Increase In Growth Hormone Levels Research Articles

Ghrelin Stimulates Appetite, Imagination of Food, GH, ACTH, and Cortisol, but does not Affect Leptin in Normal Controls

Ghrelin, a growth hormone (GH) secretagogue receptor ligand was isolated from the stomach and hypothalamus of rats and humans. In rodents, ghrelin exerts distinct orexigenic action, probably as counterpart of the anorexigenic leptin. In humans, ghrelin infusion enhances appetite. It is unknown whether single intravenous (i.v.) injections of ghrelin affect human eating behavior. Therefore, we investigated the influence of a single i.v. bolus injection of 100 microg ghrelin on appetite, ideas about food, hormone levels, and glucose concentration in young control subjects. In order to test gender differences, we included five women and four men. After ghrelin administration, appetite was enhanced in eight of nine subjects. Seven probands reported a vivid, plastic image of their preferred meal. Furthermore, ghrelin stimulated an immediate increase in plasma levels of GH (area under the curve, mean+/-SEM 35+/-16 ng/ml x min after placebo [P] to 2808+/-533 ng/ml x min after ghrelin [G]; p<0.001), cortisol (5908+/-984 ng/ml x min [P] to 10179+/-1293 ng/ml x min [G]; p<0.001), and ACTH (922+/-103 pg/ml x min [P] to 3030+/-763 pg/ml x min [G]; p<0.02), whereas leptin levels remained unchanged. Contrary to placebo, glucose concentration did not decrease markedly after administration of ghrelin. Our data suggest that i.v. ghrelin stimulates appetite and images of food in young women and men. Obviously, leptin is not involved in these effects.

Endocrine response to fasting in the overwintering captive raccoon dog (Nyctereutes procyonoides)

The raccoon dog (Nyctereutes procyonoides) is an omnivorous canid utilizing the passive wintering strategy in the boreal climate. Farmed raccoon dogs (n=12) were randomly assigned into two study groups on 26 November 2003. Between 3 December 2003 and 27 January 2004, half of the animals were fasted for 8 weeks and plasma weight-regulatory hormone concentrations determined on 26 November and 30 December 2003 and on 27 January 2004. The plasma peptide YY, ghrelin, and growth hormone (GH) concentrations increased due to food deprivation, while the T4 and Acrp30 concentrations decreased. Furthermore, the plasma GH concentrations were higher in the fasted raccoon dogs than in the fed animals, which had higher plasma insulin, glucagon, and T4 concentrations. However, fasting had no effect on the plasma leptin concentrations. The results confirm previous findings with unchanged leptin levels in fasting carnivores. Increased GH levels probably contribute to increased lipolysis and mobilization of fat stores. Ghrelin can also enhance lipolysis by increasing the GH levels. The decreased levels of T4 may reduce the metabolic rate. The plasma dopamine concentrations decreased due to fasting unlike observed previously in rats. Together with the unaffected adrenaline, noradrenaline, and cortisol concentrations, this suggests that food deprivation in winter does not cause stress to the raccoon dog but is an integral part of its natural life history.

Stereotactic conformal radiotherapy in patients with growth hormone–secreting pituitary adenoma

Purpose To evaluate the reduction of hormonal overproduction and side effects as well as survival rates after fractionated stereotactic conformal radiotherapy (FSRT) and radiosurgery in patients with growth hormone (GH)–secreting pituitary adenoma. Methods and materials Between January 1989 and May 2001, 25 consecutive patients were treated with FSRT ( n = 20) or radiosurgery ( n = 5) for GH-secreting pituitary adenoma. Nine patients were treated for recurrent disease after primary surgery. One patient had primary radiotherapy because of inoperability, and 15 patients received radiotherapy after subtotal resection due to increased GH level. Median total dose was 52.2 Gy for FSRT and 15 Gy for radiosurgery. Results Radiologic local tumor control was 100% after a median follow-up of 59.8 months (range, 20.3–168.2 months). Seventeen patients had stable disease on CT/MRI, and eight showed a reduction of tumor volume on MRI scans. Endocrinologic control was 92% (23 of 25 patients). Two patients had an endocrinologic recurrence 21 and 54 months after FSRT. A normalization of preexisting acromegalic symptoms was seen in 1 patient, 4.5 years after FSRT. GH level normalized in 21 of 25 patients after 26 months median. Five of these patients underwent concurrent Octreotid therapy because of increased insulin-like growth factor I levels. Improvement of visual acuity was seen in 1 patient. New onset of clinically evident hypopituitarism as an adverse reaction of stereotactic radiotherapy was only infrequently observed in this series. Conclusion Stereotactic conformal radiotherapy is effective and safe in the treatment of GH-secreting pituitary adenoma to reduce hormonal overproduction and to improve local control. It is an alternative option to surgery especially for patients at high risk of surgical complications due to comorbidity.

