Efeito in vitro da adição do levonorgestrel sobre a concentração intracelular de calcio em espermatozoides de homens ferteis

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The spermatozoa is a highly specialized cell because it contains morfophysiological modifications that guarantees fecundation success. Spermatozoa must undergo three sequential changes before they acquire their fertilizing capacity: maturation in epididymis, capacitation and acrosome reaction (RA). Capacitation is a process that takes place in the female reproductive tract and is defined as a biochemical modification on the spermatozoa plasmatic membrane. The presence of progesterone (P) and the intracellular calcium concentration increase inside the spermatozoa are typical and obligatory events in the capacitation stage for further RA. Levonogestrel (LNG) is a synthetic progestin, similar to P, which has being used as a female contraceptive in several manners, among them they are: emergency contraception (EC), contraceptive pills combine and with the intrauterine system (IUS). Nevertheless, there are no available data or the scientific literature that correlate LNG contraceptive efficacy with possible effects of the hormones over human spermatozoa. Therefore, to add data over the contraceptive action mechanism of LNG, the aim of this study was to evaluate the effect of 5 concentrations of LNG somes comparable to the levels found in serum following ingestion of LNG as EC on the calcium intracellular concentration ([ Ca POT 2+ ]i) rates of capacitated spermatozoa of fertile men. A total of 24 semen samples from 4 fertile men were evaluated. The spermatozoa were selected by Percoll gradient, following incubation with human tubal fluid medium supplemented with bovine serum albumin (HTF/BSA) under capacitating conditions. The sperm suspensions were incubated with Fura2/AM Subsequently the cells were exposed to the following concentration of LNG: 8, 10, 14, 1,000 and 10,000 ng/mL, and two controls (positive and negative). The positive control was P (32 mu M=11,000 ng/ml) and the negative one was medium (HTF). Cells were transferred to a quartz cuvette to make the reading in the spectrofluorometer at 340 nm excitation with emission at 510nm. Fluorescence measurements were converted to [ Ca POT 2+ ]i by the equation of Grynkiewicz et al. (1985). The Grynkiewicz equation shown that LNG concentration of 8, 10, 14, and 1,000 ng/mL were able to induce increase in the [ Ca POT 2+ ]i with significantly higher values, when compared with the rate obtained with HTF medium ( as a negative control), and significantly lower than the rate obtained with natural P (as a positive control). However, the exception was the LNG concentration of 10,000 ng/mL (32 ?mu M) in which values of [ Ca POT 2+ ]i were similar to those observed with P at a concentration of 11,000 ng/mL (32 mu M). In conclusion, it is possible to suggest that although LNG in vitro, in low concentration, increase the [ Ca POT 2+ ]i in the spermatozoids. Despite the fact that this mechanism is not the only responsible for the RA induction the calcium obtained through high concentration of LNG (10,000 ng/ml) might have a contraceptive action in the spermatozoa

ASSUNTO(S)

levonorgestrel espermatozoides calcium calcio spermatozoa

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