scholarly journals Hypothalamic responses to peripheral glucose infusion in food-restricted sheep are influenced by photoperiod

2005 ◽  
Vol 184 (3) ◽  
pp. 515-525 ◽  
Author(s):  
Z A Archer ◽  
S M Rhind ◽  
P A Findlay ◽  
C E Kyle ◽  
M C Barber ◽  
...  
Keyword(s):  
Gene Expression ◽  
Weight Maintenance ◽  
Plasma Concentrations ◽  
Insulin Receptors ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Hypothalamic Arcuate Nucleus ◽  
Maintain Body Weight ◽  
Gonadotrophin Releasing Hormone ◽  
Male Sheep

Nutritional feedback provided by systemic hormones, such as insulin and leptin, influences reproductive neuroendocrine output within the hypothalamus, yet the mechanisms and their interaction with photoperiodic cues remain unresolved in seasonal species. Here, peripheral glucose (G) infusion was used to increase endogenous concentrations of insulin and leptin in food-restricted sheep kept in either long-day (LD) or short-day (SD) photoperiod, and responses were examined in terms of pulsatile luteinising hormone (LH) (gonadotrophin-releasing hormone by inference) output and hypothalamic gene expression for nutritionally sensitive neuropeptides and receptors. We addressed the hypothesis that these hypothalamic responses were correlated and influenced by photoperiod. Oestradiol-implanted, castrated male sheep were kept 16 weeks in SD (8 h light/day) or LD (16 h light/day) and then transferred to the opposite photoperiods for 8 weeks, during which food was restricted to 90% requirement to maintain body weight (maintenance). For the final 6 days, food was reduced to 75% maintenance, and sheep in both photoperiods were infused intravenously with G (60 mM/h) or saline (S) (n=8/group). G-infused sheep had higher mean plasma concentrations of G, insulin and leptin than S-infused sheep, with no effect of photoperiod. In LD, but not in SD, G infusion increased LH pulse frequency and pulse amplitude. In LD, but not in SD, gene expression in the hypothalamic arcuate nucleus was lower in G- than S-infused sheep for neuropeptide Y (NPY) and agouti-related peptide (AGRP) and was higher in G- than S-infused sheep for pro-opiomelanocortin (POMC). Gene expression for leptin and insulin receptors was not affected by photoperiod or infusion. These results are consistent with the involvement of NPY, AGRP and POMC in mediating the reproductive neuroendocrine response to increased systemic nutritional feedback, and they support the hypothesis that hypothalamic responses to nutritional feedback are influenced by photoperiod in sheep.

scholarly journals Contrasting effects of different levels of food intake and adiposity on LH secretion and hypothalamic gene expression in sheep

2002 ◽  
Vol 175 (2) ◽  
pp. 383-393 ◽  
Author(s):  
ZA Archer ◽  
SM Rhind ◽  
PA Findlay ◽  
CE Kyle ◽  
L Thomas ◽  
...  
Keyword(s):  
Gene Expression ◽  
Food Intake ◽  
Leptin Receptor ◽  
In Situ Hybridisation ◽  
Plasma Concentrations ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Hypothalamic Arcuate Nucleus ◽  
Lh Secretion