Supplemental Oral Arginine Prior To Exercise Results In A Blunted Gh Response

2082 Arginine is known to invoke an increase in growth hormone (GH) levels. Many athletes and resistance weight lifters ingest oral arginine as a supplement in an effort to increase GH levels and to induce an anabolic effect. However, little is known regarding the biological response when oral arginine and exercise are combined. PURPOSE The purpose of this study was to examine the GH response to both resistance exercise and, oral arginine. METHODS Eight healthy males (ages 18–22 yrs), were studied on 4 separate occasions (placebo, arginine, exercise alone, arginine + exercise). On a study day, the subject arrived at 0700 h following an overnight fast, and a catheter was placed in a forearm vein. Blood samples were taken every 10 minutes for 4 hours. Thirty minutes after sampling commenced, the subject ingested a 7-gram dose of arginine or placebo (blinded, randomly assigned). On the 2 resistance exercise days, the subject performed 3 sets, 10 reps at 80% 1RM, for 9 major muscle groups. RESULTS * p < 0.05 vs. placebo † p < 0.05 vs. exercise ** p < 0.02 vs. placebo †† p < 0.02 vs exercise Resting GH concentrations were not significantly different between each study day (p > 0.05). Integrated area under the curve on the placebo day was not different from the arginine day (p > 0.05), yet significantly less than the exercise and arginine + exercise days (p < 0.05). The arginine day was significantly less than the exercise only day (p 0.05). Exercise alone was found to induce a greater response (P < 0.05) than the combination of arginine exercise. CONCLUSIONS These data reveal that supplemental oral arginine taken prior to exercise may blunt the exercise GH response, and arginine and exercise potentially stimulate the GH response by different mechanisms.Table

Different effects of physiologically and pharmacologically increased growth hormone levels on cholecalciferol metabolism at prepubertal age

The aim of the study was to investigate the influence of physiologically and pharmacologically increased plasma growth hormone (GH) levels on cholecalciferol metabolism at prepubertal age. Three groups of dogs raised on the same diet were studied from weaning till 21 weeks of age, i.e., small breed dogs ( n=7, control group); large breed dogs with 15-fold greater growth rates compared to the control group ( n=8, LB-group); and small breed dogs treated with pharmacological doses of growth hormone ( n=6, GH-group; 0.5 IU GH per kg body per day) from 12 to 21 weeks of age. Excess of GH had the expected anabolic effect on growth rate and phosphate sparing. Increased plasma GH levels in the LB- and GH-groups versus the control group were accompanied by (1) greater plasma insulin-like growth factor I (IGF-I) levels, (2) greater plasma 1,25-dihydroxycholecalciferol (1,25(OH) 2D 3) levels, and (3) lower plasma 24,25(OH) 2D 3 levels. In the LB-group, excess of GH favored plasma 1,25(OH) 2D 3 levels by decreasing the clearance of 1,25(OH) 2D 3, whereas in the GH-group by increasing the production of 1,25(OH) 2D 3. The lowered plasma 24,25(OH) 2D 3 levels in the LB- and GH-groups were likely attributed to a competitive inhibition of the production of 24,25(OH) 2D 3 by GH and/or IGF-I.

In vitro and in vivo effects of ghrelin on luteinizing hormone and growth hormone release in goldfish.

