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PubMed2005

Defective signalling in salivary glands precedes the autoimmune response in the non-obese diabetic mouse model of sialadenitis.

The spontaneous non-obese diabetic (NOD) mouse model of Sjögren's syndrome provides a valuable tool to study the onset and progression of both the autoimmune response and secretory dysfunction. Our purpose was to analyse the temporal decline of salivary secretion in NOD mice in relation to the autoimmune response and alterations in various signalling pathways involved in saliva secretion within each salivary gland. A progressive loss of nitric oxide synthase activity in submandibular and parotid glands started at 12 weeks of age and paralleled the decline in salivary secretion. This defect was associated with a lower response to vasoactive intestinal peptide in salivary flow rate, cAMP and nitric oxide/cGMP production. No signs of mononuclear infiltrates or local cytokine production were detectable in salivary glands in the time period studied (10-16 weeks of age). Our data support a disease model for sialadenitis in NOD mice in which the early stages are characterized by defective neurotransmitter-mediated signalling in major salivary glands that precedes the autoimmune response.

Animals↗
PubMed2006

Ion and fluid transport properties of small airways in cystic fibrosis.

RATIONALE: Small airways constitute a major site of pathology in cystic fibrosis (CF) and provide most of the surface area of the conducting airways of the lung. Little is known, however, about the impact of CF on ion and fluid transport in small (bronchiolar) airways. OBJECTIVES: To describe the ion and fluid transport properties of CF bronchiolar epithelium. METHODS: Primary cultures of human bronchial and bronchiolar (non-CF and CF) epithelial cells were obtained. The bioelectric properties were studied in Ussing chambers and the airway surface liquid (ASL) height was measured with confocal microscopy. MAIN RESULTS: Primary cultures of DeltaF508 CF bronchiolar epithelial cells displayed higher transepithelial resistance than non-CF cultures, whereas baseline short circuit current and amiloride-inhibitable short circuit current were similar in both preparations. The ASL height was significantly smaller in CF compared with non-CF preparations. In the presence of amiloride, addition of forskolin increased short circuit current in non-CF but not in CF bronchiolar cultures, and the ATP-induced increase in short circuit current was lower in CF than in non-CF cultures. Non-CF bronchiolar preparations displayed larger short circuit current and fluid secretion in responses to forskolin than non-CF bronchial preparations, suggesting that CFTR-dependent Cl(-) transport may play a more important role in the regulation of fluid transport in small airways than in large airways. CONCLUSION: In CF small airways, defective Cl(-) secretion combined with unregulated (persistent) Na(+) absorption results in ASLdepletion.

Body Water↗
PubMed1997

Intestinal physiology and pathology in gene-targeted mouse models of cystic fibrosis.

Cystic fibrosis (CF) is a fatal genetic disorder that affects approximately 1 in 2,500 live Caucasian births. The disease can be described as a generalized exocrine disease affecting a variety of epithelial tissues, with early manifestation as meconium ileus in a significant number of neonates. Cloning of the gene causing CF was accomplished in 1989, and the protein product, cystic fibrosis transmembrane conductance regulator (CFTR), has been conclusively shown to be an adenosine 3',5'-cyclic monophosphate (cAMP)-regulated Cl- channel. Subsequently, several mouse models of CF were generated by gene-targeting approaches in an attempt to further understand this disease. The initial excitement generated by the emergence of these mouse models was somewhat tempered by the finding that none of the models developed airway disease, which is currently responsible for most of the morbidity and mortality in the human CF population. However, the various CF mouse models, of which there are now 10, are remarkably similar to their human counterparts with respect to intestinal pathophysiology. Most importantly, the intestinal tract of the CF mouse models demonstrates the absence of cAMP-mediated Cl- transport, which is a hallmark of CF disease. Furthermore, the murine CF intestinal tract also shows an inability to secrete HCO3-, defective cAMP regulation of electroneutral NaCl absorption, and elevated electrogenic Na+ transport in the distal colon, as well as other ion transport perturbations. Besides the fundamental mechanisms of ion transport studied in the murine CF intestinal tract, these models have also been important in understanding other tissues with regard to CF. Mice heterozygous for the CFTR knockout gene have a reduced ability to secret Cl- and fluid and therefore provide further support for the CF "heterozygote advantage" hypothesis. Some CF mouse models maintain a limited ability to secrete Cl-, which may be due to accessory genes that are hypothesized to ameliorate disease severity in the intestines of these mice. This review describes the CF models generated and compares the murine defects in ion transport with observed abnormalities in the human CF intestine.

