Reproductive loss in high-producing dairy cattle: where will it end?

https://digitalcommons.chapman.edu/cgi/viewcontent.cgi?article=1381&context=pharmacy_articles

Melatonin membrane receptors in peripheral tissues: distribution and functions.

The discovery of melatonin and its derivatives as antioxidants has stimulated a very large number of studies which have, virtually uniformly, documented the ability of these molecules to detoxify harmful reactants and reduce molecular damage. These observations have clear clinical implications given that numerous age-related diseases in humans have an important free radical component. Moreover, a major theory to explain the processes of aging invokes radicals and their derivatives as causative agents. These conditions, coupled with the loss of melatonin as organisms age, suggest that some diseases and some aspects of aging may be aggravated by the diminished melatonin levels in advanced age. Another corollary of this is that the administration of melatonin, which has an uncommonly low toxicity profile, could theoretically defer the progression of some diseases and possibly forestall signs of aging. Certainly, research in the next decade will help to define the role of melatonin in age-related diseases and in determining successful aging. While increasing life span will not necessarily be a goal of these investigative efforts, improving health and the quality of life in the aged should be an aim of this research.

Reducing oxidative/nitrosative stress: a newly-discovered genre for melatonin.

https://www.fertstert.org/article/S0015-0282(08)01130-8/pdf

Melatonin and the ovary: physiological and pathophysiological implications

This brief review summarizes new findings related to the reported beneficial effects of melatonin on reproductive physiology beyond its now well-known role in determining the sexual status in both long-day and short-day seasonally breeding mammals. Of particular note are those reproductive processes that have been shown to benefit from the ability of melatonin to function in the reduction of oxidative stress. In the few species that have been tested, brightly colored secondary sexual characteristics that serve as a sexual attractant reportedly are enhanced by melatonin administration. This is of potential importance inasmuch as the brightness of ornamental pigmentation is also associated with animals that are of the highest genetic quality. Free radical damage is commonplace during pregnancy and has negative effects on the mother, placenta, and fetus. Because of its ability to readily pass through the placenta, melatonin easily protects the fetus from oxidative damage, as well as the maternal tissues and placenta. Examples of conditions in which oxidative and nitrosative stress can be extensive during pregnancy include preeclampsia and damage resulting from anoxia or hypoxia that is followed by reflow of oxygenated blood into the tissue. Given the uncommonly low toxicity of melatonin, clinical trials are warranted to document the protection by melatonin against pathophysiological states of the reproductive system in which free radical damage is known to occur. Finally, the beneficial effects of melatonin in improving the outcomes of in vitro fertilization and embryo transfer should be further tested and exploited. The information in this article has applicability to human and veterinary medicine.

https://bioone.org/journals/biology-of-reproduction/volume-81/issue-3/biolreprod.108.075655/Melatonin-and-Reproduction-Revisited/10.1095/biolreprod.108.075655.pdf

Melatonin and Reproduction Revisited

Hormonal control of reproduction in small ruminants

Seasonal changes in oestrus activity and ovulation rate in Rasa Aragonesa ewes maintained at two different body condition levels

We recently demonstrated the presence of melatonin in ram seminal plasma and differences in its concentration in this fluid between the breeding and nonbreeding season. In this study, we investigate the hypothesis that in vitro treatment with melatonin affects ram sperm quality, and that this is reflected in the in vitro fertilization (IVF) results. Semen from nine rams was collected during the nonreproductive season and treated with 1 mum, 10 nm and 100 pm melatonin. Samples were incubated at 39 degrees C and 5% CO2, and motility, viability, capacitation status and phosphatidylserine (PS) translocation were assessed before and after melatonin addition, either 1 or 3 hr of incubation. Fertility rate of the melatonin-treated samples was determined by means of IVF. Although melatonin failed to affect both sperm kinematic parameters and viability, the exposure of ram spermatozoa to melatonin has a direct effect, decreasing capacitation and PS translocation at 1 mum, and increasing short-term capacitation at 100 pm, which caused an increased oocyte fertilization rate following IVF. Furthermore, cleavage rate of oocytes fertilized with 100 pm melatonin-treated spermatozoa was higher than that with 1 mum melatonin and control samples (P < 0.1). These results prove that melatonin has a direct effect on ram spermatozoa in the nonreproductive season, which can be explained, at least in part, by the melatonin capacity as a reactive oxygen species scavenger and antioxidant. These findings might help to select the optimal experimental conditions for IVF and to improve sperm preservation protocols.

