The insulin-like growth factor (IGF) system and gonadotropin regulation: actions and interactions.

Insulin-like growth factors (IGF) are polypeptides that regulate growth, differentiation and survival in a multitude of cells and tissues. The IGF system consists of ligands, receptors, binding proteins and binding protein proteases. The influence of the IGF system on reproductive parameters, specifically gonadotropin release and interactions between the IGF system and other effectors of gonadotropin release will be examined in this review.

Mode of gonadotropin secretion in infantile female rats and the role of estrogen in feedback regulation.

The temporal aspects of gonadotropin release were studied in infantile (14-day-old) female rats. Blood samples were collected using vena cava cannulae at 10-, 15-, 20-, or 30-min intervals and assayed for either LH alone or for both LH and FSH. Within individual animals, blood LH levels exhibited a degree of variability suggestive of a pulsatile release of the hormone. Wide fluctuations in circulating FSH were also observed, indicating that FSH might also be secreted in a pulsatile manner. Peak values for both gonadotropins were 2- to 5-fold higher than baseline levels. The majority of pups exhibited a nonrhythmic release of hormones. In some animals, LH and FSH appeared to be secreted in a temporally coincident manner. Administration of LHRH to cannulated pups evoked a simultaneous discharge of both gonadotropins. To determine whether endogenous 17 beta-estradiol (E2) plays a physiological role in the control of LH secretion in infantile rats, circulating LH levels were monitored in cannulated pups which had been treated twice daily with anti-E2 serum for 4 days. Passive immunization to E2 did not affect pulsatile LH secretion. Therefore, the results of this study demonstrate that in infantile female rats, LH is secreted in a pulsatile manner which is independent of E2 feedback regulation.

Cytoplasmic estrogen receptors and estrogen concentrations in bovine uterine endometrium.

Specific cytoplasmic binding of 17beta-[3H]estradiol ([3H]E2beta) by unoccupied receptors in bovine uterine endometrium was determined by saturation analysis and correlated with endometrium levels of E2beta in 21 cows. The concentrations of these estrogen receptors (ER) during the estrous cycle were significantly greater during proestrus, estrus, and postestrus (days 18-20 and 0-4 of the cycle) than during the midluteal period (days 10-12; P less than 0.05). These increases in ER concentration paralleled increases in endometrial and plasma E2beta concentrations. In a preliminary experiment involving six heifers killed during the estrous cycle, a comparison of the ER concentrations of the horns ipsilateral and contralateral to the corpus luteum showed no significant differences, as did a study of the dissociation constant of the steroid-receptor interaction during the estrous cycle and early pregnancy. The order of inhibition of cytoplasmic binding of [3H]E2beta by estrogens was as follows: E2beta greater than E1 greater than E2alpha greater than E3 at 4 C. The concentration of ER in six pregnant animals was higher on days 2-3 than on days 13-14 after insemination, which was similar to that found in cycling animals; however, the difference between days was not significant. Ovariectomy of two heifers resulted in slightly higher ER concentrations than in intact heifers, whereas immunization of two heifers with an E2beta conjugate resulted in levels 2-fold higher. In these altered animals plasma progesterone (P4) was nearly nondetectable. ER concentration was inversely related to the level of plasma P4 in cycling heifers (r = -0.58, P less than 0.01). Endometrial estrogen and plasma estrogen levels were also inversely correlated with plasma P4 levels (r = -0.65, P less than 0.01 and r = -0.48, P less than 0.05, respectively). Thus, if P4 level influences ER levels, the hormone may make the tissue less responsive to ovarian estrogens at such time as the luteal phase of the cycle and during pregnancy.

Fluctuations in the proportions of growth hormone- and prolactin-secreting cells during the bovine estrous cycle.

