Melatonin deprival modifies follicular and corpus luteal growth dynamics in a sheep model

Abstract

This study assessed the effect of melatonin deprival on ovarian status and function in sheep. Experimental procedures were carried out within two consecutive breeding seasons. Animals were divided into two groups: pinealectomised (nZ6) and sham-operated (nZ6). The completeness of the pineal gland removal was confirmed by the plasma concentration of melatonin. Ovarian status was monitored by ovarian ultrasonography for 1 year to study reproductive seasonality. Follicular and corpus luteal growth dynamics were assessed during an induced oestrous cycle. As the effects of melatonin on the ovary may also be mediated by its antioxidant properties, plasma Trolox equivalent antioxidant capacity (TEAC) was determined monthly for 1 year. Pinealectomy significantly extended the breeding season (310G24.7 vs 217.5G24.7 days in controls; P!0.05). Both pinealectomised and sham-operated ewes showed a well-defined wave-like pattern of follicle dynamics; however, melatonin deficiency caused fewer waves during the oestrous cycle (4.3G0.2 vs 5.2G0.2; P!0.05), because waves were 1 day longer when compared with the controls (7.2G0.3 vs 6.1G0.3; P!0.05). The mean area of the corpora lutea (105.4G5.9 vs 65.4G5.9 mm 2 ; P!0.05) and plasma progesterone levels (7.1G0.7 vs 4.9G0.6 ng/ml; P!0.05) were significantly higher in sham-operated ewes compared with pinealectomised ewes. In addition, TEAC values were significantly lower in pinealectomised ewes compared with control ones. These data suggest that melatonin, besides exerting its well-known role in the synchronisation of seasonal reproductive fluctuations, influences the growth pattern of the follicles and the steroidogenic capacity of the corpus luteum. Free Italian abstractAn Italian translation of this abstract is freely available at

Characterization of the LH peak after short and long fixed‐time artificial insemination protocols in sheep raised in the tropics

“…In Santa Inês sheep, raised in Brazil, melatonin nocturnal plasma concentration is higher in the autumn/winter than spring/summer (Coelho et al., ). Recent studies have provided strong evidence of the direct actions of melatonin on the ovaries in the corpus luteum, maintaining the production of progesterone (Taketani et al., ), and in the follicle, altering the pattern of follicular growth waves (Barros et al., ; Berlinguer et al., ; Maganhin et al., ; Manca et al., ).…”

“…In Santa Inês sheep, raised in Brazil, melatonin nocturnal plasma concentration is higher in the autumn/winter than spring/summer (Coelho et al, 2006). Recent studies have provided strong evidence of the direct actions of melatonin on the ovaries in the corpus luteum, maintaining the production of progesterone (Taketani et al, 2011), and in the follicle, altering the pattern of follicular growth waves (Barros et al, 2013;Berlinguer et al, 2009;Maganhin et al, 2013;Manca et al, 2014). Gillan et al (1997) demonstrated that the best pregnancy indices are obtained by depositing the semen at the location and moment nearest to ovulation using a laparoscope since frozen semen has low viability in the female reproductive tract, surviving for approximately 6 hr after insemination (Gillan et al, 1997;Salamon & Maxwell, 1995;Watson, 2000).…”

Ovarian tissue culture in the presence of VEGF and fetuin stimulates follicle growth and steroidogenesis

“…The extension of discoloration was considered an index of total antioxidant activity of the sample. The TEAC level was calculated using Trolox as a standard (Re et al 1999, Manca et al 2014.…”

Follicular wave emergence in Santa Inês ewes subjected to long-term, progesterone-based estrous synchronization protocols at different times of the year

“…In sheep maintained in temperate climates Thieíry et al (2003), found out that serum P 4 concentrations did not differ between varying day lengths following ovariectomy and CIDR treatment. However, in multiparous Sarda ewes (Italy), melatonin deficiency was associated with fewer emerging follicular waves during the induced estrous cycle, mainly because the average lifespan of all waves was longer in pinealectomized ewes compared with the control animals (Manca et al, 2014). Collectively, these observations may be interpreted to suggest that melatonin, in addition to its well-known effects on the secretion of GnRH, may directly influence the growth pattern of ovarian antral follicles.…”