Adipokinetic hormone enhances nodule formation and phenoloxidase activation in adult locusts injected with bacterial lipopolysaccharide

Interactions between the locust endocrine and immune systems have been studied in vivo in relation to nodule formation and activation of the prophenoloxidase cascade in the haemolymph. Injection of bacterial lipopolysaccharide (LPS) extracted from Escherichia coli induces nodule formation in larval and adult locusts but does not increase phenoloxidase activity in the haemolymph. Nodule formation starts rapidly after injection of LPS and is virtually complete within 8 h, nodules occurring mainly associated with the dorsal diaphragm on either side of the heart, but sometimes with smaller numbers associated with the ventral diaphragm on either side of the nerve cord. Co-injection of adipokinetic hormone-I (Lom-AKH-I) with LPS stimulates greater numbers of nodules to be formed in larval and adult locusts, and activates phenoloxidase in the haemolymph of mature adults but not of nymphs. The effect of co-injection of Lom-AKH-I with LPS on nodule formation is seen at low doses of hormone; only 0.4 pmol of Lom-AKH-I per adult locust is needed to produce a 50% increase in the number of nodules formed. When different components of LPS from the E. coli Rd mutant are tested, the mono- and the diphosphoryl Lipid A components have similar effects to the intact LPS. Remarkably, detoxified LPS activates phenoloxidase in the absence of Lom-AKH-I, although co-injection with hormone does enhance this response. Both diphosphoryl Lipid A and detoxified LPS induce a level of nodule formation that is enhanced by co-injection of Lom-AKH-I, but monophosphoryl Lipid A does not initiate nodule formation even when injected with hormone. Co-injection of a water-soluble inhibitor of eicosanoid synthesis, diclofenac (2-[(2, 6-dichlorophenyl)amino] benzeneacetic acid), reduces nodule formation in response to injections of LPS (both in the absence and presence of hormone) in a dose-dependent manner, but does not prevent activation of phenoloxidase in adult locusts. It is shown that nodule formation and activation of the prophenoloxidase in locust haemolymph can both be enhanced by Lom-AKH-I, but it is argued that these processes involve distinct mechanisms in which eicosanoid synthesis is important for nodule formation, but not for the increased phenoloxidase activity.     

Differences in adipokinetic response of Pyrrhocoris apterus (Heteroptera) in relation to wing dimorphism and diapause

Three experimental groups of adult females (reproductive and diapausing brachypters, and macropters with reproductive arrest) of Pyrrhocoris apterus (Linnaeus) (Heteroptera: Pyrrhocoridae) from a temperate population were analysed for their adipokinetic responses. The adipokinetic response, expressed as an increase of haemolymph lipids after injection of adipokinetic hormone from Locusta migratoria (Lom-AKH-I), was assessed in relation to age, wing dimorphism and type of reproductive arrest. Two pmols of Lom-AKH-I were used for determination of adipokinetic responses. The increase of haemolymph lipids in all experimental groups of females induced by this dose of the hormone was comparable with that induced by crude extract of the bug’s own corpora cardiaca. The level of adipokinetic response after injection of 2 pmol of Lom-AKH-I was significantly higher in macropterous and diapausing brachypterous females than in reproductive brachypterous females. However, significantly higher contents of haemolymph lipids in control macropterous females than those found in the control reproductive and diapausing brachypterous females of the corresponding age revealed wing-morph-related differences in lipid metabolism. The observed wing morph- and diapause-related differences in the content of haemolymph lipids and adipokinetic response, respectively, are discussed in relation to the different roles of two wing morphs in the life history of this heteropteran.     

