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.     

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)     

Plasma GH, IGF-I, and conception rate in cattle treated with low doses of recombinant bovine GH

Blood and uterine concentrations of GH and insulin-like growth factor (IGF)-I are correlated with improved fertility in cattle. We tested incremental doses of a 14-d sustained release recombinant bovine GH (rbGH) to increase blood GH and IGF-I (Experiments 1 and 2). Conception rate after administration of an optimized rbGH dose was also tested (Experiment 3). In Experiment 1, lactating Holstein cows (n = 18) were randomly assigned to receive 0 (n = 5), 100 (n = 5), 200 (n = 5), or 500 (n = 3) mg sc rbGH. Increasing the doses of rbGH was associated with increased serum concentrations of GH and IGF-I. The 100- and 200-mg doses caused an IGF-I release that was below and above, respectively, the perceived optimum response. Therefore, Experiment 2 was designed to test a rbGH dose (167 mg), which was intermediate to the doses tested in Experiment 1. Lactating and nonlactating postpartum beef cows were treated with 0 (n = 9) or 167 (n = 9) mg rbGH at insemination. Plasma concentrations of GH and IGF-I were greater in rbGH-treated cows than in controls. Lactating cows had initial IGF-I concentrations that were lower than nonlactating cows. The 167-mg dose of rbGH increased plasma IGF-I concentrations in lactating cows to the levels of those of nonlactating cows. In Experiment 3, cows and heifers were administered either 0 or 167 mg rbGH at insemination. The conception rate for rbGH-treated and control cows was 54.4 and 49.5% (n = 617), and 46.0 and 46.3% for heifers (n = 1123), respectively. Herd (P<0.01) and parity (P<0.01) affected conception rate, but conception rates for rbGH and control cattle were similar. In summary, low doses of rbGH increased blood GH and restored blood IGF-I concentrations in lactating cows to those of nonlactating cows, but the conception rate in cows and heifers was not affected by administration of 14-d sustained-release rbGH at insemination.     

Differential abundance of IGF1, bile acids,and the genes involved in their signaling in the dominant follicle microenvironment of lactating cows and nulliparous heifers

It is well documented that incidence of fertility problems is high in lactating cows but not in heifers of the same genetic merit. Understanding the metabolic and molecular differences between fertile heifers and relatively infertile lactating cows will help us understand the pathogenesis of infertility in dairy cows. Follicular waves in lactating cows (30–50 days in milk; n = 12) and heifers (n = 10) were synchronized by ultrasound-guided follicle ablation. Follicular fluid and granulosa cells of the dominant follicle were collected by ultrasound-guided aspiration along with blood sampling on Day 6 after synchronization. Dominant and subordinate follicles were larger in lactating cows than in heifers. Metabolic stress in lactating cows was evidenced by lower glucose and higher ß-hydroxy butyric acid compared with heifers. Insulin-like growth factor 1 signaling was reduced in the dominant follicle in lactating cows through reduced insulin-like growth factor 1 concentrations in plasma and follicular fluid of the dominant follicle, and reduced expression of pregnancy-associated plasma protein A (PAPPA) in their granulosa cells. We also found increased levels of total bile acids in the follicular fluid of the dominant follicle of lactating cows compared with heifers. Granulosa cells of the dominant follicle had higher expression of SLC10A2 and GPBAR1 (bile acid transporter and receptor, respectively) in lactating cows. These novel data are indicative of increased bile acid signaling within the dominant follicles of lactating cows compared with heifers. Overall, we demonstrate in the present study the metabolic, endocrine, and molecular differences within the microenvironment of the dominant follicles in lactating cows and heifers. These differences in follicular microenvironment may contribute toward abnormal ovarian function in lactating dairy cows.     

Prolactin secretion after hypothalamic deafferentation in beef calves: response to haloperidol, alpha-methyl-rho-tyrosine, thyrotropin-releasing hormone and ovariectomy