Melatonin prevents capacitation and apoptotic-like changes of ram spermatozoa and increases fertility rate.

Two experiments were carried out in order to determine whether melatonin can improve secretion of progesterone in vivo, and its effect on embryonic development in vitro. In the first experiment, blood samples were collected from 5 ewes at 15 min intervals for 2 h at 7 and 10 days after withdrawal of progestagen pessaries. The first hour constituted a control period, which ended with an intravenous administration of 3 microg/(kg bw)(0.75) melatonin. All the ewes on day 7 and three of the ewes on day 10 showed a progesterone response to melatonin challenge, defined as an increase in the plasma progesterone concentration in at least two consecutive samples during the post-treatment period above the mean+2SD of the values in the pre-treatment period. A paired t-test revealed a significant effect of melatonin on the overall plasma progesterone concentrations before and after the challenge, both on day 7 (pre, 0.61 +/- 0.11; post, 0.73 +/- 0.13 ng/ml; p<0.01) and day 10 (pre, 1.16 +/- 0.19; post, 1.30 +/- 0.20 ng/ml; p<0.05). Ninety-one thawed embryos (46 morulae and 45 blastocysts) were used in the second experiment, being cultured with or without 1 microg/ml melatonin. If the embryos were blastocysts when the culture started. melatonin increased the percentage that had hatched after 24 h of culture (p<0.01), and there was a lower percentage of degenerated embryos at the end of the incubation period (p<0.05). It may be concluded that melatonin treatment in sheep can increase both fertility and prolificacy by improving luteal function and embryonic survival.

The effect of melatonin on the secretion of progesterone in sheep and on the development of ovine embryos in vitro.

The relationship between nutrition and reproduction in sheep has been the subject of research in several international groups. This review will particularly focus on the effects of under- nutrition on the potential causes of reproductive failure including abnormalities of the ovum or the embryo, luteal inadequacy and failure of the supply of progesterone to the uterus, or the mechanisms involved in maternal recognition of pregnancy. The level of nutrition and peripheral progesterone concentrations are inversely related, and increased rates of embryo loss, associated with higher pro- gesterone concentrations in ewes with low levels of nutrition have been reported. Undernutrition may act through changes in the distribution of progesterone in the endometrium. Thus, lower en- dometrial levels on day 5 of the cycle in ewes fed half of their maintenance requirements have been observed, providing a link between the known role of progesterone in embryo survival by the modu- lation of uterine function and the higher embryo losses found in undernourished ewes. The evidence of an effect of maternal nutrition on IFNτ secretion from the conceptus and of PGF2α production from the uterus is presented. Moreover, undernutrition provokes a reduction in the sensitivity of the endometrium to progesterone that may affect embryo survival. Finally, a state of undernutrition induces changes in the endometrial sensitivity to steroid hormones at early stages of pregnancy that could adversely alter uterine environment to the detriment of embryo survival. sheep / nutrition / reproduction / progesterone / embryo

/pdf/the-effect-of-undernutrition-on-the-establishment-of-4bts7jx5mc.pdf

José-Alfonso Abecia

Papers

Hormonal control of reproduction in small ruminants

Seasonal changes in oestrus activity and ovulation rate in Rasa Aragonesa ewes maintained at two different body condition levels

Melatonin prevents capacitation and apoptotic-like changes of ram spermatozoa and increases fertility rate.

The effect of melatonin on the secretion of progesterone in sheep and on the development of ovine embryos in vitro.

The effect of undernutrition on the establishment of pregnancy in the ewe