Adipokinetic hormones concentrations in the haemolymph of Schistocerca gregaria,measured by radioimmunoassay

A new procedure for the measurement of adipokinetic hormone (AKH) concentrations in locust (Schistocerca gregaria) haemolymph is described: Haemolymph is extracted with chloroform/methanol/water and the aqueous layer is fractionated with reverse-phase cartridges and HPLC. The fractions corresponding to AKH-I (Lom-AKH-I) and AKH-II (Scg-AKH-II) are then measured in a competitive binding assay using specific antibodies and [3H]AKHs. The procedures could be applied to any peptides containing N-terminal pyroglutamate residues including all members of the adipokinetic/hyperglycaemic/red pigment concentrating hormone family. Results show that the concentrations of both AKH-I and AKH-II increase within 5 min of initiation of flight and are maintained at approx. 15-fold (AKH-I) and 6-fold (AKH-II) the resting levels over flights of at least 60 min. Poisoning of locusts with either the insecticide deltamethrin or with potassium chloride also caused release of hormones. Starvation for 6 h caused elevation of hormone levels in 5th instar nymphs, but starvation for 6 or 20 h had little effect on hormones in adults, despite an increase in haemolymph diacylglycerols at 20 h.     

Isolation and structure elucidation of a novel adipokinetic hormone (Lom-AKH-III) from the glandular lobes of the corpus cardiacum of the migratory locust, Locusta migratoria

A new adipokinetic hormone (named Lom-AKH-III) was isolated from the glandular lobes of the corpora cardiaca of Locusta migratoria. At the N-terminus it is blocked by a 5-oxoproline (pyroglutamic acid) residue (less than Glu). After enzymatic deblocking, the amino acid sequence of the N-terminus was partly established by automatic Edman degradation to be [less than Glu]-Leu-Asn-Phe-Thr-Pro-. Fast-atom-bombardment spectrometry (FAB-MS) revealed that the new hormone is an octapeptide, which is amidated at the C-terminus, and has a relative molecular mass of 1072. Based on the FAB-MS data the complete sequence is less than Glu-Leu-Asn-Phe-Thr-Pro-Trp-Trp-NH2, which was confirmed by chemical synthesis. All characteristics from HPLC, FAB-MS and biological activity of the natural hormone and the synthetic peptide appeared to be identical. Although the structure of this new hormone resembles that of Lom-AKH-I (less than Glu-Leu-Asn-Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH2), its amino acid sequence points to a completely different route for its biosynthesis, involving a third prohormone. High-[K+]-containing media can cause release of all three adipokinetic hormones in vitro. Interestingly, the new hormone is absent in another locust species. Schistocerca gregaria. Based on in vitro biosynthesis experiments the turnover for this hormone is very high, suggesting an important physiological function. Locusta migratoria is the first insect species in which three different adipokinetic hormones have been demonstrated.     

Changes in lipophorins are related to the activation of phenoloxidase in the haemolymph of Locusta migratoria in response to injection of immunogens

In Locusta migratoria, activation of phenoloxidase in the haemolymph in response to injection of laminarin is age-dependent: being absent in fifth instar nymphs and newly emerged adults, and only becoming evident four days after the final moult. This pattern of change in phenoloxidase activation correlates with the pattern of change in the concentration of apolipophorin-III (apoLp-III) in the haemolymph. Injection of a conspecific adipokinetic hormone (Lom-AKH-I) has no effect on the phenoloxidase response in nymphs or newly emerged adults but, in adults older than four days, co-injection of the hormone with laminarin prolongs the activation of phenoloxidase in the haemolymph: a similar enhancement of the response to laminarin is observed in locusts that have been starved for 48 h but not injected with AKH-I. During most of the fifth stadium, injection of laminarin results in a decrease in the level of prophenoloxidase in the haemolymph; an effect that is not observed in adults of any age. Marked changes in the concentration of apoLp-III, and the formation of LDLp in the haemolymph, are observed after injection of laminarin (or LPS) and these are remarkably similar, at least qualitatively, to those that occur after injection of AKH-I. The involvement of lipophorins in the activation of locust prophenoloxidase in response to immunogens is discussed.     

