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J. Anim. Sci. 2003. 81:1440-1446
© 2003 American Society of Animal Science

Effect of photoperiod on hepatic growth hormone receptor 1A expression in steer calves1

P. E. Kendall*, T. L. Auchtung*, K. S. Swanson*, R. P. Radcliff{dagger}, M. C. Lucy{dagger}, J. K. Drackley* and G. E. Dahl*,2

* Department of Animal Sciences, University of Illinois, Urbana 61801 and and {dagger} Department of Animal Sciences, University of Missouri, Columbia 65211

2 Correspondence:
230 Animal Sciences Laboratory, 1207 W. Gregory Dr. (phone: 217-244-3152; fax: 217-333-7088; E-mail:
gdahl{at}uiuc.edu).


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 
Photoperiod manipulation, specifically a long-day photoperiod (LDPP), increases milk production in lactating cattle. We have previously reported that the galactopoietic effect of LDPP is associated with an increase in circulating IGF-I, which seems to occur independently of changes in concentrations of GH, IGFBP-2, and IGFBP-3. This study tested the hypothesis that LDPP increases the expression of GH receptor (GHR) 1A messenger RNA (mRNA) in the liver. Two groups of Holstein steer calves (98 ± 4 d old) were maintained indoors and exposed to LDPP (16-h light:8-h dark; n = 6) or short-day photoperiod (SDPP; 8-h light:16-h dark; n = 6) for 60 d. Calves were individually fed a grain- and alfalfa-based diet. Jugular blood samples were collected weekly and via cannula at 15-min intervals for a 4-h period on d 1, 26, and 55 of the study to monitor pulsatile hormone secretion. Serum was harvested and assayed for IGF-I, prolactin (PRL), and GH using RIA. Liver biopsies were obtained at 3-wk intervals to quantify changes in hepatic IGF-I and GHR 1A mRNA using real-time PCR. Steer BW increased during the study but did not differ between treatments. No differences in ADG or total DMI were observed. Relative to SDPP, calves on LDPP had higher (P < 0.05) serum IGF-I concentrations. Concentrations of PRL increased (P < 0.01) in calves exposed to LDPP compared with calves exposed to SDPP. Differences (P < 0.05) in pulsatile GH secretion were also detected. Hepatic IGF-I and GHR 1A mRNA were positively correlated with circulating IGF-I concentrations, and although both increased with time, they were not affected by photoperiod treatment. These results confirm that LDPP increases circulating concentrations of IGF-I, but this occurs independently of changes in IGF-I synthesis and GHR 1A mRNA expression in the liver. Therefore, our hypothesis that LDPP increases the expression of GHR 1A mRNA in the bovine liver is rejected.

Key Words: Cattle • Insulin-Like Growth Factor • Photoperiod • Receptors • Somatotropin


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 
Long-day photoperiod (LDPP, 16 to 18 h of light) is galactopoietic in dairy cows (reviewed by Dahl et al., 2000). Typically, milk yield increases 2 to 3 kg/d, with little or no change in milk composition. Although photoperiod management is used by many producers to increase profit, the endocrine mechanism underlying the response is unknown. Relative to cows exposed to photoperiods of less than 12 h (short-day photoperiod, SDPP) circulating prolactin (PRL) increases in cows on a LDPP (Peters et al., 1981; Stanisiewski et al., 1988; Newbold et al., 1991). However, there is compelling evidence to indicate that PRL does not cause the galactopoietic effect on cows under LDPP (reviewed in Dahl et al., 2000).