Reverse hemolytic plaque assays were performed on monodispersed pituitary cells from cattle at various stages of the estrous cycle in an attempt to determine whether short term fluctuations in the gonadal steroid milieu influenced the proportions of pituitary cells that released GH and/or PRL. Phase of the estrous cycle was initially determined by gross ovarian morphology and later confirmed by determination of estradiol-17 beta and progesterone peripheral serum concentrations. Animals were subdivided into four groups according to phase of cycle: early luteal (EL; day 1-10), midluteal (ML; day 11-16), late luteal (LL; day 17-19), and follicular (F; day 20-21). Plaque assays demonstrated that the percentage of all pituitary cells that released PRL was greater in the EL phase than during the ML or F phases, whereas the relative abundance of GH-secreting cells remained unchanged. A more critical analysis of hormone-secreting subtypes revealed that the increase in total PRL secretors could be attributed almost exclusively to an increase in the abundance of those cells that released both GH and PRL (mammosomatotropes). Accompanying this augmentation of dual hormone-secretors was a decrease in the proportion of cells that released GH alone without a change in the abundance of cells that secreted only PRL. These results strongly suggest that during the estrous cycle there is a bidirectional interconversion among cells that release only GH and mammosomatotropes. Moreover, the relationship between ratios of acidophilic subpopulations and stage of reproductive cycle indicates that ovarian steroids may regulate this phenomenon.

Comparisons of various acidic treatments of bovine serum on insulin-like growth factor-I immunoreactivity and binding activity.

Untreated serum exhibited two forms of insulin-like growth factor-I (IGF-I)-binding protein complexes during gel chromatography: one of Mr 150,000 and the other of Mr 40,000-45,000. The majority of the immunoreactive IGF-I was associated with the Mr 150,000 complex. Following acid-ethanol extraction of serum, the binding activity at Mr 150,000 disappeared and a reduced binding activity appeared in the albumin size range. Acid incubation of serum was slightly less effective than acid-ethanol extraction in reducing the binding activity. Acid-ethanol-extracted or acid-incubated serum were parallel to IGF-I standard in the dose-response displacement of iodinated IGF-I. Gel filtration of serum with 1 mol acetic acid/l almost completely separated IGF-I and the binding proteins. Binding-protein fractions from gel filtration interfered with the immunoreactivity of IGF-I with its antibodies, causing a non-parallel displacement curve in the radioimmunoassay (RIA). Serum IGF-I could be isolated as a single peak by high performance C18 reverse-phase liquid chromatography (HPLC). The concentrations of IGF-I measured in bovine sera by RIA were similar between acid gel filtration and HPLC; the concentrations by acid-ethanol extraction and acid incubation being about 30% smaller than those measured with former methods. The lower concentration of IGF-I measured in bovine serum with acid-ethanol extraction or acid incubation appears to be due to interference of IGF-binding proteins not removed by either treatment.

Suppression of LH secretion by oestradiol, dihydrotestosterone and trenbolone acetate in the acutely castrated bull.

Twenty acutely castrated bulls were used to investigate the role of androgenic and oestrogenic steroids in the feedback control of LH secretion. The effects of 5 alpha-dihydrotestosterone (DHT) or the growth stimulants trenbolone acetate (TBA) or oestradiol-17 beta (OE2) on serum LH secretory profiles were measured. In addition, pituitary LH responses to exogenous LH releasing hormone (LHRH) were determined to differentiate between hypothalamic and pituitary sites of steroid action. At the time of castration, two groups of animals were given implants of either 45 mg OE2 or 200 mg TBA. Another group received equivalent to 30 mg daily injections of DHT. Control steers showed an increase in LH from 2.4 +/- 0.5 (S.E.M.) micrograms/l to 7.0 +/- 0.5 micrograms/l during the week after castration. Treatment with DHT and TBA prevented the post-castration rise in serum LH. In contrast, steers given implants of OE2 showed a significantly greater increase in LH than controls 1 day after castration, but by day 5 LH declined in the OE2-treated group to precastration values. Five weeks after castration control steers secreted LH in pulses at intervals of 40-50 min and with an amplitude of 4.2 +/- 0.4 micrograms/l. Pulses were not detected in the LH profiles of the steroid-treated steers. Dihydrotestosterone and TBA significantly reduced pituitary LH responses to exogenous LHRH, whereas steers receiving OE2 showed LH responses to LHRH which were similar to those observed in castrated controls. These results support the hypothesis that androgenic and oestrogenic components participate separately in the feedback control of LH secretion in the bull.(ABSTRACT TRUNCATED AT 250 WORDS)

Residues from anabolic preparations after good veterinary practice.

