Authors:Ewa L. Gregoraszczuk, Agnieszka Rak, Anna Wójtowicz, Anna Ptak, Tatiana Wojciechowicz and K. W. Nowak
Leptin (L) is recognised as an important regulator of puberty and a factor which controls reproduction. Whole pig ovarian follicles were incubated with different doses of leptin (2, 20 and 200 ng/ml) added alone or in combination with 100 ng/ml of GH or 50 ng/ml of IGF-I. The expression of the functional long form leptin receptor (Ob-Rb) mRNA was examined by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) in follicular cells cultured with GH or IGF-I. Both GH and IGF-I increased leptin receptor expression in prepubertal pig ovaries. In separate experiments, the action of leptin on ovarian follicular steroidogenesis and cell apoptosis was examined. After 24 h of incubation with leptin alone or in combination with GH or IGF-I, oestradiol (E2) levels were determined in the culture medium while follicular tissue was used for the estimation of caspase-3 activity. Leptin increased E2 secretion and significantly diminished caspase-3 activity at all doses used. Both GH and IGF-I stimulated oestradiol secretion and decreased caspase-3 activity. No differences were demonstrable in oestradiol secretion and caspase-3 activity between cells treated with GH plus leptin and GH alone or cells treated with IGF-I plus leptin as compared to cultures treated with GH or IGF-I alone. However, GH diminished leptin-stimulated oestradiol secretion while IGF-I was without effect on it. Both GH and IGF-I reversed the anti-apoptotic action of leptin. In conclusion, we infer that (1) leptin directly affects ovarian function in prepubertal animals by its action on oestradiol secretion and cell apoptosis, (2) GH and IGF-I modulate the action of leptin, and (3) at least in part, the direct effect of GH/IGF-I on leptin production is due to an action on leptin receptor expression.
citations yields a new equivalent of the h -index, I denote the gh -index. Contrary to the h -index, the gh -index is a function of the total number of citations of each paper. A highly cited paper allows automatically a better allocation for all co
Authors:P. Van As, C. Careghi, V. Bruggeman, O. M. Onagbesan, S. Van der Geyten, V. M. Darras and E. Decuypere
growth hormone (GH) secretagogue L-692,429 in the chicken. Gen. Comp. Endocrinol. 111 , 186-196.
Pituitary and extrapituitary action sites of the novel nonpeptidyl growth hormone (GH) secretagogue L-692,429 in the chicken
Authors:R. Gouv?a dos Santos, M. A. Soares, J. S. Cruz, R. Mafra, R. Lomeo, M. N. Cordeiro, A. M. Pimenta and M. E. De Lima
The aim of this work was to use the binding assay of tritiated-dihydropyridine and radioiodinated Tx1, isolated from the Phoneutria nigriventer venom, in order to show the presence of Cav1 calcium channels on pituitary tumour cell (GH3). We showed that GH3 cells have specific sites for 125I-Tx1, which are sensitive to nifedipine (~20%). Reverse competition assay with 3H-PN200-110 (40% inhibition) and electrophysiological data (50% inhibition) suggest that Cav1 calcium channels are target sites for this toxin. To summarize, Tx1 binds to specific sites on GH3 cells and this interaction
results in Cav1 calcium channel blockade. 3H-PN200-110 and 125I-Tx1 binding assays proved to be useful tools to show the presence of calcium channels on GH3 cells.
The attenuation of baroreflex gain associated with hereditary hypertension couldinvolve abnormal signalling by nitric oxide or substance P. Baroreflex gain was measured in age-matched male genetically hypertensive (GH) and normotensive (N) anaesthetised rats from heart rate changes in response to i.v. phenylephrine or sodium nitroprusside. In subgroups of these animals, nitric oxide synthesis was inhibited using NG-nitro-L-arginine methyl ester (L-NAME, 30 mg.
The construction, the isothermal operation (26.2±0.06) and the calibration of a differential calorimeter of high performance are described. Its construction is based on the conduction principle by using copper resistors noninductively coiled on thin aluminium cylinders used as temperature sensors with very low inertia. Thermal flows are measured by using an ac bridge with a lock-in amplifier. The calibration, both of the height (h) and of the area (A) of the recorded peaks, is performed by using calibrated heat pulseswp with errors under 0.5%. A reproducible value of ratioh/A is obtained on a large number ofwp values, which represents a figure of merit of the high-performance calorimeter. This value is an immediate index of the nature of the general transformation process. For a clear-cut definition of the process, the universal procedure recently established on the topoenergetic principles is applied.