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Biomedical subjects

Felipe F Casanueva

Publications and source records attributed to Felipe F Casanueva.

At least 19 recordsLinked to original sources
PubMed2007

Obestatin-mediated proliferation of human retinal pigment epithelial cells: regulatory mechanisms.

In this work, we have evaluated the effect of the new discovered peptide obestatin on cell proliferation in primary cultures of human retinal epithelial cells (hRPE cells). The results showed that this peptide induced, in a dose-dependent manner, cell proliferation by MEK/ERK 1/2 phosphorylation. A sequential analysis of the obestatin transmembrane signaling pathway showed that the ERK 1/2 activity is partially blocked after preincubation of the cells with pertussis toxin (PTX), as well as by wortmannin (an inhibitor of PI3K), claphostin C (an inhibitor of PKC), and PP2 (which inhibits the non receptor tyrosine kinase Src). Upon administration of obestatin, the intracellular levels of phospho-PKCepsilon-, theta-, and micro-isoenzymes rise with different time courses, from which PKCepsilon might be responsible for ERK 1/2 response. Based on the experimental data, a signaling pathway involving the consecutive activation of Gi, PI3K, novel PKC (probably PKCepsilon), and Src for ERK 1/2 activation is proposed. These results incorporate a new mitogenic factor to the group of factors that regulate proliferation of hRPE cells.

Cell Count↗
PubMed2006

One ancestor, several peptides post-translational modifications of preproghrelin generate several peptides with antithetical effects.

Preproghrelin is the polypeptide precursor of ghrelin. First discovered in gastric extract as a growth hormone releasing peptide and food intake modulator, it has more recently been revealed to have other physiological aspects. The fine molecular mechanisms of ghrelin biosynthesis show that this peptide is but one piece of a puzzle which contains many other peptides obtained from alternative splicing of the same gene or from extensive post-translational modifications. Recent developments have shown that pro-ghrelin cleavage generates another active peptide named obestatin with an intriguingly subtle but opposite physiological action to ghrelin. Noteworthy, and similar to ghrelin, which requires post-translational processing close to its amino terminus by acylation, the biological activity of the ghrelin-associated peptide obestatin also depends on modification, but by amidation at its carboxyl terminus. In this review we will summarize the steps which led to the identification of pre-proghrelin gene products and will examine the significance and perspectives of the different peptides generated from the same ancestor gene.

Animals↗
PubMed2006

High risk of hypopituitarism after traumatic brain injury: a prospective investigation of anterior pituitary function in the acute phase and 12 months after trauma.

CONTEXT: Recent data have demonstrated that traumatic brain injury (TBI)-mediated hypopituitarism could be more frequent than previously known. However, most previous data were obtained from retrospective studies. OBJECTIVES: The aim of this study was to determine 1) the prevalence of anterior pituitary hormone deficiencies in the acute phase of TBI and after 12 months, 2) whether severity of trauma correlated with basal hormone levels, and 3) whether initial hormone deficiencies predicted medium-term hormonal status. DESIGN AND PATIENTS: Fifty-two TBI patients (43 men and nine women) were included in the prospective study. Pituitary function was evaluated within 24 h of admission and after 1 yr. RESULTS: Some 5.8% of the patients had TSH deficiency, 41.6% had gonadotropin deficiency, 9.8% had ACTH deficiency, and 20.4% had GH deficiency (GHD). Twelve months after TBI, 5.8% had TSH deficiency, 7.7% had gonadotropin deficiency, 19.2% had ACTH deficiency, and 37.7% had GHD. Twenty-six patients (50.9%) had at least one anterior pituitary hormone deficiency, 21 patients (41.2%) had isolated hormone deficiencies, and five patients (9.7%) had combined hormone deficiencies. Overall, the pituitary hormone deficiencies recovered in 30 (57.7%) patients after 1 yr, and new pituitary hormone deficiencies were present in 27 (51.9%) patients after 1 yr. CONCLUSIONS: GHD is the most common pituitary deficit 12 months after TBI, and 50.9% of the patients had at least one anterior pituitary hormone deficiency. Pituitary function may improve or worsen in a considerable number of patients over 12 months.

