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Biomedical subjects

A Trenkle

Publications and source records attributed to A Trenkle.

At least 19 recordsLinked to original sources
PubMed2006

Circulating ghrelin concentrations fluctuate relative to nutritional status and influence feeding behavior in cattle.

The objective of these experiments was to establish the relationship of plasma ghrelin concentrations with feed intake and hormones indicative of nutritional state of cattle. In Exp.1, 4 steers (BW 450 +/- 14.3 kg) were used in a crossover design to compare plasma ghrelin concentrations of feed-deprived steers with those of steers allowed to consume feed and to establish the relationship of plasma ghrelin concentrations with those of GH, insulin (INS), glucose (GLU), and NEFA. After adaptation to a once-daily feed offering (0800), 2 steers continued the once-daily feeding schedule (FED), whereas feed was withheld from the other 2 steers (FAST). Serial blood samples were collected via indwelling jugular catheter from times equivalent to 22 h through 48 h of feed deprivation. Average plasma ghrelin concentrations were greater (P < 0.001) in FAST compared with FED (690 and 123 +/- 6.5 pg/mL) steers. Average plasma ghrelin concentrations for FED steers prefeeding were elevated (P < 0.001) when compared with those postfeeding (174 and 102 +/- 4.2 pg/mL, respectively). Average plasma GH concentration was elevated (P < 0.05) for FAST steers compared with FED steers. Plasma GLU concentrations were not different; however, for FAST steers, NEFA concentrations were elevated (P < 0.001) and INS concentrations were decreased (P < 0.001). In Exp. 2, 4 steers (BW 416 +/- 17.2 kg) were used in a crossover design to determine the effects of i.v. injection of bovine ghrelin (bGR) on plasma GH, INS, GLU, and NEFA concentrations; length of time spent eating; and DMI. Steers were offered feed once daily (0800). Serial blood samples were collected from steers via indwelling jugular catheter. Saline or bGR was injected via jugular catheter at 1200 and 1400. A dosage of 0.08 microg/kg of BW bGR was used to achieve a plasma ghrelin concentration similar to the physiological concentration measured in a FAST steer in Exp. 1 (1,000 pg/mL). Injection of bGR resulted in elevated (P < 0.005) plasma GH concentrations after the 1200 but not the 1400 injection. Plasma INS, GLU, and NEFA concentrations were not affected by bGR injection. For the combined 1-h periods postinjection, length of time spent eating was greater (P = 0.02) and DMI tended to be increased (P = 0.06) for bGR steers. These data are consistent with the hypothesis that ghrelin serves as a metabolic signal for feed intake or energy balance in ruminants.

Animal Nutritional Physiological Phenomena↗
PubMed2004

Feeding 25-hydroxyvitamin D3 to improve beef tenderness.

The objective of this trial was to determine if a single oral bolus of 25-hydroxyvitamin D3 (25-OH D3) given at various times before slaughter would enhance the tenderness of beef loin steaks. One hundred eight crossbred steers were allotted to 18 pens so that the mean weight of the cattle in each pen was similar. Treatments (25-OH D3 dose [62.5 or 125 mg]) and time of administration of the single oral bolus (4, 7, 21, or 35 d before slaughter) were assigned randomly to each pen of steers. Serial plasma samples were collected at each bolus administration time for control animals. For steers assigned to a treatment group, a baseline blood sample was collected before bolus administration and at each subsequent administration when other treatment groups received their bolus. Plasma samples were assayed for 25-OH D3 and calcium concentrations. Troponin-T degradation and Warner-Bratzler shear force were measured as indicators of tenderness for loin steaks collected at slaughter and aged for 6 or 14 d postmortem. Muscle samples, collected concurrently, were assayed for 25-OH D3 and calcium concentrations. A single oral bolus of 25-OH D3 was sufficient to increase plasma 25-OH D3 concentrations (P < 0.001) through slaughter, regardless of dose or time of bolus administration. The single oral bolus of 25-OH D3, however, did not increase plasma calcium concentrations (P > 0.05). As a result, neither troponin-T degradation nor Warner-Bratzler shear force was improved (P > 0.05) by treatment. Muscle 25-OH D3 concentrations were increased (P > 0.001) by treatment with 25-OH D3. Although sustained plasma 25-OH D3 concentrations did not increase plasma or muscle calcium at slaughter nor influence tenderness, the use of 25-OH D3 as a nutritional means of improving beef tenderness is in its infancy, and more research to delineate an effective dose and the potential interaction of seasonal exposure to ultraviolet light is warranted.