We studied the in vitro and in vivo effects of octanoylated goldfish ghrelin peptides (gGRL-19 and gGRL-12) on luteinizing hormone (LH) and growth hormone (GH) release in goldfish. gGRL-19 and gGRL-12 at picomolar doses stimulated LH and GH release from dispersed goldfish pituitary cells in perifusion and static incubation. Incubation of pituitary cells for 2 h with 10 nM gGRL-12 and 1 or 10 nM gGRL-19 increased LH-beta mRNA expression, whereas only 10 nM gGRL-19 increased GH mRNA expression. Somatostatin-14 abolished the stimulatory effects of ghrelin on GH release from dispersed pituitary cells in perifusion and static culture. The GH secretagogue receptor antagonist d-Lys(3)-GHRP-6 inhibited the ghrelin-induced LH release, whereas no effects were found on stimulation of GH release by ghrelin. Intracerebroventricular injection of 1 ng/g body wt of gGRL-19 or intraperitoneal injection of 100 ng/g body wt of gGRL-19 increased serum LH levels at 60 min after injection, whereas significant increases in GH levels were found at 15 and 30 min after these treatments. Our results indicate that, in addition to its potent stimulatory actions on GH release, goldfish ghrelin peptides have the novel function of stimulating LH release in goldfish.

Regulation of active ghrelin levels by various feedback mechanisms

Background: Ghrelin is a potent stimulator of growth hormone (GH) secretion. Furthermore, it is involved in energy homeostasis. Octanoylation of the peptide at serine-3 is necessary for biological activity. We investigated changes in active ghrelin plasma levels due to two different putative feedback mechanisms. Methods: Twelve healthy humans were tested by intravenous administration of the synthetic ghrelin analogue GHRP6 (1µg/kg), possibly activating a short feedback loop. On a different day, GH levels were increased by intravenous administration of growth hormone-releasing hormone (GHRH, 100µg iv) plus Arginine (30g iv over 30′) to test for a GH-dependent feedback mechanism. Blood samples were taken for measurement of ghrelin and GH. Active ghrelin-levels were determined by a specific radioimmunoassay that exclusively detects the octanoylated form of ghrelin. Results: Basal active ghrelin levels demonstrated significant inter-individual differences, but very little intra-individual variation (r=0.93, p<0,005). Administration of GHRP6 resulted in a 20-fold increase in GH levels. However, no significant changes of active ghrelin levels were observed over a 90′ period. Application of GHRH+Arginine led to an even higher 63-fold increase of GH levels, again without any significant change in levels of active ghrelin over a period of 120′. Conclusions: Acute increases in GH levels either by GHRP6 or by GHRH+Arginine did not feedback on systemic concentrations of active ghrelin. Furthermore, a ghrelin analogue had no short loop feedback effects on systemic active ghrelin levels. Due to its metabolic role, systemic ghrelin levels may be more dependent on energy homeostasis.

Insulin resistance in the liver-specific IGF-1 gene-deleted mouse is abrogated by deletion of the acid-labile subunit of the IGF-binding protein-3 complex: relative roles of growth hormone and IGF-1 in insulin resistance.

Liver IGF-1 deficient (LID) mice demonstrate a 75% reduction in circulating IGF-1 levels and a corresponding fourfold increase in growth hormone (GH) levels. At 16 weeks of age, LID mice demonstrate, using the hyperinsulinemic-euglycemic clamp, insulin insensitivity in muscle, liver, and fat tissues. In contrast, mice with a gene deletion of the acid-labile subunit (ALSKO) demonstrate a 65% reduction in circulating IGF-1 levels, with normal GH levels and no signs of insulin resistance. To further clarify the relative roles of increased GH and decreased IGF-1 levels in the development of insulin resistance, we crossed the two mouse lines and created a double knockout mouse (LID+ALSKO). LID+ALSKO mice demonstrate a further reduction in circulating IGF-1 levels (85%) and a concomitant 10-fold increase in GH levels. Insulin tolerance tests showed an improvement in insulin responsiveness in the LID+ALSKO mice compared with controls; LID mice were very insulin insensitive. Surprisingly, insulin sensitivity, while improved in white adipose tissue and in muscle, was unchanged in the liver. The lack of improvement in liver insulin sensitivity may reflect the absence of IGF-1 receptors or increased triglyceride levels in the liver. The present study suggests that whereas GH plays a major role in inducing insulin resistance, IGF-1 may have a direct modulatory role.