Adolescent↗
PubMed2006

Effect of obesity and morbid obesity on the growth hormone (GH) secretion elicited by the combined GHRH + GHRP-6 test.

OBJECTIVE: Obesity is characterized by low basal levels of growth hormone (GH) and impeded GH release. However, the main problem arises in the diagnosis of GH deficiency in adults, as all accepted cut-offs in the diagnostic tests of GH reserve are no longer valid in obese subjects. In this work, the role of obesity in the GH response elicited by the GHRH + GHRP-6 test was assessed in a large population of obese and nonobese subjects. PATIENTS: GHRH + GHRP-6-induced GH peaks were evaluated in 542 subjects. One hundred and five were healthy obese, 50 were morbid obese, and 261 were nonobese (both normal weight and overweight). One hundred and seventy-six GH-deficient patients (obese and nonobese) were also studied. RESULTS: A regression analysis of the 366 subjects with normal pituitary function indicated that adiposity had a negative effect on the elicited GH peak (r = -0.503, P < 0.0001). A receiver operating characteristic (ROC) curve analysis showed that in subjects with a BMI < or =35, the currently accepted cut-offs of the GHRH + GHRP-6 test (GH peaks > or =20 microg/l: normal secretion; GH peaks < or =10 microg/l: GH deficiency), were fully operative. However, in subjects with a BMI > 35, normality was indicated by GH peaks > or =15 microg/l and GH deficiency by peaks < or =5 microg/l (1 microg/l = 2.6 mU/l). CONCLUSIONS: This study confirms: (a) that the combined provocative test is adequate to separate normal and GH-deficient subjects; (b) the negative effect of obesity on GH secretion; (c) that obesity accounts for 25% of the reduction of GH release; and (d) that present cut-off values are applicable to normal weight, overweight and grade I obesity subjects, whereas in obese subjects with a BMI exceeding 35, all the normative limits of the GHRH-GHRP +6 test must be reduced by 5 microg/l.

Adolescent↗
PubMed2006

Guidelines of the Pituitary Society for the diagnosis and management of prolactinomas.

In June 2005, an ad hoc Expert Committee formed by the Pituitary Society convened during the 9th International Pituitary Congress in San Diego, California. Members of this committee consisted of invited international experts in the field, and included endocrinologists and neurosurgeons with recognized expertise in the management of prolactinomas. Discussions were held that included all interested participants to the Congress and resulted in formulation of these guidelines, which represent the current recommendations on the diagnosis and management of prolactinomas based upon comprehensive analysis and synthesis of all available data.

Adenoma↗
PubMed2006

Does long-term GH replacement therapy in hypopituitary adults with GH deficiency normalise quality of life?

OBJECTIVE: To determine whether impaired quality of life (QoL) in adults with GH deficiency (GHD) is reversible with long-term GH therapy and whether the responses in QoL dimensions differ from each other. METHODS: QoL was measured by the Quality of Life-Assessment for Growth Hormone Deficiency in Adults (QoL-AGHDA) in general population samples in England & Wales, The Netherlands, Spain and Sweden (n = 892, 1038, 868 and 1682 respectively) and compared with corresponding patients' data from KIMS (Pfizer International Metabolic Database) (n = 758, 247, 197 and 484 respectively) for 4-6 years a follow-up. The subsets of patients from England and Wales, and Sweden with longitudinal data for 5 years' follow-up were also analysed. The change of the total QoL-AGHDA scores and responses within dimensions were evaluated. Subanalyses were performed to identify any specificity in response pattern for gender, age, disease-onset and aetiology. RESULTS: Irrespective of the degree of impairment, overall QoL improved dramatically in the first 12 months, with steady progress thereafter towards the country-specific population mean. Problems with memory and tiredness were the most serious burden for untreated patients, followed by tenseness, self-confidence and problems with socialising. With treatment, these improved in the reverse order, normalising for the latter three. CONCLUSIONS: Long-term GH replacement results in sustained improvements towards the normative country-specific values in overall QoL and in most impaired dimensions. The lasting improvement and almost identical pattern of response in each patient subgroup and independent of the level of QoL impairment support the hypothesis that GHD may cause these patients' psychological problems.