Administration, Oral↗
PubMed1996

Control of growth hormone synthesis.

A large body of research, primarily in the rodent and human species, has elucidated many of the details regarding the control of GH synthesis and release. Cell type-specific transcriptional control has been identified as the main mechanism of the somatotroph-specific expression of GH. The recent detailed analysis in rodents and humans of a highly specific transcriptional activator protein, PIT-1, has opened several new areas of study. This is especially true for research in the farm animal species, where PIT-1 has been cloned and its binding elements on the GH gene are being investigated in a number of economically important species. Genetic and biochemical analyses of PIT-1 and other GH regulators have shown the central role of PIT-1 not only in the cell-autonomous stimulation of GH gene transcription, but also in the participation of PIT-1 in the response at the GH gene to exogenous hormones such as RA and TH. PIT-1 has been implicated in the proliferative development of the pituitary itself, in the maintenance of anterior pituitary cell types once cell types are defined, and in the mechanism by which the hypothalamic signal for GH release is transduced. However, PIT-1 by itself does not activate the GH gene, so that additional unknown factors exist that need to be identified to fully understand the cell type-specific activation of the GH gene. In addition, GH gene regulatory elements acting through well-characterized systems such as TH have seemingly different effects; the specific context of the regulatory elements relative to the promoter elements appear to be crucial. These contextual details of GH gene regulation are not well understood for any species and need to be further studied to be able to make predictions for particular elements and regulatory mechanisms across species. The regulation of the pulsatile secretion of GH by GHRH and SRIH is reasonably well understood after the cloning and analysis of the two releasing factors and their receptors. Modification or manipulation of the pathways involved in the regulation of GH secretion is a potential means of enhancing the lean tissue growth of meat animals. However, further understanding of the systems controlling the in vivo release of GH is needed before such manipulations are likely to be productive. Several other research questions regarding the control of GH expression and release remain to be answered. What is the biochemical connection between exogenous signal transduction (i.e., GRH/GHRH-R, TR, ER, RAR) and PIT-1 at the GH gene? Are there additional coactivators or repressors of GH that respond to cAMP levels? Do ubiquitous regulatory factors such as GHF-3 and Zn-15, identified thus far only in the rat, exist in humans or livestock? Zn-15 is expected to be found in many mammalian species, because its recognition sequence between the PIT-1 binding sites is highly conserved across mammals (Figure 2). What is the mechanism causing GH levels to drop during aging? Does PIT-1 expression decrease during the lifespan of animals? Is it possible to increase GH gene expression within target tissues by directing the expression of PIT-1 to these tissues via transgenesis, or are other factors limiting in peripheral tissues so that the lack of PIT-1 expression is not the deciding factor? Finally, is there genetic variation in the expression of GHRH and/or SRIH or in their respective receptors? These questions are relevant to and could be investigated in several of the livestock species.

Animals↗
PubMed1991

Relationship of thyroid status to growth hormone and insulin-like growth factor-I (IGF-I) in plasma and IGF-I mRNA in liver and skeletal muscle of cattle.

Steers were made hyperthyroid or hypothyroid to study the effects of physiological alterations in thyroid hormone status on plasma growth hormone (GH) profiles, plasma insulin-like growth factor-I (IGF-I) concentrations, and relative abundance of IGF-I mRNA in skeletal muscle and liver. Eighteen yearling crossbred steers (360 to 420 kg) were randomly allotted to hyperthyroid (subcutaneous injection 0.6 microgram/kg BW L-thyroxine for 10 d), hypothyroid (oral thiouracil; 0.25% diet plus 12.5 g capsule/d for 17 d), or control (subcutaneous injection 0.9% NaCl) treatment groups. Blood samples were taken for measurement of GH, IGF-I, thyroxine (T4) and triiodothyronine (T3) by RIA. Samples of liver and skeletal muscle were taken by biopsy for measurement of IGF-I mRNA by solution hybridization. Steers receiving thiouracil had 57 and 53% (P less than .05) lower T4 and T3, respectively, than control steers (84.1 and 1.7 ng/ml). The hyperthyroid steers had 228 and 65% greater (P less than .05) T4 and T3 than control steers. Neither increased nor decreased thyroid status had any significant effects on plasma GH profiles, liver IGF-I mRNA, or plasma concentration of IGF-I. There was no effect of thyroid hormone alteration on skeletal muscle IGF-I mRNA concentrations. The results of this study suggest that short-term changes in thyroid status of cattle had no major impact on the GH-IGF-I axis or skeletal muscle IGF-I mRNA.