In ruminant species photoperiod regulates prolactin (PRL) secretion. It is hypothesized that the inhibition of PRL secretion resides in dopaminergic neurons of the medial basal hypothalamus (MBH). To test this hypothesis, anterior (AHD), posterior (PHD) and complete (CHD) hypothalamic deafferentation and sham operation control (SOC) surgeries were carried out during May (long-day photoperiod) in beef heifer calves (6-8 mo old) to measure basal PRL secretion and PRL secretion as affected by intravenous secretagogues. On the day of surgery (day 0), PRL secretion reflected stress of anesthesia and surgery in all groups. Thyrotropin-releasing hormone (TRH), alpha-methyl-rho-tyrosine (alphaMrhoT), and haloperidol (HAL) was iv injected on days 11, 13 and 15, respectively. AHD, PHD, CHD, and SOC calves responded to TRH (100 microg) with an acute increase in PRL that peaked within 20 min. All heifers responded to alphaMrhoT (10 mg/kg BW) with an acute elevation in PRL within 10 min and remaining elevated for 3 h. HAL (0.1 mg/kg BW) induced an acute increase in PRL secretion in all groups, peaking within 15-30 min. Seven months later (December, short-day photoperiod) these heifers were ovariectomized. Basal plasma PRL levels were seasonally low, PRL secretion in AHD, PHD and CHD animals abruptly increased within 15 min to iv injection of 100 microg TRH to a greater amount than seen in SOC heifers. Although a biphasic effect on PRL secretion entrains under long-day and short-day photoperiods, hypothalamic deafferentation in cattle did not affect the pituitary gland's responsiveness to secretagogues.     

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 a single growth hormone (rbST) treatment at breeding on conception rates and pregnancy retention in dairy and beef cattle

Initiation of long-term treatment with rbST (Posilac, Monsanto, St. Louis, MO) coincident with first insemination increased pregnancy rates in dairy cattle, but neither the efficacy of using only the initial injection, nor its effects on retention of pregnancy are known. Lactating dairy cows, dairy heifers, and lactating beef cows were assigned at random to treatment (rbST) or control. Dairy cows, dairy heifers, and beef cows received 500 mg rbST (n = 48, 35, 137 inseminations, respectively) at artificial insemination or were left untreated (n = 62, 33, 130 inseminations, respectively). Pregnancy was diagnosed by ultrasonography at 28-36 days. Treatment with rbST at insemination improved conception rates in dairy cows (60.4% versus 40.3%; P < 0.05), but not in dairy heifers or beef cows. Conception rates did not differ in dairy cows at < or =100 days in milk (DIM), but were improved in cows treated with rbST after 100 DIM (64.3% versus 25.8%; P < 0.05). Retention of pregnancy to approximately 60 days and sizes of CL, diameter of follicles > or =5 mm, and crown-rump lengths of embryos were not affected by treatment. The second objective was to examine the effects of rbST at insemination on birth weight and post-natal calf growth in beef cows. However, birth and weaning weights of beef calves were not affected by treatment. In conclusion, a single treatment with rbST at insemination increased conception rates in dairy cows, specifically in those >100 DIM.     

Effects of ghrelin injection on plasma concentrations of glucose, pancreatic hormones and cortisol in Holstein dairy cattle

Ghrelin affects not only growth hormone secretion but also nutrient utilization and metabolic hormone secretion in humans and experimental animals. The effects of ghrelin on plasma metabolic hormone and metabolite levels in domestic herbivores remain unclear despite the fact that the physiological characteristics of nutrient digestion and absorption imply specific responses to ghrelin. Therefore, the effects of ghrelin on plasma glucose, pancreatic hormones and cortisol concentrations were investigated in Holstein dairy cattle in various physiological states. Ghrelin (0.3 nmol/kg) or placebo (2% bovine serum albumin in saline) was intravenously injected in pre-ruminant calves (pre-rumen function), adult non-lactating (functional rumen) and lactating cows (functional rumen and lactation), and plasma glucose, insulin, glucagon and cortisol concentrations were then determined. Ghrelin injection increased plasma glucose concentrations in adult cows, especially in lactating cows. No hyperglycemic response was observed in pre-ruminant calves. A transient rise of insulin and glucagon levels was distinctively found in lactating cows in response to the ghrelin administration. Ghrelin injection decreased the insulin level in pre-ruminant calves. Ghrelin increased cortisol secretion independently of the physiological state. The results of the present study suggest that the effects of ghrelin on plasma glucose and pancreatic hormone levels may reflect differences in the physiological states of dairy cattle.     