Immunohistochemical localisation of the hypertrehalosaemic hormone II (Cam-HrTH-II) and related peptides in the nervous system of Carausius morosus and Sarcophaga bullata

Summary A polyclonal antiserum was prepared against an N-terminal modified Cam-HrTH-II (Leu-Asn-Phe-...), one of the members of the large AKH/RPCH peptide family, first isolated from Carausius morosus. The localisation of this peptide was performed by means of immunocytochemical methods in the brain and corpora cardiaca-corpora allata complex of the stick insect, Carausius morosus and the grey fleshfly, Sarcophaga bullata. The distribution patterns of molecules reactive to the Cam-HrTH-II and the LomAKH-I antisera in both insect species were compared. In Carausius, both antisera reacted in the same cell bodies. In Sarcophaga, some neurons were stained by both, others only by one of the two antisera. By combining two different antisera, we demonstrated that there are no Lom-AKH-I-like molecules present in Carausius and that there must occur at least three different AKH-like molecules in the brain of Sarcophaga. One is similar to Cam-HrTH-II, the second to Lom-AKH-I and the third is an AKH/RPCH-like peptide, different from Lom-AKH-I and Cam-HrTH-II.     

Structure–function studies on hypertrehalosaemic and adipokinetic hormones: activity of naturally occurring analogues and some N- and C-terminal modified analogues

Abstract The relative potencies, with respect to mobilization of lipids in Locusta migratoria L. and in Schistocerca gregaria Forsk. and of carbohydrates in Periplaneta americana L., of eleven naturally-occurring members of the AKH/RPCH-family of peptides and of some analogues that lacked the N-terminal pyroglutamate residue or had a free threonine acid at the C-terminus instead of an amide are assessed. The time courses for carbohydrate and lipid release shown for the peptides suggest that their transport and degradation rates are similar. Therefore, their relative activities reflect most probably the different abilities to bind to the receptors on the fat body cells of the cockroaches and locusts tested. The results show clearly that the N- and C-terminally modified analogues give poor or almost no responses regardless of the bioassay employed. Compared with the structural requirements of the cockroach receptor(s), the receptor(s) of the locusts appear more specific. In the cockroach bioassay, only the two octapeptides Lom-AKH-II and Grb-AKH, both lacking a proline residue at position 6, have high ED₅₀ values, whereas the ED₅₀ values of all other peptides are between 0.4 and 2.7 pmol. The exception is the nonapeptide Mas-AKH, lacking proline and having a serine residue at position 7 (a unique feature compared with the other peptides): no activity is exerted below 100 pmol and only a poor response is elicited with higher dosages. The L. migratoria receptor(s) bind the decapeptides best (exception: Bld-HrTH). Octapeptides, even Scg-AKH-II and Grb-AKH which lack a proline residue, elicit a maximum response, but ED₅₀ values are 7–15-fold higher than with Lom-AKH-I. Lom-AKH-II, however, gives only a truncated response. The nonapeptide Mas-AKH is able to elicit a maximum response, but 50 pmol are needed instead of 2 pmol (Lom-AKH-I). In 5.gregaria a maximum response is achieved with Lom-AKH-I and Grb-AKH, but injections of Scg-AKH-II, Lom-AKH-II and Rom-CC-I result in only truncated responses. The importance of a β-turn in the molecules and the presence of proline is discussed. No evidence is found for an antagonistic effect on binding of those peptides that fail to achieve maximum responses.     

Transport of steroid hormones facilitated by serum proteins.

The affinities with steroid hormones (alpha-estradiol, ethynylestradiol, progesterone, androsterone, dehydroisoandrosterone and testosterone) were observed for Cohn's fraction IV-1 and V (albumin). It was estimated from the comparison with the binding coefficient K (protein-bound form/free form of hormone) in a 3.5% (w/v) bovine serum albumin (BSA) solution that 40-80% of bound hormone in bovine serum is the BSA-bound form. It becomes clear in a liquid membrane system consisting of a hexane source phase (I), a water phase and a hexane receiving phase (II) that the transport flux of hormone is governed primarily by the partition coefficients between the water/hexane phases. In the case of a hormone with a lower partition coefficient, the uptake process from the hexane phase (I) to the water phase is a rate-determining step in the transport system and the serum proteins accelerate the transport of hormones, while with an increase in the partition coefficient the rate-determining step changes from the uptake step to the release step from the water phase to the hexane phase (II) and the hormone transport is decelerated owing to the significant decrease of free hormone concentration in the aqueous phase by the associated with serum proteins for the system having the restricted amount of hormone in the hexane source phase.     