Animals↗
PubMed1991

Growth hormone parameters at four ages in intact and castrated male and female cattle.

Plasma Growth hormone (GH) profiles, secretion rates (SR), metabolic clearance rates (MCR) of intravenously infused GH, and response to 0.0165, 0.067, and 0.267 microgram of growth hormone-releasing factor (GHRF)/kg body weight (bwt) were studied in intact and castrated male and female cattle (4 of each) at 5, 8, 12, and 15 mo of age. As cattle aged, overall GH levels in the plasma decreased (P less than .01), GH baseline concentrations declined (P less than .05), SR decreased (P less than .01), half-life of GH decreased (P less than .01), and the GH response to intravenous injections of GHRF declined (P less than .05). Bulls had elevated overall and baseline GH concentrations (P less than .05), greater amplitude and number of GH secretory periods (P less than .01), and greater SR (P less than .05) than steers, heifers, or ovariectomized heifers. Males had more frequent GH spikes and secretory periods of higher amplitudes, greater SR, and greater GH responses to 0.0165 microgram GHRF kg bwt (P less than .05) than females. Castration had no impact on the GH status of heifers. It is suggested that testosterone or its metabolites enhanced GH secretion in bulls.

Aging↗
PubMed1991

Insulin-like growth factor-I concentrations in plasma of intact and castrated male and female cattle at four ages.

The influence of age, sex and castration on plasma concentrations of insulin-like growth factor-I (IGF-I) and other metabolic hormones related to growth was studied in cattle. Plasma was sampled from bulls, steers, heifers, and ovariectomized heifers at 20-min intervals for 12 hr at 5, 8, 12, and 15 mo of age. Plasma samples from each animal taken during each 12-hr period were composited for analysis of IGF-I, testosterone, total estrogens, thyroxine, triiodothyronine, insulin, and glucose. The mean plasma IGF-I concentration in all cattle increased from 61.6 to 158.6 ng/ml as the animals aged (p less than .01). Over all ages, bulls had greater concentrations of IGF-I than steers, heifers, or ovariectomized heifers (P less than .01). Bulls also had higher concentrations of testosterone (P less than .01) and total estrogens (P less than .01). Triiodothyronine concentration was greater in ovariectomized heifers than in bulls (P less than .01) or steers (P less than .05). Females had higher concentrations of thyroxine than males (P less than .01). Concentrations of triiodothyronine in the cattle were greater (P less than .01) during the winter and early spring as compared with the summer. Concentrations of insulin and glucose were not influenced by sex or castration; however, insulin increased in all cattle with age (P less than .01). The mean increase in IGF-I concentration with age within each of the four groups was associated with an increase in concentration of plasma insulin but the differences due to sex were not related to differences in insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1991

Relationship of liver and skeletal muscle IGF-1 mRNA to plasma GH profile, production of IGF-1 by liver, plasma IGF-1 concentrations, and growth rates of cattle.

Growth hormone (GH), insulin-like growth factor-1 (IGF-1), and thyroid hormone (T3 and T4) concentrations in blood plasma of 18 crossbred cattle (six bulls, six steers, and six heifers) were measured over an 8-hr period. One week later at slaughter, IGF-1 production by liver slices and IGF-1 mRNA concentrations in skeletal muscle and liver were measured. Bulls had higher (P less than 0.05) mean plasma GH and GH peak amplitudes (P less than 0.01) than heifers, and values for steers were intermediate between bulls and heifers. Baseline GH concentrations and number of GH peaks were not significantly different for the three groups. Bulls had 1.6-fold (P less than 0.01) and 3.0-fold (P less than 0.01) greater liver IGF-1 mRNA concentrations than steers or heifers, respectively, whereas the steers had 1.8-fold (P less than 0.05) greater IGF-1 mRNA in liver than heifers. Production of IGF-1 by liver slices was greater (P less than 0.05) in bulls than steers or heifers. Bulls had 1.3-fold greater plasma IGF-1 than steers (P less than 0.01), whereas steers had 1.8-fold greater plasma IGF-1 than heifers (P less than 0.01). There were no significant differences in concentrations of skeletal muscle IGF-1 mRNA between the three groups of animals. Liver IGF-1 mRNA, liver IGF-1 production, and plasma IGF-1 were all significantly correlated with gain and mean GH peak amplitude, but not with GH baseline, GH peak frequency, or concentrations of T3 and T4. Concentrations if IGF-1 mRNA in skeletal muscle were not correlated to gain or any parameter of the GH profile. Plasma concentrations of T3 were significantly (P less than 0.05) negatively correlated to plasma GH baseline concentrations. Muscle IGF-1 mRNA concentration was negatively related to plasma T4 and T3. The results of this study suggest that the cascade of events starting with secretion of GH from the pituitary, expression of liver IGF-1 mRNA, and secretion of IGF-1 by the liver are important phenomena for growth of cattle.

