Biomedical subjects

H Lapierre

Publications and source records attributed to H Lapierre.

At least 37 records · Page 2Linked to original sources

PubMed2000

The effect of intake level on whole body kinetics and hepatic removal of somatotropin in growing beef steers.

The effect of level of intake of a high concentrate diet (0.6, 1.0 and 1.6 x maintenance requirements, M) on whole body somatotropin (St) kinetics was evaluated in six growing, multicatheterized beef steers (398+/-27 kg), using a double 3x3 Latin Square design with 21 d-periods. Simultaneously to St kinetics, net hepatic removal of St was measured in 4 of the 6 steers. On the last day of each period, concentrations and net fluxes of St were determined, first in basal conditions for 5 hr, and then, during a primed (0.5 mg of St) infusion of bovine St (1.5 mg/hr) administered for 3 hr. The following results are LSM +/- SEM for 0.6, 1.0, and 1.6 x M, respectively. Increasing feed intake linearly decreased (P<0.01) basal St concentrations (5.6, 4.6, 3.1+/-0.62 ng/ml), mainly through a linear increment (P<0.01) in the metabolic clearance rate (32.7, 37.1, 43.4+/-2.60 l/hr), although secretion rate also tended to decrease (P = 0.09; 189, 185, 135+/-27.2 microg/hr). During the infusion period, net liver removal of immunoreactive ST averaged 60% of the total inflow of St. This confirms the liver is capable of removing large amounts of St, suggesting it has an important role in metabolic clearance of the hormone. Net liver removal of St, however, was not affected by intake. There was a strong correlation between the metabolic clearance rate of St with either whole body protein synthesis (r = 0.75, P<0.01) or protein retention (r = 0.68, P<0.01). Together these results indicate the importance of postsecretory metabolism of St in determining both arterial plasma concentrations of St and whole body protein anabolism.

Animal Feed↗

PubMed2000

The effect of feed intake level on splanchnic metabolism in growing beef steers.

The effect of feed intake level (.6, 1.0, and 1.6 x maintenance energy and protein requirements, M) on splanchnic (portal-drained viscera [PDV] plus liver) metabolism was evaluated in six multicatheterized beef steers (398 +/- 27 kg), using a double 3 x 3 Latin square design. On the last day of each 21-d experimental period, six hourly blood samples were collected from arterial, portal, and hepatic vessels. Due to catheter patency, PDV fluxes were measured on five steers, and liver and splanchnic fluxes on four steers. Increasing intake elevated (P < .01) splanchnic release of total (T) amino acids (AA), through increases (P < .01) in PDV release of both essential (E) and nonessential (NE) AA, in spite of a tendency (P < .20) for increased liver removal of NEAA. The PDV release of AA N represented 27 and 51% of digested N for 1.0 and 1.6 x M, respectively. At 1.0 and 1.6 x M, the liver removed 34% of total AA released by the PDV. For individual AA, portal flux of most EAA increased (P < .05) with feed intake, and the increase (P < .10) in splanchnic flux was accompanied by increased arterial concentration for all EAA except histidine, lysine, and methionine. This suggests that these might be limiting AA for this diet. On a net basis, most individual NEAA were released by the PDV except glutamate and glutamine, which were removed by the digestive tract. There was a net removal of NEAA by the liver, except for aspartate and especially glutamate, which were released. Ammonia release by the PDV tended (P < .20) to increase with intake and represented 69, 53, and 45% of digested N at .6, 1.0, and 1.6 x M, respectively. Urea removed by the PDV, unaffected by intake, represented 32, 33, and 21% of the digested N. Arterial glucose concentration increased linearly (P < .01) with greater intake, whereas net liver and splanchnic glucose release increased in a quadratic (P < .05) manner. Net PDV glucose release represented 26% of net glucose hepatic release at 1.6 x M. Intake elevated (P < .10) both insulin and glucagon arterial concentrations, resulting from a larger increment of portal release (P < .01) than hepatic removal (P < .05). Intake-based variations in IGF-I and NEFA arterial concentrations (P < .05) were not related to changes in splanchnic metabolism. These results clearly show the crucial role of the splanchnic tissues in regulating the profile and quantity of AA and concentrations of glucose and pancreatic hormones reaching peripheral tissues.