Rhizobacterial mediation of plant hormone status

Plant growth-promoting rhizobacteria are commonly found in the rhizosphere (adjacent to the root surface) and may promote plant growth via several diverse mechanisms, including the production or degradation of the major groups of plant hormones that regulate plant growth and development. Although rhizobacterial production of plant hormones seems relatively widespread (as judged from physico-chemical measurements of hormones in bacterial culture media), evidence continues to accumulate, particularly from seedlings grown under gnotobiotic conditions, that rhizobacteria can modify plant hormone status. Since many rhizobacteria can impact on more than one hormone group, bacterial mutants in hormone production/degradation and plant mutants in hormone sensitivity have been useful to establish the importance of particular signalling pathways. Although plant roots exude many potential substrates for rhizobacterial growth, including plant hormones or their precursors, limited progress has been made in determining whether root hormone efflux can select for particular rhizobacterial traits. Rhizobacterial mediation of plant hormone status not only has local effects on root elongation and architecture, thus mediating water and nutrient capture, but can also affect plant root-to-shoot hormonal signalling that regulates leaf growth and gas exchange. Renewed emphasis on providing sufficient food for a growing world population, while minimising environmental impacts of agriculture because of overuse of fertilisers and irrigation water, will stimulate the commercialisation of rhizobacterial inoculants (including those that alter plant hormone status) to sustain crop growth and yield. Combining rhizobacterial traits (or species) that impact on plant hormone status thereby modifying root architecture (to capture existing soil resources) with traits that make additional resources available (e.g. nitrogen fixation, phosphate solubilisation) may enhance the sustainability of agriculture.     

Stimulation and inhibition of food intake in sheep by centrally-administered hypothalamic releasing factors

Short-term effects of hypothalamic releasing factors on feeding behavior and digestive motility patterns were assessed in hay-fed sheep trained to eat more than half the total amount eaten over 8 h within the first 3 h after food presentation. Thyrotropin-releasing hormone (TRH) given intracerebroventricularly (ICV, 30 ng/kg) or intravenously at higher doses (IV, 3 micrograms/kg) reduced food consumption by 20 p. cent. The ICV or IV TRH-induced reduction was associated with behavioral excitation and stimulation of antroduodenal motor activity without changes in water intake. The ovine corticotropin releasing factor (oCRF 41) decreased food and water intake by 30-50% when administered ICV (60 ng/kg) but was not active when given systemically at doses up to 6 micrograms/kg. The synthetic human growth hormone releasing factor (hGRF 44) administered centrally (60 ng/kg) increased the amount of food intake and the antral motor activity without behavioral excitation. The results indicate a centrally-mediated facilitation of food intake by GRF and its inhibition by CRF which also affect water consumption. The presence of digestive motor effects suggests that extrapituitary pathways may be involved, as for TRH, in the action of both GRF and CRF.     

Initial water deficit effects on Lupinus albus photosynthetic performance, carbon metabolism, and hormonal balance: metabolic reorganization prior to early stress responses

