The relationship between plasma insulin-like growth factor-I (IGF-I) level and body weight in the horse.

The relationship between plasma insulin-like growth factor-I (IGF-I) level and body weight was studied in six breeds of horse. The correlation coefficients between plasma IGF-I and body weight in males and females of 1 year old heavy horses (Percheron and Breton breeds) were 0.62 and 0.12 respectively. The mean plasma IGF-I of males was higher than that of females (p < 0.01). However, the plasma IGF-I levels of heavy horses did not exceed those of light horses (Thoroughbred) or ponies (Shetland and Falabella). These data suggest that IGF-I is at least related to the difference of body weights between sexes in heavy horses.

Effects of TRH on circulating growth hormone, prolactin and triiodothyronine levels in the bovine.

The effects of administration of synthetic thyrotropin-releasing hormone (TRH) on circulating growth hormone (GH), PROLACTIN (PRL) and triiodothyronine (T3) levels of lactating dairy cows, non-lactating dairy heifers, and beef cows were studied. Intravenous administration of 0.1, 1, and 5 microgram of TRH per kg of body weight (bw) elevated plasma GH and PRL levels of lactating cows within 5 min. The plasma GH and PRL levels increased in proportion to the dose of TRH and reached a peak 10 to 30 min after TRH injection. Intravenous administration of 1 microgram of TRH per kg of bw to 7 non-lactating heifers, 14 lactating dairy cows, and 5 non-lactating beef cows elevated plasma GH level to peak values after 15 min, the increase rates being 6.9, 5.6, and 3.8 times as high as those in the pretreatment levels. The mean maximum vale was also in that order. Plasma T3 levels of non lactating dairy heifers at pre- and post-injection of TRH were significantly higher than those of lactating cows. The peak values of plasma PRL were obtained between 5 to 30 min after TRH administration. The increase rates of lactating dairy cows, heifers, and beef cows were 19.2, 13.9, and 20.9 times as high as those in the pretreatment. In contrast to GH and T3, plasma PRL levels of both pre- and post-injection with TRH in lactating cows and heifers were significantly higher in May than in October, though the increase rates were similar. Plasma PRL levels of lactating dairy cows at pre- and post-injection with TRH were significantly higher than those of non-lactating heifers. Subcutaneous administration of TRH was also effective to increase plasma TH, rl, and T3 levels in lactating cows. No significant change of GH or PRL response to TRH was observed after a short-term pretreatment of thyroid hormones.

Plasma insulin-like growth factor-I response to cold exposure in barrows.

Information about the plasma IGF-I concentrations in domestic animals in a cold environment is still limited. And mechanisms to change plasma IGF-I concentrations in cold environments are not fully elucidated. In this study, plasma insulin-like growth factor-I (IGF-I) in relation to plasma growth hormone (GH) and metabolite concentrations was investigated in pigs living at 20 degrees C and at 4 degrees C. Six pigs (Landrase breed; barrows, 118 days old, 51.0 +/- 3.5 kg body weight) were maintained for 2 weeks at 20 degrees C in a climatic room. Then a placebo or recombinant bovine GH (100 micrograms/kg body weight) was injected subcutaneously. Blood samples were taken through a catheter at -2, 0, 1, 2, 3, 4, 5, 6, 9, 12, 22, and 24 h after the injections. The same experiments were conducted on days 5 and 6 after the room temperature was changed to 4 degrees C. Mean (+/- SD) basal plasma GH concentrations in pigs without bovine GH administration living at 20 degrees C and at 4 degrees C were 4.8 +/- 1.7 ng/ml and 4.6 +/- 2.8 ng/ml, respectively. There were no significant differences between GH concentrations. On the other hand, the mean plasma IGF-I concentrations were 80.8 +/- 25.1 ng/ml and 57.3 +/- 14.3 ng/ml respectively. Plasma IGF-I concentrations in pigs living at 4 degrees C were significantly lower than in pigs living at 20 degrees C (P < 0.05). Plasma glucose and non-esterified fatty acid (NEFA) concentrations in pigs at 4 degrees C were significantly higher than in pigs at 20 degrees C (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of alpha 2-adrenergic agonist clonidine on plasma growth hormone and insulin-like growth factor-I concentrations in barrows.

