Mercury affects uterine myogenic activity even without producing any apparent toxicity in rats: Involvement of calcium-signaling cascades

Environmental and occupational exposure of metals and female reproductive health

Untainted environment promotes health, but the last few decades experienced steep upsurge in environmental contaminants posing detrimental physiological impact. The responsible factors mainly include the exponential growth of human population, havoc rise in industrialization, poorly planned urbanization, and slapdash environment management. Environmental degradation can increase the likelihood of human exposure to heavy metals, resulting in health consequences such as reproductive problems. As a result, research into metal-induced causes of reproductive impairment at the genetic, epigenetic, and biochemical levels must be strengthened further. These metals impact upon the female reproduction at all strata of its regulation and functions, be it development, maturation, or endocrine functions, and are linked to an increase in the causes of infertility in women. Chronic exposures to the heavy metals may lead to breast cancer, endometriosis, endometrial cancer, menstrual disorders, and spontaneous abortions, as well as pre-term deliveries, stillbirths. For example, endometriosis, endometrial cancer, and spontaneous abortions are all caused by the metalloestrogen cadmium (Cd); lead (Pb) levels over a certain threshold can cause spontaneous abortion and have a teratogenic impact; toxic amounts of mercury (Hg) have an influence on the menstrual cycle, which can lead to infertility. Impact of environmental exposure to heavy metals on female fertility is therefore a well-known fact. Thus, the underlying mechanisms must be explained and periodically updated, given the growing evidence on the influence of increasing environmental heavy metal load on female fertility. The purpose of this review is to give a concise overview of how heavy metal affects female reproductive health.

Myometrial Calcium and Potassium Channels Play a Pivotal Role in Chromium-Induced Relaxation in Rat Uterus: an In Vitro Study

Hexavalent chromium, a well-known environmental toxicant, adversely affects female reproduction and results in abnormal implantation, fetal resorption, and reduction in litter size. Uterine myogenic activity is under control of number of receptors and ion channels, and it regulates fetal-implantation and feto-maternal communication. Despite several known adverse effects of chromium on female reproduction, direct action of chromium on myometrial activity is yet to be understood. In the present study, the effect of in vitro exposure of hexavalent chromium (Cr-VI) on the myogenic activity of isolated myometrial strips of rats was evaluated after mounting the tissue in thermostatically (37 ± 0.5 °C) controlled organ bath under a resting tension of 1 g. Chromium produced concentration-dependent (0.1 nM-0.1 mM) inhibitory effect on myometrial activity. Following pre-treatment of the myometrial strips with glibenclamide (a K_ATP channel blocker) and 4-aminopyridine (a K_v channel blocker), the concentration-response curve (CRC) of chromium was significantly (P < 0.05) shifted towards right with decrease in the maximum relaxant effect. Contractile effects of CaCl₂ and BAY K-8644 (a selective opener of L-type Ca²⁺ channel) were significantly (P < 0.05) attenuated in the presence of chromium. Chromium-induced myometrial relaxation was also significantly (P < 0.05) reduced in the presence of ICI 118,551 (a selective β₂-antagonist) and SR 59230A (a selective β₃-antagonist). These findings evidently suggest that chromium produced relaxant effect on rat myometrium by interfering with Ca²⁺ entry through voltage-dependent Ca²⁺ channels, and by interacting with beta-adrenoceptors (β₂ and β₃) and potassium channels (especially K_ATP and K_v channels). Graphical Abstract Proposed signaling pathway(s) of chromium (VI)-induced myometrial relaxations in rats. K_ATP: ATP-sensitive K⁺ channel; K_V: voltage-dependent K⁺ channel; VDCC: voltage-dependent Ca²⁺ channel; [Ca²⁺]_i: intracellular calcium concentration, stimulatory mechanism, inhibitory mechanism.

Effects of Cadmium, Lead, and Mercury on the Structure and Function of Reproductive Organs

Reproductive organs are essential not only for the life of an individual but also for the survival and development of the species. The response of reproductive organs to toxic substances differs from that of other target organs, and they may serve as an ideal “barometer” for the deleterious effects of environmental pollution on animal and human health. The incidence of infertility, cancers, and associated maladies has increased in the last fifty years or more, while various anthropogenic activities have released into the environment numerous toxic substances, including cadmium, lead, and mercury. Data from epidemiological studies suggested that environmental exposure to cadmium, lead, and mercury may have produced reproductive and developmental toxicity. The present review focused on experimental studies using rats, mice, avian, and rabbits to demonstrate unambiguously effects of cadmium, lead, or mercury on the structure and function of reproductive organs. In addition, relevant human studies are discussed. The experimental studies reviewed have indicated that the testis and ovary are particularly sensitive to cadmium, lead, and mercury because these organs are distinguished by an intense cellular activity, where vital processes of spermatogenesis, oogenesis, and folliculogenesis occur. In ovaries, manifestation of toxicity induced by cadmium, lead, or mercury included decreased follicular growth, occurrence of follicular atresia, degeneration of the corpus luteum, and alterations in cycle. In testes, toxic effects following exposure to cadmium, lead, or mercury included alterations of seminiferous tubules, testicular stroma, and decrease of spermatozoa count, motility and viability, and aberrant spermatozoa morphology.