Effects of parity and periconceptional metabolic state of Holstein–Friesian dams on the glucose metabolism and conformation in their newborn calves

The metabolic state of pregnant mammals influences the offspring’s development and risk of metabolic disease in postnatal life. The metabolic state in a lactating dairy cow differs immensely from that in a non-lactating heifer around the time of conception, but consequences for their calves are poorly understood. The hypothesis of this study was that differences in metabolic state between non-lactating heifers and lactating cows during early pregnancy would affect insulin-dependent glucose metabolism and development in their neonatal calves. Using a mixed linear model, concentrations of glucose, IGF-I and non-esterified fatty acids (NEFAs) were compared between 13 non-lactating heifers and 16 high-yielding dairy cows in repeated blood samples obtained during the 1st month after successful insemination. Calves born from these dams were weighed and measured at birth, and subjected to intravenous glucose and insulin challenges between 7 and 14 days of age. Eight estimators of insulin-dependent glucose metabolism were determined: glucose and insulin peak concentration, area under the curve and elimination rate after glucose challenge, glucose reduction rate after insulin challenge, and quantitative insulin sensitivity check index. Effects of dam parity and calf sex on the metabolic and developmental traits were analysed in a two-way ANOVA. Compared with heifers, cows displayed lower glucose and IGF-I and higher NEFA concentrations during the 1st month after conception. However, these differences did not affect developmental traits and glucose homeostasis in their calves: birth weight, withers height, heart girth, and responses to glucose and insulin challenges in the calves were unaffected by their dam’s parity. In conclusion, differences in the metabolic state of heifers and cows during early gestation under field conditions could not be related to their offspring’s development and glucose homeostasis.     

Long-term bromocriptine therapy and predictive tests in acromegaly

The value of predictive tests in bromocriptine therapy and the effects of long-term bromocriptine therapy were investigated in acromegalic patients. In 72 acromegalic patients, there was a tendency for patients with a plasma GH response to TRH or with an elevated basal plasma PRL level, but without a plasma GH response to LHRH, to have a plasma GH response to bromocriptine, though statistical analysis did not reveal a significant difference. Acute and chronic effects of bromocriptine were significantly interrelated, while the chronic effect of bromocriptine and abnormal plasma GH response to TRH or elevated plasma PRL levels were not, in 18 acromegalic patients. These results suggest that the acute bromocriptine test is a better predictor than the TRH test and plasma PRL levels for evaluating the effects of chronic bromocriptine therapy. To maintain the low plasma GH levels, increasing doses of bromocriptine were needed in most patients, and failure to control the elevated GH level despite increasing doses was observed in 2 of 18 patients.     

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.     

Effect of the metabolic environment at key stages of follicle development in cattle: focus on steroid biosynthesis

Cellular mechanisms that contribute to low estradiol concentrations produced by the preovulatory ovarian follicle in cattle with a compromised metabolic status are largely unknown. To gain insight into the main metabolic mechanisms affecting preovulatory follicle function, two different animal models were used. Experiment 1 compared Holstein-Friesian nonlactating heifers (n = 17) and lactating cows (n = 16) at three stages of preovulatory follicle development: 1) newly selected dominant follicle in the luteal phase (Selection), 2) follicular phase before the LH surge (Differentiation), and 3) preovulatory phase after the LH surge (Luteinization). Experiment 2 compared newly selected dominant follicles in the luteal phase in beef heifers fed a diet of 1.2 times maintenance (M, n = 8) or 0.4 M (n = 11). Lactating cows and 0.4 M beef heifers had higher concentrations of β-hydroxybutyrate, and lower concentrations of glucose, insulin, and IGF-I compared with dairy heifers and 1.2 M beef heifers, respectively. In lactating cows this altered metabolic environment was associated with reduced dominant follicle estradiol and progesterone synthesis during Differentiation and Luteinization, respectively, and in 0.4 M beef heifers with reduced dominant follicle estradiol synthesis. Using a combination of RNA sequencing, Ingenuity Pathway Analysis, and qRT-PCR validation, we identified several important molecular markers involved in steroid biosynthesis, such as the expression of steroidogenic acute regulatory protein (STAR) within developing dominant follicles, to be downregulated by the catabolic state. Based on this, we propose that the adverse metabolic environment caused by lactation or nutritional restriction decreases preovulatory follicle function mainly by affecting cholesterol transport into the mitochondria to initiate steroidogenesis.     