The effects of infusion of clonidine, an alpha2-adrenergic agonist, on plasma insulin-like growth factor-I (IGF-I) concentrations were investigated with a single growth hormone (GH) injection in pigs. Four barrows were subjected to four treatments: saline infusion with a vehicle injection, clonidine infusion (0.5 nmol/kg/min for 8 h) with a vehicle injection, saline infusion with a bovine GH (bGH: 100 micrograms/kg) injection, and clonidine infusion with a bGH injection. Infusion was started 1 h before the injection. Plasma IGF-I, bGH, porcine GH (pGH), insulin, glucose, non-esterified fatty acid (NEFA), and blood urea nitrogen (BUN) concentrations were measured. Plasma IGF-I concentrations during saline infusion increased after a bGH injection (P < 0.05). However, the IGF-I concentrations during clonidine infusion did not increase after the bGH injection. Plasma endogenous GH (pGH) was not increased during clonidine infusion. The plasma glucose concentration was noticeably increased during clonidine infusion and moderately increased after the GH injection. Despite the extreme increase in plasma glucose during clonidine infusion, plasma insulin did not change. Neither plasma NEFA nor BUN was changed by these treatments. These results demonstrate that the alpha 2-adrenergic agonist clonidine altered the action of GH to increase the plasma IGF-I concentrations.

Plasma concentrations of hormones and metabolic substrates in growing pigs after bovine growth hormone injections under various nutritional conditions.

The effects of GH injections on the concentrations of plasma hormones and metabolic substrates in pigs were studied under various nutritional conditions. In experiment 1, four pigs (Large white, barrows, 108 days old) were maintained at three feeding levels: (1) high level (8,501 +/- 46 kcal/ day), (2) maintenance level (2,104 +/- 44 kcal/day), and (3) fasting (last meal was on day -2). The bovine GH (100 micrograms/kg BW) was subcutaneously injected on experiment days 0, 1, and 2. In experiment 2, four pigs (Landrase, barrows, 120 days old) were maintained at the high feeding level and the bovine GH (100 micrograms/kg BW) was injected 2, 26, and 50 h after the last meal. The plasma hormone and metabolic substrate concentrations were measured. In experiment 1, the plasma IGF-I concentrations increased on days 1-4 in the high feeding level and maintenance fed pigs, but did not increase in the fasting pigs. The plasma glucose concentrations increased after the GH injection in the high feeding level and maintenance fed animals. The plasma NEFA concentrations increased after the GH injection in the maintenance fed and fasting animals. In experiment 2, the plasma IGF-I gradually decreased after the last meal. The GH injection administered 26 or 50 h after the last meal still produced an increase in the plasma IGF-I levels. These data clearly show that the effect of GH was modified depending on the nutritional condition of the pigs.

A receptor site for prolactin in lactating mouse mammary tissues.

Prolactin iodinated by lactoperoxidase method showed immunologically, electrophoretically and biolo9gically similar properties to native prolactin and possessed enough specific radioactivity for receptor studies. 1251-prolactin was incubated with mouse mammary tissues at 8 days of lactation. Both binding and release of 1251-prolactin depended on incubation time and temperature and were maximal at 37 degrees C. Michaelis constant was estimated to be 1.4 X 10(-9) M from Lineweaver-Burk plot and to be 1.2 X 10(-9) M from id-value of the dose-response curve for displacement with native prolactin. Total number of binding sites for prolactin was 1.38 X 10(-15) mole per mg weight of tissue. Ovine prolactin, human growth hormone and human placental lactogen complete with 1251-prolactin and dose-response curves for these three hormones were all parallel. These results suggest the existence of a specific receptor site with high affinity for prolactin in lactating mouse mammary glands.

Effect of a prolonged release formulation of recombinant bovine somatotropin on plasma concentrations of hormones and metabolites, and milk production in dairy cows.

The effect of a prolonged release formulation of recombinant DNA derived bovine somatotropin (rbST) on the plasma concentrations of growth hormone (GH), insulin-like growth factor-I (IGF-I), insulin, glucose, blood urea nitrogen (BUN) and nonesterified fatty acids (NEFA), and milk production in lactating dairy cows was studied. Eight cows were divided into two equal groups. One group was the noninjected control, and cows in the other group received a single subcutaneous injection of 640 mg rbST. Plasma GH levels in the rbST-treated cows were higher than in the control cows for 10 days after the injection. Plasma IGF-I concentrations were significantly higher in the rbST-treated cows than in the control for 14 days after the treatment. In the rbST-treated cows, the plasma concentrations of insulin and glucose tended to be higher than those in the control until 7 days after the injection. Also, plasma NEFA levels were higher in the rbST-treated cows for 10 days. In contrast, plasma BUN levels were significantly lower in the rbST-treated cows for 17 days after the treatment. For 28 days after the injection, the mean daily milk yield in rbST-treated cows was 4.5 kg (21.2%) more than that in the control cows. In the rbST-treated cows, a highly positive correlation was observed between the mean daily milk yield and the mean plasma concentration of IGF-I throughout the postinjection period.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth hormone, thyrotropin and prolactin responses to simultaneous administration of human growth hormone-releasing factor and thyrotropin releasing hormone in the bovine.