Animals↗
PubMed1990

Dynamic of the GRF-induced GH response in genetically obese Zucker rats: influence of central and peripheral factors.

To determine the time onset of the growth hormone (GH) alteration in the genetically obese rat, we studied the in vivo and in vitro rat growth hormone releasing factor (rGRF(1-29)NH2)-induced GH secretion in 6- and 8-week-old lean and obese male Zucker rats. Under sodium pentobarbital anesthesia, rGRF(1-29)NH2 (GRF) was injected intravenously at two doses: 0.8 and 4.0 micrograms/kg b.w. Basal serum GH concentrations were similar in lean and obese age-matched animals. The GH response to both GRF doses tested was unchanged in 6-week-old obese rats as compared to their lean litter mates. In contrast, a significant decrease of the GH secretion in response to 4.0 micrograms/kg b.w. GRF was observed in the 8-week-old obese rats. The effect of GRF (1.56, 6.25 and 12.5 pM) was further studied in vitro, in a perifusion system of freshly dispersed anterior pituitary cells of lean and obese Zucker rats. Basal GH release was similar in the 6-week-old animal group. In contrast, it was significantly decreased in 8-week-old obese rats as compared to their lean litter mates. Stimulated GH response to 1.56 and 6.25 pM GRF was significantly greater in the 6-week-old obese group than in the age-matched control group. In contrast, the GH response to all GRF concentrations tested was significantly decreased in the 8-week-old obese rats as compared to their respective lean siblings. In 8-week-old obese rats, a decrease of GH pituitary content and an increase of hypothalamic somatostatin (SRIF) concentration were observed. Insulin and free fatty acid serum were significantly increased in 8-week-old obese rats. In contrast, lower insulin-like growth factor I serum levels were observed in the obese animals as compared to their lean litter mates. Finally, to further clarify the role of the periphery in the inhibition of GH secretion observed in the 8-week-old fatty rats, we exposed cultured pituitary cells of 8-week-old lean animals to 17% serum of their obese litter mates. A significant decrease of GRF-stimulated GH secretion of lean rat pituitary cells exposed to the obese serum was noted (P less than 0.05). This study demonstrates that, in the obese Zucker rat, an alteration of the GH response to GRF is evident by the 8th week of life. This defective GH secretion could be related to peripheral and central abnormalities.

Age Factors↗
PubMed2002

Yersinia enterocolitica type III secretion: mutational analysis of the yopQ secretion signal.