Amino Acids↗

PubMed2000

Comparison of the in situ and in vivo intestinal disappearance of ruminally protected methionine.

We designed a switchback expriment to compare the intestinal disappearance of ruminally protected Met determined in situ or in vivo over three consecutive periods. Four nonlactating Holstein heifers (477+/-36 kg) with cannulae in the rumen, duodenum, and ileum were fed a diet based on timothy silage to meet requirements for maintenance (dry matter intake = 8.72+/-0.15 kg). A total of 16 bags, containing 1.5 g of ruminally protected Met, were incubated in the rumen (4.5 h) of each cow and transferred to an acid-pepsin solution to simulate the abomasum (2.5 h). Following each incubation, bags were recovered and three bags were dried at 55 degrees C and analyzed for Met. Remaining bags were introduced directly into the duodenal or ileal cannula for the in situ method, while for the in vivo method, the content of remaining bags was transferred into gelatin capsules before their introduction in the duodenal or ileal cannula. Spot samples of digesta were collected during a 96-h period, with Co-EDTA and Cr-mordanted fiber used as indigestible markers to estimate in vivo digestibility. The disappearance of Met in the small intestine determined in vivo tended to be higher than in situ (74.45 vs. 43.65+/-1.79%). Our results indicate that when used to assess intestinal availability of ruminally protected Met, the mobile nylon bag technique can underestimate the true bioavailability of Met.

Animals↗

PubMed2000

External pudic venous reflux into the mammary vein in lactating dairy cows.

A representative blood sample from the mammary vein depends on the functional integrity of the valves in the external pudic vein (EPV). To determine if the EPV valves maintain blood flow into the inguinal direction during the second and subsequent lactations, we used eight lactating cows catheterized in the EPV, the lateral branch of the cranial mammary vein (MV), and the external pudic artery (EPA). The averaged daily milk yields were 25.0 +/- 1.8 kg in cows in second lactation and 31.5 +/- 2.9 kg in older cows. The relative time taken by a pulse dose of p-amino hippuric acid (PAH) injected into the EPV, to reach the EPA and the MV, was measured in a first trial. In a second trial, we assessed the extent of alteration of the mammary PAH blood concentration with blood originating from other tissues using a continuous infusion of PAH into the EPA simultaneously with blocking or not any EPV backflux. From the first experiment, the PAH injected into the EPV appeared first in the EPA and then in the MV in cows in second lactation, suggesting that blood flow was towards the inguinal region. But in a third-lactation cow, the order of appearance was reversed. In parallel, the occlusion trial demonstrated that the concentration of PAH in the MV was diluted by 14 to 39% with blood draining nonmammary tissues only in cows in third or fourth lactation. This resulting reversed flow from the EPV towards the MV would have a detrimental impact on conclusions of mammary gland metabolism studies conducted with cows in their third lactation or higher.

Animals↗

PubMed1999

The effect of intake on protein metabolism across splanchnic tissues in growing beef steers.