Growth hormone is galactopoietic in cows (Bauman and Vernon, 1993; Miller et al., 1999), but there is little evidence that LDPP alters secretion of GH (Peters and Tucker, 1978; Miller et al., 1999). The response of milk yield to GH is likely mediated by the action of IGF-I at the mammary gland (Prosser et al., 1990) since bST increases circulating IGF-I (Dahl et al., 1991; Bauman and Vernon, 1993) and alters circulating concentrations of IGFBP (Cohick et al., 1992). We have previously reported that IGF-I increases in lactating cows exposed to a LDPP, but that the increase in IGF-I was independent of changes in GH, IGFBP-2, or IGFBP-3 (Dahl et al., 1997). Collectively, this evidence suggests that the increase in IGF-I in response to LDPP could result from an increase in the secretion of the hormone rather than a change in the clearance of IGF-I. A liver-specific GH receptor, GHR 1A, has recently been identified in cattle (Kobayashi et al., 1999a,b). Nutritional and physiological challenges regulate expression of GHR 1A (Lucy et al., 2001), and thus it is a candidate for mediation of photoperiodic effects in lactating cattle. In the present study, our objective was to quantify changes in GHR 1A messenger RNA (mRNA) expression in response to a LDPP.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Implications
 Literature Cited
 
Experimental Design and Animals
All animal procedures were approved by the University of Illinois Institutional Animal Care and Use Committee. Twelve Holstein steer calves, which averaged 98 ± 4 d in age, were used in this study. Calves were housed for 60 d in temperature-controlled indoor cubicles (20.3 ± 0.1°C) in the Edward R. Madigan Laboratory (Urbana, IL), commencing in October 2000. The calves were balanced for BW, and after a 2-wk acclimation period at 12 h of light and 12 h of darkness (12L:12D), they were assigned to one of two treatments, which consisted of either a LDPP (16L:8D) or a SDPP (8L:16D). Lighting of approximately 553 ± 14 lx at eye level was provided by fluorescent lights, which were controlled by an automatic timer. Lights were turned on at 0700 daily and off at 1500 or 2300 for the SDPP and LDPP treatments, respectively. The design of the experiment is depicted in Figure 1Go (Panel A). Calves were fed individually at 1000 to 1200 daily a diet of a grain mix and cubed alfalfa hay to meet NRC guidelines for protein and energy (NRC, 1989). Feed intake was adjusted for BW every 2 wk and refusals were recorded daily. Water was available at all times.



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  		Figure 1. Panel A: Experimental design showing the hours of light for calves (n = 6) exposed to a long daily photoperiod (16 h/d) and for calves (n = 6) exposed to a short daily photoperiod (8 h/d). Panel B: Circulating concentrations of IGF-I of calves exposed to long ({circ}; 16 h/d) or short (•; 8 h/d) photoperiods. Each symbol represents the mean of calves (n = 6) within that group for the single sample collected weekly. Standard error of the difference (SED) for comparison between groups within each day is indicated by the bar.

 
Blood Sampling
Blood samples (10 mL) were collected weekly by jugular venipuncture using serum vacutainer tubes using 18-gauge needles (Becton Dickinson and Co., Franklin Lakes, NJ) between 0800 and 1000 (i.e., prior to feeding). Additionally, calves were fitted with indwelling jugular cannulas (NLS Animal Health, Kansas City, MO) on d 1, 26, and 55 of the study to collect blood samples at 15-min intervals for a 4-h period to assess pulsatile secretion of GH and PRL. Samples were stored at room temperature for 4 to 6 h and then at 4°C for up to 36 h. Serum was harvested from whole blood after centrifugation for 20 min at 2000 x g and stored at -20°C until assayed for IGF-I, PRL, and GH.

Hormone Analysis
Serum concentrations of IGF-I were determined by RIA after glycylglycine extraction as previously described (Auchtung et al., 2001), with a primary antibody (hIGF-I AFP-4892898; kindly donated by A. F. Parlow, NHPP and NIDDK, Torrance, CA) diluted to a final tube dilution of 1:150,000. Sensitivity for the IGF-I assay averaged 6.4 ng/mL and the intraassay and interassay CV (three assays) averaged 8.6 and 14.5%, respectively. Serum GH was measured by RIA (Connor et al., 1999) with a primary antibody (oGH AFP-C0123080, A. F. Parlow) diluted to a final dilution of 1:72,000. Mean intraassay and interassay CV (three assays) were 9.2 and 10.5%, respectively; assay sensitivity averaged 1.7 ng/mL. Finally, PRL was determined using a previously validated RIA (Miller et al., 1999) with a primary antibody (bPRL AFP-753180, A. F. Parlow) diluted to 1:200,000. Sensitivity averaged 0.3 ng/mL, and the intraassay and interassay CV (six assays) averaged 6.8 and 6.3%, respectively.

