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Biomedical subjects

M I Berman

Publications and source records attributed to M I Berman.

At least 19 recordsLinked to original sources
PubMed1987

Alpha 1-adrenergic regulation of TSH-stimulated cyclic AMP accumulation in rat thyroid cells.

Addition of epinephrine to cultured FRTL-5 rat thyroid cells led to a concentration-dependent reduction of TSH- and forskolin-stimulated cAMP accumulation. Clonidine, which preferentially activates the alpha 2-adrenoreceptor, had no effect on cAMP levels. The reduction of cAMP levels by epinephrine was selectively blocked by prazosin, an alpha 1-adrenoreceptor antagonist, but not by yohimbine, an alpha 2-adrenoreceptor antagonist. Pretreatment of FRTL-5 cells with pertussis toxin failed to abolish the inhibitory effect of epinephrine on cAMP accumulation. The bioactivity of the pertussis toxin preparation in this cell line was verified by its ability to ADP-ribosylate the alpha-subunit of the inhibitory guanine nucleotide regulatory protein, Ni, as well as its ability to abolish the inhibitory effect of N6-[L-2-phenylisopropyl]-adenosine on TSH-stimulated cAMP formation. The inhibitory effect of epinephrine on cAMP levels was dependent on Ca2+ and was reversed by 3-isobutyl-1-methylxanthine. Taken together, these results suggest that epinephrine reduces cAMP levels via alpha 1-adrenoreceptors. The failure of pertussis toxin to abolish this alpha-adrenergic effect is consistent with the conclusion that epinephrine-induced attenuation of cAMP accumulation occurs through activation of a Ca2+-calmodulin-sensitive phosphodiesterase and does not involve Ni or Ni-like proteins.

1-Methyl-3-isobutylxanthine↗
PubMed1987

Stimulation of inositol phosphate formation in FRTL-5 rat thyroid cells by catecholamines and its relationship to changes in 45Ca2+ efflux and cyclic AMP accumulation.

Catecholamines specifically stimulated the rapid formation of inositol phosphates, bisphosphates and trisphosphates in a concentration-dependent manner in FRTL-5 thyroid cells. Further analysis by high performance liquid chromatography revealed the presence of two isomers of inositol trisphosphate, 1,4,5- and 1,3,4-trisphosphate, suggesting that the 1,4,5-trisphosphate of inositol is further metabolized to the 1,3,4-trisphosphate isomer. The alpha 1-adrenoreceptor antagonist, prazosin, inhibited the effects of epinephrine, while the alpha 2-adrenoreceptor antagonist, yohimbine, was without effect. Treatment of FRTL-5 cells with pertussis toxin (to inhibit Ni) did not abolish the epinephrine effect on inositol trisphosphate formation. Carbachol, N6-[L-2-phenylisopropyl]-adenosine and forskolin were without effect on phosphoinositide metabolism. Both epinephrine and the calcium ionophore A23187 stimulated 45Ca2+ efflux from 45Ca2+-loaded FRTL-5 cells. The time-course of the epinephrine effect indicates that inositol 1,4,5-trisphosphate formation (t1/2 approximately 1 s) precedes both the efflux of 45Ca2+ (t1/2 approximately 30 s) as well as the reduction of cyclic AMP levels (t1/2 approximately 90 s) in response to epinephrine. These results strongly suggest that inositol 1,4,5-trisphosphate has the appropriate properties to act as a second messenger by which alpha 1-adrenergic hormones, through mobilization of intracellular Ca2+ and activation of cyclic AMP phosphodiesterase, reduce cyclic AMP levels in FRTL-5 cells.

Animals↗
PubMed1986

Inhibition of thyrotropin-stimulated adenosine 3',5'-monophosphate formation in rat thyroid cells by an adenosine analog. Evidence that the inhibition is mediated by the putative inhibitory guanine nucleotide regulatory protein.