The effects of intravenous injection of synthetic human pancreatic growth hormone-releasing factor-44-NH2 (hpGRF-44) and synthetic thyrotropin releasing hormone (TRH), or hpGRF-44 in combination with TRH on growth hormone (GH), thyrotropin (TSH), and prolactin (PRL) release in dairy female calves (6- and 12-month-old) were studied. When 0.25 microgram of hpGRF-44 per kg of body weight (bw) was injected in combination with TRH (1.0 microgram per kg of bw), the mean plasma GH concentration of the 12-month-old calves rose to a maximum level of 191.5 ng/ml (P less than 0.001) at 15 min from the value of 6.8 ng/ml before injection at 0 min. The maximum level was 3.1 and 6.1 times as high as the peak values obtained after injection of hpGRF-44 (0.25 microgram per kg of bw) and TRH (1.0 microgram per kg of bw), respectively (P less than 0.001). The area under the GH response curve for the 12-month-old calves for 3 hr after injection of hpGRF-44 in combination with TRH was 2.5 times as large as the sum of the areas obtained by hpGRF-44 and TRH injections. In contrast, the mean plasma GH level was unchanged in saline injected calves. The magnitudes of the first and the second plasma GH responses in the 6-month-old calves to two consecutive injections of hpGRF-44 in combination with TRH at a 3-hr interval were very similar. The peak values of plasma GH in the calves after hpGRF-44 injection were 2-4 times as high as those after TRH injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Response of growth hormone release to human growth hormone-releasing factor and its analogs in the bovine.

Responses of growth hormone (GH) release to synthetic human growth hormone-releasing factor (hGRF)-44-NH2 analogs were determined, and the GH-releasing potency based on dose per kg of body weight (bw) was compared with that of hGRF-44-NH2 in female dairy calves. Four- and 12-month-old calves were injected intravenously with 0.25 microgram of hGRF-44-NH2 or its analogs per kg of bw. Blood samples were collected before, and during 180 min after each injection, and plasma GH concentrations were measured by radioimmunoassay. Areas under the GH response curves for 180 min after injection of hGRF-44-NH2 and its analogs were used as an index of the GH-releasing potency of each peptide. The GH-releasing potency of hGRF(1-26)-NH2 was significantly lower than that of hGRF-44-NH2 (P less than 0.05). On the other hand, hGRF(1-29)-NH2 possessed similar potency to hGRF-44-NH2. [D-Tyr1]-hGRF-44-NH2 showed prolonged GH-releasing activity, though its potency was similar to that of hGRF-44-NH2. Also, [D-Ala2]-hGRF(1-29)-NH2 exhibited prolonged GH-releasing activity, and its potency was 2.5 (P less than 0.05) and twice (P less than 0.05) as great as that of hGRF-44-NH2 and hGRF(1-29)-NH2, respectively. These results demonstrate that the N-terminal 29 amino acid residues of hGRF possess the activity site required for full GH release in vivo, and [D-Ala2]-hGRF(1-29)-NH2 has longer and greater activity, on a dose basis, than hGRF-44-NH2 in the calves.

Separation of rabbit mammary-gland prolactin receptors by ion-exchange chromatography, h.p.l.c.-gel filtration and ultracentrifugation.

Rabbit mammary-gland prolactin (Prl) receptors in the microsomal fraction were solubilized in 7.5 mM-Chaps) or 1% Triton X-100 and analysed by ion-exchange chromatography using DEAE-Bio-Gel A. Prl receptors in the presence of 7.5 mM-Chaps were separated into two different fractions (Fr. A and B), both of which showed identical specificity of binding to peptide hormones as those in the Chaps or Triton extract. oPrl and human growth hormone (hGH) bound to the same site, but other non-lactogenic hormones (follicle-stimulating hormone, oGH, luteinizing hormone and insulin) failed to bind to the Prl receptors. The dissociation constant (Kd) for Prl binding to the receptors in Fr. A was about 50% of those in Fr. B, suggesting that the rabbit mammary gland contains two types of Prl receptors, one with a high, and one with a low, Kd for Prl binding. A decrease in the concentration of Chaps in the column buffer to 4 mM caused aggregation of the receptors in Fr. A. H.p.l.c.-gel filtration, using Shim pack 150 and 300 columns connected in series, separated the receptor as a protein with an Mr of 74,000 +/- 4,900 (mean +/- S.D.) in the presence of 5 mM-Chaps, or of 36,800 +/- 2,100 in the presence of 7.5 mM-Chaps. Sucrose-gradient-centrifugation analysis showed that the Prl-receptor complexes in the presence of 5 mM-Chaps were sedimented between gamma-globulin and bovine serum albumin (5.56 +/- 0.22 S). As the Chaps concentration was increased to 7.5 mM, a further peak of the Prl-receptor complexes (4.01 +/- 0.23 S) appeared below ovalbumin. The present data suggest that the binding subunit causes the monomeric subunit to aggregate with itself or with another specific associated protein of similar Mr.