The early (2-4 d) effects of slowly imposed soil water deficit on Lupinus albus photosynthetic performance, carbon metabolism, and hormonal balance in different organs (leaf blade, stem stele, stem cortex, and root) were evaluated on 23-d-old plants (growth chamber assay). Our work shows that several metabolic adjustments occurred prior to alteration of the plant water status, implying that water deficit is perceived before the change in plant water status. The slow, progressive decline in soil water content started to be visible 3 d after withholding water (3 DAW). The earliest plant changes were associated with organ-specific metabolic responses (particularly in the leaves) and with leaf conductance and only later with plant water status and photosynthetic rate (4 DAW) or photosynthetic capacity (according to the Farquhar model; 6 DAW). Principal component analysis (PCA) of the physiological parameters, the carbohydrate and the hormone levels and their relative values, as well as leaf water-soluble metabolites full scan data (LC-MS/MS), showed separation of the different sampling dates. At 6 DAW classically described stress responses are observed, with plant water status, ABA level, and root hormonal balance contributing to the separation of these samples. Discrimination of earlier stress stages (3 and 4 DAW) is only achieved when the relative levels of indole-3-acetic acid (IAA), cytokinins (Cks), and carbon metabolism (glucose, sucrose, raffinose, and starch levels) are taken into account. Our working hypothesis is that, in addition to single responses (e.g. ABA increase), the combined alterations in hormone and carbohydrate levels play an important role in the stress response mechanism. Response to more advanced stress appears to be associated with a combination of cumulative changes, occurring in several plant organs. The carbohydrate and hormonal balance in the leaf (IAA to bioactive-Cks; soluble sugars to IAA and starch to IAA; relative abundances of the different soluble sugars) flag the initial responses to the slight decrease in soil water availability (10-15% decrease). Further alterations in sucrose to ABA and in raffinose to ABA relative values (in all organs) indicate that soil water availability continues to decrease. Such alterations when associated with changes in the root hormone balance indicate that the stress response is initiated. It is concluded that metabolic balance (e.g. IAA/bioactive Cks, carbohydrates/IAA, sucrose/ABA, raffinose/ABA, ABA/IAA) is relevant in triggering adjustment mechanisms.     

Involvement of the V2 Vasopressin Receptor in Adaptation to Limited Water Supply

Mammals adapted to a great variety of habitats with different accessibility to water. In addition to changes in kidney morphology, e.g. the length of the loops of Henle, several hormone systems are involved in adaptation to limited water supply, among them the renal-neurohypophysial vasopressin/vasopressin receptor system. Comparison of over 80 mammalian V2 vasopressin receptor (V2R) orthologs revealed high structural and functional conservation of this key component involved in renal water reabsorption. Although many mammalian species have unlimited access to water there is no evidence for complete loss of V2R function indicating an essential role of V2R activity for survival even of those species. In contrast, several marsupial V2R orthologs show a significant increase in basal receptor activity. An increased vasopressin-independent V2R activity can be interpreted as a shift in the set point of the renal-neurohypophysial hormone circuit to realize sufficient water reabsorption already at low hormone levels. As found in other desert mammals arid-adapted marsupials show high urine osmolalities. The gain of basal V2R function in several marsupials may contribute to the increased urine concentration abilities and, therefore, provide an advantage to maintain water and electrolyte homeostasis under limited water supply conditions.     

Brain serotonin turnover and plasma prolactin and growth hormone concentrations during changes in osmotic balance in the domestic fowl

Summary Young cockerels injected 24 h earlier with 0.9% saline,para-chorophenylalanine (pCPA, brain serotonin depletor) or alpha-methylpara-tyrosine (AMPT, brain catecholamine depletor) were deprived of access to water for 24 h. Plasma prolactin concentrations were markedly elevated by water deprivation and returned to normal on rehydration. pCPA, but not AMPT, significantly reduced the increase in prolactin. Concentrations of growth hormone were not affected by water deprivation. Brain serotonin concentrations were reduced by treatment with pCPA. Groups of cockerels were maintained under normal conditions or without access to drinking water for 12 h or 24h. Some were injected with the monoamine oxidase inhibitor pargyline, which increased the prolactin and decreased the growth hormone concentration in the plasma of the hydrated birds. The inhibitory effect of pargyline on growth hormone was augmented following water deprivation. Serotonin levels were not significantly affected by water deprivation but turnover (defined as accumulation of serotonin after pargyline treatment) was increased in the hypothalamus but not in remaining tissue. Injecting 30% saline solution intravenously markedly increased plasma prolactin whilst growth hormone concentrations were decreased. Serotonin turnover was increased in the hypothalamus but not in other brain regions. The results show that secretion of prolactin and growth hormone by the pituitary gland during osmotic imbalance in the fowl may be mediated by changes in hypothalamic scrotonin turnover.     