Adult↗
PubMed2006

Adenosine does not bind to the growth hormone secretagogue receptor type-1a (GHS-R1a).

Ghrelin regulates GH secretion and energy homeostasis through the GH secretagogue receptor type-1a (GHS-R1a). This G-protein coupled receptor shows the peculiarity to transduce information provided not just by ghrelin as well as by adenosine through a supposed binding site different from the characterized ghrelin-binding pocket. Indeed, adenosine triggers intracellular calcium rise through a distinct signaling pathway to the one described for ghrelin, although it fails to stimulate GH secretion. Despite multiple active conformations of GHS-R1a, suggested as an explanation for a ligand-dependent activation of the downstream signaling, the concept of adenosine as agonist for GHS-R1a has been re-evaluated. The results revealed that calcium rise of both ghrelin and adenosine appears to be mediated by receptors that did not show the same sensitivity to protein kinase C (PKC) activity in GHS-R1a-transfected HEK 293 cells (HEK-GHS-R1a cells). The binding analyses showed the same number of adenosine-binding sites in both HEK 293 (B(max) = 2.01 +/- 0.15 fmol/cell) and HEK-GHS-R1a cells (B(max) = 1.90 +/- 0.11 fmol/cell). This binding was unaltered by different GHS-R1a antagonists. Western blot analysis showed a similar endogenous expression of endogenous adenosine receptor type-2b and -3 in both cell lines. The K(d) values for adenosine were 1.78 microM in HEK 293 cells and 6.30 microM in HEK-GHS-R1a cells, pointing to a modification of agonist affinity induced by overexpression of the GHS-R1a. Additionally, adenosine failed to induce the GHS-R1a endocytosis, although it attenuates the ghrelin-induced GHS-R1a endocytosis. In conclusion, adenosine is not an agonist of the GHS-R1a and its action is mediated by the endogenous adenosine receptor type-2b and -3, which is able to partially use the intracellular signaling machinery of HEK-GHS-R1a cells.

Adenosine↗
PubMed2005

The bovine vitreous-derived lipid factor (bVLF) is a powerful inhibitor of retinal pigmented epithelial (hRPE) cell proliferation.

Human retinal pigmented epithelial cell (hRPE) proliferation plays a significant role in various proliferative diseases associated to the retina that leads to loss of vision, such as proliferative vitreoretinopathy. In the current study, the role of the bovine vitreous lipid factor (bVLF) in hRPE cell proliferation has been investigated. bVLF is a bioactive lipid isolated from the bovine vitreous body with strong Ca(2+)-mobilizing activity in fibroblast. In the first approach, the effects of bVLF on Ca(2+)-mobilizing activity were investigated in hRPE. The results showed that bVLF induced, in a dose-dependent manner, a Ca(2+) mobilization from PA-sensitive intracellular stores [non-Ins(1,4,5)P(3)-sensitive stores], in which extracellular Ca(2+) participated. The increase in intracellular Ca(2+) was associated with a dose-dependent inhibiting effect on cell proliferation. At a dose of 10 microg/mL, bVLF caused a 26% or a 44% inhibition in hRPE cell proliferation during the 3- or the 6-day culture periods, respectively. These effects appear to be specific in hRPE cells, since EFGR-T17 fibroblast cells treated with equivalent amounts of bVLF did not show any inhibiting effects. This inhibitory action was not associated to apoptotic/necrotic processes. Furthermore, bVLF inhibited EGF-, bFGF-, IGF-I-, PDGF-, HGF- and VEGF-induced proliferation of the hRPE cells. Moreover, this inhibitory response was also observed in FBS-induced hRPE cell proliferation. bVLF, at a concentration of 10 microg/mL, induced 16% inhibition of proliferation during a culture period of 3 days. This inhibitory action was greater during the 6-day culture period, exceeding 40%. With regard to this action, the results showed that bVLF has a potent inhibitory effect on ERK1/2 activation, and plays a key role in the control of hRPE cell proliferation. These observations contribute to the knowledge of inhibitory factors responsible for keeping antiproliferative environment that preserve the RPE-associated activities in normal states. It advances the interesting possibility that this factor or a factor with characteristics common to bVLF might be involved in the pathogenesis of abnormal proliferative eye processes.

