scholarly journals INFLUENCE OF SEASON AND SOCIAL ENVIRONMENT ON THE REPRODUCTIVE-ENDOCRINE STATUS OF THE ADULT LANDRACE BOAR

1990 ◽  
Vol 70 (1) ◽  
pp. 121-128 ◽  
Author(s):  
V. L. TRUDEAU ◽  
L. M. SANFORD
Keyword(s):  
Social Environment ◽  
Late Summer ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Social Environments ◽  
Blood Samples ◽  
Testosterone Secretion ◽  
Endocrine Status ◽  
Reproductive Endocrine ◽  
Basal Concentration

Seasonal variations in LH, FSH, and testosterone secretion were investigated for adult Landrace boars housed in different social environments for 1 yr. Socially nonrestricted boars (n = 4) were penned adjacent to ovariectomized gilts that were hormonally brought into estrus every 2 wk, while socially restricted boars (n = 4) were kept in pens with solid walls. Mean hormone concentrations were determined from the assay of single AM and PM blood samples collected from the jugular vein by venipuncture once a month. In November, February, May and August, blood samples were collected serially over 12 h from jugular catheters for assessment of pulsatile LH and testosterone secretion, and the LH response to a GnRH injection (1 μg kg−1 body weight). Mean LH and testosterone concentrations were relatively high in all boars during the late summer and fall, and often were greater for the socially nonrestricted versus the restricted boars (group × month), P < 0.05) in the winter (December and January). Mean FSH concentration also varied with month (P < 0.05). Pulse analysis indicated that higher mean testosterone concentrations in November and August were the result of increases (month, P < 0.05) in testosterone-pulse frequency and basal concentration. Maximal mean LH concentration in August was associated with maximal (month, P < 0.05) LH-pulse amplitude and basal concentration. The amplitude of the LH peak following GnRH injection increased (P < 0.05) between November and May, and remained high in August. Key words: Gonadotropins, testosterone, blood, season, social environment, boar

Effects of light and food on plasma leptin concentrations in ewes

2000 ◽  
Vol 71 (2) ◽  
pp. 235-242 ◽  
Author(s):  
T. Tokuda ◽  
T. Matsui ◽  
H. Yano
Keyword(s):  
Diurnal Rhythm ◽  
Energy Requirement ◽  
Pulse Length ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Pulse Plasma ◽  
Dark Cycle ◽  
Blood Samples ◽  
The Mean ◽  
Plasma Leptin

AbstractPlasma leptin concentration shows pulsatility and diurnal rhythm in humans. However, there are few reports concerning the 24-h profile of circulating leptin levels in ruminants. Five crossbred ewes were housed in metabolism cages under a 1-h light-dark cycle. The ewes were offered alfalfa hay daily to meet their energy requirement. Blood samples were collected at 15-min intervals for 24 h. Plasma leptin concentrations were determined using a radioimmunoassay and the profile of plasma leptin levels was analysed by the PULSAR algorithmic program for detecting pulse. Plasma leptin concentration changed in a pulsatile fashion. The mean leptin concentration was 2·93 ng/ml. The mean pulse frequency was 4·8 pulses per day and the mean pulse amplitude was 0·67 ng/ml with an average pulse length of 1:13 h. Plasma leptin level was not affected by feeding or lighting cycle. These results indicate that plasma leptin level in sheep shows pulsatility but diurnal rhythm is not exhibited.

scholarly journals The absence of corpus luteum formation alters the endocrine profile and affects follicular development during the first follicular wave in cattle

Reproduction ◽  
2008 ◽  
Vol 136 (6) ◽  
pp. 787-797 ◽  
Author(s):  
Ken-Go Hayashi ◽  
Motozumi Matsui ◽  
Takashi Shimizu ◽  
Natsuko Sudo ◽  
Ayako Sato ◽  
...  
Keyword(s):  
Corpus Luteum ◽  
Area Under The Curve ◽  
Follicular Development ◽  
Experimental Period ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Blood Collection ◽  
Gh Secretion ◽  
Endocrine Profile ◽  
Basal Concentration