The purpose of this study was to determine the endogenous concentrations of estrogens, particularly estradiol-17beta (E2beta, in edible tissues of beef cattle (females and intact and neutered males) and the concentrations of E2beta, and trenbolone beta and alpha (betaTb, alphaTb) after an E2beta and/or trenbolone acetate (TA) ear implant. Radioimmunoassays were validated for quantitation of E2beta (active isomer), E2alpha, estrone (E1), betaTb and alphaTb for bovine muscle, liver, kidney and fat tissues. The criteria of accuracy, precision, specificity and sensitivity were applied according to the standards of the U.S. Food & Drug Administration. In steer tissues, endogenous E2beta was <15 ppt, as was heifer muscle; but heifer liver and kidney were 3-fold greater. An E2beta implant in steers had no effect on muscle E2beta concentration, but increased E2beta in liver and fat 4- and 3-fold, respectively, but by 24 h post-implant removal, E2beta had fallen by half. Tissue E1 concentrations in cyclic females were similar to E2beta, but rose many fold greater than did E2beta during gestation; E2beta rose 3-fold during gestation. After E2beta/TA implant, steer tissues had E2beta concentrations equal to (for muscle and fat) and one-half (for liver) the E2beta measured in E2beta implant only steers; betaTb was in a low range (250-380 ppt) in muscle, liver and fat and alphaTb was even lower, except in liver (800-1500 ppt). An implant of TA only (no E2beta) resulted in betaTb and alphaTb concentrations 2-3-fold greater in liver, kidney and fat, but no greater in muscle than betaTb in tissues of E2beta/TA implant steers. In conclusion, anabolic implants in steers resulted in tissue E2beta concentrations less than the FDA allowable increment and betaTb in the lowest quartile (0.25) of a part per billion 30 days after implant.

Actions and interactions of the IGF system in Alzheimer's disease: review and hypotheses.

Insulin-like growth factors (IGF) are pleiotrophic polypeptides affecting all aspects of growth and development. The IGF system, including ligands, receptors, binding proteins and proteases is also involved in pathophysiological conditions, such as cancer and degenerative conditions. In this review, the actions and interactions of the IGF system as it relates to Alzheimer's disease will be investigated.

Measurement of leptin and insulin-like growth factor-I in seminal plasma from different species.

The multi-functional proteins, insulin-like growth factor-I (IGF-I) and leptin were present in seminal plasma from different species. Concentrations of IGF-I in equine and porcine semen were 20 and 17.5 ng/ml, respectively. Seminal plasma concentrations of leptin were 1 ng/ml in human and 11 ng/ml in porcine samples.

Synergistic approach to cancer therapy: exploiting interactions between anti-estrogens, retinoids, monoterpenes and tyrosine kinase inhibitors.

Non-responsiveness and toxicity are large problems encountered during cancer treatment. Utilization of compounds that synergize should increase treatment efficacy while avoiding problems of toxicity. This review explores interactions between classes of compounds, including anti-estrogens, retinoids, monoterpenes and tyrosine kinase inhibitors, that are effective independent, and how their synergistic interaction could be exploited in cancer treatment. The effects of these compounds on insulin-like growth factors (IGF) and transforming-growth factor-beta (TGF-beta) will also be examined.

Crosstalk and considerations in endocrine disruptor research.

The presence of endocrine disrupting chemicals in the environment has prompted action on several fronts to assess the potential health risks of these compounds. To fully understand the mechanisms behind the observed endocrine disruption, crosstalk and other factors should be considered. In this article we will discuss how crosstalk modulates estrogen action in several common assays and how this and other considerations appear to have been overlooked. In addition, a paradigm shift from theoretical linear response pathways to interaction maps should aid in the understanding and analysis of endocrine disruption.

Serum hormone and metabolite concentrations in fasted young bulls and steers.