Body reserves (long-term) and food intake (short-term) both contribute nutritional feedback to the hypothalamus. Reproductive neuroendocrine output (GnRH/LH) is stimulated by increased food intake and not by high adiposity in sheep, but it is unknown whether appetite-regulating hypothalamic neurons show this differential response. Castrated male sheep (Scottish Blackface) with oestradiol implants were studied in two 4 week experiments. In Experiment 1, sheep were fed to maintain the initial body condition (BC) score of 2.0+/-0.00 (lower BC (LBC), n=7) or 2.9+/-0.09 (higher BC (HBC), n=9), and liveweight of 43+/-1.1 and 59+/-1.6 kg respectively. LBC and HBC sheep had similar mean plasma LH concentration, pulse frequency and amplitude, but HBC animals had higher mean plasma concentrations of insulin (P<0.01), leptin (P<0.01) and glucose (P<0.01). Gene expression (measured by in situ hybridisation) in the hypothalamic arcuate nucleus (ARC) was higher in LBC than HBC sheep for neuropeptide Y (NPY; 486% of HBC, P<0.01), agouti-related peptide (AGRP; 467%, P<0.05) and leptin receptor (OB-Rb; 141%, P<0.05), but lower for cocaine- and amphetamine-regulated transcript (CART; 92%, P<0.05) and similar between groups for pro-opiomelanocortin (POMC). In Experiment 2, sheep with initial mean BC score 2.4+/-0.03 and liveweight 55+/-0.8 kg were fed a liveweight-maintenance ration (low intake, LI, n=7) while sheep with initial mean BC score 2.0+/-0.03 and liveweight 43+/-1.4 kg were fed freely so that BC score increased to 2.5+/-0.00 and liveweight increased to 54+/-1.4 kg (high intake, HI, n=9). Compared with LI, HI sheep had higher mean plasma LH (P<0.05), baseline LH (P<0.01) and pulse amplitude (P<0.01) and showed a trend towards higher pulse frequency. Although there were no differences in final mean plasma concentrations, there were significant increases over time in mean concentrations of insulin (P<0.001), leptin (P<0.05) and glucose (P<0.001) in HI sheep. Gene expression for AGRP in the ARC was higher in HI than LI animals (453% of LI; P<0.05), but expression levels were similar for NPY, OB-Rb, CART and POMC. Thus, the hypothalamus shows differential responses to steady-state adiposity as opposed to an increase in food intake, in terms of both reproductive neuroendocrine activity and hypothalamic appetite-regulating pathways. Differences in hypothalamic gene expression were largely consistent with contemporary levels of systemic leptin and insulin feedback; however, increased nutritional feedback was stimulatory to GnRH/LH whereas constant high feedback was not. The hypothalamus therefore has the ability to retain a nutritional memory that can influence subsequent responses.

Effect of chronic food restriction on pulsatile luteinizing hormone secretion and hypothalamic neuropeptide Y gene expression in castrate male sheep

1997 ◽  
Vol 152 (2) ◽  
pp. 329-337 ◽  
Author(s):  
C L Adam ◽  
P A Findlay ◽  
C E Kyle ◽  
P Young ◽  
J G Mercer
Keyword(s):  
Gene Expression ◽  
Neuropeptide Y ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
High Energy ◽  
Low Energy ◽  
High Protein ◽  
Castrate Male ◽  
Low Protein ◽  
Male Sheep

Abstract Castrate male sheep (wethers, average liveweight 38 ± 0·6 kg) were given one of the following diets for 10 weeks followed by euthanasia (n=8/group): high-energy high-protein providing 1·5 times the energy required to maintain liveweight (maintenance) (group 1·5M), low-energy low-protein at 0·5 maintenance (0·5M), or low-energy high-protein at 0·5 maintenance (0·5M+P). 1·5M wethers gained 22% liveweight whereas 0·5M and 0·5M+P wethers lost 18 and 13% liveweight respectively. Relative to the 1·5M group, the 0·5M and 0·5M+P groups had similar plasma concentrations of glucose and cortisol throughout, but elevated non-esterified fatty acids (P<0·001) and reduced IGF-I and insulin (P<0·05, 0·01 or 0·001) from 1 week onwards. Each week blood samples were taken every 12 min for 4 h and plasma assayed for LH. Mean concentration over 4 h, LH pulse frequency and LH pulse amplitude showed no progressive change in 1·5M sheep. However, in both 0·5M and 0·5M+P groups mean LH increased (P<0·001 and P<0·01 respectively), pulse frequency decreased (P<0·01 and P<0·01) and pulse amplitude increased (P<0·001 and P<0·01) over the 10-week period. Anterior pituitary LH content was greater in 0·5M (P<0·01) and 0·5M+P (P<0·05) than in 1·5M sheep. Coronal sections (20 μm) of hypothalamic brain tissue were subjected to in situ hybridisation to determine gene expression for neuropeptide Y (NPY). NPY mRNA was concentrated in the arcuate nucleus and median eminence, with total amounts greater in both 0·5M (310%, P<0·001) and 0·5M+P (333%, P<0·01) groups than in 1·5M sheep (100%). These data reveal that chronic low dietary energy intake by long-term castrates, with high or low protein intake, reduces LH pulse frequency but increases the circulating levels of LH by virtue of an increase in pulse amplitude, and concomitantly increases hypothalamic NPY gene expression. Journal of Endocrinology (1997) 152, 329–337

