Gerard J. Hickey

Chronic MCH-1 receptor modulation alters appetite, body weight and adiposity in rats

Central administration of the neuropeptide melanin-concentrating hormone (MCH) stimulates feeding in rodents. We studied the effects of intracerebroventricular (i.c.v.) administration of an MCH-1 receptor agonist (Compound A) and an MCH-1 receptor antagonist (Compound B) on feeding in satiated rats. Compound B (10 microg, i.c.v.) blocked the acute orexigenic effect of Compound A (5 microg, i.c.v.). In an experiment designed to either stimulate or inhibit MCH-1 receptor signaling over an extended period, rats received continuous i.c.v. infusions of vehicle (saline), Compound A (30 microg/day), Compound B (30 or 48 microg/day) or neuropeptide Y (24 microg/day, as positive control) via implantable infusion pumps. Continuous MCH-1 receptor activation recapitulated the obese phenotype of MCH-over-expressor mice, manifest as enhanced feeding (+23%, P<0.001), caloric efficiency and body weight gain (+38%, P<0.005) over the 14-day period relative to controls. Chronic MCH-1 receptor activation also elevated plasma insulin and leptin levels significantly. Conversely, continuous MCH-1 receptor antagonism led to sustained reductions in food intake (-16%, P<0.001), body weight gain (-35%, P<0.01), and body fat gain relative to controls, without an effect on lean mass. Antagonism of the MCH-1 receptor may be an effective approach for the treatment of obesity.

SEQUENCE OF THE DOG IMMUNOGLOBULIN ALPHA AND EPSILON CONSTANT REGION GENES

The immunoglobulin alpha (IGHAC) and epsilon (IGHEC) germline constant region genes were isolated from a dog liver genomic DNA library. Sequence analysis indicates that the dog IGHEC gene is encoded by four exons spread out over 1.7 kilobases (kb). The IGHAC sequence encompasses 1.5 kb and includes all three constant region coding exons. The complete exon/intron sequence of these genes is described.

Hypophyseal-Portal Concentrations of Growth Hormone-Releasing Factor and Somatostatin in Conscious Pigs: Relationship to Production of Spontaneous Growth Hormone Pulses:

Abstract A method of collecting hypophyseal portal blood (HPB) in conscious pigs was used to show the relationship between GRF and somatostatin (SRIF) concentration and peripheral GH response. Six male castrate pigs (approximately 63 kg body weight) had HPB and jugular blood collected individually for an average of 175 min each. Twenty-seven spontaneous GH pulses were detected in the 1050 min of total HPB collection. Of the associations examined, the only significant finding was that GH pulse maxima occurred nonrandomly within periods of SRIF descent (63%; P = 0.005). Although 48% (13/27) of GH pulse maxima were associated with an ascent in portal GRF concentration, these associations were not determined to be nonrandom (P = 0.14). Only 7 of 27 (26%) GH pulse maxima were associated with an ascent in portal GRF concentration and a descent in SRIF concentration occurring simultaneously. A saline infusion given approximately 120 min after beginning blood collection resulted in an increase in SRIF pulse frequency and a decrease in GH-AUC and GRF-AUC. The cause of this saline effect is unknown, but it may have been related to acclimation of the pigs to the blood collection procedure. These data show the complexity of the relationship between SRIF and GRF concentrations and GH secretion and may indicate a close relationship with SRIF in GH pulse generation in the pig. In addition, these data support the hypothesis that, in the pig, mediation of GH release cannot be explained simply by antagonism between GRF and SRIF.

Synthesis and biological activities of phenyl piperazine-based peptidomimetic growth hormone secretagogues.

A new class of potent, orally active phenyl piperazine-based GH secretagogues have been discovered from attempts to mimic the arrangement of the phenyl substituent in the spiroindanyl piperidine and spiroindoline sulfonamide privileged structures of 4 and 1, respectively. The best of these compounds, 18 (EC50 = 2.8 nM) is nearly as potent as MK-0677 for releasing GH from rat pituitary cells.

