BERKELEY, CA (UroToday.com) - Nicotine is one of the most widely consumed legal drugs worldwide. According to the World Health Organization, one-third of the world population smokes, and 10.4% of pregnant women report smoking during pregnancy in the United States. Fertility rates reduction can occur in both men and women as a consequence of nicotine intake. This reduction is likely due to alterations in the sexual hormone synthesis caused by steroid aromatization inhibition. However, the data concerning the effects of cigarette smoking and nicotine on testosterone levels are conflicting. There are several studies showing that nicotine reduces testosterone levels;[7, 8, 9] on the other hand, some other reports show that it actually increases testosterone levels.[10, 11, 12]
Cigarette consumption can also be associated with a decrease in the synthesis of HDL cholesterol, the substrate of steroid sexual hormones. In vitro studies suggest that the production of sexual hormones is indirectly altered if the Leydig cells (LC), which are responsible for the synthesis of testosterone, undergo apoptosis induced by nicotine. In addition to its fundamental role in sexual behaviour, testosterone also plays a key role in either the development of the male genital system or the maintenance of spermatogenesis. Thus, alterations in testosterone levels could lead to testicular damage and cause erectile and gonadal dysfunctions, as well as male infertility.
The function and maintenance of LC, including steroidogenesis control, are influenced by macrophages (MO) present in the testicular interstitial tissue. Thus, alterations in the LC and in testosterone synthesis could involve the participation of testicular MO, since these cells contain the 25-hydroxylase enzyme that converts cholesterol in 25-HC, an important mediator involved in the interaction between MO and LC.
It has been shown that nicotine causes damage to the reproductive health of male offspring of smoking mothers seeing that it crosses the placental membrane and is present in breast milk of smoking mothers. However, data regarding the exposition to nicotine during the intrauterine and early postnatal life and its possible harmful action on LC and testicular MO populations are scarce. In rats, the morphological differentiation of fetal LC begins from 15 to 16.5 days post coitum (dpc), concomitantly with the testis cord development;[14, 21] its number increases until 19 dpc but it is minimal at 14-days post partum (dpp), when the first type of adult Leydig cell is observed Besides, rat testicular MO can be found at 19 dpc, whereas, in the human testis, they are only observed from the 7th week of pregnancy on.
Thus, in order to investigate whether nicotine administration to pregnant and lactating rats changes cholesterol and sexual hormone levels and LC and MO populations of offspring, female rats received nicotine (2mg/Kg/day) through osmotic minipumps from the first day of pregnancy up to the end of weaning, in order to simulate the usual exposure of pregnant and lactating smoking women. At 1, 30, 60 and 90 dpp, male offspring were anaesthetized and had their plasma cholesterol and testosterone levels obtained as well as the biometric, histopathological, and stereological testicular parameters.
We observed that nicotine reduced the body weight, cholesterol levels, and lipid droplet number in fetal LC in newborn rats from nicotine-exposed mothers. However, significant alterations in the plasma testosterone levels were not observed in these rats. The alteration in the lipid droplet distribution in the cytoplasm of the fetal LC could be related to the reduction of body weight, since this reduction is a consequence of a general lipid and cholesterol decrease induced by nicotine. This alteration could also be related to possible changes in the metabolism of cholesterol, since the lipid droplets are a source of cholesterol.
On the other hand, increased plasma cholesterol and testosterone levels were observed in the 90 dpp exposed-rats, besides hypertrophy of mature Leydig cells, suggesting that nicotine exposure in the weaning phase leads to important late alterations in hormone levels and Leydig cell function. It has been shown that smokers and ex-smokers generally display increased plasma testosterone levels.[11, 12] An increase of HDL cholesterol and an important gain in body weight in ex-smokers were also referred to by Campbell et al.
The mild alterations in the prepubertal (30dpp) and pubertal (60dpp) exposed-rats suggest that, under the protocol of nicotine administration used in this study, the negative nicotine effects are bypassed during testis postnatal development but appear again in adulthood, so it is possible that the effects of nicotine are dependent on the maturation of LC, which is reached around 56dpp and/or on the hormone levels of the adult phase. In addiction, in spite of the presence of apparently degenerated LC, no significant changes were observed in the adult LC numerical density or in their apoptotic rate. No alterations in the numerical densities of MO happened either. Nevertheless, Kim et al. showed that LC death depends on the dose of nicotine in vitro; thus, it is possible that the dose used in the present study was not high enough to induce substantial LC death.
The presence of MO inside the seminiferous cords of 1dpp exposed-rats suggests an important negative effect of nicotine on seminiferous cord development. The MO presence in the seminiferous tubule has been described in association with different pathological conditions such as germ cell arrest, Sertoli-only syndrome, and even in idiopathic infertility with normal spermatogenesis. Thus, it is possible that intrauterine nicotine administration can lead to future damage to spermatogenesis. Indeed, it has been shown that exposure to prenatal smoking leads to low sperm counts.
In conclusion, this study indicates that nicotine crosses the placental membrane and is excreted in the breast milk, reaching offspring blood and leading to age-dependent morphofuctional alteration of Leydig cells, of MO distribution in neonates, as well as of cholesterol and testosterone levels. These alterations, especially the late ones, point to the possibility of spermatogenic and seminal parameters alterations after exposure to moderate nicotine doses during pregnancy and lactation. This hypothesis is under investigation.
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C.C. Paccola, F. M. O. Neves, I. Ciprianoa, T. Stumppa, and S.M. Miragliaa as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
Laboratory of Developmental Biology, Department of Morphology and Genetics, Federal University of Sao Paulo, Sao Paulo, Brazil