We previously established a bovine experimental model showing that the corpus luteum (CL) does not appear following aspiration of the preovulatory follicle before the onset of LH surge. Using this model, the present study aimed to determine the profile of follicular development and the endocrinological environment in the absence of CL with variable nadir circulating progesterone (P4) concentrations during the oestrous cycle in cattle. Luteolysis was induced in heifers and cows and they were assigned either to have the dominant follicle aspirated (CL-absent) or ovulation induced (CL-present). Ultrasound scanning to observe the diameter of each follicle and blood collection was performed from the day of follicular aspiration or ovulation and continued for 6 days. The CL-absent cattle maintained nadir circulating P4throughout the experimental period and showed a similar diameter between the largest and second largest follicle, resulting in co-dominant follicles. Oestradiol (E2) concentrations were greater in the CL-absent cows than in the CL-present cows at day −1, day 1 and day 2 from follicular deviation. The CL-absent cows had a higher basal concentration, area under the curve (AUC), pulse amplitude and pulse frequency of LH than the CL-present cows. After follicular deviation, the CL-absent cows showed a greater basal concentration, AUC and pulse amplitude of growth hormone (GH) than the CL-present cows. These results suggest that the absence of CL accompanying nadir circulating P4induces an enhancement of LH pulses, which involves the growth of the co-dominant follicles. Our results also suggest that circulating levels of P4and E2affect pulsatile GH secretion in cattle.

Generation of growth hormone pulsatility in women: evidence against somatostatin withdrawal as pulse initiator

2001 ◽  
Vol 280 (3) ◽  
pp. E489-E495 ◽  
Author(s):  
Eleni V. Dimaraki ◽  
Craig A. Jaffe ◽  
Roberta Demott-Friberg ◽  
Mary Russell-Aulet ◽  
Cyril Y. Bowers ◽  
...  
Keyword(s):  
Body Mass Index ◽  
Growth Hormone ◽  
Postmenopausal Women ◽  
Normal Saline ◽  
Driving Force ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Blood Samples ◽  
Stable Plasma ◽  
Plasma Gh

To test whether endogenous hypothalamic somatostatin (SRIH) fluctuations are playing a role in the generation of growth hormone (GH) pulses, continuous subcutaneous octreotide infusion (16 μg/h) was used to create constant supraphysiological somatostatinergic tone. Six healthy postmenopausal women (age 67 ± 3 yr, body mass index 24.7 ± 1.2 kg/m2) were studied during normal saline and octreotide infusion providing stable plasma octreotide levels of 2,567 ± 37 pg/ml. Blood samples were obtained every 10 min for 24 h, and plasma GH was measured with a sensitive chemiluminometric assay. Octreotide infusion suppressed 24-h mean GH by 84 ± 3% ( P = 0.00026), GH pulse amplitude by 90 ± 3% ( P = 0.00031), and trough GH by 54 ± 5% ( P = 0.0012), whereas GH pulse frequency remained unchanged. The response of GH to GH-releasing hormone (GHRH) was not suppressed, and the GH response to GH-releasing peptide-6 (GHRP-6) was unaffected. We conclude that, in women, periodic declines in hypothalamic SRIH secretion are not the driving force of endogenous GH pulses, which are most likely due to episodic release of GHRH and/or the endogenous GHRP-like ligand.

Pulsatile and nocturnal growth hormone secretions in men do not require periodic declines of somatostatin

2003 ◽  
Vol 285 (1) ◽  
pp. E163-E170 ◽  
Author(s):  
Eleni V. Dimaraki ◽  
Craig A. Jaffe ◽  
Cyril Y. Bowers ◽  
Peter Marbach ◽  
Ariel L. Barkan
Keyword(s):  
Growth Hormone ◽  
Diurnal Rhythm ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Pulse Generation ◽  
Sexually Dimorphic ◽  
Blood Samples ◽  
Gh Secretion ◽  
Stable Plasma ◽  
Hormone Secretions