Animals↗
PubMed1990

Evaluation of condensed molasses fermentation solubles as a nonprotein nitrogen source for ruminants.

Condensed molasses fermentation solubles (CMS), an effluent from the production of lysine, was evaluated as a nonprotein nitrogen supplement for ruminants by measuring the availability of its nitrogen to rumen microorganisms grown in batch cultures and by comparing CMS to urea as a source of supplemental nitrogen for growing cattle. In vitro dry matter digestion studies showed that, with 1 ml or less of rumen inoculum, microbial digestion was enhanced more (P less than .05) by the addition of CMS than by the addition of urea to 100 mg of cellulose. These stimulatory effects of CMS were absent when either the amount of inoculum (5.0 ml) or cellulose (250 mg) was increased and when wheat straw or alfalfa replaced cellulose as the substrate. Growth rate and feed intake for cattle fed a high-cob/cracked-corn diet containing 2.5 or 5.0% CMS were lower (P less than .05) than for cattle fed the control diet containing urea. Digestibility of dry matter, crude protein, neutral detergent fiber and acid detergent fiber were reduced (P less than .05) by the addition of CMS. Addition of CMS also decreased feed utilization, although the differences were not statistically significant. In conclusion, the nitrogen in CMS was available to rumen microorganisms growth in batch culture; however, CMS was not satisfactory as a substitute for all the urea in a diet for growing cattle containing over 45% of dietary N from the supplemental N source.

Animal Feed↗
PubMed1989

Influence of feeding on growth hormone secretion and response to growth hormone-releasing factor in sheep.

This study was designed to examine the effects of feeding and factors associated with feeding on growth hormone (GH) secretion and response to growth hormone-releasing factor (GHRF) in sheep. Feeding reduced (P less than 0.05) plasma GH concentrations to 60% of prefeeding concentrations within 45 min. Allowing the animals to anticipate being fed or artificial distention of the cranial sac of the rumen with a water-filled balloon did not significantly reduce plasma GH. Feeding, distention of the rumen and anticipation of being fed each reduced (P less than 0.05) the GH response to intravenous injection of 0.067 micrograms GHRF/kg body weight. It is concluded that GH secretion is reduced within 15 min after feeding in ruminants and that part of the reduced secretion may be the result of reduced response to GHRF.

Animals↗
PubMed1988

Growth hormone-releasing factor on growth hormone secretion in prepubertal calves.

The effects of iv administration of growth hormone-releasing factor (GRF) on growth hormone (GH) release and on nitrogen metabolism were measured in prepubertal calves. Crossbred beef heifers (111 kg) were used in a Latin square design to test the effects of 0, 0.01, 0.033, 0.067, and 0.1 microgram human pancreatic (hp) GRF [hpGRF (1,40)OH]/kg body wt on plasma GH concentrations. When they were given doses of 0.067 and 0.1 microgram hpGRF/kg body wt, plasma GH increased (P less than 0.05) within 5-15 min, compared with injections of control buffer, and then returned to preinjection concentrations. The response to 0.067 microgram hpGRF/kg body wt every 3 hr for 42 hr was studied in five heifers (137 kg body wt). The animals responded to 50% of the GRF injections with an increase in plasma GH during every 6-hr period measured. Nitrogen retention, hormone concentrations, and weight gain were measured in five bull calves (90 kg body wt) administered 0 or 0.067 microgram Nle rat hypothalamic GRF (1,29)NH2/kg body wt every 4 hr for 10 days. Metabolic parameters were interpreted to indicate an anabolic response to GRF even though increases of 16% in nitrogen retention, 23% in plasma somatomedin C concentrations, and 36% in weight gain with pulsatile GRF treatment were variable and statistically similar to those of controls. These results indicate that GRF induces peak GH secretion within 15 min in prepubertal calves and that calves can respond to multiple injections of GRF with an increase in plasma GH.