Inhibitory effects of cysteamine on neuroendocrine function

The action of cysteamine on anterior pituitary hormone secretion was studied in vivo using conscious, freely moving male rats and in vitro using anterior pituitary cells in monolayer culture. Administration of 500 micrograms cysteamine into the lateral cerebral ventricles of normal rats caused the complete inhibition of pulsatile GH secretion for a minimum of 6 h. This treatment also significantly decreased plasma concentrations of LH for at least 6 h in orchiectomized rat, TSH in short-term (0.5 month) thyroidectomized rats, and PRL in long-term (6 months) thyroidectomized rats. The in vivo stimulation of GH, LH, TSH and PRL with their respective releasing hormones 60 min after administration of cysteamine was not different from the response observed in rats pretreated with saline except for PRL where cysteamine pretreatment significantly inhibited the expected PRL increase. In vitro, 1 mM cysteamine decreased basal and TRH stimulated PRL release while not affecting basal or stimulated GH, LH, TSH and ACTH secretion. These data demonstrate the dramatic and wide-ranging effects of cysteamine on anterior pituitary hormone secretion. This action appears to be mediated through hypothalamic pathways for GH, LH and TSH and through a pituitary pathway for PRL.     

Plasma progesterone profiles and factors affecting embryo-fetal mortality following embryo transfer in dairy cattle

The relationship between plasma progesterone (P4) levels and embryo survival, and the value of P4 profiles for the selection of cattle embryo transfer recipients is still a matter of controversy. This study reports a comparison between lactating cows and heifers (n = 407) from a single dairy herd, after transfer of either fresh or frozen-thawed good quality embryos, of their ability to sustain embryo-fetal development to term. Plasma P4 concentrations on the day of estrus (Day 0 = D0), Day 4, Day 7 and on Day 21 were measured and related to embryo survival. Plasma P4 levels on Days 0, 4 and 7 were similar in recipients later found pregnant or open. Plasma P4 levels on Day 7 were significantly higher (P < 0.01) in heifers than in cows, but they were similar in pregnant and nonpregnant heifers and in pregnant and nonpregnant cows. Pregnancy rates for fresh and frozen-thawed embryos were higher in heifers than in cows, but the differences did not reach significance. However, the overall late embryonic mortality was significantly higher (P < 0.01) and the calving rate for frozen-thawed embryos was significantly lower (P < 0.05) in cows than in heifers. As expected, plasma P4 on Day 21 was significantly higher (P < 0.001) in pregnant than in nonpregnant recipients, but there was no difference between pregnant cows and pregnant heifers. Plasma P4 levels on Day 7 of recipients presumed pregnant on Day 21 and later found pregnant or nonpregnant were similar, but plasma P4 levels on Day 21 were significantly higher (P < 0.001) in pregnant than in nonpregnant recipients. The results of this study suggest that plasma P4 levels until the day of transfer, except for the rejection of recipients with abnormal luteal function, are of limited practical use for embryo transfer recipient selection. However, in lactating cows low plasma P4 values on Day 7 might negatively affect embryo survival, while in heifers this effect is not noticeable. Lactating cows are more prone to embryo loss than heifers, especially in the case of frozen-thawed embryos; this is associated with a lower competence of the corpus luteum at Day 7.     

The use of embryo transfer in the field for increased calf crops in beef and dairy cattle

Non-surgical transfer of one embryo to 63 previously synchronized inseminated recipients was performed on farms to induce twinning in beef and dairy cattle. All the transfers were done by technicians of A.I. centers. After calving, a twinning rate of 44.4% was achieved with no differences between beef Charolais heifers (45.4%), lactating Normande cows (42.8%) and dairy Friesian cows (45.4%). Compared with controls, the calving crop after a three-breeding-cycle period was significantly higher with recipients: 1.16 calf per treated recipient vs. 0.83 calf per control animal. It would seem that the possibility of obtaining about one-third more calves with embryo transfer could be of economical interest to increase meat production from cattle herds.     

Effect of insulin and growth hormone on plasma leptin in periparturient dairy cows

After parturition, dairy cows suffer from an intense energy deficit caused by the onset of copious milk secretion and an inadequate increase in voluntary food intake. We previously showed that this energy deficit contributes to a decline in plasma leptin. This decline mirrors that of plasma insulin but is reciprocal to the profile of plasma growth hormone (GH), suggesting that both hormones may regulate plasma leptin in periparturient dairy cows. To study the role of insulin, hyperinsulinemic-euglycemic clamps were performed on six dairy cows in late pregnancy (LP, 31 days prepartum) and early lactation (EL, 7 days postpartum). Infusion of insulin (1 microg.kg body wt-1.h-1) caused a progressive rise in the plasma concentration of leptin that reached maximum levels at 24 h during both physiological states. At steady states, the absolute increase in plasma leptin was greater in LP than in EL cows (2.4 vs. 0.4 ng/ml). Insulin infusion increased leptin mRNA in adipose tissue during LP but not during EL. During lactation, mammary epithelial cells expressed leptin mRNA but insulin did not increase milk leptin output. In contrast, a 3-day period of GH administration had no effect on plasma leptin during LP or EL. Therefore, insulin increases plasma leptin in LP by stimulating adipose tissue synthesis but has only marginal effects in EL, when cows are in negative energy balance. Other factors, such as increased response of adipose tissue to beta-adrenergic signals, probably contribute to the reduction of plasma leptin in early lactating dairy cows.     