Osmoregulation and growth in a wild and a selected strain of Atlantic salmon smolts on two photoperiod regimes

Abstract Atlantic salmon ( Salmo salar ) smolts originating from wild (Imsa) and selected (AquaGen) strains were maintained on simulated natural photoperiod (SNP) or constant light (LL) in replicate tanks between 3 December 1998 and 26 May 1999. Gill Na + ,K + -ATPase activity, plasma growth hormone (GH) levels, condition factor (CF) as well as individual food intake, growth and food conversion were monitored regularly in all groups during the experimental period. Freshwater temperature was kept constant at approximately 12 °C. In both strains, GH levels and gill Na + ,K + -ATPase activity rose steadily in the SNP groups, whereas the abrupt increase in day-length caused a significant increase in GH levels within 4 weeks, concurrent with an increase gill Na + ,K + -ATPase activity. The close relationship between GH levels and gill Na + ,K + -ATPase activity indicates that GH plays and important role in the development of hypo-osmoregulatory ability during smolting. Overall, a higher growth rate was seen in smolts from the AquaGen strain compared with the Imsa strain. No differences in food consumption were seen between strains, whereas an improved food conversion was observed in smolts from the AquaGen strain. Photoperiod was found to enhance growth through stimulation of food intake. It is concluded that the observed differences in growth and food conversion between wild and selected smolts are genetic, and probably reflect the fact that the AquaGen fish have been bred for rapid growth for several generations.

Effects of acute hexarelin administration on cardiac performance in patients with coronary artery disease during by-pass surgery

Growth hormone (GH) secretagogues are synthetic molecules with neuroendocrine but also cardiovascular activities mediated by specific GH secretagogue-receptors. The acute administration of hexarelin, a peptidyl GH secretagogue, increases left ventricular ejection fraction in normal subjects and even in patients with severe GH deficiency. We evaluated cardiac performances in patients with coronary artery disease after acute administration of hexarelin (2.0 μg/kg, i.v.) compared to that in patients given with GH-releasing hormone (GHRH; 2.0 μg/kg, i.v.), recombinant human (rh)-GH (10.0 μg/kg, i.v.) or placebo. Cardiac performance was studied in 24 male patients (age [mean±S.E.M.]: 59.5±1.1 years; body mass index: 24.6±0.9 kg/m 2; left ventricular ejection fraction: 57.2±1.4%) with coronary artery disease undergoing by-pass surgery during general anesthesia. Left ventricular ejection fraction, left ventricular end diastolic volume, cardiac index and cardiac output were evaluated by intraoperative omniplane transoesophageal echocardiography while wedge pressure, central venous pressure, mean arterial pressure and systemic vascular resistance index were evaluated by systemic and pulmonary arterial catheterization. RhGH, GHRH and placebo did not exert any hemodynamic effect while hexarelin induced a prompt (after +10 min) increase in left ventricular ejection fraction ( P<0.001), cardiac index ( P<0.001) and cardiac output ( P<0.001) lasting up to +90 min without any variation in left ventricular end diastolic volume. Accordingly, hexarelin induced a reduction of wedge pressure ( P<0.01). These changes occurred in the presence of increased mean arterial pressure ( P<0.05) and transient decrease of central venous pressure ( P<0.05 at +30 min only) but no change in systemic vascular resistance index. Heart rate after hexarelin was similar to that after placebo. Hexarelin induced a slight increase in GH levels which was similar to that after GHRH but far lower ( P<0.01) than that after rhGH. Thus, in patients with coronary artery disease undergoing by-pass surgery, the acute administration of hexarelin clearly improves cardiac performance without any relevant variation in systemic vascular resistance. The cardiotropic effect of hexarelin is not shared by GHRH or by rhGH, indicating that it is not mediated by the increase in circulating GH levels but more likely reflects activation of specific cardiovascular GH secretagogue receptors.