Animals↗
PubMed1988

Effects of growth hormone-releasing factor and somatostatin on growth hormone secretion in hypophysial stalk-transected beef calves.

The effects of growth hormone-releasing factor (GHRF) on growth hormone (GH) secretion were studied in beef calves after hypophysial stalk transection (HST). Peripheral GH concentration during surgery was elevated for 60 min after the initiation of anesthesia to 15 ng/ml, which was greater than plasma levels after HST and during the recovery period (0-30 hr mean, 3 ng/ml; P less than 0.05). Episodic GH secretion normally seen in sham-operated controls (SOC) was abolished after HST. Before HST, calves responded to 80% of the GHRF challenges, whereas after HST calves responded to every challenge of GHRF with an increase in plasma GH. A dose of 0.067 microgram human pancreatic (hp) hpGHRF(1-40)OH/kg body wt 3 days after HST increased plasma GH to 55 ng/ml from a control period mean of 5 ng/ml (P less than 0.04). On Day 8, HST calves received two injections of 0.067 microgram hpGHRF/kg body wt at 3-hr intervals, with feeding 70 min after the first injection. During two preinjection control periods, basal GH averaged less than 4 ng/ml and increased to 17 (P less than 0.02) and 9 (P less than 0.04) ng/ml immediately after the first and second injection of hpGHRF, but the response declined over the 8-day period after surgery. On Days 19 and 20, the HST calves were infused iv with 0.033 and 0.067 microgram somatostatin(SS)-14 (SRIH)/kg body wt, during which a pulse injection of 0.067 microgram hpGHRF/kg body wt was administered. GH increased to 9 and 5 ng/ml during the 0.033- and 0.067-microgram SRIH infusions after GHRF; no somatotropic rebound was observed after the SRIH was discontinued as was seen in the animals while the hypothalamic-hypophysial connections were intact. Five and six months after HST the responses to two analogs of rat hypothalamic GHRF were similar to those in SOC calves. These results indicate that HST calves responded to exogenous GHRF with an abrupt increase in plasma GH, but GH response to GHRF during SRIH infusion was greatly inhibited.

Animals↗
PubMed1987

Maintenance nitrogen requirements and intestinal microorganisms in rats.

Nitrogen (N) balance trials with young growing rats fed diets with and without nonabsorbable antibiotics and with various concentrations of crude protein (CP) were conducted to measure maintenance N requirements. In addition, cecal contents were analyzed for ammonia (NH3), urea (U) and free amino acids (AA) to study the reduction in maintenance N requirements due to the action of antibiotics. Results of the N-balance trials verified the reduction in maintenance N requirements with antibiotics as described in the literature. The reduction, however, was not as large as previously demonstrated, possibly because of severe diarrhea and greater liquid accumulation in the cecum of rats fed antibiotics. The concentration of free AA and U in the postabsorptive region of the intestine (cecum) of rats consuming antibiotics was greater than when antibiotics were not consumed. Cecal N concentrations supported the concept that the mode of action of antibiotics in reducing maintenance N requirements was via reduced destruction of AA of body origin in the lower intestine. Cecal levels of NH3 were similar in both antibiotic and nonantibiotic groups. The amount of N needed for body maintenance when conditions favored minimum destruction of body AA by lower intestine microorganisms was small, less than 1% dietary CP. Maintenance N may be limited to the needs for tissues on the exterior of the body, such as hair, which are poorly recycled through the digestive tract.

Amino Acids↗
PubMed1987

Concentrations of hormones in plasma from cattle with different growth potentials.

Blood samples were taken from four large- and four small-frame steers each month for 12 mo to study the effect of size on plasma hormone concentrations in cattle from 5 to 17 mo of age. The rate of gain and daily feed intake were 45% (P less than .05) and 51% (P less than .001) greater for the large steers. The large-frame steers had higher mean concentrations of growth hormone (P less than .001), insulin (P less than .06), thyroxine (P less than .06) and cortisol (P less than .002). The concentration of growth hormone was highest in the young cattle (P less than .01) and gradually declined with increasing age. Insulin concentrations were lowest in the young cattle (P less than .01) and gradually increased with age. The results of this study suggested that there are differences in hormone concentrations that are related to size rather than being the result of differences in physiological maturity of different breeds of cattle.