The contribution of the total splanchnic tissue (TSP; portal-drained viscera (PDV) plus liver) to whole-body protein metabolism was estimated in relation to intake (0.6, 1.0 and 1.6 x maintenance requirements), in six multicatheterized growing beef steers used in a double 3 x 3 Latin square design. At the end of each 21 d experimental period, [1-13C]leucine was infused into a jugular vein (1.05 mmol/h for 5 h, preceded by a priming dose of 1.05 mmol). Arterial, portal and hepatic blood samples were collected hourly during the infusion. The increment in TSP leucine irreversible loss rate (ILR) observed with increasing intake reached significance (P < 0.10) only for PDV, while whole-body ILR increased markedly (P < 0.001) with intake. The relative contribution of TSP to whole-body leucine ILR averaged 44% (25% from PDV and 19% from the liver). Although these proportions were not affected by intake, on an incremental basis more than 70% of the increase of whole-body leucine ILR between the 0.6 and 1.0 x maintenance originated from the changes in TSP ILR, while the corresponding value was below 13% between 1.0 and 1.6 x maintenance. Total whole-body leucine oxidation and fractional oxidation increased (P < 0.05) with intake. Protein retention increased with intake (P < 0.01), as a result of a greater increase in protein synthesis compared with protein degradation. Protein breakdown had a major impact on protein turnover as 65% of the protein synthesized was degraded when intake varied from 1.0 to 1.6 x maintenance. Net leucine portal absorption increased (P < 0.001) with intake and represented 1, 16 and 23% of whole body leucine ILR, for 0.6, 1.0 and 1.6 x maintenance, respectively. Although leucine oxidation was not a major component of whole body ILR (9.3-19.9%), it represented 69% of the net available leucine (portal absorption) even at 1.6 x maintenance. The lower relative contribution of the TSP to whole-body leucine ILR at higher intake indicates the proportional increase in the metabolic activity of peripheral tissues as the animals moved into positive protein balance.

Analysis of Variance↗

PubMed1998

Effect of aging on growth hormone-induced insulin-like growth factor-I secretion from cultured rat chondrocytes.

The physiological roles of growth hormone (GH) and insulin-like growth factor-I (IGF-I) in adult other than their effects on tissue growth is to maintain the integrity of the organism. It has been proposed that reduced availability of both hormones in late adulthood may contribute to the initiation of the major alterations and senescent changes in body composition that characterize normal human aging. Since accumulated evidence points to a direct interplay of GH with chondrocytes in cartilage, we determined in the present study the effect of aging on both basal and GH-stimulated IGF-I production from rat cultured chondrocytes. Namely, we investigated the effect of 0, 10 and 100 ng/ml of growth hormone on IGF-I levels during 1, 2, 4 and 8 days in monolayer cultured costal chondrocytes from 2-, 6-, 14- and 18-month-old rats. Measurement of IGF-I levels was done by a radioimmunoassay following a validated formic acid-heating-acetone extraction procedure. In 6- and 14-month-old rat chondrocytes, basal IGF-I secretion was higher than that of the 2-month-old control rats. In 18-month-old rat chondrocytes, basal IGF-I secretion was lower than in any other age group. Whereas in 2-, 6- and 14-month-old rat chondrocytes, GH induced a dose-related IGF-I response which was highly significant on day 8, the 18-month-old rat chondrocytes no longer responded to GH treatments. Our results suggest that the decrease in IGF-I production from cultured rat chondrocytes could be related to the blunted GH secretion in the course of aging. Therefore, GH availability in the course of aging appears to be a determinant factor in tissue responsiveness and underscores the hypothesis that GH replacement could present a therapeutic potential against the aging senescent changes.

Aging↗

PubMed1998

Nitrogen balance and mineral excretion in growing male pigs injected with a human growth hormone-releasing factor analog.