Plasma growth hormone, insulin-like growth factor-I, and milk production responses to exogenous human growth hormone-releasing factor analogs in dairy cows.

Responses of plasma growth hormone (GH) and insulin-like growth factor-I (IGF-I), and milk production to subcutaneous (sc) injection(s) of two synthetic human growth hormone-releasing factor (hGRF) analogs were studied in dairy cows. Two mg of each hGRF analog dissolved in 5 ml saline per cow were injected into the shoulder area of each experimental animal, and jugular venous blood samples were collected via an indwelling catheter or by venipuncture. Plasma GH and IGF-I concentrations were measured by radioimmunoassay methods. In dry cows, the mean concentration of plasma GH after a single sc injection of hGRF analogs rose to 22.0-28.3 ng/ml at about 5 h from 1.4-1.7 ng/ml at 0 h (just before injection), and returned to the level before injection after 10-12 h. On the other hand, the plasma IGF-I began to increase after a lag of 4-6 h following a single injection of hGRF analogs, and reached maximum values of 71.1-89.4 ng/ml at 20 h from 43.7-46.4 ng/ml at 0 h. The IGF-I concentration at 24 h after a single injection of hGRF analogs was still higher than the value for the dry cows given saline. In lactating cows, the plasma concentration of GH at 2 h after daily sc injections of hGRF analogs during 14 consecutive days (an injection period) was higher than those for the lactating cows which received saline. Also, during the injection period, the concentration of IGF-I was higher in the lactating cows which received hGRF analog injections than in the cows which received saline injections. During the last 7 days of the injection period, the administration of hGRF analogs increased the mean milk yield by 11-19% in comparison with those for the saline injected cows. A positive correlation was observed between the mean plasma IGF-I concentration and the mean milk yield in the lactating cows treated with hGRF analogs throughout the injection and a postinjection (11 consecutive days after cessation of hGRF analog injection) periods. The results demonstrate that a single sc injection of hGRF analogs stimulates both GH release and the circulating level of IGF-I in dry cows, and that daily sc injections of hGRF analogs over 14 days enhance milk production, and plasma GH and IGF-I levels in lactating cows.

Growth hormone response to human pancreatic growth hormone releasing factor in cattle.

The effects of a growth hormone releasing factor, human pancreatic growth hormone releasing factor-44 (hpGRF-44), on growth hormone (GH) secretion in calves, heifers and cows were studied. A single intravenous (iv) injection of 0.1, 0.25, 0.5 or 1.0 microgram of synthetic hpGRF-44 per kg of body weight (bw) in calves significantly elevated the circulating GH level within 2-5 min, while no increase in plasma GH was observed in saline injected control calves. The plasma GH level increased proportionally to the log dose of hpGRF-44, and reached a peak at 5-10 min (p less than 0.01). Subcutaneous injection of hpGRF-44 also elevated the plasma GH level, but the peak value at 15 min was 37% of that of iv injection (p less than 0.05). Intravenous injection of 0.25 microgram of hpGRF-44 per kg of bw to female calves, heifers, and cows significantly elevated mean the GH levels from 8.5, 2.3, and 1.6 ng/ml at 0 time to peak values of 97, 26, and 11.6 ng/ml, respectively (p less than 0.01). The plasma GH response and basal level in calves were significantly higher than those of heifers or cows (p less than 0.025). The plasma GH response to hpGRF-44 as well as the basal level decreased with advancing age. The plasma GH response to hpGRF-44 and basal GH in male calves were significantly greater than those in female calves (p less than 0.001). These results indicate that synthetic hpGRF-44 is a potent secretogogue for bovine GH, and suggest its usefulness in the assessment of GH secretion and reserve in cattle.