Animals↗
PubMed1986

In vivo metabolism of leucine and alpha-ketoisocaproate in the pig: influence of dietary glucose or sucrose.

The influence of dietary glucose (G) and sucrose (S) on leucine metabolism was evaluated in 10 immature pigs. The diets were isoenergetic and isonitrogenous with 40% of energy being derived from G or S. Animals were fed their diets at least 1 wk prior to the study. Each animal was studied by using a continuous infusion of L-[4,5-3H]leucine and [U-14C] alpha-ketoisocaproate (KIC) to permit measurement of the metabolism of leucine. After a meal, the pigs fed the glucose meal had higher mean plasma glucose and insulin concentrations than pigs fed a sucrose-containing meal. Arterial KIC concentration decreased after feeding either meal, but the arterial leucine concentration remained unchanged. In pigs fed sucrose, plasma fructose increased after the meal and was cleared by the hind limb in the same proportion as plasma glucose (11%). The hind limb glucose clearance was 16% in the glucose-fed pigs. Animals fed the glucose meal had three times greater hind limb uptake of leucine than animals fed the sucrose meal. No dietary influence on hind limb metabolism of KIC could be detected from arterial-venous differences. The whole-body leucine-KIC kinetic data suggested that preprandial tissue proteolysis was greater in pigs fed glucose than in those fed sucrose. Postprandial protein synthesis increased (24%) over fasting values only in pigs fed glucose. This was accompanied by a decrease in the percentage of the leucine pool converted to KIC. These observations indicate that both pre- and postprandial aspects of protein metabolism can be influenced by the dietary carbohydrate source.

Animals↗
PubMed1986

Equilibration and passage of water in the gastrointestinal tract of cattle in relation to estimating body water by compartmental kinetic models.

The volume of water in the rumen of four steers was increased (P less than .01) 47% when the level of ground cobs in the diet fed to the steers was changed from 10% to 50%. The difference in gut water content due to diet was not accurately (P greater than .10) estimated by deuterium oxide dilution using either one-, two- or three-compartmental models. Gut water was overestimated and empty body water underestimated when calculated by two-compartment models. The proportions of total body water within each compartment of a three-compartment model were quite variable among steers. When the two-compartment model was solved on the basis of measurements taken from either compartment, different compartment volumes were obtained. This indicated that the two-compartment model did not accurately describe the water equilibration process. Water in the contents of the proximal duodenum and terminal ileum equilibrated with blood in 30 min (range, 10 to 75 min), fecal water equilibrated in 4.3 h (range, 1.7 to 6.7 h) and water in rumen contents equilibrated in 8.3 h (range, 3.8 to 12.5 h). Diet did not affect (P greater than .10) equilibration time or the mean retention time of water in the gastrointestinal tract. Mean retention time was much longer than equilibration time; thus, the equilibration of water in the gastrointestinal tract contents was primarily dependent upon movement of water across the gut mucosa and not upon the flow of water through the gut. One-third of the water in the contents of the gastrointestinal tract was located outside the rumen. Compartmental modeling based only upon D2O disappearance from blood did not enable either gut water or rumen water to be accurately estimated.

Animals↗
PubMed1986

Secretion and clearance rates of glucagon in dairy cows.

Eight Holstein cows were sampled to examine plasma concentrations of hormones and some energy related metabolites. Sampling was every hour for 12 h at about 2 wk prepartum, at 3 wk postpartum, during an energy restriction ketonemia, and after a recovery period. Cows were fed ad libitum except for four cows induced into ketonemia by restricting feed intake 50%. Pulse doses of glucagon were injected intravenously during each period. Feed restriction increased concentrations of growth hormone, acetoacetate, beta-hydroxybutyrate, and free fatty acids in blood plasma. Concentrations of insulin and glucose showed some tendencies to decrease. Distribution space and turnover rate of glucagon were not different between periods, and pool size was increased in the dry period. Metabolic clearance rate of glucagon was not significantly different between periods. Insulin and glucose concentrations were increased 1 to 2 min after injection of glucagon and remained increased for 25 min. Covariance analysis showed that glucagon injection caused glucose concentration to increase proportionally in all periods, suggesting that cows had equal gluconeogenic capacity in all periods. Basal concentration, pool size, and secretion rate of glucagon showed some tendency to be decreased during ketonemia.

Acetoacetates↗