The effect of dietary energy restriction on serum insulin, insulin-like growth factor I (IGF-I), growth hormone, (GH), cortisol, plasma urea nitrogen (PUN) and nonesterified fatty acid (NEFA) concentrations was examined. Angus bulls and steers (10 mo) were allotted to two groups of 12 animals and assigned a treatment order. In a switchback design, animals in order 1 were fed a high grain diet, then fasted, while order 2 animals were fasted, and then fed. Animals were allowed 60 hr to acclimate between treatments. Serum and plasma were obtained at 20 min intervals and 60 min, respectively, for 6 hr after feeding and for the last 6 hr of a 30 hr fast. Serum was assayed for insulin, IGF-I, GH, and cortisol (total and free). Plasma was assayed for PUN and NEFA. Mean insulin (ng/ml) differed between fed (.95 +/- .08) and fasted (.26 +/- .08) animals (P less than 01). Both mean total and free cortisol (ng/ml) were lower in fed (11.48 +/- .99) (1.06 +/- .12) than in fasted (17.10 +/- .93) (1.62 +/- .12) animals, respectively (P less than .01). Animals in order 1 differed in mean IGF-I (ng/ml) between fed (199.0 +/- 8.0) and fasted (116.5 +/- 7.2) treatments (P less than .01). Mean IGF-I for animals in order 2 was 146.7 +/- 7.2 in fed and 213.9 +/- 7.2 in fasted animals (P less than .01). Mean GH did not differ between treatments. Mean PUN and NEFA were higher in fasted than in fed animals (P less than .01). Except for % free cortisol (P less than .05), the hormones did not differ between bulls and steers.(ABSTRACT TRUNCATED AT 250 WORDS)

Secretory patterns of growth hormone and insulin-like growth factor-I during peripubertal period in intact and castrate male cattle.

Fifteen Angus bulls and 15 Angus steers 9 months of age and 275 kg of body weight were bled at 20-min intervals over a 6-hr period and serum GH and IGF-I concentrations were measured by RIA. There were no differences between bulls and steers in the mean GH concentration, pulse frequency and amplitude when analyzed by the computer program PULSAR. Mean IGF-I concentration was not different between the two sex phenotypes, nor was there a significant correlation between the integrated IGF-I and GH concentrations. Subsequently, five bulls and five steers were selected from the 30 animals, full-fed a diet for growth in individual pens for 3 months and bled at 15-min intervals over a 24-hr period. Bulls tended to show a greater weight gain and feed conversion efficiency (P less than .10) than steers during the 3-month period. Serum GH concentrations had a pulsatile pattern in all animals with no apparent diurnal rhythm during the 24-hr bleeding. Although mean GH concentration was not different between the two sex phenotypes, bulls tended to have lower baseline levels (P less than .10) and greater peak amplitudes than steers. Serum IGF-I concentrations fluctuated within a two-fold concentration range, with no obvious pulsatility similar to that of GH. Mean IGF-I concentrations of each of the 10 animals were correlated with mean peak GH amplitudes (r = .79), but not with mean GH. These results suggest that gonadal hormone(s) modulates the GH secretory pattern and increases IGF-I secretion which may be related to the greater growth rate of bulls compared with steers.

Is nutritional anestrus precipitated by subfunctional corpora lutea in beef cows?

