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Biomedical subjects

J G Tezon

Publications and source records attributed to J G Tezon.

8 recordsLinked to original sources
PubMed1994

Participation of glycosylated residues in the human sperm acrosome reaction: possible role of N-acetylglucosaminidase.

Sperm binding to the egg zona pellucida is mediated by complementary protein-carbohydrate interaction. This binding results in the exocytosis of the sperm acrosome, or acrosome reaction (AR). We report the effect of different neoglycoproteins (sugar residues covalently bound to bovine serum albumin) on the human sperm AR. p-Aminophenyl-N-acetyl-beta-D-glucosaminide-BSA (BSA-GlcNAc) and p-aminophenyl-alpha-D-mannopyranoside-BSA (BSA-Man) at 1 micrograms/ml were capable of inducing the greatest percentages of AR (3-fold stimulation with respect to controls), while other NeoGPs had only a weak effect on this process. The BSA-GlcNAc-induced acrosome reaction was inhibited by N-acetylglucosamine (GlcNAc), p-nitrophenyl-GlcNAc, and purified soluble beta-N-acetylglucosaminidase (beta NAG). The induction of the AR with BSA-Man could be inhibited by mannose, while soluble alpha-mannosidase was only partially effective. These data suggest that binding sites for GlcNAc and mannose may be involved in the induction of the AR in human sperm. The characteristics of the BSA-GlcNAc induction suggest that the beta NAG molecule may be the mediator of this effect.

Acetylglucosaminidase↗
PubMed1994

Effect of NPPB on chloride (Cl-) transport in distal colon of potassium (K+) adapted rats.

Secondary hyperaldosteronism enhances the rate of K secretion in distal colon, at least in part, through the stimulation of Na(+)-K(+)-Cl- cotransport across the basolateral membrane. To maintain a constant intracellular Cl- activity an increase in Cl- transport out of the cell must be assumed. We explored, under amiloride 10(-4) M and short circuited conditions, conductive pathways for Cl- exit in the distal colon of K(+)-adapted rats by means of a putative Cl- channel blocker, NPPB (5-nitro-2(3-phenyl-propylamino-benzoate. Results prior to NPPB showed an increase in JClms after K+ loading from 5.84 +/- 0.66 to 8.33 +/- 0.86 and JClsm from 4.77 +/- 0.55 to 8.16 +/- 0.96 microEq h-1 cm-2 (P < 0.001), when compared with controls. Net fluxes were not different between groups. Luminal NPPB in K+ adaptation resulted in a decrease of JClsm, from 7.85 +/- 1.5 to 6.69 +/- 1.5 microEq h-1 cm-2 (P < 0.05). There were no changes in both unidirectional Cl- fluxes in controls under luminal NPPB and in potential difference (V) and short-circuit current (Isc) under any condition. Finally, K+ adaptation resulted in an increase of luminal cyclic AMP (cAMP) concentration (0.09 +/- 0.02 to 0.20 +/- 0.03 pmol 100 microliters -1, P < 0.005), when compared with control rats. The data may suggest a transcellular recycling of Cl- and an activated NPPB inhibitable serosal to mucosal Cl- pathway on luminal membrane in the K+ adapted state, possibly mediated by an increase in cAMP production.

Adaptation, Physiological↗
PubMed1992

Characterization of fibronectin as a marker for human epididymal sperm maturation.

Fertilization involves adhesive interactions between gametes similar to those mediated by fibronectin (FN) in other cellular systems. Fibronectin has been found on the equatorial segment of ejaculated human serum. As sperm capacity to interact with the oocyte is acquired during epididymal transit, the possible participation of FN in human sperm maturation was studied. The presence of FN in both epididymal sperm and fluid was demonstrated by the detection of a major component of 220 kD in immunoblot studies using anti-FN antisera. The concentration of FN in soluble tissue extracts of epididymis was determined by enzyme-linked immunosorbent assay (ELISA). A gradual increase along the length of the organ, averaging 12-fold from proximal caput to distal corpus, was detected. Immunocytochemistry assays indicated that the number of spermatozoa with immunoreactive FN over the equatorial segment increased from 18% in caput to 64% in distal corpus epididymis. Immunoprecipitation of medium from epididymal explants culture with anti-FN antiserum demonstrated the de novo synthesis of FN in vitro. The greater number of FN-positive sperm coincident with FN accumulation in distal regions of the epididymis supports the role of FN in sperm maturation.