Mechanism of Action of GHRP-6 and Nonpeptidyl Growth Hormone Secretagogues

Growth hormone (GH) secretion from the pituitary gland is regulated by the hypothalamic peptide hormones growth hormone releasing hormone (GHRH) and somatotropin release inhibiting factor (SRIF) (Scheme 11.1). The factor controlling the episodic nature of GH release is unknown but its effects are probably mediated by feedback loops involving the positive effector GHRH and the negative regulator SRIF (1). In 1984, Bowers and Momany and coworkers (2, 3) described the synthesis and properties of a series of small peptide GH secretagogues that were based on the structure of Leu and Met enkephalins. Growth hormone releasing peptide (GHRP)- 6 was the most potent of these peptides and was subsequently shown to be active in man (4, 5). Because of the limited oral bioavailability of peptides we sought a class of GH secretagogues more amenable to chemical modification so that oral bioavailability and pharmacokinetic properties could be optimized. Implicit in establishing assays to identify new small molecules was an understanding of the mechanisms regulating GH release from the anterior pituitary gland. Based on its size, GHRP-6 was considered a potential template for a small molecule peptide mimetic. Our approach was based on screening selected structures in functional and mechanism based assays. Following identification of a benzolactam lead structure, L-692,429 was synthesized and used as a prototype to investigate specificity and efficacy in clinically relevant target populations (6–11).

Estrogen receptor (ER) subtype agonists alter monoamine levels in the female rat brain.

We assessed the effects of subtype-selective ER agonists on monoamine levels in discrete regions of the female rat brain. Ovariectomized (ovx) rats were treated for 4 days with vehicle, 17β-estradiol (E; 0.05mg/kg), an ERβ agonist (C19; 3mg/kg) or an ERα agonist (PPT; 3mg/kg) and samples from brain regions were assessed for monoamines and metabolites. We also assessed effects of ERβ modulation on baseline and fenfluramine-induced release of monoamines in hippocampus using microdialysis. In the first study, E and the ERα agonist increased norepinephrine in cortex and all three ER ligands increased it in the ventral hippocampus. Changes in levels of the noradrenergic metabolite, MHPG and the dopaminergic metabolite, DOPAC were noted in brain areas of ER ligand-treated animals. E also increased levels of 5HIAA in three brain areas. In the microdialysis study, there were no differences among groups in baseline levels of monoamines. However, E and the ERβ agonist increased levels of the dopaminergic metabolite, HVA following fenfluramine. In summary, activation of the two nuclear ERs with selective agonists affects monoamine and metabolite levels in discrete brain areas, a number of which are known to play key roles in cognitive and affective function.

Peptidomimetic growth hormone secretagogues: synthesis and biological activities of analogs varied at the indole nucleus of the prototypical spiropiperidine L-162,752

Abstract SAR studies around the indole nucleus of the prototypical peptidomimetic L-162,752 revealed that the D-Trp could be replaced with 3-phenylpropyl-D-glycine and O-benzyl-D-serine to provide secretagogues with comparable intrinsic activity but with significantly better oral activity in dogs. Use of dimethyl β-alanine amino side-chains led to a considerable loss of activity in the D-homophenylalanine and O-benzyl-D-serine series.

BENZOLACTAM GROWTH HORMONE SECRETAGOGUES : CARBOXAMIDES AS REPLACEMENTS FOR THE 2'-TETRAZOLE MOIETY OF L-692,429

Abstract A variety of 2′-carboxamides was investigated as replacements for the 2′-tetrazole moiety of L-692,429. Investigation of the structure-activity relationships of the carboxamide series determined that primary and secondary carboxamides are potent growth hormone secretagogues in vitro . L-700,653 ( 11 ) was identified as an orally active GH secretagogue in dogs.

The synthesis and activity of spiroindane growth hormone secretagogues

Abstract The synthesis and activities of a series of spiroindane growth hormone secretagogues is reported. Modification of the benzylic position of the spiroindane has resulted in a dramatic increase in potency resulting in subnanomolar peptidomimetic growth hormone secretagogues. In vivo data demonstrating the good oral activity of these analogs is reported.

Substituted bridged phenyl piperidines: orally active growth hormone secretagogues

A new series of growth hormone secretagogues have been discovered. The best compound, 26j, shows excellent ability to release growth hormone both in vitro and in vivo. The synthesis and biological activity of these compounds are discussed.