Liver Biopsies
Hepatic tissue (300 to 700 mg) was obtained using the technique developed by Swanson et al. (2000). Biopsies were collected on d -2, 19, 40, and 58. Briefly, the calves were moderately sedated with 0.2 mg of xylazine/kg (Vedco, Inc., St. Joseph, MO) and placed on a surgical table in left-lateral recumbency. The right caudo-thoracic area was clipped and scrubbed with an iodophor agent. Following the subcutaneous administration of 1 mL of local anesthetic (lidocaine; Abbott Laboratories, North Chicago, IL), a small incision was made in the skin between the 9th and 10th ribs, approximately 30 cm from the dorsal midline. The biopsy trocar was inserted through the body wall and peritoneum and advanced into the liver using a circular motion. After collection, the liver tissue was immediately frozen in liquid N2 and stored at -80°C until RNA extraction. Following the biopsy, the cutaneous incision was sutured (Henry Schein, Melville, NY) and an antiseptic agent (Prodine; Phoenix Pharmaceutical, Inc., St. Joseph, MO) was applied. Analgesia (Banamine; Schering-Plough Animal Health Corp., Union, NJ) was administered at a dose of 2.2 mL/100 kg of BW following the procedure to alleviate postsurgical discomfort. Additionally, a broad-spectrum prophylactic antibiotic (Excenel; Pharmacia & Upjohn, Kalamazoo, MI) was administered 24 h prior to surgery and immediately postsurgery.

Ribonucleic Acid Extraction
Total cellular RNA was isolated from each liver sample using the TRIzol procedure (Life Technologies Inc., Gaithersburg, MD) and dissolved in 1 mL of UltraPure RNAse free distilled water (Life Technologies Inc.). Concentrations of RNA were determined by measuring absorbance at 260 nm. The purity of the RNA was determined by calculating the ratio of absorbances at 260 nm and 280 nm, and by electrophoresis of an RNA aliquot (2.5 µg) from each sample through a 1% agarose gel in Tris-borate/EDTA buffer (0.09 M Tris-borate and 0.002 M EDTA) with ethidium bromide (0.5 µg/mL). Isolated RNA was stored at -80°C until analysis by real-time PCR (RT-PCR).

Real-Time Polymerase Chain Reaction
Two micrograms of total RNA were used for complementary DNA (cDNA) synthesis using the GIBCO BRL Superscript First-Strand RT-PCR kit (Life Technologies Inc.). Probe and primer sets for bovine GHR 1A, bovine IGF-I, and bovine cyclophilin I (Table 1Go) were purchased from Applied Biosystems (Foster City, CA) and designed using their Primer Express Software. The IGF-I forward primer (in exon 3), reverse primer (in exon 4), and probe (in exon 4) are located in the coding region for the mature IGF-I peptide. The GHR 1A and IGF-I probes were labeled at the 5' end with the reporter dye, FAM, and at the 3' end with the quencher dye, TAMRA. The bovine cyclophilin I probe was labeled with VIC and TAMRA at the 5' and 3' ends, respectively. Amplification mixes (25 µL final reaction volume) contained 2.5 ng of cDNA (2.5 µL), 500 nM of forward primer (2.5 µL), 500 nM of reverse primer (2.5 µL), 100 nM of probe (0.025 µL), 12.5 µL of Taqman Universal PCR Master Mix and 5 µL of RNAse free water. An equal volume of water (no template control) and internal controls (liver samples previously determined to have low, medium, and high expression of GHR 1A mRNA by RPA; our unpublished observations) were run in separate wells on the same plate. All samples and controls were analyzed in triplicate and the reactions were fluorescence quantified with the ABI Prism 7700 sequence detector (Applied Biosystems) based on current methodology (Bustin, 2002). Thermal-cycling conditions for the PCR reaction were 50°C for 2 min, 95°C for 10 min, and then 40 cycles of 95°C for 15 s, and 60°C for 60 s. Analyses of amplification plots were done using Applied Biosystems’ sequence detection software. Threshold cycle (CT) was defined as the cycle at which a sample’s fluorescence equaled the arbitrary threshold (10 times basal fluorescence from cycle 3 through 10) set by the software. The CT values of samples and controls were adjusted initially for the amount of the housekeeping gene, cyclophilin I (CT{Delta}; CT of sample or control-CT of cyclophilin), and then compared to the medium control by subtracting its CT{Delta} to yield a CT{Delta}{Delta}. The final values for samples are reported as a fold difference relative to the expression of the medium control (calculated as 2-CT{Delta}{Delta}), with the medium control arbitrarily set to 1.


