows stimulated follicular growth as manifested by increased secretion of estrogen; however, the amount of follicular growth was apparently inadequate to hasten the onset of estrus after weaning.

Influence of follicular ablation during lactation on postweaning interval to estrus, ovulation rate, and endocrine function in sows

Duroc sows farrowed second litters in March and lactated 35 +/- 2 days. At 36 hr before weaning, electrocautery of follicles greater than or equal to 3 mm in diameter (n = 8) or sham surgery (n = 5) was performed to test the hypothesis that ablation of medium-sized follicles would prolong the duration of postweaning anestrus. Number of follicles and diameters at surgery were: 1.3 +/- .6 (greater than 5 mm diameter), 26 +/- 1 (3 to 5 mm) and greater than 20 (less than 3 mm). Blood samples were collected at 15 min intervals for 3 hr beginning at -12, 0, 12, 60 and 96 hr from weaning. Interval to estrus was 3.4 +/- .2 days in seven of eight cauterized sows and 3.6 +/- .6 days for sham-surgery sows. The remaining cauterized sow was anestrus at slaughter, 40 days after weaning. Number of corpora lutea and pregnancy rate were 15.8 +/- .6 and 92%, respectively, and were similar between sham-surgery and cauterized sows. Concentration of follicle stimulating hormone (FSH) at 12 hr before weaning was greater in sows subjected to electrocautery than for sham-surgery sows, but FSH values were similar at other sampling times. Concentrations of estradiol were similar at all times for both treatment groups. Luteinizing hormone (LH) was higher (P less than .05) at 60 hr in cauterized sows because of the onset of the preovulatory LH surge in one sow. We conclude that destruction of medium-sized ovarian follicles before weaning did not influence postweaning reproductive performance.

IMMUNIZATION AGAINST GROWTH HORMONE-RELEASING FACTOR SUPPRESSES IGF-I AND ABOLISHES OPIOID AGONIST INDUCED RELEASE OF GROWTH HORMONE IN LACTATING CATTLE

Publisher Summary This chapter elaborates the immunization against growth hormone-releasing factor (GRF). The effects of active immunization against GRF in lactating beef cows on concentrations of IGF-I, milk production, reproductive performance, and changes in GH following an opioid agonist and antagonist are studied. Immuno-neutralization of GRF resulted in lower milk yield in GRF than in human serum albumin (HAS) cows on day 86 and 96 pp. Interval from calving to elevated progesterone averaged 53 ± 0 and 72 ± 9 day in GRF and HSA cows, respectively. Immunization against GRF abolished the opioid agonist stimulated release of GH. Administration of FK33-824 elevated GH in HSA, but not in GRF cows and FK33-824 was effective in elevating GH only on day 47 and 119 pp in HSA cows. A single injection of naloxone failed to alter concentrations of GH in either GRF or HSA cows. In HSA cows, concentration, but not frequency, of GH release was greater on days 47 and 119 than on day 19. It is found that abolishment of GH pulses by active immunization against GRF suppressed IGF-I concentrations, lowered milk yield and reduced the interval from calving to oestrus.

CONTROL OF GROWTH HORMONE SECRETION DURING GESTATION AND LACTATION IN GILTS ACTIVELY IMMUNIZED AGAINST GROWTH HORMONE-RELEASING FACTOR

Publisher Summary This chapter describes the control of growth hormone (GH) secretion during gestation and lactation in gilts actively immunized against growth hormone-releasing factor (GRF). Changes in pattern of GH secretion during gestation and lactation, as well as possible opioid involvement in the control of GH during lactation, are not well understood in the pig. Immunization against growth hormone-releasing factor in the gilt suppresses episodic release of GH and inhibits release of GH in response to stimulation with an opioid agonist. Administration of naloxone during lactation suppressed GH in both GRF and HSA gilts. In HSA gilts, frequency of release and mean GH, respectively, were lower following naloxone than following saline. Naloxone lowered average GH in GRF gilts and however, frequency of GH release was not affected by naloxone. In summary, immuno-neutralization of GRF suppressed GH release during lactation, but failed to significantly alter GH during gestation. Administration of naloxone during lactation decreased GH in all gilts. The effect of naloxone on concentrations of GH in GRF-immunized gilts was independent of changes in frequency of release of GH.