BACKGROUND: IGF-I gene expression and IGF-I plasma concentration decline with age. A decreased sensitivity to GH has been suggested to be a contributory mechanism to this, in addition to attenuated GH secretion. OBJECTIVE: This study focuses on the sensitivity to exogenous GH and the reversibility of the reduced IGF-I gene expression in aging male rats. DESIGN: Three groups of male Wistar rats aged 3 months (young adult), 11 months (middle-aged) and 27 months (old), received recombinant human GH (rhGH) (150 microg/12 h s.c.) for seven consecutive days. RESULTS: This rhGH treatment completely reversed plasma immunoreactive IGF-I (IR-IGF-I) and hepatic IGF-I mRNA levels in 11-month-old and 27-month-old animals to the levels of the young group of animals. The sensitivity in the old group (percentage of increment after the same or lower dose of rhGH per body weight) was increased for both parameters; serum IGF-I increment: 15% in 3-month-old, 42.6% in 11-month-old and 119.1% in 27-month-old rats; and hepatic IGF-Ib mRNA increase: 45% in 3-month-old, 27.8% in 11-month-old and 64.3% in 27-month-old rats. IGF binding protein-3 (IGFBP-3) mRNA level in the liver was significantly decreased in the old group and only a partial reversion occurred in this group after rhGH treatment; the percentage of increment was also higher in the old group of rats. In extrahepatic tissues IGF-I mRNA was not significantly different in the kidney and the testis of the three groups, and the rhGH treatment produced a significant and similar increase of IGF-I mRNA level in the kidney of the three groups of rats and in the testis of the 27-month-old animals. The GHr/GHBP mRNA remained unchanged in the liver and in the kidney or the testis of the three groups, and was not influenced by the rhGH treatment. Exogenous rhGH decreased pituitary GH mRNA accumulation in a more intense manner in the old group versus control of each group: young adult, 25%; middle-aged, 41.2%; and old rats, 55%. The action of rhGH on pituitary immunoreactive GH (IR-GH) content was only significantly evident in the young group. CONCLUSIONS: These results establish that exogenous rhGH recovers the attenuated liver IGF-I gene expression and the diminished plasma IR-IGF-I in old rats to the levels of young adult animals. They also indicate that the hepatic and extrahepatic (kidney and testis) sensitivity to one established dose per weight of exogenous rhGH is not altered in old animals, or could be potentially increased in some tissues.
B Velasco, L Cacicedo, E Melian, G Fernandez-Vazquez and F Sanchez-Franco
J. M. Saez, F. Haour, B. Loras, P. Sanchez and A. M. Cathiard
In vivo administration of oestradiol to male rats modifies plasma LH, FSH and testosterone levels, cAMP and testosterone production and DNA synthesis in isolated interstitial cells. Intramuscular injection of oestradiol benzoate (Oe2B) at the dose of 1 or 100 μg/day for 6 days induced a 5- and 10-fold decrease in plasma testosterone, respectively, and a 2-fold decrease in plasma LH and FSH. Plasma testosterone was already significantly decreased 2 h after the Oe2B injection at which point the plasma LH and FSH levels were not yet significantly decreased. In vivo steroidogenic responsiveness to hCG evaluated by plasma and testicular contents was already significantly lower than that of controls 2 h following oestradiol administration. Thereafter response to hCG progressively decreased during the 6 days of 1 or 100 μg oestradiol treatment, reaching 30 and 10 %, respectively, of that of controls on the last day. On the contrary the testicular cAMP content 2 h after hCG injection was significantly higher in oestradiol treated animals than in controls after 24 h. The number of hCG binding sites in isolated Leydig cells decreased to approximately 50 % of that of controls on days 3 to 6 following Oe2B treatment. In vitro testosterone production by isolated interstitial cells, either under basal conditions or under stimulation by hCG or N6O2 dibutyryl adenosine 3′,5′-monophosphate (DbcAMP), was lowered as early as 2 h following the injection of Oe2B to the animals. From 1 to 6 days following Oe2B administration, testosterone secretion, in response to both stimuli, was approximately 4 times lower than that of the control animals. Paradoxically, by the second day of oestrogen treatment, basal and hCG induced in vitro cAMP production by interstitial cells was significantly higher than controls despite a significant decrease in the number of binding sites. The incorporation of thymidine into interstitial cells DNA were decreased following 2 days of oestrogen administration. However, the conversion of pregnenolone to testosterone was unchanged. These inhibitory effects of oestradiol were not overcome by simultaneous administration of hCG.
These results strongly suggest that the rapid inhibitory action of oestradiol on interstitial cell function, steroidogenesis, and DNA synthesis, occurs at the testicular level. Changes observed in gonadotrophin receptor sites or in plasma LH levels may have a long term effect on the steroidogenic refractoriness to hCG. However this refractoriness is primarily related to an abnormality of some step of steroidogenesis beyond cAMP formation.