A human growth hormone-releasing factor analog ([Desamino-Tyr1,D-Ala2,Ala15] hGRF(1-29) NH2) has been reported to reduce feed intake and increase growth and feed efficiency in a dose-dependent manner in growing pigs. The aim of this study was to determine the effect of this analog on nitrogen (N) balance and mineral excretion. Fifteen castrated male Yorkshire x Landrace pigs (45.9 +/- 1.4 kg) were randomly allotted to 2 groups: control (saline, n = 7) and GRF (6.66 micrograms/kg sc, TID, n = 8). The animals were injected for 20 consecutive days: feces and urine were collected during the last 10 d of injection. The animals had free access to water and food until satiety (approximately 15 min) at 07:00, 11:00, 15:00, 19:00, 23:00 and 07:00 h. The diet consisted of a hog fattening ration (18.0% crude protein). Blood samples were collected on the last day of the study by venipuncture. This analog increased (P < 0.05) insulin-like growth factor-1 and glucose serum concentrations and decreased (P < 0.05) serum urea nitrogen concentration and feed intake. The GRF-treated animals ingested less N, excreted less N in urine and feces to retain a similar amount of N than controls. The apparent coefficient of digestibility of the N has been slightly increased (P < 0.05) by GRF. Urinary excretion of P, K, and Cl decreased (P < 0.01) with GRF treatment. In conclusion, this GRF analog increased N digestibility and retention relative to N ingestion and reduced urinary N, P, K, and Cl excretion.

Animals↗

PubMed1997

Biochemistry reference values for Quebec lactating dairy cows, nursing sows, growing pigs and calves.

Reference values for lactating dairy cows, nursing sows, growing calves and pigs were established on jugular cannulated animals. On each day of sampling, 13 samples were taken every hour from dairy cattle, growing calves and pigs and 5 samples were taken every 2 h from nursing sows to minimize day and analysis bias. Results show that aging influences more biochemical factors in pigs than in calves, and in nursing sows variations observed between day 5 and 15 after farrowing are of greater amplitude than between day 15 and 25.

Aging↗

PubMed1995

The effect of feed intake and growth hormone-releasing factor on lactating dairy cows.

Twenty-four lactating dairy cows, averaging 30.0 kg/d of milk and 159 d of lactation, were used to study the effect of feed intake and growth hormone-releasing factor in a 2 x 2 factorial arrangement. For the first 10-d period, cows had free access to a TMR and received a fixed amount of high moisture corn, protein supplement, and hay. In the second 10-d period, 12 cows were maintained on this high intake, and 12 cows received 70% of their previous intake (low intake). During the following 10-d period, each intake group was divided, and each of two subgroups (n = 6) received twice daily s.c. injections of saline or growth hormone-releasing factor (10 micrograms/kg of BW per injection). Feed restriction decreased milk production by 24%. Milk production increase was not different following growth hormone-releasing factor treatment for cows maintained at high intake (4.6 kg/d) or low intake (3.4 kg/d). Feed restriction increased concentration of growth hormone but did not affect IGF-I concentration. Growth hormone-releasing factor increased IGF-I concentration similarly for both intake groups but increased concentrations of insulin and IGF-binding proteins-1 and -3 only in the high intake group. Low intake did not affect growth hormone, IGF-I, or milk responses to growth hormone-releasing factor, but suppressed the increase in concentrations of insulin and IGF-binding proteins-1 and -3 following treatment with growth hormone-releasing factor for cows on high intake.

Animal Feed↗

PubMed1993

Age-related changes in secretion rate and post-secretory metabolism of growth hormone in swine.

The effect of age on growth hormone (GH) metabolism and GH-releasing factor (GRF)-induced GH concentrations were studied in 7 young (3 mo, 39 kg) and 7 old (30 mo, 156 kg) Yorkshire x Landrace female pigs. Jugular catheters were surgically inserted and 60 hr later total serum volume was determined. The following day, all animals were infused for 3 hr with GH (30.3 ng.min/kg B.W.) in order to calculate GH metabolic clearance rate (MCR), secretion rate (SR) and half-life (t 1/2). Two days later, 15 micrograms/kg of GRF was injected i.v. into all pigs. On a per animal basis, aging increased (P < .01) MCR (299 vs 132 ml/min), SR (714 vs 422 ng/min) and serum volume (6.6 vs 2.01), whereas t1/2 was unaltered (P > .1). Basal GH concentrations were lower in older pigs (P < .10) but the GRF-induced GH concentrations (measured as GH peak or area under the curve, AUC) were not affected by age (P > .1). Yet, when induced total GH secretion (AUC x MCR) and average total serum GH (mean GH post-injection x serum volume) were calculated per pig, these variables significantly increased between 3 and 30 mo of age. Basal IGF-I concentrations were lower in older pigs (P < .01), yet, there was a tendency (P = .10) for these pigs to show a greater IGF-I response to GH infusion. The present data therefore indicate that age alters both SR and post-secretory metabolism of GH.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1992

Effect of age and intake on growth hormone kinetics in dairy heifers.