Using a continuous subcutaneous octreotide infusion to create constant supraphysiological somatostatinergic tone, we have previously shown that growth hormone (GH) pulse generation in women is independent of endogenous somatostatin (SRIH) declines. Generalization of these results to men is problematic, because GH regulation is sexually dimorphic. We have therefore studied nine healthy young men (age 26 ± 6 yr, body mass index 23.3 ± 1.2 kg/m2) during normal saline and octreotide infusion (8.4 μg/h) that provided stable plasma octreotide levels (764.5 ± 11.6 pg/ml). GH was measured in blood samples obtained every 10 min for 24 h. Octreotide suppressed 24-h mean GH by 52 ± 13% ( P = 0.016), GH pulse amplitude by 47 ± 12% ( P = 0.012), and trough GH by 39 ± 12% ( P = 0.030), whereas GH pulse frequency and the diurnal rhythm of GH secretion remained essentially unchanged. The response of GH to GH-releasing hormone (GHRH) was suppressed by 38 ± 15% ( P = 0.012), but the GH response to GH-releasing peptide-2 was unaffected. We conclude that, in men as in women, declines in hypothalamic SRIH secretion are not required for pulse generation and are not the cause of the nocturnal augmentation of GH secretion. We propose that GH pulses are driven primarily by GHRH, whereas ghrelin might be responsible for the diurnal rhythm of GH.

LH pulsatility and in vitro bioactivity in women with anorexia nervosa-related hypothalamic amenorrhea

1991 ◽  
Vol 125 (6) ◽  
pp. 614-620 ◽  
Author(s):  
Jacques Allouche ◽  
Antoine Bennet ◽  
Pierre Barbe ◽  
Monique Plantavid ◽  
Philippe Caron ◽  
...  
Keyword(s):  
Anorexia Nervosa ◽  
Pulse Generator ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
In Vitro Bioactivity ◽  
Hypothalamic Amenorrhea ◽  
Blood Samples ◽  
Lh Pulsatility ◽  
Normal Women

Abstract. LH nocturnal pulsatility and bioactivity to immunoreactivity (B/I) ratio were determined in 16 patients with anorexia nervosa-related hypothalamic amenorrhea and low sex steroid levels, and in 12 normal women in the midfollicular phase. The patients were subdivided into 2 groups: IA (N=7) without, and IB (N=9) with documented recent weight gain. Blood samples were taken from each subject at 10-min intervals from 00.00 to 06.00 h. Immunoreactive LH data were analysed with cluster analysis algorithm. A pool of aliquots from all the samples was used to evaluate bioactive LH, immunoreactive LH and LH B/I ratio in each subject. LH pulse frequency was lower in Group IA than in controls, whereas it did not differ significantly between Group IB and controls. LH pulse amplitude was lower in Group IA, and higher in Group IB than in controls. LH B/I ratio was below the control range in 3/16 patients. In conclusion, persistent hypothalamic amenorrhea does not require a permanent inhibition of the GnRH pulse generator; transient inhibition of pulsatility and qualitative abnormalities of gonadotropins could be involved in the mechanism, at least in some patients.

Changes in FSH and the pulsatile secretion of LH during treatment of ewes with bovine follicular fluid throughout the luteal phase of the oestrous cycle

1986 ◽  
Vol 111 (2) ◽  
pp. 317-327 ◽  
Author(s):  
J. M. Wallace ◽  
A. S. McNeilly
Keyword(s):  
Follicular Fluid ◽  
Luteal Phase ◽  
Treatment Cycle ◽  
Day Treatment ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Feedback Effects ◽  
Blood Samples ◽  
Three Stages ◽  
Lh Secretion

ABSTRACT Treatment of Damline ewes with twice-daily i.v. injections of bovine follicular fluid during the luteal phase for 10 or 2 days before prostaglandin-induced luteolysis resulted in a delay in the onset of oestrous behaviour and a marginal increase in ovulation rate. During the treatment cycle, blood samples were withdrawn at 15-min intervals for 25 h from 08.00 h on days 1, 6 and 10 (day 0 = oestrus). At all three stages of the luteal phase, plasma FSH concentrations were suppressed relative to controls 3 h after the 09.00 h injection of follicular fluid and remained low until 06.00 h on the following day. In the 10-day treatment group LH pulse amplitude was significantly greater than that of controls on days 6 and 10. Pulse frequency remained high throughout treatment and was significantly higher relative to controls on day 10 despite normal progesterone levels. The results suggest that the higher pulsatile LH secretion during the luteal phase is due to reduced negative feedback effects of oestradiol occurring as a result of the follicular fluid-induced reduction in FSH. J. Endocr. (1986) 111, 317–327

Pulsatile secretion of inhibin, oestradiol and androstenedione by the ovary of the sheep during the oestrous cycle