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  		Table 1. Sequences encoding primers and probes for bovine GH receptor (GHR) 1A, bovine IGF-I, and bovine cyclophilin I
 
Statistical Analyses
Data were analyzed as a repeated measures design in Data Desk v. 6.1 (Data Description, Inc., Ithaca, NY). The model contained the fixed effects of treatment and time and the interaction of treatment and time. In all analyses, the pretreatment value for that variable was used as a covariate in the ANOVA model; therefore, adjusted treatment means (least squares means) are reported. Hormone concentrations were log transformed before analysis to allow assumption of homogeneous variance. Relationships between serum IGF-I concentration and liver GHR 1A mRNA and IGF-I mRNA abundance were analyzed using the Pearson product-moment correlation function.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Implications
 Literature Cited
 
Dry Matter Intake, Body Weight, and Average Daily Gain
The total DMI from grain and alfalfa hay cubes did not differ (P = 0.64) between treatments, averaging 5.6 and 5.4 kg/d (± 0.3 kg/d) for calves under SDPP and LDPP, respectively (Table 2Go). On average, BW increased from 120.1 ± 6.5 to 173.1 ± 7.3 kg during the study, but there were no differences between treatments for the initial and final BW or for the ADG of LDPP and SDPP calves (Table 2Go).


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  		Table 2. Effects of treatment on dry matter intake, body weight, average daily gain, and serum GH concentrations in calves exposed to a short-day photoperiod (SDPP) or to a long-day photoperiod (LDPP)
 
Insulin-Like Growth Factor-I, Growth Hormone, and Prolactin
Serum IGF-I concentrations increased (P < 0.001) in both treatment groups over the duration of the experiment, with values consistently higher (P < 0.05) for calves exposed to a LDPP relative to those on a SDPP (Figure 1Go, Panel B). Photoperiod treatment did not affect (P = 0.31) weekly circulating GH concentrations (pooled means were 33.2 ± 1.8 ng/mL and 29.4 ± 3.5 ng/mL for LDPP and SDPP calves, respectively; Table 2Go). No differences (P = 0.95) in pulsatile GH secretion were measured on d 1 of the experiment (pretreatment). However, GH secretion was significantly (P < 0.05) higher in LDPP calves compared with SDPP calves on d 26, and although GH concentrations decreased in both treatment groups by d 55, values tended (P < 0.10) to be higher in LDPP calves (Table 2Go). No differences in pulsatile PRL secretion were detected on d 1 of the experiment, but PRL concentrations were higher (P < 0.01) in calves exposed to a LDPP by d 26 and remained elevated at d 55 compared to their SDPP counterparts (Figure 2Go). This trend was consistent throughout each 4-h sampling period (Figure 2Go, inset) and over the duration of the experiment (Auchtung et al., 2002).



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  		Figure 2. Circulating concentrations of prolactin (PRL) of calves exposed to long ({square}; 16 h/d) or short ({blacksquare}; 8 h/d) photoperiod. Each symbol represents the pooled means (± the standard error of the difference, SED) of calves (n = 6) within that group for the 13 samples collected during each 4-h period on d 1, 26, and 55 of the experiment. aDenotes differences between treatments (P < 0.01). The inset depicts pulsatile PRL secretion of a representative calf exposed to either a long ({circ}) or a short (•) photoperiod from samples collected during the 4-h period on d 26 of the experiment.