GH‐independent cardiotropic activities of hexarelin in patients with severe left ventricular dysfunction due to dilated and ischemic cardiomyopathy

To investigate acute cardiotropic activities of hexarelin in patients with severe left ventricular dysfunction due to ischemic (iCMP) and dilated cardiomyopathy (dCMP). We studied the effect of intravenous hexarelin administration on growth hormone (GH) levels and left ventricular ejection fraction (LVEF) evaluated by radionuclide angiography in eight patients with dCMP (age 53.0+/-2.8, LVEF 16.7+/-2.1%) and five patients with iCMP (age 52.0+/-2.8 years, LVEF 22.6+/-2.1). Results were compared with a group of seven normal subjects (age 37.4+/-3.4 years, LVEF 64.0+/-1.5%) and seven patients with severe growth-hormone deficiency (GHD; age 42.0+/-4.4 years, LVEF 50.0+/-1.9%) previously studied with the same methodology. In dCMP and iCMP patients hexarelin induced a similar significant (P<0.05) increase in GH levels. In iCMP patients hexarelin induced a LVEF increase (peak LVEF 26.2+/-2.5%, P<0.05) as observed in normals and GHD, while in dCMP LVEF was unchanged (peak LVEF 17.7+/-1.7, P=NS). In all groups other hemodynamic parameters were unchanged. Acute hexarelin administration increases LVEF in iCMP patients (as in normals and GHD) but not in dCMP patients in spite of a similar GH releasing effect and basal LVEF. A possible explanation of the positive inotropic effect of hexarelin in iCMP could be a direct stimulation on viable myocardium or myocardial contractile reserve.

A case of fibrous dysplasia which occurred widely in facial bones, with associated increased growth hormone level

A case of fibrous dysplasia which occurred widely in facial bones, with associated increased growth hormone level

Somatostatin Analogue Attenuates Estrogen-Induced Augmentation of Glomerular Injury in Spontaneous Hypercholesterolemic Female Imai Rats

Background: Aggravating effect of estrogen replacement therapy on glomerular injury associated with an elevation of growth hormone (GH) levels has been reported. Therefore, in the present study, to clarify an association between GH elevation and the aggravating effect of estrogen on glomerular injury, we investigated the effect of somatostatin, an inhibitor of GH secretion, on glomerular injury in estrogen-treated hypercholesterolemic female Imai rats. Method: Control female rats were assigned to group 1 (Cont, n = 10). Group 2 (Cont-E, n = 10) received estrogen, and groups 3 (Cont-E-LS, n = 10) and 4 (Cont-E-HS) received estrogen and either a low dose of somatostatin analogue or a high dose of somatostatin analogue. Body weight, urinary protein, serum albumin, total cholesterol, triglycerides, blood urea nitrogen and serum creatinine were investigated every 4 weeks from 10 weeks through 30 weeks of age. At 30 weeks of age, rats were studied morphologically. Results: Estrogen administration resulted in an increase in urinary protein excretion rates and serum total cholesterol levels, and aggravated glomerular injury associated with an increase in GH. In contrast, somatostatin treatment reduced both urinary protein excretion rates and total cholesterol levels and attenuated glomerular injury to levels close to those of controls associated with a reduction of GH levels. Conclusion: The results suggest that increased GH levels may contribute to an enhancing effect of estrogen administration on glomerular injury.

Growth Hormone Secretion after Baclofen Administration in Different Phases of the Menstrual Cycle in Healthy Women

Aim: The aim of this study was to investigate the effect of baclofen administration on growth hormone (GH) secretion during different phases of the menstrual cycle. Methods: Twelve healthy women (33.6 ± (SD) 2.8 years; range 23–40 years) with regular menstrual cycles were enrolled. The phases of the menstrual cycle were determined using transvaginal ultrasonography (TV-US) and detecting hormonal serum levels. Plasma GH levels were evaluated during the early follicular, periovulatory and luteal phases of the cycle before and after the baclofen challenge test. Results: After acute baclofen administration, GH levels increased significantly (p < 0.001) compared to basal values during the periovulatory and luteal phases, while no significant variation was detected during the early follicular phase. In addition, plasma GH levels resulted significantly (p < 0.001) higher during the luteal phase than during the periovulatory phase. Conclusion: Acute baclofen administration induces a significant increase in plasma GH levels in healthy females during the periovulatory and luteal phases, but not during the early follicular phase. These data suggest a modulator role of plasma sex steroids levels on GH release induced by baclofen.