Role of substance P in water homeostasis.

The effect of the naturally occurring peptide substance P on release of antidiuretic hormone (ADH) was studied in anesthetized dogs. Intravenous infusions of substance P in doses of 0.5, 5.0, and 50 ng/kg/min increased plasma concentrations of ADH in a dose-related fashion. At the two low doses, this increase occured in the absence of changes in urine volume, sodium excretion, free water clearance, and urinary cyclic AMP excretion. In addition, when substance P was administered in a concentration of 0.5 ng/kg/min, plasma levels of ADH were increased even though blood pressure did not change, suggesting that substance P may release antidiuretic hormone by a direct mechanism. Intrarenal infusions at a rate of 0.5 and 5 ng/kg/min caused dose-related decreases in free water clearance and significant increases in urinary cyclic AMP excretion. These data suggest that substabce P may play an important role in the regulation of water balance.     

Calcitonin-like diuretic hormones in insects

Insect neuropeptides control various biological processes including growth, development, homeostasis and reproduction. The calcitonin-like diuretic hormone (CT/DH) is one such neuropeptide that has been shown to affect salt and water transport by Malpighian tubules of several insects. With an increase in the number of sequenced insect genomes, CT/DHs have been predicted in several insect species, making it easier to characterize the gene encoding this hormone and determine its function in the species in question. This mini review summarizes the current knowledge on insect CT/DHs, focusing on mRNA and peptide structures, distribution patterns, physiological roles, and receptors in insects.     

Renal function and pituitary hormone release during cerebral osmostimulation and TRH in dogs

The effects of increases in serum osmolality on renal function and plasma levels of radioimmunoassayable prolactin (PRL) and luteinizing hormone (LH) were examined during intracarotid (IC) infusions of hypertonic NaCl in conscious dogs with a sustained water diuresis (SWD). A 10 minute bilateral IC infusion of 45 μmole/kg·min·artery of NaCl during SWD which raised jugular osmolality by 10.1 mOsm/kg, without significantly altering peripheral venous osmolality, produced a significant decrease in free water clearance (C_H2O) at 20 to 40 minutes postinfusion. IC infusions of 0.9% NaCl did not produce an antidiuretic response. No change in heart rate or blood pressure from preinfusion control values occurred during NaCl infusions. Elevations in cerebral osmolality did not result in changes in circulating levels of LH or PRL which qualitatively differed from levels of these hormones recorded during IC infusions of 0.9% NaCl. Although fluctuations in levels of LH occurred during experiments, renal function was not concomitantly affected. The results suggest that a specificity exists in the hormonal response to selective elevations of cerebral osmolality. The administration of TRH 3.8–4.2 μg/kg produced a transient increase in blood pressure and inhibited a water diuresis, the latter possibly as a result of releasing antidiuretic hormone.     

Diuresis in the housefly (Musca domestica) and its control by neuropeptides

Diuresis was studied in vivo by measuring the loss of tritiated water. The basal rate of water loss (5 nl/min) represents respiratory and cuticular losses, whereas higher rates reflect urine output, which reaches 20 nl/min after injection of 1 microl distilled water. This response to hypervolemia involves release of a diuretic hormone(s) into the hemolymph. However, housefly diuretic peptides increased urine output to a maximum of only 7 nl/min, and higher rates may require fluid reabsorption from the hindgut to be reduced. Diuresis is partially blocked by injected anti-muscakinin antibodies, providing evidence of a hormonal function for this insect myokinin.     

Hypothalamic-pituitary somatotropic function in prepubertal hypothyroid rats: effect of growth hormone replacement therapy.