Biomarkers↗
PubMed1990

Bicarbonate dependence of cAMP accumulation induced by phorbol esters in hamster spermatozoa.

Phorbol esters stimulate cyclic adenosine 3',5'-monophosphate (cAMP) accumulation in hamster spermatozoa under conditions for in vitro capacitation. The 20-50-fold elevation of cAMP levels induced by 1 microM phorbol 12-myristate 13-acetate (PMA) in spermatozoa depends on the presence of sodium bicarbonate in the medium (ED50: 15 mM) and it is independent of extracellular pH. Sodium bicarbonate stimulates adenylate cyclase activity in membrane preparations by 4-fold (ED50: 40 mM). After solubilization, the bicarbonate-sensitive moiety elutes as a single peak of 55 kDa in a gel filtration column. Blockers of bicarbonate chloride antiporters diisothiocyanate stilbene 2,2'-disulfonic acid (DIDS) or acetamido 4'-isothiocyanate stilbene 2,2'-disulfonic acid (SITS) inhibit the bicarbonate dependent PMA effect on cAMP in living spermatozoa (ED50: 100 microM). Maximal (85%) inhibition in cAMP accumulation is observed at 1 mM. Motility is inhibited only at high concentrations of the blockers. Pretreatment of living cells with 1 mM DIDS does not affect membrane adenylate cyclase activity which remains responsive to bicarbonate. These results suggest that controlled transport of bicarbonate through the sperm plasma membrane could be associated to the regulation of cAMP synthesis.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1987

Studies on the mechanism of the antiandrogenic effect of a putative 5 alpha-reductase inhibitor.

The mechanism of the antiandrogenic effect of 5,10-seco-19-norpregnane-4,5-diene-3,10,20-trione (secosteroid), reputedly an irreversible inhibitor of 5 alpha-reductase, was investigated. Its addition (10 microM) to culture media effectively suppressed the synthesis of rat epididymal proteins specifically induced by 0.1 microM testosterone (T) or dihydrotestosterone (DHT). Under the same conditions, secosteroid did not change the rate at which labeled T was metabolized to 5 alpha-reduced compounds. In a comparative study, secosteroid inhibited 5 alpha-reductase in an isolated microsomal fraction while not affecting the enzyme activity in minced tissue. Secosteroid was shown to be a competitor of the binding of [3H]T and [3H]DHT (both at 4 nM) to the epididymal cytosol androgen receptor, with ID50 of 1 microM for the former and 4 microM for the latter, thus explaining the mechanism involved in its antiandrogenic properties.

5-alpha Reductase Inhibitors↗
PubMed1984

Androgen dependence of protein N-glycosylation in rat epididymis.

The rat epididymis is known to produce and secrete glycoproteins which interact with spermatozoa during the maturation process. The synthesis of the protein core of these compounds is dependent on androgenic stimulation. As a consequence, we studied the possible androgenic control of the N-glycosylation process dependent on the dolichol (Dol) pathway. Glucosyl and mannosyl transferase activities in rat epididymal microsomes decreased by approximately 76% after only 2 days of castration with respect to intact controls. Depleted mannosyl transferase activity could be restored to control values by administration of 100 micrograms/day testosterone propionate (TP) for 4 days. The effect of 20 micrograms/day TP was blocked by the simultaneous administration of 500 micrograms/day of the antiandrogen cyproterone acetate. The addition of excess dolichyl phosphate (12 times the Michaelis-Menten constant (Km) value) to the incubation mixture did not eliminate the difference in mannosyltransferase activity between epididymal microsomes from castrated rats and these from control or testosterone-treated animals. Moreover, the endogenous pool of dolichyl phosphate was found unchanged in the different hormonal situations. Finally, the incorporation of [14C]mannose into lipid-bound oligosaccharides and into glycoproteins was decreased by approximately 60% as a result of castration and reinduced to control values by treatment with TP (50 micrograms/day for 4 days). The results demonstrate the androgen dependence of the initial steps of N-glycosylation in the rat epididymis and suggest that the hormonal regulation is exerted at the level of Dol-nucleotide sugar transferases, rather than upon the size of the endogenous Dol phosphate pool.

Androgen Antagonists↗