1990 ◽  
Vol 126 (3) ◽  
pp. 385-393 ◽  
Author(s):  
B. K. Campbell ◽  
G. E. Mann ◽  
A. S. McNeilly ◽  
D. T. Baird
Keyword(s):  
Luteal Phase ◽  
Venous Blood ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Follicular Phase ◽  
Oestrous Cycle ◽  
Blood Samples ◽  
Early Follicular Phase ◽  
Lh Secretion ◽  
Late Follicular Phase

ABSTRACT The pattern of pulsatile secretion of inhibin, oestradiol and androstenedione by the ovary at different stages of the oestrous cycle in sheep was studied in five Finn–Merino ewes in which the left ovary had been autotransplanted to the neck. The ewes had jugular venous blood samples collected at 4-hourly intervals from 42 h before the induction of luteolysis by i.m. injection of cloprostenol (100 μg) on day 10 of the oestrous cycle, until day 3 of the following cycle. There were five periods of intensive blood sampling, when both ovarian and jugular venous blood samples were collected, as follows: (a) mid-luteal phase, before the second injection of cloprostenol on day 10 (15-min intervals for 6 h); (b) early follicular phase, 24 h after the second injection of cloprostenol (10-min intervals for 4 h); (c) late follicular phase, 48 h after the second injection of cloprostenol (10-min intervals for 4 h); (d) after the LH surge on day 1 of the cycle, 76 h after the second injection of cloprostenol (10-min intervals for 4 h); (e) early luteal phase on day 3 of the cycle, 120 h after the second injection of cloprostenol (10-min intervals for 3 h). Plasma was collected and the samples assayed for LH, FSH, progesterone, oestradiol, androstenedione and inhibin. The ovarian secretion rates for oestradiol, androstenedione and inhibin were calculated. All ewes responded normally to the luteolytic dose of cloprostenol with the preovulatory surge of LH occurring within 56·4±1·6 h (mean ± s.e.m.) followed by the establishment of a normal luteal phase. The pulse frequency of LH, oestradiol and androstenedione increased in the transition from the luteal to the follicular phase (P<0·01). On day 1 of the cycle LH secretion consisted of low-amplitude high-frequency pulses (1·0±0·1 pulse/h) to which androstenedione, but not oestradiol, responded. On day 3 of the cycle LH secretion was similar to that on day 1 but both androstenedione and oestradiol secretion were pulsatile in response to LH, indicating the presence of oestrogenic follicles. The stage of the cycle had no significant effects on LH pulse amplitude and nadir but the ovarian secretory response to LH stimulation did vary with the stage of the cycle. Prolactin pulse frequency, amplitude and nadir were higher (P<0·05) during the follicular phase than the luteal phase. Prolactin pulse frequency was depressed (P<0·05) on day 1 of the cycle but increased to follicular phase levels on day 3. Prolactin pulse frequency was significantly correlated to oestradiol pulse frequency (r = 0·54; P<0·01). During the luteal phase there were insufficient oestradiol pulses to obtain an estimate of pulse amplitude and nadir but both these parameters reached their highest level during the late follicular phase, fell to negligible levels on day 1 and increased to early follicular phase levels on day 3. Androstenedione pulse amplitude and nadir exhibited similar but less marked variation. Inhibin secretion was episodic at all stages of the cycle examined but did not exhibit significant variation with stage of cycle in any of the parameters of episodic secretion measured. Inhibin pulses were not related to either LH or prolactin at any stage of the cycle. FSH secretion was not detectably pulsatile but jugular venous concentrations of FSH at each stage of the oestrous cycle were negatively correlated with mean oestradiol (r= −0·52; P<0·01 but not inhibin secretion (r = 0·19). We conclude that (i) LH secretion is pulsatile at all stages of the oestrous cycle but the steroidogenic responses of the ovary varies with the stage of the cycle, reflecting changes in characteristics of the follicle population, (ii) ovarian inhibin secretion is episodic and displays little change with the stage of the oestrous cycle and (iii) episodic inhibin secretion is not related to either pulses of LH or prolactin. The aetiology of these inhibin pulses therefore remains unknown. Journal of Endocrinology (1990) 126, 385–393

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.