Pathogenic Yersinia spp. secrete Yop proteins via the type III pathway. yopQ codons 1 to 15 were identified as a signal necessary and sufficient for the secretion of a fused reporter protein. Frameshift mutations that alter codons 2 to 15 with little alteration of yopQ mRNA sequence do not abolish type III transport, suggesting a model in which yopQ mRNA may provide a signal for secretion (D. M. Anderson and O. Schneewind, Mol. Microbiol. 31:1139-1148, 2001). In a recent study, the yopE signal was truncated to codons 1 to 12. All frameshift mutations introduced within the first 12 codons of yopE abolished secretion. Also, multiple synonymous mutations that changed the mRNA sequence of yopE codons 1 to 12 without altering the amino acid sequence did not affect secretion. These results favor a model whereby an N-terminal signal peptide initiates YopE into the type III pathway (S. A. Lloyd et al., Mol. Microbiol. 39:520-531, 2001). It is reported here that codons 1 to 10 of yopQ act as a minimal secretion signal. Further truncation of yopQ, either at codon 10 or at codon 2, abolished secretion. Replacement of yopQ AUG with either of two other start codons, UUG or GUG, did not affect secretion. However, replacement of AUG with CUG or AAA and initiating translation at the fusion site with npt did not permit Npt secretion, suggesting that the translation of yopQ codons 1 to 15 is a prerequisite for secretion. Frameshift mutations of yopQ codons 1 to 10, 1 to 11, and 1 to 12 abolished secretion signaling, whereas frameshift mutations of yopQ codons 1 to 13, 1 to 14, and 1 to 15 did not. Codon changes at yopQ positions 2 and 10 affected secretion signaling when placed within the first 10 codons but had no effect when positioned in the larger fusion of yopQ codons 1 to 15. An mRNA mutant of yopQ codons 1 to 10, generated by a combination of nine synonymous mutations, was defective in secretion signaling, suggesting that the YopQ secretion signal is not proteinaceous. A model is discussed whereby the initiation of YopQ polypeptide into the type III pathway is controlled by properties of yopQ mRNA.

3' Untranslated Regions↗
PubMed1981

Impaired insulin secretion in human diabetes mellitus III. The effect of the serotonin antagonist metergoline.

The present study was aimed at investigating the effect of metergoline, a powerful and long-lasting antiserotoninergic agent, on insulin responses to glucose and arginine in adult-onset diabetic subjects. The repeated administration of this agent (10 mg daily for two days plus a 4 mg dose 1 hour before the post-treatment test) or placebo did not influence acute insulin response to intravenous glucose (20 g), total insulin secretion or glucose disappearance rates. Similarly, plasma glucose and insulin levels following arginine (30 g perfused over a period of 40 min) were similar before and after metergoline treatment. These results do not support the hypothesis that an endogenous monoamine mechanism plays an important part in defective insulin secretion in human non insulin-dependent diabetes mellitus.

Adult↗
PubMed1995

Identification of a Bacillus subtilis secretion mutant using a beta-galactosidase screening procedure.

High-level synthesis of exportable beta-galactosidase (LacZ) fusion proteins in Bacillus subtilis results in a lethal phenotype, and has been suggested as a tool for the selection of secretion mutants. We tested a plasmid-based, inducible lacZ fusion gene system for this purpose, but frequent mutations in cis, which reduced expression of the fusion gene, forced abandonment of the induction-selection strategy. Instead, after modification of the indicator plasmid, a screening procedure for increased basal LacZ activity levels was adopted. This led to the identification of a conditional B. subtilis secretion mutant after nitrosoguanidine mutagenesis. At 42 degrees C, but not at 30 degrees C, this mutant displayed extreme growth retardation when the LacZ fusion protein was produced, and and was also defective in the secretion of subtilisin Carlsberg. The processing kinetics and secretion of a subtilisin Carlsberg-alkaline phosphatase fusion derivative were found to be defective specifically at the non-permissive temperature. The secretion defect was not linked to the secA/div locus.

Bacillus subtilis↗
PubMed1987

Cryopreservation disturbs stimulus-response coupling in a platelet subpopulation.

Cryopreservation of platelet suspensions leads to a severe reduction in the functional responses of these cells. This defect primarily resides in a subpopulation which consists of about half the total platelet mass and shows an increased susceptibility to the cryopreservation procedure. Following freeze-thawing this subpopulation failed to aggregate upon stimulation with collagen despite a normal appearance of membrane glycoproteins. Also the contents of alpha granules was similar to the whole suspension and since changes in alpha and dense granule contents often occur in parallel, the poor aggregability could not be attributed to a defect in secretion granules. In contrast, the generation of phosphatidyl-inositol metabolites, the increase in cytosolic Ca2+ content and the phosphorylation of proteins of mol wt 47,000 and 20,000 seen when normal platelets are activated, were completely absent in the subpopulation. These data reveal a severe defect in stimulus-response coupling mechanisms in about half of the platelets after freeze-thawing. The other half of the suspension endures this treatment relatively unharmed and may be used for transfusion.