Animals↗
PubMed2005

Expression and regulation of adiponectin and receptor in human and rat placenta.

CONTEXT: Adiponectin is an adipocyte hormone involved in glucose and lipid metabolism. Recently, two receptors of this protein, called adiponectin receptor 1 (Adipo-R1) and Adipo-R2, have been cloned. OBJECTIVE: The aim of this study was to examine whether adiponectin and its receptors are expressed in human and rat placentas and to evaluate the regulation of these factors by gestational age and nutritional status. RESULTS: Our results demonstrate that adiponectin and Adipo-R2 are localized in both human and rat placentas. Human adiponectin and Adipo-R2 are presented in cytotrophoblast and syncytiotrophoblast cells. However, rat adiponectin and Adipo-R2 change their specific cell type immunostaining during gestation. Furthermore, placental adiponectin mRNA expression is increased during pregnancy in the rat, whereas Adipo-R2 has the contrary pattern. We also assessed the effect of food restriction (30%) during gestation, and we observed that adiponectin mRNA levels decrease after 16 d of undernutrition. In contrast, placental Adipo-R2 mRNA is unchanged by undernutrition. Finally, treatment with adiponectin during gestation decreases Adipo-R2, glucose transporter 3, lipoprotein lipase, and TGF-beta mRNA expression. CONCLUSION: Taken together, our results suggest that, at least in rodents, adiponectin may be involved in the regulation of several placental functions.

Adiponectin↗
PubMed2005

Leptin, from fat to inflammation: old questions and new insights.

Leptin is 16 kDa adipokine that links nutritional status with neuroendocrine and immune functions. Initially thought to be a satiety factor that regulates body weight by inhibiting food intake and stimulating energy expenditure, leptin is a pleiotropic hormone whose multiple effects include regulation of endocrine function, reproduction, and immunity. Leptin can be considered as a pro-inflammatory cytokine that belongs to the family of long-chain helical cytokines and has structural similarity with interleukin-6, prolactin, growth hormone, IL-12, IL-15, granulocyte colony-stimulating factor and oncostatin M. Because of its dual nature as a hormone and cytokine, leptin links the neuroendocrine and the immune system. The role of leptin in the modulation of immune response and inflammation has recently become increasingly evident. The increase in leptin production that occurs during infection and inflammation strongly suggests that leptin is a part of the cytokine network which governs the inflammatory-immune response and the host defense mechanisms. Leptin plays an important role in inflammatory processes involving T cells and has been reported to modulate T-helper cells activity in the cellular immune response. Several studies have implicated leptin in the pathogenesis of autoimmune inflammatory conditions, such as experimental autoimmune encephalomyelitis, type 1 diabetes, rheumatoid arthritis, and intestinal inflammation. Very recently, a key role for leptin in osteoarthritis has been demonstrated: leptin indeed exhibits, in concert with other pro-inflammatory cytokines, a detrimental effect on articular cartilage by promoting nitric oxide synthesis in chondrocytes. Here, we review the recent advances regarding leptin biology with a special focus on those actions relevant to the role of leptin in the pathophysiology of inflammatory processes and immune responses.