Effect of the body condition of ewes on the secretion of LH and FSH and the pituitary response to gonadotrophin-releasing hormone

1989 ◽  
Vol 120 (3) ◽  
pp. 497-502 ◽  
Author(s):  
S. M. Rhind ◽  
S. McMillen ◽  
W. A. C. McKelvey ◽  
F. F. Rodriguez-Herrejon ◽  
A. S. McNeilly
Keyword(s):  
Body Condition ◽  
Luteal Phase ◽  
Body Condition Score ◽  
Pulse Amplitude ◽  
Ovarian Hormones ◽  
Pulse Frequency ◽  
Follicular Phase ◽  
High Body ◽  
Condition Score ◽  
Gonadotrophin Releasing Hormone

ABSTRACT The effects of body fat content (body condition) of ewes on hypothalamic activity and gonadotrophin-releasing hormone (GnRH) secretion and on pituitary sensitivity to GnRH were investigated using Scottish Blackface ewes. Two groups of 12 ewes were fed so that they achieved either a high body condition score (2·98, s.e.m. = 0·046; approximately 27% of empty body weight as fat) or a low body condition score (1·94, s.e.m. = 0·031; approximately 19% of empty body weight as fat) by 4 weeks before the period of study. Thereafter, they were differentially fed so that the difference in mean condition score was maintained. Oestrus was synchronized, and on day 11 of the subsequent cycle half of the ewes of each group were ovariectomized. On day 12, the remaining ewes were injected (i.m.) with 100 μg prostaglandin F2α analogue and ovariectomized 30 h later. Numbers of large ovarian follicles and corpora lutea present at ovariectomy were recorded. Blood samples were collected at 15-min intervals for 12 h on day 10 of the cycle (luteal phase) and at 10-min intervals from 24 to 30 h after prostaglandin injection (follicular phase). At days 2 and 7 after ovariectomy, samples were collected at 15-min intervals for 8 h and ewes were then injected with 10 μg GnRH and samples were collected for a further 3 h. Samples were assayed for LH and FSH. Ewes in high body condition had more more large follicles than ewes in low body condition during the luteal phase (15·3 vs 6·5; P < 0·05) and follicular phase (11·5 vs 7·0; NS) and a slightly higher mean ovulation rate (1·50 vs 1·20; NS). However, during the luteal and follicular phases of the cycle before ovariectomy there was no effect of condition score on mean LH or FSH concentrations or mean LH pulse frequency or pulse amplitude. Two days after ovariectomy, ewes of high body condition had a higher mean LH pulse frequency than ewes of low body condition (P < 0·05) and higher mean FSH concentrations (P < 0·05). Mean LH concentration and pulse amplitude were not affected. LH and FSH profiles were not affected by body condition on day 7. GnRH-induced increases in LH and FSH concentrations on days 2 and 7 were not affected by body condition. At day 7, but not day 2, ewes ovariectomized during the luteal phase of the cycle had a significantly (P < 0·05) greater GnRH-induced LH release compared with ewes ovariectomized during the follicular phase. It is concluded that body condition directly affects hypothalamic activity and GnRH secretion, but not pituitary sensitivity to GnRH, and that effects on reproductive performance are also mediated through changes in ovarian hormones or in hypothalamo-pituitary sensitivity to ovarian hormones. Journal of Endocrinology (1989) 120, 497–502

Intrinsic secretory characteristics of luteinizing hormone and prolactin episodic release during pubertal development

1994 ◽  
Vol 131 (1) ◽  
pp. 80-85 ◽  
Author(s):  
Alessandro D Genazzani ◽  
Felice Petraglia ◽  
Mario Gastaldi ◽  
Fausta Massolo ◽  
Monica Cellini ◽  
...  
Keyword(s):  
Luteinizing Hormone ◽  
Plasma Levels ◽  
Pubertal Development ◽  
Plasma Concentrations ◽  
Tanner Stage ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Group A ◽  
Group B ◽  
Plasma Prl