Addition of N6-(L-2-phenylisopropyl)-adenosine (PIA) to cultured FRTL-5 rat thyroid cells led to a concentration-dependent inhibition of TSH-stimulated cAMP formation. Half-maximal inhibition was attained with approximately 0.5 nM PIA. Forskolin and cholera toxin-stimulated cAMP production were also inhibited by PIA. 3-Isobutyl-methylxanthine inhibited the effect of PIA. These results are consistent with the presence of inhibitory adenosine receptors (Ri). Ri-sites were further demonstrated by the binding of 3H-cyclohexyl-adenosine to FRTL-5 plasma membranes. High (Kd = 0.50 +/- 0.07 nM) and low affinity (Kd = 5.95 +/- 2.33 nM) binding sites were observed. Pretreatment of FRTL-5 cells with pertussis, but not cholera, toxin effectively antagonized the inhibitory effects of PIA on cAMP production. ADP-ribosylation of FRTL-5 membranes with [32P]-NAD in the presence of cholera or pertussis toxin specifically labeled a 45,000 and 41,000 Mr species, respectively, which correspond to the alpha subunit of the stimulatory and inhibitory guanine nucleotide regulatory proteins. These results demonstrate that PIA inhibits TSH-stimulated cAMP production via Ri-sites on FRTL-5 thyroid cells. PIA appears to exert its inhibitory effects through the inhibitory guanine nucleotide regulatory protein.

Adenosine↗
PubMed1985

The role of the carbohydrate moiety in thyrotropin action.

The relative binding affinity of deglycosylated human TSH was 6-fold higher than that of native TSH. Although deglycosylated human TSH significantly stimulated adenylate cyclase, it was less effective than the native hormone. When deglycosylated human TSH was added with bovine TSH, however, a dose-dependent antagonism was observed. In particular, submaximal and maximal concentrations of bovine TSH and deglycosylated human TSH resulted in cAMP values much lower than the sum of activities of the individual hormones. The data suggest that although the effects of TSH deglycosylation are not as dramatic as with the gonadotropins, the carbohydrates of TSH appear to be required for maximal activation of adenylate cyclase by the hormone.

Adenylyl Cyclases↗
PubMed1985

Characterization of gonadotropin-sensitive adenylate cyclase activity in human testis: uncoupling of the receptor-cyclase complex by specific hormonal antagonist.

Basal and gonadotropin stimulated adenylate cyclase activity was assessed in testicular tissues obtained from men (20-80 years). A disparity was observed in the gonadotropin responsiveness of the human testicular adenylate cyclase system to hFSH and hCG stimulation. Of the tissues analyzed, 61% were FSH responsive and 22% showed low response to hCG. Forskolin, a diterpene which activates adenylate cyclase by a receptor independent mechanism, stimulated adenylate cyclase activity in the gonadotropin unresponsive tissues. This suggests that the tissue unresponsiveness is due to an uncoupling of the catalytic subunit of the adenylate cyclase. Several functional properties of the FSH responsive human testicular adenylate cyclase were investigated. hFSH and oFSH stimulated the enzyme activity in a concentration dependent manner. However, the hormone (DG-oFSH) in which 80% of the carbohydrate residues had been removed was inactive, despite its good binding ability to the FSH receptor. hFSH stimulated adenylate cyclase activity was inhibited by DG-oFSH but not by DG-hCG (deglycosylated hCG). The data demonstrates the existence of specific FSH and LH(hCG) receptors in human testicular membranes. The FSH receptors in some tissues are coupled to adenylate cyclase. The link between the FSH receptor and adenylate cyclase may be uncoupled in the presence of the deglycosylated form of oFSH resulting in a loss of hormone response.

Adenylyl Cyclases↗
PubMed1984

Identification of specific FSH binding sites in the testes of adult monkeys of different species.