Neither intravenous nor intracerebroventricular administration of obestatin affects the secretion of GH, PRL, TSH and ACTH in rats

To examine the effect of obestatin, a recently identified peptide derived from preproghrelin, on pituitary hormone secretion, obestatin was administered in anesthetized male rats. Intravenous administration of obestatin did not show any effect on plasma GH, PRL, ACTH and TSH levels. Since obestatin has been reported to have opposite effects of ghrelin in regulating food intake, gastric emptying and intestinal contractility, GH suppressive effect, which is opposite effect of ghrelin, was tested. Intravenous administration of GHRH or GHRP-2, a ghrelin receptor ligand, resulted in a marked plasma GH elevation. However obestatin did not show any effect on GHRH- or GHRP-2-induced GH rise. Furthermore intracerebroventricular administration of obestatin also did not influence plasma GH, PRL, ACTH and TSH levels. These findings suggest that obestatin has no effect on pituitary hormone secretions despite the presence of GPR39, a receptor for obestatin, in the pituitary.     

Paradoxical growth hormone response following thyroid-stimulating hormone administration in the polycystic ovary syndrome

Growth hormone (GH) and prolactin (PRL) responses after TRH administration were studied in 31 women presenting with the clinical, biochemical and ultrasonographic characteristics of the polycystic ovarian (PCO) syndrome; their results were compared with those of 20 normally menstruating women investigated during the early follicular phase of the cycle. Based on the GH responses two PCO subgroups were observed: (a) nonresponders (n = 16) who showed delta max GH responses (0.7 +/- 0.27 ng/ml, x +/- SE) similar to those of the normals (0.97 +/- 0.20 ng/ml), and (b) responders (n = 15), 48.4% of the PCO patients who showed a paradoxical increase in GH levels (delta max GH, 18.0 +/- 1.96 ng/ml) following thyrotropin-releasing hormone (TRH) administration significantly higher than those observed either in nonresponder PCO patients or in normals. Furthermore, basal GH levels were found to be significantly higher in the responder PCO subgroup (5.65 +/- 0.75 ng/ml) compared to either nonresponders (1.58 +/- 0.21 ng/ml) or normals (1.8 +/- 0.18 ng/ml). However, no correlation was found between basal GH levels and delta max GH responses observed. Additionally, basal PRL and delta max PRL levels following TRH administration did not differ either between the two PCO subgroups or those observed in normal controls. delta 4A, T and E2 levels were similar between the two PCO subgroups. No correlation was found between the delta max GH responses to delta max PRL or the post-luteinizing hormone-releasing hormone stimulation test delta max luteinizing hormone:follicle-stimulating hormone ratio observed or to steroid levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Oxytocin Receptors in Bovine Mammary Tissue

Abstract

Oxytocin receptors were identified and characterized in bovine mammary tissue. [³H]-oxytocin was specifically bound to the 105,000 × g particulate fractions from 5 lactating cows and 5 non-lactating cows. Binding reached equilibrium by 50 min at 20°C and by 8 hr at 4°C. The half-time of displacement at 20°C was approximately 1 hr. ACTH, TRH, angiotensin I, angiotensin II, pentagastrin, bradykinin, xenopsin and L-valyl-histidyl-L-leucyl-L-threonyl-L-prolyl-L-valyl-L-glutamyl-L-lysine were not competitive in the dose range tested at 20°C. The ability of other peptides to inhibit ³H-oxytocin binding was as follows: oxytocin > vasotocin > arginine - vasopressin >lysine - vaso-pressin > Pen¹ Phe² Thr⁴ - oxytocin. The Kd of the oxytocin receptor averaged 1.66 ± 1.19 nMol/L for lactating cows and 0.97± 0.49 nMol/L for non-lactating cows, respectively. The maximum number of binding sites was 0.14 ± 0.12 nM/mg protein and 0.15 ± 0.08 nM/mg protein for lactating cows and non-lactating cows, respectively. Identification and characterization of these receptors now makes it possible to study the dynamics of hormonal binding throughout various physiological states of the animal.