Thirty-four multiparous, lactating, cyclic beef cows which calved in moderate body condition were used to determine effects of restricted nutrition on corpus luteum (CL) development and endocrine status. At 78 d postpartum, six cows were assigned to a control (CON) diet (26.0 Mcal ME), fed to increase bodyweight (BW) and body condition score (BCS), and the remaining 28 cows were fed to lose BW and BCS on a restricted (RES) diet (14.0 Mcal ME). Following a 40-d adjustment period on respective diets, estrous cycles were synchronized and cows bled daily for determination of progesterone (P4), luteinizing hormone (LH) and insulin (INS) beginning at the synchronized estrus. Ultrasonography was used to determine the ovulatory follicle and CL development. Control cows were maintained for one estrous cycle and were ovariectomized on day 11 of their second cycle. Ten cows on restricted diet (RES-C) continued to form a functional CL (P4 > 1.5 ng/ml at day 10 of an estrous cycle) through as many as 5 cycles, after which observations were discontinued. Fourteen cows on restricted diet (RES-A) were ovariectomized on day 11 of a cycle when a CL was identified by ultrasonography, but was subfunctional (P4 < 1.5 ng/ml on day 10 of that cycle). Four additional RES-A cows which had subfunctional CL were not ovariectomized but were bled for an additional 25 d. At ovariectomy, CL and ovarian weights were collected. Luteal tissue was prepared for evaluation of P4 synthesis, LH responsiveness in vitro, and for determination of P4 content and total LH receptors. Bodyweight and BCS increased in CON cows; whereas, RES cows lost BW and BCS (P < .05). In the cycle prior to ovariectomy, serum P4 and LH were not different in 18 RES-A cows which developed subfunctional CL in comparison to CON cows. Four RES-A cows not ovariectomized but bled for an additional 25 d neither exhibited estrus, ovulated, nor had P4 concentrations greater than .3 ng/ml. Serum INS was lower in RES-A cows during the cycle prior to ovariectomy than in CON cows (P < .05). During the 11-d period prior to ovariectomy, mean serum P4 and INS were lower in RES-A cows than in CON cows (P < .05); however, serum LH was not different. Furthermore, CL and ovarian weights, P4 content of CL, secretion of P4 by luteal tissue in response to LH in vitro and LH receptor number were not different between CON and RES-A cows. In conclusion, nutritional anestrus may be preceded by the formation of a CL with lower steroidogenic output in vivo. However, luteal tissue, collected from RES-A cows, did not appear to be subfunctional during in vitro incubation when substrate availability and gonadotropin support were equal between diets.

Prolongation of the luteal phase by prostaglandin E(2) during the estrous cycle in the cow. A preliminary report.

An experiment was conducted to determine the effects of prostaglandin E(2) (PGE(2)) on ovarian progesterone secretion during the estrous cycle in the cow. Intraluminal uterine catheters were implanted in three beef cows (2 treated, 1 control), and 1.3 mg of PGE(2) were infused into the uterus every 4 hours from days 9 through 21 post-estrus. Blood samples were collected from the jugular vein at 2-hour intervals from days 9 to 21 and twice daily from day 22 to 28 post-estrus. Progesterone was measured by applying a specific, direct plasma radioimmunoassay in all samples without extraction. Intrauterine infusion with PGE(2) resulted in maintenance of luteal-phase progesterone secretion until day 21 post-estrus, 4 days after luteal regression occurred in the vehicle-treated cow. In this study, we demonstrated that PGE(2) can prolong the presence of luteal phase plasma progesterone concentrations by possibly stimulating in vivo steroidogenesis by the corpus luteum during the estrous cycle in the cow.

Suckling induced cortisol secretion in young beef cows.

The profiles of plasma cortisol concentration in response to suckling were determined in 10 young, postpartum beef cows between days 25 and 85 postpartum. Two trials, comprised of five cows each, were conducted in the fall (I) and spring (II), respectively. In both trials, plasma cortisol rose within 10 minutes after suckling began and was significantly higher than pre-suckling concentrations (P<.01). Over the next 30 minutes in trial I and 40 minutes in trial II, the cortisol level progressively fell back to the pre-suckling levels. This profile was qualitatively similar among the days postpartum on which the cows were bled. Neither the profile nor the peak concentration after suckling changed significantly (P>.10) as days postpartum lapsed. Finally, there was a significant difference (P<.01) in mean plasma cortisol between the cows in trial I compared to the cows in trial II.

The active immunization of the cyclic ewe against an estrone protein conjugate.

Four mature, cyclic ewes were given injections (I.M.) of a conjugate of 1,3,5 (10)-estratrien-3-ol-6,17-dione, 6 carboxyoxime bovine serum albumin (immunized ewes) on day 3 after estrus, and at days 10, 20, 40, 58, 91 and 134 after this initial treatment. Six control ewes treated with carrier emulsion alone continued to cycle normally. Three of the immunized ewes failed to exhibit estrus, an associated preovulatory surge of LH and ovulation. One ewe showed 1 abnormally short estrous period and then became anestrus. Injection of an estrone-protein-conjugate at days 3 and 13 after estrus did not appear to interfere with the rate of structural luteolysis of the corpus luteum present, but plasma concentrations of progesterone reached abnormally high luteal phase levels and in 2 ewes failed, subsequently to decline to normal follicular phase levels. Estrone binding capacity rose as early as day 9 after first treatment, and concentrations of LH rose as early as day 14. Subsequently, plasma levels of LH, estrone and progesterone and antisera titer rose; the only significant cross reaction of the antisera was with estradiol 17beta (11.32 +/- 2.80%).