The effect of thyroid hormone deficiency and growth hormone (GH) treatment on hypothalamic GH-releasing hormone (GHRH)/somatostatin (SS) concentrations, GHRH/SS mRNA levels, and plasma GH and somatomedin-C (IGF-I) concentrations were studied in 28- and 35-day-old rats made hypothyroid by giving dams propylthiouracil in the drinking water since the day of parturition. Hypothyroid rats, at both 28 and 35 days of life, had decreased hypothalamic GHRH content and increased GHRH mRNA levels, unaltered SS content and SS mRNA levels, and reduced plasma GH and IGF-I concentrations. Treatment of hypothyroid rats with GH for 14 days completely restored hypothalamic GHRH content and reversed the increase in GHRH mRNA, but did not alter plasma IGF-I concentrations. These data indicate that, in hypothyroid rats, the changes in hypothalamic GHRH content and gene expression are due to the GH deficiency ensuing from the hypothyroid state. Failure of the GH treatment to increase plasma IGF-I indicates that the feedback regulation on GHRH neurons is operated by circulating GH and/or perhaps tissue but not plasma IGF-I concentrations. Presence of low plasma IGF-I concentrations would be directly related to thyroid hormone deficiency.     

A placebo-controlled trial of intranasal growth hormone-releasing hormone [GHRH(1-44)-NH2] administration in normal young adults

Growth hormone-releasing hormone, GHRH(1-44), was administered intranasally to 16 healthy young adult male volunteers in a placebo-controlled study using a dose of 1,000 micrograms dissolved in two different solvent vehicles: water alone and water with the surface tension-lowering agent Tween 80 (0.12%). The growth hormone (GH)-releasing effects of intranasal GHRH as well as that of the vehicle were established and compared to the effects of 80 micrograms intravenous GHRH. Plasma GH response was assessed by frequent blood sampling over an 180-min period, using both peak response and area under the curve (AUC). The results show that the GH-release effects of intranasal GHRH are comparable whichever vehicle is used, and are similar, with the dose of 1,000 micrograms, to the response obtained following the administration of 80 micrograms intravenous GHRH. Peak GH responses to GHRH (means +/- SEM) were 25.6 +/- 4.2 ng/ml (1,000 micrograms GHRH with water), 32.9 +/- 9.1 ng/ml (1,000 micrograms with water plus Tween 80) and 36.3 +/- 7.8 ng/ml (80 micrograms i.v. administration) (not significant). There was no significant GH response to placebo. Mean peak GH responses occurred after approximately 30 min in all three active treatments (29.2 +/- 2.7, 33.9 +/- 3.2 and 30.9 +/- 3.9 min, respectively). The AUC values (ng.min.ml-1) were not statistically different: 1,914.4 +/- 386.7 (water), 2,176.2 +/- 599.9 (water plus Tween 80) and 2,419.2 +/- 506.9 (i.v.) (not significant). Intranasal GHRH administration was well tolerated in all subjects. Occasional local reactions consisted of a prickly sensation in the nostrils or sneezing irrespective of the vehicle used.(ABSTRACT TRUNCATED AT 250 WORDS)     

The 20-kD human growth hormone reduces body fat by increasing lipolysis and decreasing lipoprotein lipase activity

AIM: The aim of this study was to estimate the lipolytic activity of the human growth hormone variant, 20-kD human growth hormone (20K-hGH). METHODS: Obese KV-A(y) mice were given daily subcutaneous injections of 20K-hGH (0.25, 0.5, 1.0 mg/kg), 22K-hGH (0.25 mg/kg) or saline as a control for 2 weeks. Body composition (fat, water and protein), lipolysis and lipoprotein lipase (LPL) activity were measured 24 h after the final injection. RESULTS: Both growth hormone isoforms significantly reduced relative fat pad and whole body lipids. In addition, 20K-hGH produced an inhibition of LPL activity in adipose tissue and stimulated lipolysis in adipocytes. CONCLUSION: These data strongly suggest that inhibition of LPL activity in adipose tissue and stimulation of lipolysis in adipocytes by 20K-hGH treatment reduce adipose tissue mass, resulting in body fat reduction.