The effects of aging and intake on growth hormone (GH) kinetics and GH-releasing factor (GRF)-induced GH concentrations were studied in two groups of 12 Holstein heifers each (80 d, 85 kg: young; and 273 d of age, 246 kg: old). Each group was then equally subdivided into full-fed (FF) and restricted-fed (RF) subgroups. After 11 d of intake treatment, animals were infused for 3 hr with GH (1.5 mg/hr) in order to calculate GH metabolic clearance rate (MCR), secretion rate (SR) and half-life (t 1/2). Two d later, total plasma volume was determined and the following day, all heifers received a GRF challenge (5 micrograms/kg i.v.). The following values are LSM +/- SE for young-FF, young-RF, old-FF and old-RF. Rate of secretion was not affected by any treatment, averaging 1.51, 1.25, 1.34, and 1.40 +/- .23 micrograms/min. Aging increased (P < .01) MCR (186, 159, 382, and 300 +/- 21 ml/min) and increased plasma volume (P < .01), which resulted in lower basal GH concentrations. Aging also decreased (P < .01) the area under the GH response curve following GRF injection (AUC: 12442, 21114, 5155, and 6308 +/- 1776 ng.min/ml) but did not affect average GH quantity in the plasma after the GRF challenge. Feed restriction decreased (P < .05) MCR, but not enough to affect basal GH concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1992

Effects of growth hormone-releasing factor and feed intake on energy metabolism in growing beef steers: net hormone metabolism by portal-drained viscera and liver.

Effects of growth hormone-releasing factor (GRF) and intake on arterial concentrations and net visceral metabolism of hormones were measured in six growing Hereford x Angus steers using a split-plot design with 4-wk injection periods within 8-wk intake periods. Steers were fed a 75% concentrate diet at two intakes and were injected s.c. twice daily with saline or GRF (10 micrograms/kg of BW). Arterial concentrations of growth hormone (GH) were measured on d 1 and d 8 to 10 of injections. Eleven measurements, obtained at 30-min intervals, of arterial concentration and net flux of hormones across portal-drained viscera (PDV) and liver were obtained on d 8 to 10 of injections (six hourly measurements were used for insulin-like growth factor-I [IGF-I] and somatostatin). The area under the GH curve and average and peak GH concentrations were increased (P less than .01) by GRF and were greater (P less than .10) at low than at high intake. Liver removal of GH was not affected by GRF or intake. Arterial IGF-I concentration was increased (P less than .05) by GRF and not affected by intake. Treatments did not affect IGF-I flux across the liver. Arterial insulin concentration was greater (P less than .05) at high than at low intake, in part because of greater (P less than .01) PDV release. Increased (P less than .10) arterial insulin concentration in GRF-treated steers was not attributable to significant changes in PDV or liver net flux. Arterial glucagon concentration was greater (P less than .01) at high than at low intake, in part because of greater (P less than .05) PDV glucagon release and decreased (P less than .10) liver extraction ratio. Effects of intake on arterial concentration of insulin and glucagon were in part due to changes in visceral metabolism, but GRF did not affect PDV or liver hormone metabolism.

Animals↗

PubMed1992

Effects of growth hormone-releasing factor and feed intake on energy metabolism in growing beef steers: net nutrient metabolism by portal-drained viscera and liver.