Animals↗
PubMed2005

Low plasma ghrelin level in gastrectomized patients is accompanied by enhanced sensitivity to the ghrelin-induced growth hormone release.

Ghrelin is a brain-gut peptide with potent GH-releasing activities. It has been suggested that the majority of circulating ghrelin originates from the stomach, with a smaller portion from the small intestine. Gastrectomy (GASTRX) significantly reduces circulating ghrelin concentrations. The implication of decreased circulating ghrelin on the somatotropic axis post GASTRX has not been studied. Therefore, we aimed to investigate the somatotropic axis in 10 gastrectomized patients who underwent total GASTRX for various reasons at least 2 yr ago. At baseline circulating total ghrelin, GH, IGF-I, and IGF binding protein (IGFBP)-3 levels were measured. The GH stimulation test consisted of an insulin-induced hypoglycemia, ghrelin in two iv bolus doses (0.1 and 1 microg/kg), and a GHRH test. GH sensitivity was assessed by an IGF-I generation test. All the tests were performed 2 wk apart. At baseline serum ghrelin levels were reduced by 55% in GASTRX patients, compared with the control group (P < 0.05). IGF-I (P < 0.05) and IGFBP-3 (P < 0.01) levels were also significantly lower than in controls. GH response to the insulin-induced hypoglycemia test in both GASTRX and control subjects was of similar magnitude, whereas circulating plasma ghrelin levels in GASTRX patients were not modified during hypoglycemia. Both doses (0.1 and 1.0 microg/kg) of ghrelin stimulated GH release significantly more in GASTRX than control subjects, respectively (peak mean GH +/- se: 18.2 +/- 5.6 vs. 5.4 +/- 1.3 microg/liter, P < 0.03; and 58.7 +/- 7.5 vs. 35.3 +/- 1.9 microg/liter, P < 0.01). There was no difference in GHRH-induced GH response between GASTRX patients and control subjects (P > 0.05). Concomitantly, increased increments in IGF-I and IGFBP-3 to a single bolus of GH were found (P < 0.03). In conclusion, our data suggest that low circulating ghrelin levels, found in GASTRX patients, are accompanied by enhanced ghrelin sensitivity with respect to GH response. This is associated with increased GH responsiveness. GASTRX is a state of acquired chronic hypoghrelinemia that may require replacement with ghrelin, and it is tempting to speculate that this may affect the GH-IGF-IGFBP axis.

Adult↗
PubMed2005

Hypopituitarism and growth hormone deficiency in adult subjects after traumatic brain injury: who and when to test.

Traumatic brain injury (TBI) was traditionally considered an infrequent cause of hypopituitarism. However recent reports strongly suggest that TBI-mediated pituitary hormones deficiency may well be more frequent than previously thought. As the prevalence of hypopituitarism is not dependent on the severity of the trauma and considering the high number of TBI events in all industrialized countries a screening procedure for detecting hormone deficiencies in all TBI patients is not possible. In the present work a suggestion for screening a subgroup of TBI patients is discussed in order to increase the effectiveness of the whole procedure.

Brain Injuries↗
PubMed2005

Traumatic brain injury as a relevant cause of growth hormone deficiency in adults: A KIMS-based study.