Genazzani AD, Petraglia F, Gastaldi M, Massolo F, Cellini M, Iori G, Surico N, Genazzani AR. Intrinsic secretory characteristics of luteinizing hormone and prolactin episodic release during pubertal development. Eur J Endocrinol 1994;131:80–5. ISSN 0804–4643 The intrinsic characteristics of LH and prolactin (PRL) episodic secretion were evaluated in a group of 18 children (8M and 10F). The children were divided into two groups according to the Tanner stage: Group A (Tanner ≤ 1, N = 7, 3M and 4F, 6–10 years of age) and group B (Tanner 2–3, N = 11, 5M and 6F, 9–11 years of age). A pulsatility study of 4 h, sampling every 10 min, was carried out in all children. LH and PRL plasma levels were assayed by IFMA and RIA respectively. LH and PRL secretory episodes were then identified on plasma determinations using the program detect. Instantaneous secretory rates (ISR) were then computed for both LH and PRL using the specific algorithm within the detect program. Plasma LH levels were different between the two groups of children. Group A children showed undetectable LH plasma levels (below the minimal detectable dose of 0.1 mIU/ml), while group B demonstrated LH plasma levels in the normal range of values for age and sexual development (1.5±0.3 mIU/ml, mean ± sem), LH pulse frequency for group B was 3.2 ±0.4 peaks/4 h. No significant differences in mean plasma PRL levels, pulse frequency and pulse amplitude were observed between the two groups of children. Computation of ISR for LH (group B only) and PRL (both groups) identified the intrinsic episodic characteristics of the two hormones. No significant differences in LH and PRL pulse frequencies were observed when comparing the results estimated on ISR with those estimated on plasma concentrations. No significant changes in PRL pulse amplitude were observed between the two groups. Conversely, a shorter duration of LH and PRL secretory episodes was found. In conclusion, in children PRL secretory bursts from lactotropes lasted the same number of minutes independently of the Tanner stages. Moreover, the LH secretory events were clearly detectable during the daytime only when puberty had already started. The duration of PRL and LH secretory events was similar to adult fertile subjects. These data indicate that the gonadal maturation does not modify LH and PRL secretory events from the pituitary. Alessandro D Genazzani, Department of Obstetrics and Gynecology, University of Modena, Via del Pozzo 71, 41100 Modena, Italy

Responses of sheep to annual cycles in nutrition 1. Rôle of endogenous growth hormone during undernutrition

1996 ◽  
Vol 62 (2) ◽  
pp. 279-286 ◽  
Author(s):  
N. R. Adams ◽  
J. R. Briegel ◽  
R. D. G. Rigby ◽  
M. R. Sanders ◽  
R. M. Hoskinson
Keyword(s):  
Growth Hormone ◽  
Weight Loss ◽  
Plasma Concentrations ◽  
Live Weight ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Corpora Lutea ◽  
Annual Cycles ◽  
Wool Growth ◽  
And Control

AbstractPlasma concentrations of growth hormone (GH) are elevated in sheep during undernutrition. The present study attempted to determine whether this increased secretion mediated nutritional effects on reproduction or wool growth, using sheep immunized against growth hormone-releasing hormone and given a low-quality, sub-maintenance diet. Immunization reduced plasma concentrations of GH at all times measured (P < 0·01), through reduced pulse frequency, reduced pulse amplitude, and reduced baseline concentrations. Plasma insulin-like growth factor-1 (1GF-1) was also reduced in the immunized sheep (P < 0·01). Despite this, rates of live-weight loss and wool growth were similar in immunized and control ewes. Plasma concentrations ofLH and FSH were also similar in immunized and control ewes, both during the late luteal phase and after ovariectomy and supplementation with oestradiol and progesterone. Numbers of ovarian follicles and corpora lutea were also unaffected by immunization. It is concluded that high endogenous concentrations of GH in sheep given food below maintenance are necessary to maintain plasma IGF-1, but do not affect the concentration of gonadotropins or ovarian follicular growth. Furthermore, rates of live-weight loss and the depression in wool growth in such animals were also independent of concentrations ofGH or IGF-1.