Blood Platelets↗
PubMed1999

Different effects of tolbutamide and diazoxide in alpha, beta-, and delta-cells within intact islets of Langerhans.

Interaction between the different types of cells within the islet of Langerhans is vital for adequate control of insulin release. Once insulin secretion becomes defective, as in type 2 diabetes, the most useful drugs to increase insulin release are sulfonylureas. It is well-known that sulfonylureas block K(ATP) channels, which results in depolarization of the membrane that provokes calcium influx and increases intracellular calcium concentration ([Ca2+]i), which thereby triggers insulin secretion. The sulfonamide diazoxide produces the opposite effect: it activates K(ATP) channels, resulting in a decreased insulin secretion. Despite such evidence, little is known about the effect of sulfonylureas and sulfonamides in non-beta-cells of the islet of Langerhans. In this article, we describe the effects of tolbutamide and diazoxide on [Ca2+]i in alpha-, beta-, and delta-cells within intact islets of Langerhans. Tolbutamide elicits an increase in [Ca2+li in beta- and delta-cells, regardless of glucose concentrations. Remarkably, tolbutamide is without effect in alpha-cells. When diazoxide is applied, glucose-induced [Ca2+]i oscillations in beta- and delta-cells are abolished, whereas [Ca2+]i oscillations in alpha-cells remain unaltered. Furthermore, the existence of sulfonylurea receptors is demonstrated in beta-cells but not in alpha-cells by using binding of glybenclamide-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) combined with immunostaining for insulin and glucagon.

Animals↗
PubMed1994

[Insulin resistance: role in type 2 diabetes].

Type 2, non-insulin-dependent, diabetes is a disease of glucose homeostasis involving up to 5% of the adult population. The percentage of the population with glucose intolerance is even greater, 10%. These later patients are not diagnosed as "diabetics", but 50% of them have non-insulin-dependent diabetes. Globally, 10% of the adult population has or will have Type 2 diabetes, a major health care problem. Characteristically, in patients with Type 2 diabetes, pancreatic insulin secretion is deficient, liver glucose production is increased during the post-absorption period and peripheral glucose consumption, particularly in striated muscles, is decreased due to insulin resistance. There has been much progress in our understanding of the pathogenic mechanisms involved. When clinical manifestations have become apparent, the relative roles of defective insulin secretion and insulin resistance are difficult to distinguish. However, in persons with oral glucose intolerance or in persons with a high risk of developing Type 2 diabetes, these two mechanisms are more easily differentiated. High risk patients can be identified on the basis of our knowledge of genetic factors in Type 2 diabetes. The incidence of Type 2 diabetes is considerably increased in subjects with two diabetic parents. In addition to genetic factors, environmental factors also influence the development of non-insulin-dependent diabetes, contributing to the multifactorial nature of Type 2 diabetes. In order to establish the relative importance of these different factors, it is useful to define the different stages with characteristic degrees of metabolic disorder, insulin secretion abnormalities and insulin secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetes Mellitus, Type 2↗
PubMed1988

Abnormal differentiation of immunoregulatory T-lymphocyte subpopulations in the major histocompatibility complex (MHC) class II antigen deficiency syndrome.