 
Insulin-Like Growth Factor-I and Growth Hormone Receptor 1A Messenger RNA Expression
In general, hepatic IGF-I mRNA expression increased over time but was not affected (P = 0.67) by photoperiod treatment (Figure 3Go). Likewise, the amount of GHR 1A mRNA increased from pretreatment values, but there was no difference (P = 0.56) between LDPP and SDPP calves on subsequent days (Figure 3Go). Analysis of all calves regardless of treatment and time revealed that the expression of IGF-I mRNA was positively correlated with serum IGF-I concentration (r = 0.49, P < 0.001). There was also a positive relationship between circulating IGF-I concentrations and hepatic GHR 1A mRNA abundance (r = 0.43, P < 0.01).



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  		Figure 3. Relative abundance of GH receptor (GHR) 1A mRNA (top panel) and IGF-I mRNA (bottom panel) collected from liver on d -2, 19, 40, and 58 from calves (n = 6) exposed to long ({square}; 16 h/d) or short ({blacksquare}; 8 h/d) photoperiods. Values are expressed as the fold difference in arbitrary units (AU) relative to the expression from a medium control. Bars represent means ± standard error of the difference (SED).

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Implications
 Literature Cited
 
The observation that a LDPP increased circulating PRL concentrations in cattle relative to those exposed to a SDPP is consistent with other reports (Peters et al., 1981; Stanisiewski et al., 1988; Newbold et al., 1991), confirming the marked influence of photoperiod on PRL secretion. A divergence of PRL concentration profiles in LDPP calves vs. SDPP calves was apparent within 1 wk of photoperiod treatment and remained different for the duration of the experiment. In general, PRL concentration increased by 2.1-fold in calves exposed to a LDPP, which was of a magnitude similar to earlier studies (Peters et al., 1981; Newbold et al., 1991). Of interest, serum PRL concentrations also exhibited a temporal increase in SDPP steers in the present study. This increase was likely due to the abrupt change in ambient temperature (Smith et al., 1977), as the calves were originally subjected to cooler autumn temperatures prior to entering their temperature-controlled cubicles.

As seen in previous studies (Spicer et al., 1994; Dahl et al., 1997), our results showed that serum IGF-I concentration in cattle was affected by photoperiod. That is, IGF-I concentrations were consistently higher in steers exposed to a LDPP when compared with their counterparts under a SDPP regime. In lactating dairy cows, such an endocrine environment is accompanied by a corresponding increase in milk yield (Dahl et al., 1997). An age-dependent increase in circulating IGF-I concentrations is well known in the bovine (Plouzek and Trenkle, 1991; Spicer et al., 1994; Cordano et al., 2000), and this trend was also seen in our study irrespective of photoperiod treatment. Steers exposed to LDPP, however, exhibited the greatest temporal increase in serum IGF-I concentrations, which is indicative of the control that the pineal hormone melatonin exerts on the endocrine system as a mediator of photoperiodic responses (Reiter, 1991). Indeed, melatonin feeding to mimic a SDPP suppresses the long day-induced increment of IGF-I secretion in cattle (Smith et al., 1997). Since the animals in our study were fed to a controlled individual intake and no differences in BW or ADG between LDPP and SDPP steers were observed, it is unlikely that changes in the IGF system could be attributed to variation in nutritional status (McGuire et al., 1992).

Contrary to the influence of photoperiod on PRL and IGF-I concentrations, there has been little evidence to suggest that LDPP has any effect on GH secretion in heifers (Peters and Tucker, 1978), steers (Borromeo et al., 1994), or cows (Miller et al., 1999). Weekly GH concentrations in LDPP and SDPP steers in our experiment concur with this premise. However, the measurement of pulsatile GH secretion at three separate time points (d 1, 26, and 55 of photoperiod treatment) revealed that GH concentrations were higher in LDPP steers vs. SDPP steers on d 26 and 55. This discrepancy may be indicative of the problems with using a single weekly sample to ascertain patterns of secretion in pulsatile hormones such as GH, although another study found no photoperiod-induced differences in pulsatile GH secretion in prepubertal cattle (Zinn et al., 1986). Furthermore, there was an appreciable temporal decline in GH concentration, in agreement with another report (Plouzek and Trenkle, 1991) that GH levels decreased as prepubertal cattle aged.