OBJECTIVES: To characterize further the clinical manifestations and the efficacy of growth hormone (GH) replacement therapy in patients with adult-onset growth hormone deficiency (GHD) reported in the KIMS (Pfizer's international metabolic database) as caused by traumatic brain injury (TBI) and to compare them with nonirradiated patients whose GHD was due to a nonfunctioning pituitary adenoma (NFPA). DESIGN: Observational study. SETTING: Subjects selected from the KIMS database. PARTICIPANTS: Fifty-one patients with GHD resulting from TBI and 688 patients with GHD resulting from NFPA. Both groups were selected from the KIMS and had adult-onset GHD with GH replacement therapy only after KIMS entry and before and after KIMS entry. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Age, body mass index, age at disease onset, age at disease diagnosis, age at KIMS entry, final height, GH peak at testing, GH replacement dose, routine biochemical analysis, clinical manifestations of disease, and quality of life measurements. RESULTS: Patients with TBI were significantly younger at study entry and were younger both at pituitary disease onset and at GHD diagnosis, but they showed a significant delay in treatment. When comparing patients not treated with GH before entering in the KIMS, patients with TBI were significantly shorter (167.2+/-1.7 cm) than those with NFPA (171.6+/-0.4 cm) in final height. TBI patients had lower GH reserves than NFPA patients, and although the latter group experienced more positive changes, both groups benefited from GH replacement therapy. CONCLUSIONS: Patients with GHD due to TBI showed a significant reduction in height and a reduction in pituitary GH reserve and were diagnosed and treated with inappropriate delay.

Adult↗
PubMed2005

Ghrelin, the same peptide for different functions: player or bystander?

Ghrelin is a recently discovered brain-gut peptide with two main physiological actions: growth hormone secretagogue activity and food intake inducer. Although its production is prevalently gastric, ghrelin is widely expressed in several tissues, where it might therefore act as a paracrine or autocrine factor. It is becoming clear that ghrelin is much more than a simple growth hormone secretagogue. In addition to its formerly envisaged role, ghrelin has other activities including stimulation of pituitary hormones secretion, modulation of food intake and control of energy metabolism, regulation of gastric and pancreatic activity, and cardiovascular and hemodynamic activities. In addition, modulation of cartilage and bone homeostasis, sleep and behavioral influences, and modulation of the immune system, as well as effects on cell proliferation, are other relevant actions of ghrelin. Thus, the peptide appears to be an important component of an integrated multifaceted regulatory system. In this review, we summarize several aspects of ghrelin biology and attempt to inform the reader with information regarding unexpected functions of this gastric peptide.

Acylation↗
PubMed2005

Prevalence of hypopituitarism and growth hormone deficiency in adults long-term after severe traumatic brain injury.

OBJECTIVE: Traumatic brain injury (TBI) has been associated with hypopituitarism and GH deficiency. However, TBI-mediated hypopituitarism may be more frequent than previously thought. The present work, performed in patients with severe TBI at least 1 year before, had three aims: (i) to evaluate the prevalence of hypopituitarism, (ii) in particular to evaluate the prevalence of GH deficiency, and (iii) to compare three different tests of GH reserve in this cohort. DESIGN AND PATIENTS: From a nonselected group of 249 patients admitted to our Clinical Centre for severe TBI over the last 5 years, 200 of them answered a custom made questionnaire of symptoms of hypopituitarism enclosed in the invitation letter to participate in the study. A total of 170 (99 men and 14 women), accepted to participate in the study (study cohort); 57 had normal questionnaires and were not further studied, 14 discontinued the study, and 99 attended the hospital for dynamic tests of pituitary hormone deficiencies. From these, 44 subjects with IGF-I in the lower range were tested with GHRH+GHRP-6; ITT; and glucagon tests of GH reserve, on three different occasions. MEASUREMENTS: Pituitary hormones plus IGF-I and target gland hormones were analysed. RESULTS: With regard to the initial cohort of 170 subjects (100%), three (1.7%) showed diabetes insipidus; 10 (5.8%) TSH deficiency, 11 (6.4%) ACTH deficiency and 29 (17%) gonadotrophin deficiency. In 10 subjects (5.8%), GH deficiency was diagnosed by strict criteria. Finally, 15 (8.8%) showed combined deficit of several hormones. CONCLUSION: After severe head trauma, gonadotrophin deficiency was the most common pituitary deficit. GH deficiency showed a prevalence similar to ACTH and TSH deficits, i.e. near 6% of the cohort. Taken together, 24.7% of the subjects studied showed any type of pituitary hormone deficiency.