The major histocompatibility complex (MHC) class II deficiency syndrome is a rare immunodeficiency disease associated with defective expression of class II MHC antigens. We have examined the consequences of this defect for the differentiation and functional capabilities of immunoregulatory T-cell subpopulations in an affected patient. Although the number of circulating T cells was normal, there was a striking reduction in the number of CD4+ T cells. Furthermore, purified CD4+ cells from the patient were unable to provide help for antibody secretion. This defect in helper function appeared to be due to the abnormal differentiation of the few CD4+ cells present, virtually all of which expressed the CD4+HB11+ phenotype characteristic of immature "virgin" T cells. Abnormal development of immunoregulatory CD8+ T cells was also observed. Although increased numbers of CD8+ T cells were present, virtually none had phenotypic properties of suppressor cells (i.e., CD3+/CD8+/9.3- granular lymphocytes that coexpress the Leu-15 or Leu-7 antigens), and purified CD8+ cells from the patient had no suppressor activity. Thus, the absence of class II MHC antigens profoundly disrupts the development of immunoregulatory T cells. We propose that these effects occur by the following mechanisms: (1) the absence of intrathymic class II antigens results in deficient production of CD4+ cells, (2) the CD4+ cells that do emerge from the thymus do not undergo postthymic maturation into CD4+HB11- cells with helper capabilities, and (3) the absence of CD4+HB11- effector cells results in abortive development of suppressor cells involved in feedback suppression.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1999

Effects of overexpression of human GLUT4 gene on maternal diabetes and fetal growth in spontaneous gestational diabetic C57BLKS/J Lepr(db/+) mice.

During gestation, heterozygous C57BLKS/J-Lepr(db/+) mice develop spontaneous gestational diabetes mellitus (GDM), and the newborn fetuses are macrosomic compared with offspring from wild-type (+/+) mothers. To investigate the effects of the leptin receptor mutation on maternal metabolism and fetal growth during pregnancy, we studied +/+, db/+, and db/+ transgenic mice that overexpress the human GLUT4 gene two- to three-fold (db/+TG6). During pregnancy, fasting plasma glucose and hepatic glucose production were twofold greater in db/+ than +/+ mice, despite similar insulin levels. In skeletal muscle, insulin-stimulated tyrosine phosphorylation was decreased in pregnant +/+ mice, and even more so in db/+ mice: insulin receptor beta (IR-beta), +/+ 34%, db/+ 57% decrease, P<0.05; insulin receptor substrate 1 (IRS-1), +/+ 44%, db/+ 61% decrease, P<0.05; and phosphoinositol (PI) 3-kinase (p85alpha), +/+ 33%, db/+ 65% decrease, P<0.05. Overexpression of GLUT4 in db/+TG6 mice markedly improved glucose-stimulated insulin secretion, by 250%, and increased IRbeta, IRS-1, and p85alpha phosphorylation twofold, despite no change in concentration of these proteins. Plasma leptin concentration increased 40-fold during pregnancy, from 2.2+/-0.5 to 92+/-11 ng/ml and 3.6+/-0.1 to 178+/-34 ng/ml in +/+ and db/+ mice, respectively (P<0.01), but was increased to only 23+/-3 ng/ml in pregnant db/+TG6 mice (P<0.001). Maternal fat mass and energy intake were greater in db/+ mice, and fat mass was reduced by GLUT4 overexpression, independent of food intake. Fetal body weight was increased by 8.1 and 7.9% in db/+ and db/+TG6 mothers, respectively (P<0.05), regardless of fetal genotype, whereas fetuses from db/+TG8 mothers (four- to fivefold overexpression) weighed significantly less compared with pups from +/+ or db/+ mothers (P<0.05). These results suggest that the single mutant db allele effects susceptibility to GDM through abnormalities in insulin receptor signaling, defective insulin secretion, and greater nutrient availability. GLUT4 overexpression markedly improves insulin-signaling in GDM, resulting in increased insulin secretion and improved glycemic control. However, maternal hyperglycemia appears not to be the sole cause of fetal macrosomia. These data suggest that GDM is associated with defects in insulin receptor signaling in maternal skeletal muscle, and this may be an important factor provoking maternal and fetal perinatal complications.

Animals↗
PubMed1993

[Impaired carbohydrate tolerance in patients with hyperthyroidism--evaluation of some influencing factors].