Effects of growth hormone-releasing factor (GRF) and intake on net nutrient metabolism by portal-drained viscera (PDV) and liver were measured in six growing Hereford x Angus steers fed a 75% concentrate diet at two intakes in a split-plot design with 4-wk saline or GRF injection periods within 8-wk intake periods. Daily rations were fed as 12 equal meals delivered every 2 h. Steers were injected s.c. for 21 d with either saline or 10 micrograms/kg of (1-29)NH2 human GRF at 12-h intervals. Six hourly measurements of net nutrient flux (venous-arterial concentration different [VA] x blood flow) across PDV and liver were obtained 8 to 10 d after injections began. Energy and N balances were measured using respiration calorimetry during the last week of injections. Greater intake increased blood flow (P less than .01) and net visceral release or removal of most nutrients (P less than .10). Exceptions included a decrease (P less than .10) in net PDV glucose release with greater intake in saline-treated steers and a decrease (P less than .01) in net liver removal of lactate with greater intake. Treatment of steers with GRF decreased net liver removal of alpha-amino N (AAN; P less than .05) and ammonia N (NH3N; P less than .10) and release of urea N (UN; P less than .05), increased liver release of glutamate (P less than .05), and decreased net PDV release of NH3 N (P less than .10). Decreased liver extraction ratio for AAN in GRF-treated steers (P less than .01) implies a direct effect of GRF treatment on liver metabolism separate from changes in liver AAN supply. Proportions of body N retention not accounted for by net total splanchnic AAN release increased with GRF treatment. This suggests a change in peripheral utilization of dietary AAN supply or an increase in total splanchnic N retention.

Amino Acids↗

PubMed1992

Effects of growth hormone-releasing factor and feed intake on energy metabolism in growing beef steers: whole-body energy and nitrogen metabolism.

Effects of growth hormone-releasing factor (GRF) on energy and N metabolism in six growing Hereford x Angus steers were measured using a split-plot design with 4-wk injection periods within 8-wk intake periods. Steers were fed a 75% concentrate pelleted diet at two intakes (low: 50 g/BW.75 and high: 90 g/BW.75 as fed) and injected s.c. with saline or 10 micrograms/kg of BW of human GRF(1-29)NH2 twice daily for 3 wk. Measurements of energy and N balance were obtained during wk 3 of treatments. Diet DM digestibility (%) was decreased by greater intake (P less than .05) and increased by GRF (P less than .06). Treatment with GRF increased (P less than .01) N retention by decreasing (P less than .05) fecal and urinary excretion: N retention averaged 10.0 and 20.8 g/d at low intake and 25.9 and 46.7 g/d at high intake for control- and GRF-treated steers, respectively. Increased ME (P less than .05) in GRF-treated steers also resulted from decreased fecal (P less than .05) and urinary (P less than .07) energy excretion but was countered by increased (P less than .06) heat energy (HE). Tissue energy (TE), partial efficiency of ME use for TE retention, and estimated maintenance energy were not affected (P greater than .10) by GRF treatment. In summary, GRF treatment altered the partition of TE by increasing protein retention (108 and 80% for low and high intake, respectively) at the expense of fat retention.

Animals↗

PubMed1991

Effect of human growth hormone-releasing factor and(or) thyrotropin-releasing factor on growth, carcass composition, diet digestibility, nutrient balance, and plasma constituents in dairy calves.