Route-Dependent Endocrine and Metabolic Effects of Estrogen Replacement Therapy

The route of estrogen replacement therapy has a major impact on the growth hormone (GH)-insulin-like growth factor-I (IGF-I) axis. Estrogen administration by the oral, but not the transdermal, route reduces IGF-I and increases GH levels in postmenopausal women. This perturbation of the GH-IGF-I axis occurs with different forms of estrogen treatment, indicating that the dissociation of the somatotropic axis and concomitant increase in GH-binding protein levels are intrinsic effects of the oral route of estrogen administration. In clinical studies, oral estrogen reduced postprandial lipid oxidation, compared with transdermal estrogen. Oral estrogen was also associated with a reduction in lean body mass and an increase in fat mass, compared with transdermal estrogen. In contrast, the route of estrogen therapy had no impact on carbohydrate metabolism or the estrogen-induced increase in bone mineral density. The findings of route-dependent changes in body composition add a new dimension to health considerations concerning estrogen therapy in postmenopausal women and may have significant implications for estrogen replacement therapy in young hypogonadal females.

Photoperiod Regulation of Plasma Growth Hormone Levels during Induced Smoltification of Underyearling Atlantic Salmon

Earlier studies have established that increased daylength increases plasma growth hormone (GH) levels during spring smoltification of yearling Atlantic salmon. Recently, the Atlantic salmon aquaculture industry has started the production of underyearling (“summer”) smolts. This involves fast juvenile growth on continuous light (24L), the transfer of juveniles over 8 cm in length to short day (12L) for 6 weeks in the summer, followed by transfer to 24L for another 6 weeks before transfer to seawater in late October. Three groups were studied in fresh water from July to the following May in order to elucidate the GH response to this photoperiod manipulation: one group was kept on 24L throughout (long-day group), while the other two groups were exposed to short day from July 15th. Of these, one was brought back onto long day on September 1st (winter group) while the other was kept on short day (short-day group). Plasma GH levels of the long-day group were around 1.6 ng/ml throughout the study. The short-day transfer suppressed GH levels to 0.7 ng/ml within 2 weeks (short-day and winter groups). The long-day transfer (winter group) increased GH levels to 11 ng/ml within 3 weeks, and this elevation of GH levels was sustained for about 3 months, before declining to pretreatment levels. The study demonstrates that underyearling Atlantic salmon react to increased daylength in a way similar to traditional yearling smolts. It also demonstrates for the first time that decreased daylength can suppress plasma GH levels in fish. It is concluded that winter photoperiod manipulation causes an out-of-season initiation and completion of the parr–smolt transformation of underyearling Atlantic salmon and that growth hormone plays a major role in this process.

Free plasma thyroxine levels in coho salmon, Oncorhynchus kisutch, during parr-smolt transformation: comparison with total thyroxine, total triiodothyronine, and growth hormone levels

Free plasma thyroxine (FT4) levels were measured in coho salmon, Oncorhynchus kisutch, during parr-smolt transformation (smoltification) using an equilibrium dialysis system followed by a radioimmunoassay. The FT4 data were correlated to total plasma thyroxine (TT4), triiodothyronine (TT3), and growth hormone (GH). Plasma samples were taken weekly from early April to late May, when the salmon where released from the hatchery. Free thyroxine and GH levels increased gradually through smoltification. TT4 levels increased significantly in mid-April and in mid-May. TT3 levels increased in April and remained elevated until late-May after which they declined to the lowest levels. During the first increase in TT4 levels, FT4 levels remained low and TT3 levels did not increase until FT4 levels increased in late-April. In addition, after TT4 levels decreased in late May, FT4 levels remained elevated. These data show that there are differences between the plasma FT4 and TT4 profiles during smoltification. Nevertheless, regression analysis indicates that FT4 levels are highly correlated to the increases in the levels of GH (r=0.73) and TT4 (r=0.70). In addition, GH is less correlated to TT4 and TT3 (r=0.24 and r=−0.46, respectively) compared with FT4 (r=0.73), suggesting a close relationship between the increases of FT4 and GH. In addition, these data suggest that this method of measuring free plasma thyroxine may provide a new tool for studying the timing of thyroid hormone action and regulation during parr-smolt transformation in salmonids.