The oestrogen-induced surge of LH requires a 'signal' pattern of gonadotrophin-releasing hormone input to the pituitary gland in the ewe

1989 ◽  
Vol 122 (1) ◽  
pp. 127-134 ◽  
Author(s):  
I. J. Clarke ◽  
J. T. Cummins ◽  
M. Jenkin ◽  
D. J. Phillips
Keyword(s):  
Pituitary Gland ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Lh Surge ◽  
Releasing Hormone ◽  
Gnrh Secretion ◽  
Signal Pattern ◽  
Oestradiol Benzoate ◽  
Gonadotrophin Releasing Hormone ◽  
Baseline Values

ABSTRACT Two experiments were conducted with ovariectomized and hypothalamo-pituitary disconnected (HPD) ewes to ascertain the pattern of inputs, to the pituitary gland, of gonadotrophin-releasing hormone (GnRH) necessary for the full expression of an oestrogen-induced LH surge. The standard GnRH replacement to these sheep was to give pulses of 250 ng (i.v.) every 2 h; at the onset of experimentation, pulses were given hourly. In experiment 1, groups of sheep (n = 7) were given an i.m. injection of 50 μg oestradiol benzoate, and after 10 h the GnRH pulse frequency or pulse amplitude was doubled. Monitoring of plasma LH concentrations showed that a doubling of pulse frequency produced a marked increase in baseline values, whereas a doubling of amplitude had little effect on the LH response. In a second experiment, ovariectomized HPD sheep that had received hourly pulses of GnRH for 16 h after an i.m. injection of oil or 50 μg oestradiol benzoate were given either a 'bolus' (2·25 μg GnRH) or a 'volley' (500 ng GnRH pulses 10 min apart for 30 min, plus a 500 ng pulse 15 min later). Both groups then received GnRH pulses (250 ng) every 30 min for the next 13 h. Oestrogen enhanced the LH responses to the GnRH treatments, and the amount of LH released was similar in ovariectomized HPD ewes given oestrogen plus bolus or volley GnRH treatments and ovariectomized hypothalamopituitary intact ewes given oestrogen. These results suggest that the oestrogen-induced LH surge is initiated by a 'signal' pattern of GnRH secretion from the hypothalamus. Journal of Endocrinology (1989) 122, 127–134

Dynamics of the responses in secretion of luteinising hormone, leptin and insulin following an acute increase in nutrition in mature male sheep

2004 ◽  
Vol 16 (8) ◽  
pp. 823 ◽  
Author(s):  
Song Zhang ◽  
Dominique Blache ◽  
Margaret A. Blackberry ◽  
Graeme B. Martin
Keyword(s):  
Luteinising Hormone ◽  
Control Period ◽  
Dietary Treatment ◽  
Pulse Frequency ◽  
Diet Group ◽  
Metabolic Hormones ◽  
Group A ◽  
Acute Increase ◽  
Gonadotrophin Releasing Hormone ◽  
Male Sheep

In Merino rams, an increase in the plane of nutrition increases the frequency of luteinising hormone (LH) pulses within a few days and this response is correlated with changes in the circulating concentrations of metabolic hormones. To analyse early dynamic aspects of these responses, we studied mature rams fed with diets that contained either low or high amounts of energy and protein. Jugular blood was sampled every 20 min for 96 h, including a control period of 24 h before the change of diet in the high-diet group. In the high-diet group, a significant increase in LH pulse frequency was first detected 6 h after the increase in nutrition on Day 1 and the frequency remained significantly elevated throughout the 72-h treatment period, except for a 12-h period on Day 2. Following the change of diet, insulin concentrations increased within 3 h and leptin concentrations increased within 7 h, after which time the concentrations of both hormones remained high. Dietary treatment did not affect the concentrations of thyroxine or insulin-like growth factor-I, but the high diet increased the concentrations of tri-iodothyronine. These observations are consistent with insulin and leptin playing a role in the early activation of the gonadotrophin-releasing hormone–LH axis by nutritional inputs.

scholarly journals Suppression of the secretion of luteinizing hormone due to isolation/restraint stress in gonadectomised rams and ewes is influenced by sex steroids

1999 ◽  
Vol 160 (3) ◽  
pp. 469-481 ◽  
Author(s):  
AJ Tilbrook ◽  
BJ Canny ◽  
MD Serapiglia ◽  
TJ Ambrose ◽  
IJ Clarke
Keyword(s):  
Sex Steroids ◽  
Restraint Stress ◽  
Testosterone Propionate ◽  
Plasma Concentrations ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Blood Samples ◽  
Release Device ◽  
Lh Secretion ◽  
Female Sheep