M. Ramirez, B. Sanchez, G. Arechaga, S. Garcia, P. Lardelli, D. Venzon and J. M. de Gandarias
The thyroliberin and luliberin contents exhibit a diurnal rhythm within the brain and an asymmetrical distribution of both neuropeptides has been demonstrated in the hypothalamus. Since they have been described as substrates of pyroglutamyl peptidase I, this activity was analysed in several rat brain regions and other structures, in order to investigate its putative diurnal variations and changes in relation to the distribution of these neuropeptides and/or other susceptible substrates. Fluorometric activity was assayed in the retina, pituitary gland, superior cervical ganglia, pineal gland, some selected brain regions, and serum of adult male rats at six different time points of a 12:12 h light:dark cycle, using pyroglutamyl-β-naphthylamide as substrate. A significant circadian rhythm was demonstrated in the retina, the hypothalamus, and the intermediate-posterior pituitary lobe. In addition, a small but significant asymmetrical distribution of this activity, at certain time points, was disclosed: The activity was higher in the left than in the right retina at 10 h of the light period, whereas it was predominant in the right side at 01 h of the dark period. Furthermore, the activity was higher in the left anterior than in the right hypothalamic area at 13 and 01 h. These results could be indicative of a role of this enzymatic activity in the control of the functional status of its endogenous substrates.
M Schlumberger, G Berg, O Cohen, L Duntas, F Jamar, B Jarzab, E Limbert, P Lind, F Pacini, C Reiners, F Sanchez Franco, A Toft and WM Wiersinga
OBJECTIVE: Because differentiated (follicular and papillary) thyroid cancer (DTC) may recur years after initial treatment, the follow-up of patients with DTC is long term. However, this population has changed, with more individuals being discovered at an earlier stage of the disease, so that previous follow-up protocols based mostly on data from high-risk patients no longer apply. We sought to develop an improved protocol for the follow-up of low-risk patients with DTC based on the findings of recent studies. METHODS: We analysed recent literature on the follow-up of DTC. RESULTS: Recent large studies have produced three important findings: (i) in patients with low-risk DTC with no evidence of disease up to the 6- to 12-month follow-up, diagnostic whole-body scan adds no information when serum thyroglobulin (Tg) is undetectable and interference from anti-Tg antibodies is absent; (ii) use of recombinant human thyroid-stimulating hormone to aid Tg measurement is effective and provides greater safety, quality-of-life and work productivity than does levothyroxine withdrawal with its attendant hypothyroidism; and (iii) ultrasonography performed by an experienced operator is the most sensitive means of detecting neck recurrences of DTC. CONCLUSIONS: We present a revised follow-up protocol for low-risk patients taking into account the above findings. This protocol should help clinicians enter a new era of monitoring characterized by greater safety, simplicity, convenience and cost savings.
M Schlumberger, F Pacini, WM Wiersinga, A Toft, JW Smit, F Sanchez Franco, P Lind, E Limbert, B Jarzab, F Jamar, L Duntas, O Cohen and G Berg
As differentiated (follicular and papillary) thyroid cancer (DTC) may recur years after initial treatment, follow-up of patients with DTC is long term. However, this population has changed, with more individuals being discovered at an earlier stage of disease, so that previous follow-up protocols based mostly on data from high-risk patients no longer apply. We have proposed, in a previous issue of this Journal, an improved protocol for the follow-up of low-risk patients with DTC based on the findings of recent studies. We report here the case of a paradigmatic patient with papillary thyroid carcinoma, with the goal of illustrating the benefits of applying this algorithm in routine clinical practice. We also offer expanded and additional comments on various issues in the management of DTC.
Paloma Almeda-Valdes, Donaji V Gómez Velasco, Olimpia Arellano Campos, Omar Yaxmehen Bello-Chavolla, Magdalena del Rocío Sevilla-González, Tannia Viveros Ruiz, Alexandro J Martagón Rosado, Claudia J Bautista, Liliana Muñoz Hernandez, Ivette Cruz-Bautista, Hortensia Moreno-Macias, Alicia Huerta-Chagoya, Karen Guadalupe Rodríguez-Álvarez, Geoffrey A Walford, Suzanne B R Jacobs, Luz E Guillen Pineda, Ma Luisa Ordoñez-Sánchez, Ernesto Roldan-Valadez, Joaquín Azpiroz, Jannette Furuzawa-Carballeda, Patricia Clark, Miguel F Herrera-Hernández, Elena Zambrano, Jose C Florez, María Teresa Tusié Luna and Carlos A Aguilar-Salinas
A haplotype at chromosome 17p13 that reduces expression and function of the solute carrier transporter SLC16A11 is associated with increased risk for type 2 diabetes in Mexicans. We aim to investigate the detailed metabolic profile of SLC16A11 risk haplotype carriers to identify potential physiological mechanisms explaining the increased type 2 diabetes risk.
We evaluated carriers (n = 72) and non-carriers (n = 75) of the SLC16A11 risk haplotype, with or without type 2 diabetes. An independent sample of 1069 subjects was used to replicate biochemical findings. The evaluation included euglycemic–hyperinsulinemic clamp, frequently sampled intravenous glucose tolerance test (FSIVGTT), dual-energy X-ray absorptiometry (DXA), MRI and spectroscopy and subcutaneous abdominal adipose tissue biopsies.
Fat-free mass (FFM)-adjusted M value was lower in carriers of the SLC16A11 risk haplotype after adjusting for age and type 2 diabetes status (β = −0.164, P = 0.04). Subjects with type 2 diabetes and the risk haplotype demonstrated an increase of 8.76 U/L in alanine aminotransferase (ALT) (P = 0.02) and of 7.34 U/L in gamma-glutamyltransferase (GGT) (P = 0.05) compared with non-carriers and after adjusting for gender, age and ancestry. Among women with the risk haplotype and normal BMI, the adipocyte size was higher (P < 0.001).
Individuals carrying the SLC16A11 risk haplotype exhibited decreased insulin action. Higher serum ALT and GGT levels were found in carriers with type 2 diabetes, and larger adipocytes in subcutaneous fat in the size distribution in carrier women with normal weight.