Activation of the renin-angiotensin-aldosterone system in mares around ovulation

Abstract

Satué K., Montesinos P., Muños A. (2017): Activation of the renin-angiotensin-aldosterone system in mares around ovulation. Czech J. Anim. Sci., 62,[259][260][261][262][263][264][265][266][267] Many physiological events occurring during the estrous cycle, including folliculogenesis, oocyte maturation, ovulation, follicular atresia, corpus luteum development, luteolysis, steroidogenesis, and angiogenesis are associated with an increased expression of the renin-angiotensin-aldosterone system (RAAS) in uterus and ovarian follicles. This enhanced expression leads to a rise in plasma concentrations of these hormones in women and laboratory animals, and the same might happen in the mare. This study aims to assess if an activation of the RAAS occurs in mares around ovulation and if this activation is related to the diameter of the predominant follicle (DPF), packed cell volume (PCV), and electrolyte concentrations. Twenty-five healthy Spanish Purebred mares were sampled during the five days before ovulation, the day of ovulation, and the first five days after ovulation. Renin (REN) concentrations increased progressively during the five days before ovulation, achieving the highest values on the day of ovulation. Angiotensin (ANG) concentrations showed a sharp decrease after ovulation, with the lowest values the fifth day after it. Aldosterone (ALD) concentrations increased progressively, from the fifth day before ovulation until the fifth day after ovulation. The highest PCV values were found on the day of ovulation. There were no relevant correlations between the RAAS components and electrolytes concentrations. Before ovulation, there was a positive relationship between REN and ALD (r = 0.760) and after ovulation, a negative correlation between ANG and ALD (r = -0.660). The DPF was correlated with REN (r = 0.740) and with ALD (r = 0.800) concentrations. Ovulation in the mare is associated with high plasma REN concentrations, and therefore, with an activation of the RAAS. In addition, after ovulation, the sharp decrease in plasma REN and ANG concentrations might be a reflex of the modulation of the previously activated RAAS, although plasma ALD concentrations increased during this period.

Scientific Evidences Supporting the Activation of the Renin-Angiotensin-Aldosterone System during Estral Cycle and Pregnancy in Mares

“…The increase in plasma renin before ovulation in other species, as has been previously attributed to the release of LH or to the stimulating effect of human chorionic gonadotropin (hCG) [24]. Another plausible explanation for this rise in plasma renin before ovulation was the increase in E2 concentrations, since a positive correlation between both variables has been found in mares (r = 0.744) [62] (Figure 3). These results in mares agree with the data provided by Sealy et al [15] in women with ovarian stimulation, in whom significant simultaneous increases in renin and E2 were detected.…”

“…A progressive increase in plasma renin concentrations was found before ovulation, peaking at the day of the ovulation [62] (Figure 2). The increase in plasma renin before ovulation in other species, as has been previously attributed to the release of LH or to the stimulating effect of human chorionic gonadotropin (hCG) [24].…”

“…Plasma ANG-II concentrations did not show significant variations before ovulation, but it experienced a sharp and progressive decrease after ovulation [62] (Figure 4). On the contrary, significant increases in ANG-II have been previously observed in sows [11] and in rats [29] before ovulation.…”

“…Another explanation for the rise in renin concentrations in the mares could be a mild hypovolemia associated with the presence of interstitial fluid in abdominal cavity during ovulation. Even though changes in Na and Cl concentrations at the renal juxtaglomerular apparatus significantly influence the release of renin [63], the correlations between renin and these electrolytes appear to be low in mares before ovulation [62]. In the same way, Roussel et al [64] described cyclic patterns of plasma Na and aldosterone concentrations in cow, but without significant correlations with the components of the RAAS.…”

“…In broodmares, Satué et al [62] evaluated the changes in circulating RAAS components around ovulation, considering the 5 days before ovulation (from day 5 to day 1), the day of the ovulation (day 0), and the 5 days immediately after ovulation (from day 1 to day 5). A summary of the main endocrine changes, including those of the RAAS, is presented in Figure 1.…”