The effects of acclimation to confinement on gonadotrophin and cortisol secretion during the estrous cycle of the ewe

1991 ◽  
Vol 71 (2) ◽  
pp. 327-332 ◽  
Author(s):  
N. C. Rawlings ◽  
S. J. Cook
Keyword(s):  
Key Words ◽  
Estrous Cycle ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Cortisol Secretion ◽  
Serum Concentrations ◽  
Blood Samples ◽  
Progesterone Secretion ◽  
Serum Lh ◽  
Lh Secretion

The purpose of the study was to examine the effects of acclimation to confined housing on tonic gonadotrophin, cortisol and progesterone secretion in ewes at different stages of the estrous cycle. On days 4, 12 and 16 of the estrous cycle separate groups of eight ewes were blood sampled every 5 min for 6 h. Of the eight ewes bled at each stage of the cycle four were moved from outside drylots to small pens in a building 2 d prior to blood sampling and four were moved 4 d prior to sampling. All blood samples were analyzed for concentrations of LH and FSH and one sample for each hour of intensive bleeding, for each ewe, was analyzed for cortisol and progesterone. All hormone concentrations were obtained by radioimmunoassay. On day 4 of the estrous cycle LH pulse frequency and mean serum concentrations of LH were higher, but mean FSH concentrations were lower, in ewes confined for 4 d, compared to those confined for 2 d (P < 0.05). On day 12 of the cycle, mean serum LH concentrations only were higher in ewes confined for 4 d (P < 0.05). At day 16 no differences were seen between ewes confined for 2 or 4 d. Serum concentrations of progesterone, cortisol and LH pulse amplitude did not vary significantly between ewes confined for 2 or 4 d. However, in ewes confined for 4 d, serum concentrations of cortisol fell from day 4 to day 16 of the estrous cycle (P < 0.05). We conclude that acclimation to confined housing in the intact cyclic ewe is reflected in changes in tonic LH secretion at stages of the estrous cycle when serum concentrations of cortisol are high. Key words: LH, FSH, cortisol, confinement, cyclic ewe

Pulsatile and diurnal secretion of GH and IGF-I in the chronically catheterized pig fetus

1996 ◽  
Vol 149 (1) ◽  
pp. 125-133 ◽  
Author(s):  
M Bauer ◽  
N Parvizi
Keyword(s):  
Gestational Age ◽  
Diurnal Rhythm ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Diurnal Variations ◽  
Ontogenetic Changes ◽  
Blood Samples ◽  
Gh Secretion ◽  
Igf I ◽  
Fetal Pig

Abstract The ontogeny of GH and IGF-I secretion was investigated in the fetal pig. Pulse studies were performed to describe the pattern of GH release. Twenty-four-hour profiles were recorded to examine possible diurnal variations in these hormones. (I) Pulse studies. Blood samples were obtained at 15-min intervals for 2-h periods from 24 male and 20 female fetuses at various gestational ages (fetal day 89–113; term 113 ± 1 s.d.). Fetuses revealed a pulsatile GH release. The GH pulse frequency did not vary with gestational age in either sex (0·95 ± 0·19 pulses/h). In males the GH pulse amplitude decreased with increasing fetal age (r= −0·41; P<0·02). In female fetuses no significant correlation could be calculated. Mean GH concentrations fell significantly in male fetuses 3 to 4 days before delivery (P<0·05) and the same tendency was observed in females (P<0·06). Between fetal days 94 and 98 GH pulse amplitude and GH and IGF-I concentrations were higher in males than in females (P<0·01, P<0·001 and P<0·02 respectively). Fetal IGF-I secretion showed no ontogenetic changes in both sexes. However, maternal IGF-I concentrations increased with progressing gestation (r=0·46; P<0·001). (II) 24-h profiles. Eight male and four female late-gestational fetuses (fetal days 104–108) were studied. Blood samples were taken at 30-min intervals over 24 h. Dams and fetuses showed an episodic GH secretion over the 24-h period but no diurnal rhythm was observed. Whereas maternal IGF-I secretion was constant, fetal IGF-I release was characterized by marked fluctuations over the 24 h. In half of the fetuses (n=6) the fluctuations appeared at regular intervals. Again no diurnal rhythm existed. These data demonstrated that: (1) porcine fetal GH secretion is pulsatile and decreases shortly before birth; (2) a sex difference in GH and IGF-I concentrations exists between fetal days 94 and 98, suggesting that IGF-I is at least partially under the control of GH before birth; (3) fetal GH and IGF-I secretion is episodic over 24 h, but does not vary diurnally; and (4) fetal and maternal GH and IGF-I secretion are regulated independently. Journal of Endocrinology (1996) 149, 125–133

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