Amino acid supplements to improve athletic performance.

This review provides a critical evaluation of the metabolic rationale for the use of individual amino acids as nutritional ergogenic (work-generating) aids in athletes. The conclusion is that in contrast to the claims made on sport nutrition products, branched-chain amino acids do not improve endurance performance, that the evidence that glutamine supplements may improve immune function is rather weak, and that the available commercial supplements contain too little arginine to increase growth hormone levels. No studies have been performed to investigate the claim that tyrosine supplements can improve explosive exercise.

Combined Therapy with Estrogen and Testosterone Eliminates the Aggravating Effect of Estrogen Replacement Therapy on Glomerular Injury in Hypercholesterolemic Female Imai Rats

Hypercholesterolemic Imai rats spontaneously develop proteinuria and glomerulosclerosis, especially male animals. Ovariectomy aggravates glomerular injury in femal Imai rats. However, estrogen replacement therapy did not abolish this aggravating effect of ovariectomy and rather aggravated glomerular injury with an increase in serum levels of lipids and growth hormone (GH). Whereas we have already reported that treatment with testosterone in addition to estrogen reduces GH levels and attenuates glomerular injury as compared with estrogen alone in male Imai rats, in the present study, to investigate whether increased GH levels may contribute to an enhancing effect of estrogen on glomerular injury, we treated ovariectomized female Imai rats with estrogen puls testosterone. Group 1 was sham operated and group 2 was ovariectomized at 6 weeks of age. Groups 3, 4, and 5 were ovariectomized and received estrogen, testosterone, or estrogen plus testosterone, respectively. Body weight, urinary protein, and serum constituents were investigated every 4 weeks from 12 to 24 weeks of age. At 24 weeks of age, the rats were studied morphologically. Each treatment with estrogen or testosterone equally aggravated glomerular injury with an increase in both proteinuria and serum lipids with increased serum GH levels in estrogen–treated rats but without influencing GH levels in testosterone–treated rats; combined treatment with estrogen plus testosterone resulted in a reduction of both proteinuria and serum lipids to levels of the controls and attenuated glomerular injury to levels close to those of controls with a reduction of the elevated serum GH levels. These results suggest that increased GH levels may contribute to an enhancing effect of estrogen replacement therapy on glomerular injury and that testosterone, when administered to the estrogen–treated rats, seems to exert an attenuating effect on glomerular injury by suppressing GH levels.

Role of melatonin in the control of growth and growth hormone secretion in poultry

The pineal hormone melatonin controls reproduction of photoperiodic mammals and is an integral part of the circadian organization in birds. Recent findings indicate an involvement of this hormone also in more basic physiological processes, including growth, development, and aging. Melatonin may modulate growth in poultry through interaction with transcriptional factors, through interaction with hormones involved in growth control, and by modulation of energy metabolism and decreasing physical activity. Our studies showed that a single melatonin injection increased plasma growth hormone (GH) concentrations in the Japanese quail. Specific serotonin receptor blocker ketanserin did not preclude a stimulatory action of melatonin on GH synthesis. Serotonin agonist quipazine increased GH levels but failed to enhance the stimulatory effect of melatonin. Pretreatment with melatonin in drinking water did not affect the magnitude of the GH response to subcutaneous (s.c.) administration of thyrotropin releasing hormone (TRH) that considerably stimulated GH secretion. Present data suggest that melatonin modulates rather central neural pathways involved in the control of GH synthesis at the hypothalamic level than the sensitivity of the pituitary gland.