Sixty male dairy grain-fed calves, raised from 70 to 223 kg BW in individual crates, were used in a 2 X 2 factorial arrangement to determine the effect of administration of human growth hormone-releasing factor (1-29)NH2 (GRF) and(or) thyrotropin-releasing factor (TRF). Calves received twice-daily s.c. injections of .9% NaCl (control), GRF (5 micrograms/kg BW), TRF (1 micrograms/kg BW) or GRF (5 micrograms/kg BW) plus TRF (1 micrograms/kg GTRF). Average daily gain and days on feed were not affected by treatments, but TRF treatment increased (P less than .05) total intake of dry matter (DM) and feed conversion ratio: 3.00, 3.02, 3.08, and 3.22 kg DM/kg weight gain for control, GRF, TRF, and GTRF, respectively. During two 7-d periods, after 66 and 75 d of treatment, feces and urine were collected from 40 calves (5 per treatment per period). Treatment with GRF increased (P less than .05) digestibility of DM, nitrogen (N), and energy and tended (P less than .20) to increase N retention. At slaughter, withers height was increased (P = .05) by GRF and carcass length was increased (P less than .05) by TRF. Pituitary and liver weights were increased (P less than .05) by TRF. The combination of GRF and TRF slightly increased (P less than .10) protein content and decreased (P less than .05) fat content of the 9-10-11th rib section. After d 1, GRF treatment chronically increased (P less than .05) insulin concentrations and also increased (P less than .10) IGF-I concentrations on d 29 and 57. In summary, chronic treatment with GRF and(or) TRF did not improve growth or efficiency, although GRF increased digestibility of DM, N, and energy and the GRF plus TRF combination resulted in slightly leaner carcasses.

Animals↗

PubMed1990

Dose effect of human growth hormone-releasing factor and thyrotropin-releasing factor on hormone concentrations in lactating dairy cows.

Two experiments were conducted to study the effects of growth hormone-releasing factor (GRF) and thyrotropin-releasing factor (TRF) administration on hormone concentrations in dairy cows. In the first trial, 12 cows were used on 5 consecutive days to determine the effect of four sc doses of GRF (0, 1.1, 3.3 and 10 micrograms.kg-1 BW) and three sc doses of TRF (0, 1.1 and 3.3 micrograms.kg-1 BW) combined in a factorial arrangement. GRF and TRF acted in synergy (P = .02) on serum growth hormone (GH) concentration even at the lowest dose tested and GH response to the two releasing factors was higher than the maximal response observed with each factor alone. TRF increased (P less than .01) prolactin (Prl), thyrotropin (TSH), triiodothyronine (T3) and thyroxine (T4) concentrations similarly at the 1.1 and 3.3 micrograms.kg-1 doses and GRF did not interact (P greater than .40) with TRF on the release of these hormones. In the second trial, the effect of GRF (3.3 micrograms.kg-1 BW, sc) and TRF (1.1 micrograms.kg-1 BW, sc) was tested at three stages (18, 72 and 210 days) of lactation on serum Prl and TSH concentrations. Eighteen cows (n = 6 per stage of lactation) were used in two replicates of a 3 X 3 latin square. The TRF and GRF-TRF treatments were equipotent (P greater than .05) in increasing Prl and TSH concentrations. Prl and TSH responses were similar (P greater than .40) throughout lactation. In summary, GRF at doses ranging from 1.1 to 10.0 micrograms.kg-1 and TRF at doses ranging from 1.1 to 3.3 micrograms.kg-1 act in synergy on GH release and do not interact on Prl, TSH, T3 and T4 concentrations in dairy cows. Furthermore, Prl and TSH response to TRF are not affected by stage of lactation.

Animals↗

PubMed1990

Insulin-like growth factor-I concentration in Holstein female cattle: variations with age, stage of lactation and growth hormone-releasing factor administration.