In this study we used an isolation/restraint stress to test the hypothesis that stress will affect the secretion of LH differently in gonadectomised rams and ewes treated with different combinations of sex steroids. Romney Marsh sheep were gonadectomised two weeks prior to these experiments. In the first experiment male and female sheep were treated with vehicle or different sex steroids for 7 days prior to the application of the isolation/restraint stress. Male sheep received either i.m. oil (control rams) or 6 mg testosterone propionate injections every 12 h. Female sheep were given empty s.c. implants (control ewes), or 2x1 cm s.c. implants containing oestradiol, or an intravaginal controlled internal drug release device containing 0.3 g progesterone, or the combination of oestradiol and progesterone. There were four animals in each group. On the day of application of the isolation/restraint stress, blood samples were collected every 10 min for 16 h for the subsequent measurement of plasma LH and cortisol concentrations. After 8 h the stress was applied for 4 h. Two weeks later, blood samples were collected for a further 16 h from the control rams and ewes, but on this day no stress was imposed. In the second experiment, separate control gonadectomised rams and ewes (n=4/group) were studied for 7 h on 3 consecutive days, when separate treatments were applied. On day 1, the animals received no treatment; on day 2, isolation/restraint stress was applied after 3 h; and on day 3, an i. v. injection of 2 microg/kg ACTH1-24 was given after 3 h. On each day, blood samples were collected every 10 min and the LH response to the i.v. injection of 500 ng GnRH administered after 5 h of sampling was measured. In Experiment 1, the secretion of LH was suppressed during isolation/restraint in all groups but the parameters of LH secretion (LH pulse frequency and amplitude) that were affected varied between groups. In control rams, LH pulse amplitude, and not frequency, was decreased during isolation/restraint whereas in rams treated with testosterone propionate the stressor reduced pulse frequency and not amplitude. In control ewes, isolation/restraint decreased LH pulse frequency but not amplitude. Isolation/restraint reduced both LH pulse frequency and amplitude in ewes treated with oestradiol, LH pulse frequency in ewes treated with progesterone and only LH pulse amplitude in ewes treated with both oestradiol and progesterone. There was no change in LH secretion during the day of no stress. Plasma concentrations of cortisol were higher during isolation/restraint than on the day of no stress. On the day of isolation/restraint maximal concentrations of cortisol were observed during the application of the stressor but there were no differences between groups in the magnitude of this response. In Experiment 2, isolation/restraint reduced the LH response to GnRH in rams but not ewes and ACTH reduced the LH response to GnRH both in rams and ewes. Our results show that the mechanism(s) by which isolation/restraint stress suppresses LH secretion in sheep is influenced by sex steroids. The predominance of particular sex steroids in the circulation may affect the extent to which stress inhibits the secretion of GnRH from the hypothalamus and/or the responsiveness of the pituitary gland to the actions of GnRH. There are also differences between the sexes in the effects of stress on LH secretion that are independent of the sex steroids.

Long-term negative feedback effects of oestrogen and progesterone on the pituitary gland of the long-term ovariectomized ewe

1989 ◽  
Vol 120 (2) ◽  
pp. 207-214 ◽  
Author(s):  
I. J. Clarke ◽  
J. T. Cummins ◽  
M. E. Crowder ◽  
T. M. Nett
Keyword(s):  
Plasma Concentrations ◽  
Pulse Amplitude ◽  
Pituitary Surgery ◽  
Pulse Frequency ◽  
Term Treatment ◽  
Gnrh Receptors ◽  
Long Term Treatment ◽  
Group 3 ◽  
Group 2