Relation between the appearance of impaired carbohydrate tolerance and such factors as the duration of hyperthyroidism, age of patients, blood serum concentrations of thyroxine, triiodothyronine and free fatty acids, as well as insulin secretion both basal and stimulated by oral and "intravenous glucose administration was studied in 62 patients with untreated hyperthyroidism. Control group consisted of 24 healthy subjects having performed oral and intravenous glucose tolerance tests. Among the studied factors, high blood serum concentrations of thyroxine and triiodothyronine, elevated concentration of free fatty acids and defective insulin secretion influenced the appearance of impaired glucose tolerance in patients with hyperthyroidism. No relation was found, however, between the impaired glucose tolerance and the duration of hyperthyroidism or the age of patients.

Adult↗
PubMed1978

Synthesis and secretion of kidney beta-galactosidase in mutant le/le mice.

We have found that the pigmentation mutant light ear in the mouse has a striking effect on lysosomes in the kidney. Male mice homozygous for the le mutant allele have a 4-fold elevated concentration of kidney beta-galactosidase (EC 3.2.1.23). The abnormal elevation of kidney beta-galactosidase is the net result of two processes. First, beta-galactosidase is elevated due to the defective urinary secretion of lysosomal enzymes which is a specific effect of the le mutation. Secondly, this effect is most evident in males and testosterone-treated females because of the induction of beta-galactosidase synthesis by testosterone, which occurs in +/+ as well as in mutant mice. The pale-ear mutation (ep) which mimics the pigmentation phenotype of le also has a similar effect on kidney lysosomes.

Aging↗
PubMed1985

Impaired insulin secretion in human diabetes mellitus. Interactions between naloxone, phentolamine and lysine acetylsalicylate upon glucose induced insulin release.

Non insulin-dependent diabetes mellitus (Type II) is characterized by the loss of the acute insulin response to glucose. Met-enkephalin, catecholamines and prostaglandin E (PGE) have all been reported to inhibit the acute insulin response to glucose in normal humans. To evaluate the hypothesis that an increased sensitivity to these endogenous substances may play a role in defective insulin secretion in diabetes, we evaluated the effects of three blocking drugs upon the impaired insulin response to glucose in Type II diabetic subjects, as well as glucose-induced insulin secretion in normal humans. In diabetics, acute insulin responses to glucose were significantly increased by all the agents tested (naloxone, phentolamine and lysine acetylsalicylate), but only the cyclooxygenase inhibitor significantly augmented second phase insulin secretion and glucose disappearance rates. The combined infusion of the three agents caused a striking increase of the acute insulin response to glucose (response before: 3 +/- 2 uU/ml; after: 22 +/- 6 uU/ml, p less than 0.01). This was accompanied by a ninefold augmentation of the second phase of insulin secretion which was the result of a synergistic interaction between the three drugs (response significantly higher than the sum of single effects). In normals, insulin responses to glucose were also significantly increased by the combined infusions of the drugs, but to a significantly lesser extent than that of diabetics. This different degree of insulin potentiation between normals and diabetics under the infusion of the three agents persisted even when the prestimulus glucose level of normals was matched to that of diabetics by a glucose infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1996

Overall lack of regulated secretion in a PC12 variant cell clone.

A stable clone of PC12 neuroendocrine cells, named 27, known from previous studies to exhibit a defect of regulated secretion (lack of regulated secretory proteins, of synaptophysin, of dense granules and of catecholamine uptake and release; Clementi, E., Racchetti, G., Zacchetti, D., Panzeri, M. C., and Meldolesi, J. (1992) Eur. J. Neurosci. 4, 944-953) was characterized in detail to clarify the nature of its phenotype and the mechanisms of its establishment. The neuroendocrine nature of the PC12-27 phenotype was documented by specific markers: synapsins, neurofilament subunit H, neuronal kinesin, and alpha-latrotoxin receptor. Moreover, various intracellular membrane systems of PC12-27, including the endoplasmic reticulum and the Golgi complex, appeared similar to control PC12 in both morphology and marker expression. In contrast, all the investigated markers located either in dense granules (dopamine-beta-hydroxylase), in synaptic-like microvesicles (the acetylcholine transporter) or in both these regulated secretory organelles (VAMP2/synaptobrevin-2, synaptotagmin) were missing in PC12-27 cells, and the same was true also for the cytosolic and plasmalemma proteins involved in regulated exocytosis (Rab3, SNAP25, syntaxin). Pulse labeling and in vitro translation experiments revealed the defect to consist in a protein synthesis blockade that mRNA studies (reverse transcription-polymerase chain reaction, Northern blotting, and actinomycin D experiments) revealed to take place primarily at the transcriptional level. The secretion defect of PC12-27 cells was modified neither by various types of long term stimulation nor by nerve growth factor treatment. Moreover, when one of the missing regulated secretory proteins, chromogranin B, was expressed by cDNA transfection, it was secreted, however via the constitutive pathway. Our results demonstrate that PC12-27 cells are fully incompetent for both branches of regulated secretion, those of dense granules and synaptic-like microvesicles, possibly because of the impairment of a general expression control system that appears to operate independently of neuroendocrine cell differentiation.

