D. M. Henricks

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.

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)

Residues from anabolic preparations after good veterinary practice.

The purpose of this study was to determine the endogenous concentrations of estrogens, particularly estradiol‐17β (E2β), in edible tissues of beef cattle (females and intact and neutered males) and the concentrations of E2β, and trenbolone beta and alpha (βTb, αTb) after an E2β and/or trenbolone acetate (TA) ear implant. Radioimmunoassays were validated for quantitation of E2β (active isomer), E2α, estrone (E1), βTb and αTb 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 E2β was <15 ppt, as was heifer muscle; but heifer liver and kidney were 3‐fold greater. An E2β implant in steers had no effect on muscle E2β concentration, but increased E2β in liver and fat 4‐ and 3‐fold, respectively, but by 24 h post‐implant removal, E2β had fallen by half. Tissue E1 concentrations in cyclic females were similar to E2β, but rose many fold greater than did E2β during gestation; E2β rose 3‐fold during gestation. After E2β/TA implant, steer tissues had E2β concentrations equal to (for muscle and fat) and one‐half (for liver) the E2β measured in E2β implant only steers; βTb was in a low range (250–380 ppt) in muscle, liver and fat and αTb was even lower, except in liver (800–1500 ppt). An implant of TA only (no E2β) resulted in βTb and αTb concentrations 2–3‐fold greater in liver, kidney and fat, but no greater in muscle than βTb in tissues of E2β/TA implant steers. In conclusion, anabolic implants in steers resulted in tissue E2β concentrations less than the FDA allowable increment and βTb in the lowest quartile (0.25) of a part per billion 30 days after implant.

Plasma hormone levels in beef heifers during prostaglandin-induced parturition☆☆☆

Plasma hormone levels were determined at frequent intervals in 12 two-year-old Hereford heifers after treatment with prostaglandin F2α on day 267 of gestation to induce parturition. Of the 12 animals, six also received a daily injection of estradiol-17β until calving occurred. An additional six heifers received no treatment and therefore served as a control group. The treatment with PGF2α was effective since the treated heifers calved a mean of 12 days sooner than the untreated heifers (P < .01). A metabolite of PGF2α, 13, 14-dihydro-15-keto PGF2α, rose to a peak level in the plasma within one hour after injection (im) of PGF2α then declined to a baseline level within four hours. The plasma progesterone level had fallen significantly within two hours after injection, but no change in plasma estradiol-17β or estrone was observed. In the eight heifers that responded, plasma estrogen levels were greater at the time of treatment than in the four heifers that did not respond.

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.

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.

Synchronization of estrus after treatment with Luprostiol in beef cows and in beef and dairy heifers

Four trials were conducted to study synchronous estrous response in beef cows and in beef and dairy heifers to Luprostiol (13, thia-PG-F(2)alpha analog) in comparison with other prostaglandin products. In Trial 1, 60 virgin beef heifers were observed for estrus for 5 d and artificially inseminated. Heifers not observed in estrus within 5 d were randomly assigned to receive 15 mg Luprostiol or 25 mg Lutalyse. In Trial 2, 75 multiparous, lactating beef cows were randomly assigned to receive either 15 mg Luprostiol, 25 mg Lutalyse or 500 mcg Estrumate. All cows received a second injection of the respective treatment 11 d later. In Trial 3, 96 multiparous, lactating beef cows were randomly assigned to receive 15 mg Luprostiol or 25 mg Lutalyse. All cows received a second injection of the respective treatment 11 d later. In Trial 4, virgin dairy heifers were palpated per rectum. Seventy-seven heifers with a palpable corpus luteum (CL) were randomly assigned to receive 15 mg Luprostiol or 500 mcg Estrumate. In all trials animals were artificially inseminated 12 h following observed estrus. Estrous response during the 5-d synchronized period was 44% for Luprostiol and 42% for Lutalyse treated heifers in Trial 1. It was 52, 56 and 60%, respectively, for Luprostiol, Lutalyse and Estrumate treated cows in Trial 2; 23% for Luprostiol and 19% for Lutalyse treated cows in Trial 3; and 68% for Luprostiol and 70% for Estrumate treated heifers in Trial 4. Treatment with Luprostiol results in a similar synchronous estrous response as with the other prostaglandin products used in these studies.

Effect of holding time and temperature of bovine whole blood on concentration of progesterone, estradiol-17β 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.

Induction of parturition in the sow with prostaglandin F2α

Sows were injected with prostaglandin F2α to induce parturition. Blood was collected to determine the effect of PGF2α on plasma progesterone and estrogen levels. Parturition occurred significantly earlier (P<.01) in the 14 treated animals than in the 9 untreated animals. Nine out of fourteen treated sows farrowed within 48 h after treatment. Whereas untreated sows farrowed 11.6 ± 6.7 h after the predicted time of parturition, treated sows farrowed 48 ± 8.8 h before the predicted time. PGF2α was most effective in those sows in which plasma progesterone decreased quickly. Plasma estrogen levels remained reasonably constant after treatment.

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.