Physiological basis for use of insulin-like growth factors in reproductive applications: a review.

The insulin-like growth factors (IGF-I and -II) are ubiquitously expressed factors that regulate cell growth, differentiation and maintenance of differentiated cell function. All aspects of male and female reproduction are influenced by the IGF system. This review will examine the IGF system as it pertains to reproductive physiology and applications.

Effect of holding time and temperature of bovine whole blood on concentration of progesterone, estradiol-17beta and estrone in plasma and serum samples.

Bovine jugular venous blood was collected, with and without heparin, and aliquoted into 140 12-ml tubes. Four subsamples (two heparinized and two coagulated) were centrifuged immediately (time zero) and plasma or serum was aspirated and stored at -20 degrees C. One-half of the remaining subsamples were stored at 4 degrees C and the other one-half at 25 degrees C (room temperature). At 1-h intervals (0 to 24 h), 6-h intervals (24 to 72 h) and at 96 and 120 h, four subsamples (heparinized and coagulated at both 4 degrees C and 25 degrees C) were centrifuged, plasma or serum was aspirated and stored at -20 degrees C. Whole blood incubation for 1 h at 25 degrees C reduced mean plasma and serum progesterone (P(4)) concentration (P<0.05). Similarly, whole blood incubation at 4 degrees C for 2 and 3 h, respectively, reduced mean plasma and serum P(4) concentration (P<0.05). No difference was found in mean P(4) concentration between plasma and serum samples harvested from whole blood incubated at 4 degrees C or 25 degrees C. Concentration of estradiol-17beta (E(2)) and estrone (E(1)) fluctuated over time, irrespective of holding temperature. There was a blood type, heparinized or coagulated, by time interaction (P<0.01) for both E(2) and E(1) concentrations It was concluded that incubation time and temperature between collection and centrifugation of bovine blood samples influenced the assayable P(4) concentration in both plasma and serum. In contrast, incubation temperature had no effect on assayable E(2) and E(1) concentrations, but assayable E(2) and E(1) over time were differentially affected, depending on whether plasma or serum was assayed.

Oviductal fluid and growth factors failed to enhance development of porcine embryos.

Porcine embryos (1-, 2- and 4-cell) were cultured in a basal medium consisting of Krebs-Ringer bicarbonate buffer supplemented with oviductal fluid and several growth factors and observed for further development. Oviducts were flushed at either 48 h (Experiment 1) or 96 h (Experiment 2) after the onset of estrus. Observations were made every 48 h (Experiment 1) or 12 h (Experiment 2) until failure of the embryos to develop for 2 consecutive observations. Embryos were scored 0 = no development, 1 = cleavage, 2 = morula, 3 = blastocyst, or 4 = hatched blastocyst. In the first experiment, development of 1-, 2- and 4-cell embryos (n=282) in the basal medium supplemented with oviductal fluid (4:1) or 3 sets of growth factors, was less or equal to one cleavage stage. Those embryos cultured in the basal medium supplemented with bovine serum albumin (fatty acid free) (BSA) advanced to the blastocyst stage. In the second experiment, 96 h aged embryos (n=142) were cultured in the basal medium supplemented with IGF-1 and - 2 and EGF, or with BSA alone or with BSA and the three growth factors. In the treatments without BSA, the embryonic development was less than one cleavage, whereas in those treatments with BSA, embryos advanced beyond hatching and began to expand. We conclude that for culture of porcine embryos, supplementation with several growth factors or with oviductal fluid, in the concentration used in this study, was of little benefit at this stage of development. However, the type of BSA significantly affected development. More than 90% of the embryos reached the morula and blastocyst stages in medium than included BSA (fatty acid free).