The interaction of 125I-labelled hFSH with primate testicular tissue from 4 species of adult monkeys (Macaca mulatta, M. nemestrina, M. fascicularis and Papio cynocephalus) was investigated. 125I-labelled hFSH binding to a particulate fraction (P1, 40 000 g) of frozen testes was highly specific and saturable. Displacement curves generated using the P1 fraction of testes from the 4 species and 125I-labelled hFSH and unlabelled FSH were very similar. The binding of FSH to the monkey testicular receptor was not species specific because purified FSH from heterologous species such as horse, sheep, pig and rat were very effective in competing with 125I-labelled hFSH for binding. The equine FSH was about 10 times more active than hFSH in this respect. Similarly, 125I-labelled ovine FSH bound as well as labelled hFSH to the testes fractions of all 4 monkey species. In marked contrast to the high binding of 125I-labelled hFSH, binding of 125I-labelled hCG with rhesus monkey testis homogenates and P1 fractions was very low. The FSH receptor in the adult rhesus monkey testis was present in much larger quantity than the LH receptor and was more readily detectable. Our studies show that frozen primate testis can be utilized for investigating testicular-FSH interactions.

Animals↗
PubMed1983

Studies on primate gonadotropin receptors: comparison of follitropin and lutropin receptors in human testis.

The interaction of 125I-labeled human follitropin (hFSH), human lutropin (hLH), and human choriogonadotropin (hCG) with a particulate fraction prepared from the testes of adult men was investigated. The hormone specific binding was maximal at pH 7.5 and 34 degrees C in the presence of 10 mM MgCl2. The FSH receptor was relatively more stable than the LH receptor (t1/2 at 34 degrees C of 14 and 4 h, respectively). The dissociation constants (Kd) calculated for hLH or hCG were very similar (approximately 1.0 X 10(-10) - 1.4 X 10(-10) M). The affinity of FSH and LH to their receptors did not appear to change with age, as shown from analysis of testes from 17- to 80-year-old men. The number of FSH receptors was greater than the number of LH receptors in these tissues. The hFSH receptor did not show any preference to binding of the homologous hormone, because FSH from nonprimates could displace 125I-labeled hFSH, but the LH receptor showed a marked preference for hLH or hCG as the ligand.

Adolescent↗
PubMed1982

Studies on primate gonadotropin receptors: characterization of the rhesus monkey testicular follicle-stimulating hormone receptors.

The properties of adult rhesus monkey testicular FSH receptor was investigated in these experiments. The interaction of 125I-labeled human FSH with a monkey testicular particulate fraction is a time- and temperature dependent phenomenon. Equilibrium of hormone-receptor interaction occurred by about 4-6 at 37 or 34 C, was slow at 25 C, and was extremely slow at 4 C. Maximum binding occurred at pH 7-7.5, with a requirement of 5-10 mM MgCl2 or CaCl2. The half-life of the receptor with exposed sites for hormone interaction was temperature related (1 h at 37 C, 1.5 h at 34 C, 6 h at 25 C, and 36 h at 4 C). Occupancy of these sites by the labeled hormone rendered the receptor more stable. The hormone-receptor complex was highly stable, as shown by the fact that excess unlabeled hormone was unable to displace the already bound labeled hormone from the receptor. Conditions unfavorable for hormone-receptor interaction, such as pH 5.0 or pH 10 or high salt concentration (0.5 M MgCl2), induced the maximum dissociation of the preformed hormone-receptor complex. The primate testis FSH receptor was inactivated by trypsin, phospholipase C, and reducing agents, but it was not influenced by nucleases. Neuraminidase treatment of the particulate receptor may have enhanced its ability to bind labeled human FSH.

Animals↗
PubMed1979

Direct inhibitory effects of estrogens on rat Leydig cells in vitro.

In dispersed rat interstitial cells in vitro both natural and synthetic estrogens inhibited the action of pituitary luteinizing hormone (LH), as assessed by testosterone production. The estrogens also inhibited dibutyryl cyclic AMP induced steroidogenesis, suggesting that one point of inhibition could be distal to the formation of cyclic AMP in the cells. Diethyl stilbestrol and its clinically used sodium phosphate derivative (Honvol), also affected hormone-receptor interaction when tested with rat testicular homogenates. Among estradiol, estradiol benzoate, Honvol and diethyl stilbestrol only the latter at high concentration had toxic effects on Leydig cells as noted from loss of thier viability.

Animals↗