Adult↗
PubMed2005

The GHRH/GHRP-6 test for the diagnosis of GH deficiency in elderly or severely obese men.

OBJECTIVE AND DESIGN: Ageing and obesity result in decreased activity of the GH/IGF-I axis and concomitant impaired GH responses to secretory stimuli. We therefore determined the validity of the GH cut-off value of 15.0 microg/l in the GH-releasing hormone (GHRH)/GH releasing peptide-6 (GHRP-6) test for the diagnosis of GH deficiency in elderly or severely obese men. METHODS: We performed a combined GHRH/GHRP-6 test in ten elderly men (mean age 74 years; mean body mass index (BMI) 24.6 kg/m(2)), nine obese men (mean age 47 years; mean BMI 40.6 kg/m(2)) and seven healthy male controls (mean age 51 years, mean BMI 24.3 kg/m(2)). After assessment of fasting plasma GH, IGF-I and IGF-binding protein-3 (IGFBP-3), GHRH (100 microg) and GHRP-6 (93 microg) were given intravenously as a bolus injection. Repeated GH measurements were performed for two hours. RESULTS: Both peak GH levels and areas under the curve (AUC) were significantly lower in the obese than in the controls (peak 13.2 vs 53.4 microg/l, P = 0.001; AUC 707 vs 3250 microg/l x 120 min; P = 0.001). Mean GH response in the elderly was lower than in the controls (peak 35.0 microg/l; AUC 2274 microg/l x 120 min), but this was not statistically significant. In contrast, GH peak levels in seven obese men remained below the cut-off level of 15.0 microg/l associated with severe GH deficiency. All others had GH peak levels exceeding this threshold. IGFBP-3 levels were significantly lower in the elderly than in the controls (1.35 vs 2.05 mg/l, P = 0.001). Baseline GH or IGF-I did not differ significantly between groups. CONCLUSIONS: GH responses following GHRH/GHRP-6 administration were significantly reduced in severely obese men, but were not significantly reduced in elderly men, despite a negative trend. Our data indicate that the cut-off GH level of 15.0 microg/l after GHRH + GHRP-6 administration for the diagnosis of severe GH deficiency cannot be used in severely obese men.

Aged↗
PubMed2004

Novel expression of resistin in rat testis: functional role and regulation by nutritional status and hormonal factors.

Resistin, a recently cloned adipose-secreted factor, is primarily involved in the modulation of insulin sensitivity and adipocyte differentiation. However, additional metabolic or endocrine functions of this molecule remain largely unexplored. In this study, a series of experiments were undertaken to explore the potential expression, regulation and functional role of this novel adipocytokine in rat testis. Resistin gene expression was demonstrated in rat testis throughout postnatal development, with maximum mRNA levels in adult specimens. At this age, resistin peptide was immunodetected in interstitial Leydig cells and Sertoli cells within seminiferous tubules. Testicular expression of resistin was under hormonal regulation of pituitary gonadotropins and showed stage-specificity, with peak expression values at stages II-VI of the seminiferous epithelial cycle. In addition, testicular resistin mRNA was down-regulated by the selective agonist of PPARgamma, rosiglitazone, in vivo and in vitro. Similarly, fasting and central administration of the adipocyte-derived factor, leptin, evoked a significant reduction in testicular resistin mRNA levels, whereas they remained unaltered in a model of diet-induced obesity. From a functional standpoint, resistin, in a dose-dependent manner, significantly increased both basal and choriogonadotropin-stimulated testosterone secretion in vitro. Overall, our present results provide the first evidence for the expression, regulation and functional role of resistin in rat testis. These data underscore a reproductive facet of this recently cloned molecule, which may operate as a novel endocrine integrator linking energy homeostasis and reproduction.

Adipocytes↗