Consistent with a recent study (Cordano et al., 2000), measurement of hepatic IGF-I mRNA expression revealed a progressive increase associated with the development of the calves. As observed in periparturient cows (Kobayashi et al., 1999a), where changes in GHR 1A mRNA were closely linked with alterations in liver IGF-I mRNA and blood IGF-I concentrations, the amount of GHR 1A mRNA generally mirrored the relative abundance of IGF-I mRNA and serum IGF-I concentration in the present experiment. Given that IGF-I production in the liver represents the main source for circulating IGF-I (Jones and Clemmons, 1995), this relationship is consistent with the hypothesis that the overall increase in IGF-I secretion into circulation was dependent on a concomitant increase in liver IGF-I synthesis. The lack of any photoperiodic effect on the amount of IGF-I mRNA in liver was unexpected, but it should be noted that the photoperiod-induced increase in circulating IGF-I was not of the same magnitude as those previously measured in dairy cows under different experimental and physiological conditions (Kobayashi et al., 1999a,b). Therefore, it remains possible that alterations in hepatic IGF-I synthesis do indeed account for the increase in circulating levels of IGF-I under LDPP but that these changes were too small to be detected in our study. The interaction of IGF-I and its binding proteins under different physiological states or between sexes must also be considered.

Increases in circulating IGF-I concentration in LDPP calves were observed without any coincident increase in hepatic GHR 1A mRNA expression. Since GH is an important regulator of IGF-I and IGFBP (Jones and Clemmons, 1995), and GHR 1A is critical for normal IGF-I mRNA expression and normal growth in cattle (Liu et al., 1999), it was expected that the amount of GHR 1A mRNA would be increased under LDPP conditions. Certainly, treatment with bST that increases serum IGF-I concentrations and hepatic abundance of IGF-I mRNA in lactating dairy cows (Sharma et al., 1994; Kobayashi et al., 1999b) also upregulates GHR 1A mRNA (Kobayashi et al., 1999b). Other endocrine changes include a marked increase in serum IGFBP-3 levels, but a decline in IGFBP-2 levels (Cohick et al., 1992; Sharma et al., 1994). Collectively, this suggests that the galactopoietic effects of bST are likely due to increased IGF-I synthesis in the liver. However, in the absence of any consistent response of GH or significant changes in hepatic IGF-I mRNA in the present study, alternative explanations for the galactopoietic effect of LDPP must also be considered.

In dairy cows, milk yield is higher in early lactation than during late lactation, whereas concentrations of IGF-I in blood follow the inverse pattern (Sharma et al., 1994; Kobayashi et al., 1999a). Both responses are magnified in dairy cows exposed to a LDPP, although the same trend remains. This increase in IGF-I could possibly be modified by alterations in IGFBP, and therefore the activity of the IGF system at the mammary gland. In conflict with this hypothesis is the observation that serum concentrations of IGFBP-3 were unchanged over lactation, although IGFBP-2 concentrations were highest during early lactation (Vicini et al., 1991; Sharma et al., 1994). In the context of this study, photoperiod has been reported to have no effect on the abundance of IGFBP-2 and IGFBP-3 (Dahl et al., 1997), suggesting that LDPP did not increase circulating concentrations of IGF-I via a decrease in the clearance of IGF-I.

It is possible that the increase in circulating IGF-I is the result of photoperiod-induced changes in the concentration of other members of the IGFBP family. Of particular interest is IGFBP-5, which is thought to play a key role during mammary involution. More importantly, PRL, which is a major inhibitor of apoptosis, also inhibits IGFBP-5 synthesis (Tonner et al., 1997; Accorsi et al., 2002). The quantification of IGFBP-5 abundance and other key IGFBP in response to a LDPP is currently under investigation. Additionally, the responsiveness of the liver to GH may be changed by a LDPP, leading to an alteration in IGF-I synthesis. The measurement of the correlation between the GHR protein and GHR 1A mRNA with GH binding to liver would also be of interest.