Animals↗
PubMed1992

Abnormalities of the hypothalamo-pituitary-gonadal axis after head injury.

OBJECTIVE: We aimed to investigate the mechanisms of hypogonadism which develops after head injury. DESIGN: Pulsatile secretion of LH was studied in subjects 6-10 days after major head injury. PATIENTS: We studied five male subjects admitted with major head injuries and six healthy age-matched control subjects. MEASUREMENTS: During the pulsatility study, LH was measured at 5-minute intervals for 4 hours and 15-minute intervals for a further 2 hours. In addition, testosterone and LH were measured on Days 1-5, 14 and after 3-6 months. RESULTS: The analysis of pulsatile secretion of LH demonstrated an LH pulse frequency similar to control subjects, but a significantly reduced LH pulse amplitude (P less than 0.001, fixed threshold method; P less than 0.02, Detect method). Both testosterone and LH levels were reduced after injury with the nadir occurring on Day 4. CONCLUSIONS: Hypogonadism after head injury is due to defective LH secretion, with normal pulse frequency but a reduced pulse amplitude.

Adult↗
PubMed2006

Expression of hypothalamic KiSS-1 system and rescue of defective gonadotropic responses by kisspeptin in streptozotocin-induced diabetic male rats.

Hypogonadotropism is a common feature of uncontrolled diabetes, for which the ultimate mechanism remains to be elucidated. Kisspeptins, ligands of G protein-coupled receptor 54 (GPR54) encoded by the KiSS-1 gene, have recently emerged as major gatekeepers of the gonadotropic axis. Alteration in the hypothalamic KiSS-1 system has been reported in adverse metabolic conditions linked to suppressed gonadotropins, such as undernutrition. However, its potential contribution to defective gonadotropin secretion in diabetes has not been evaluated. We report herein analyses of luteinizing hormone (LH) responses to kisspeptin and hypothalamic expression of the KiSS-1 gene in streptozotocin (STZ)-induced diabetic male rats. In addition, functional studies involving kisspeptin replacement or continuous administration of leptin and insulin to diabetic male rats are presented. Kisspeptin administration evoked robust LH and testosterone bursts and enhanced postgonadectomy LH concentrations, despite prevailing attenuation of gonadotropic axis in diabetic animals. In addition, hypothalamic KiSS-1 mRNA levels were unambiguously decreased in diabetic male rats, and the postorchidectomy rise in KiSS-1 mRNA was severely blunted. Repeated administration of kisspeptin to diabetic rats evoked persistent LH and testosterone responses and partially rescued prostate and testis weights. In addition, central infusion of leptin, but not insulin, was sufficient to normalize hypothalamic KiSS-1 mRNA levels, as well as LH and testosterone concentrations. In summary, we provide evidence for altered expression of the hypothalamic KiSS-1 system in a model of uncontrolled diabetes. This observation, together with the ability of exogenous kisspeptin to rescue defective LH responses in diabetic rats, unravel the physiopathological implication, and potential therapeutic intervention, of the KiSS-1 system in altered gonadotropin secretion of type 1 diabetes.

Animals↗