Plasma insulin-like growth factor-I (IGF-I) concentrations were monitored in Holstein females through different periods of their growth, lactation and after acute or chronic growth hormone-releasing factor (GRF) administration. Plasma samples were radioimmunoassayed using a human IGF-I antibody after a 24 hr incubation in a HCl(.1N)-glycine(.2M) buffer (pH 2). In a first study, IGF-I concentrations were measured in Holstein females of different ages and(or) stages of lactation (n = 6 per group). The IGF-I concentrations in newborn calves (102.0 +/- 11.3 ng/ml) markedly decreased (P less than .01) in 1 mo old animals (50.2 +/- 7.1 ng/ml), then increased (P less than .01) to 137.0 +/- 5.1 and 137.4 +/- 11.0 ng/ml in 6 and 10 mo old heifers, respectively. In dairy cows, IGF-I concentrations were low 24 hr post-partum (44.7 +/- 7.6 ng/ml) and then increased (P less than .05) to remain stable throughout lactation (91.3 +/- 4.9, 92.8 +/- 12.9, 96.1 +/- 7.6, 90.7 +/- 8.8 ng/ml at 2, 3, 6 and 9 mo of lactation, respectively). There was a further increase (P less than .05) to 113.7 +/- 3.1 ng/ml during the dry period. In a second trial, blood samples were collected from lactating dairy cows every 2 hr for 24 hr following a sc injection of saline (n = 4) or human (h) GRF (1-29)NH2 (10 micrograms/kg BW, n = 4). The IGF-I peak concentration was reached on average 10 hr after the GRF injection and was higher (P less than .01) in treated cows than in control cows (135.4 vs 86.9 +/- 16.2 ng/ml). In the last trial, daily sc injections of 10 micrograms of hGRF(1-29)NH2 per kg BW to dairy cows (252 days of lactation) for 57 days, which increased milk production by 14% (2 kg/day), also increased (P less than .01) IGF-I concentration: 127.1 +/- 5.3 and 118.0 +/- 1.6 vs 90.7 +/- 4.7 and 96.0 +/- 5.0 ng/ml on days 29 and 57 of treatment for treated (n = 9) and control (n = 8) cows, respectively. Thus, the IGF-I concentration in dairy cattle varies with age and stage of lactation, and is increased by GRF administration in lactating dairy cows.

Aging↗

PubMed1990

Effect of long-term administration of porcine growth hormone-releasing factor and(or) thyrotropin-releasing factor on growth hormone, prolactin and thyroxine concentrations in growing pigs.

Long-term administration of porcine growth hormone-releasing factor (pGRF(1-29)NH2) and(or) thyrotropin-releasing factor (TRF) was evaluated on serum concentrations of growth hormone (GH) thyroxine (T4) and prolactin (PRL). Twenty-four 12-wk-old female Yorkshire-Landrace pigs were injected at 1000 and 1600 for 12 wk with either saline, pGRF (15 micrograms/kg), TRF (6 micrograms/kg) or pGRF + TRF using a 2 x 2 factorial design. Blood samples were collected on d 1, 29, 57 and 85 of treatment from 0400 to 2200. Areas under the GH, T4 and PRL curves (AUC) for the 6 h (0400 to 1000) prior to injection were subtracted from the postinjection periods (1000 to 1600, 1600 to 2200) to calculate the net hormonal response. The AUC of GH for the first 6 h decreased similarly (P less than .05) with age for all treatments. The GH response to GRF remained unchanged (P greater than .10) across age. TRF alone did not stimulate (P less than .05) GH release but acted in synergy with GRF to increase (P less than .05) GH release. TRF stimulated (P less than .001) the net response of T4 on all sampling days. Animals treated with the combination of GRF + TRF showed a decreased T4 AUC during the first 6 h on the last three sampling days. Basal PRL decreased (P less than .05) with age. Over the four sampling days, animals injected with TRF alone showed (P less than .01) a reduction (linear effect; P less than .01) followed by an increase (quadratic effect; P less than .05) in total PRL concentration after injection; however, when GRF was combined with TRF, such effects were not observed (P greater than .10). Results showed that 1) chronic injections of GRF for 12 wk sustained GH concentration, 2) TRF and GRF acted synergistically to elevate GH AUC, 3) TRF increased T4 concentrations throughout the 12-wk treatment period, 4) chronic TRF treatment decreased the basal PRL concentration and 5) chronic GRF + TRF treatment decreased the basal concentration of T4.

Animals↗