   Implications
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Implications
Literature Cited
 
The use of photoperiod management is gaining wider acceptance among producers in an effort to increase milk production in lactating cows. Although the increase in milk yield has been associated with an increase in circulating insulin-like growth factor-I concentration, the mechanism producing this response is unknown. This study confirms earlier observations that exposure to long-day photoperiod increases insulin-like growth factor-I concentration in cattle and provides additional evidence that the long-day photoperiod-induced increase in insulin-like growth factor-I concentration can occur independently of changes in the expression of hepatic growth hormone receptor 1A messenger ribonucleic acid, or an increase in insulin-like growth factor-I synthesis in the liver. It is possible that the galactopoietic effects of long-day photoperiod are associated with changes in the abundance of other insulin-like growth factor binding proteins, or are the result of modified binding of growth hormone to its receptor in the liver.


   Footnotes
 
1 This project was supported by the Illinois Council on Food and Agricultural Research (C-FAR) and the University of Illinois Research Board. We are grateful to the ERML Animal Care Facilities staff for the daily feeding and maintenance of the animals. Back

Received for publication July 30, 2002. Accepted for publication February 3, 2003.


   Literature Cited
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 


Accorsi, P. A., B. Pacioni, C. Pezzi, M. Forni, D. J. Flint, and E. Seren. 2002. Role of prolactin, growth hormone, and insulin-like growth factor 1 in mammary gland involution in the dairy cow. J. Dairy Sci. 85:507–513.[Abstract]

Auchtung, T. L., E. E. Connor, S. M. Barao, L. W. Douglass, and G. E. Dahl. 2001. Use of growth hormone response to growth hormone-releasing hormone to determine growth potential in beef heifers. J. Anim. Sci. 79:1566–1572.[Abstract/Free Full Text]

Auchtung, T. L., P. E. Kendall, J. Salak-Johnson, T. B. McFadden, and G. E. Dahl. 2002. Photoperiod alters prolactin receptor messenger ribonucleic acid expression in bovine liver, mammary, and lymphocytes. J. Anim. Sci. 80(Suppl. 1):34. (Abstr.)

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Connor, E. E., S. M. Barao, L. W. Douglass, S. A. Zinn, and G. E. Dahl. 1999. Predicting bull growth performance and carcass composition from growth hormone response to growth hormone-releasing hormone. J. Anim. Sci. 77:2736–2741.[Abstract/Free Full Text]

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Dahl, G. E., T. H. Elsasser, A. V. Capuco, R. A. Erdman, and R. R. Peters. 1997. Effect of a long daily photoperiod on milk yield and circulating concentrations of insulin-like growth factor-I. J. Dairy Sci. 80:2784–2789.[Abstract]

Jones, J. I., and D. R. Clemmons. 1995. Insulin-like growth factors and their binding proteins: Biological actions. Endocrinol. Rev. 16:3–34.[Medline]

Kobayashi, Y., C. K. Boyd, C. J. Bracken, W. R. Lamberson, D. H. Keisler, and M. C. Lucy. 1999a. Reduced growth hormone receptor (GHR) messenger ribonucleic acid in liver of periparturient cattle is caused by a specific down-regulation of GHR 1A that is associated with decreased insulin-like growth factor I. Endocrinology 140:3947–3954.[Abstract/Free Full Text]

Kobayashi, Y., M. J. Vandehaar, H. A. Tucker, B. K. Sharma, and M. C. Lucy. 1999b. Expression of growth hormone receptor 1A messenger ribonucleic acid in liver of dairy cows during lactation and after administration of recombinant bovine somatotropin. J. Dairy Sci. 82:1910–1916.[Abstract]

Lucy, M. C., H. Jiang, and Y. Kobayashi. 2001. Changes in the somatotropin axis associated with the initiation of lactation. J. Dairy Sci. 84:113–119.

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