ABSTRACT The effects of long-term treatment with physiological doses of oestradiol or oestradiol plus progesterone on plasma gonadotrophin levels and pituitary content of LH and gonadotrophin-releasing hormone (GnRH) receptors were studied in ovariectomized–hypothalamo-pituitary disconnected ewes given 250 ng pulses of GnRH every 2 h (i.v.). A pilot experiment showed that 3 cm long Silastic implants (s.c.) reduced both LH pulse frequency and pulse amplitude in long-term (> 6 months) ovariectomized ewes. The main experiment was conducted over 3 weeks in ovariectomized–hypothalamo-pituitary disconnected ewes that had received pulsatile GnRH replacement for 1 week after pituitary surgery. Group 1 (n = 5) received GnRH pulses alone throughout the study. Group 2 (n = 6) received oestradiol in week 2 and oestradiol plus progesterone in week 3 and in group 3 (n = 6) the steroid treatments were reversed. Oestradiol reduced (P < 0·05) the mean (± s.e.m.) amplitude of LH in pulses in group 2 (from 8·2 ± 1·6 to 5·0 ± 0·5 μg/l) and group 3 (from 11·6 ± 1·2 to 9·3 ±1·0 μg/l); an additional effect of progesterone was seen in group 2 but not group 3. The amplitudes of the LH pulses did not change in the control ewes. Plasma concentrations of FSH were reduced by approximately 50% by the oestradiol treatments with no additional effects of progesterone. There was no effect of steroidal treatment on pituitary content of LH or pituitary levels of GnRH receptors. We conclude that long-term oestradiol treatment, with or without progesterone, reduces plasma amplitudes of LH pulses by a direct pituitary effect, but the magnitude of this effect was less than that observed on GnRH secretion in short-term ovariectomized ewes in an earlier study. The reduction in plasma LH pulse amplitude is not due to a direct pituitary effect of these steroids on GnRH receptor number. Journal of Endocrinology (1989) 120, 207–214

Comparison of the effects of crude and highly purified bovine inhibin (Mr 32 000) on plasma concentrations of FSH and LH in chronically ovariectomized prepubertal heifers

1990 ◽  
Vol 125 (1) ◽  
pp. 21-30 ◽  
Author(s):  
A. J. Beard ◽  
R. J. Castillo ◽  
B. J. McLeod ◽  
R. G. Glencross ◽  
P. G. Knight
Keyword(s):  
Dose Rate ◽  
Bolus Injection ◽  
Plasma Concentrations ◽  
Protein A ◽  
Pulse Amplitude ◽  
Initial Study ◽  
Pulse Frequency ◽  
Optimal Method

ABSTRACT Chronically ovariectomized prepubertal heifers were used for a comparison of the effects of highly purified bovine inhibin (Mr 32 000) and steroid-free bovine follicular fluid (bFF) on the secretion of FSH and LH. In view of the limited availability of highly purified inhibin, an initial study was undertaken to establish the optimal method for administration of bFF inhibin activity. In comparison with the FSH response to a single large i.v. bolus injection of bFF (50 ml; 3250 mg protein), a far more effective suppression of plasma FSH concentrations was achieved when considerably less bFF (6·3 ml; 410 mg protein) was administered gradually over an extended time-period (2 days) either as a continuous i.v. infusion or as a series of 2-hourly i.v. injections. Following a single i.v. bolus injection of bFF, immunoreactive inhibin was cleared rapidly from the circulation (half-life 51 ± 8 (s.e.m.) min, n = 5), presumably accounting for its limited ability to suppress FSH secretion when administered in this manner. In a second experiment, treatment of ovariectomized heifers (three per group) with highly purified Mr 32 000 bovine inhibin at a dose rate of 15 μg/2 h for 2 days significantly (P < 0·05) suppressed plasma FSH concentrations, which reached their minimum values (40% suppression) during day 2 of treatment. At a lower dose rate (5 μg/2 h), inhibin did not significantly affect plasma FSH levels. Administration of bFF was also associated with a dose-dependent suppression of FSH secretion. For each of three dose rates tested (three heifers per group), plasma FSH concentrations were maximally suppressed during day 2 of treatment (65 mg/2 h, 86% suppression, P < 0·001; 21·7 mg/2 h, 66% suppression, P < 0·001; 7·2 mg/2 h, 15% suppression, P > 0·05). Neither highly purified inhibin nor bFF significantly affected mean plasma LH concentrations, LH pulse frequency or LH pulse amplitude. Thus we have shown for the first time that highly purified Mr 32 000 bovine inhibin does possess in-vivo biological activity in cattle, promoting a selective suppression of plasma FSH concentrations qualitatively similar to that evoked by steroid-free bFF. Quantitatively, the inhibin preparation had an in-vivo biopotency about 1000 times greater than that of bFF, a value which accords well with its biopotency (1176 × bFF) in the in-vitro rat pituitary cell bioassay. Journal of Endocrinology (1990) 125, 21–30

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