Endocrine and Electrolyte Balances during Periovulatory Period in Cycling Mares

Abstract

In cycling females, the periovulatory period is characterized by stimulation of the hypothalamic pituitary adrenal (HPA) axis. The aim of present study was to analyze the pattern and interrelationships among adrenocorticotropic hormone (ACTH), cortisol (CORT), aldosterone (ALD) and electrolytes (sodium—Na+, potassium—K+ and chloride—Cl−) during periovulatory period in cycling mares. Venous blood samples were obtained daily from a total of 23 Purebred Spanish broodmares, aged 7.09 ± 2.5 years, from day −5 to day +5 of estrous cycle, considering day 0, the day of ovulation. Plasma ACTH was measured by a fluorescent immunoassay kit, serum CORT and ALD by means of a competitive ELISA immunoassay, and plasma Na+, K+ and Cl− were quantified by an analyzer with selective electrodes for the three ions. ACTH showed higher concentrations at day 0 compared to days −5 to −1 and +1 to +3 (p < 0.05). CORT showed higher concentrations at day 0 compared to days −5 to −2 and +1 to +5 (p < 0.05). ALD showed higher concentrations at day 0 compared to days −5 to −2 (p < 0.05) and +2 (p < 0.05). Na+ and Cl− showed higher concentrations at day 0, compared to day −5 and +5. K+ showed lower concentrations at day 0 compared to day +1 (p < 0.05). The significant correlations obtained between ACTH and CORT (r = 0.20) and between ACTH and ALD (r = 0.32) suggest that although ACTH may have an effect both on CORT and ALD, there are other very important determinants that could be considered. Hence, it is possible to presume that the pituitary adrenocortical response and ALD may be involved in the ovulatory mechanisms without a direct relation with electrolyte pattern.

Reproductive Consequences of Electrolyte Disturbances in Domestic Animals

“…There is a correlation between sodium, potassium, and chloride levels and progesterone levels, as well as between estradiol and Cl − . According to Satué et al (2021) [54], ovarian steroid hormones influence the excretion of mares. At the highest concentration of estrogen, loss of Na + is observed, while at the beginning of the luteal phase in sheep, sodium reabsorption is observed, which is associated with the secretion of progesterone and aldosterone.…”

“…A correlation of Cl − with progesterone concentrations has also been demonstrated in mares and women [ 54 ]. In the research conducted by Satué et al (2021) [ 54 ] in healthy mares aged about seven years, it was shown that the highest concentration of sodium and chloride were recorded during ovulation (day zero) compared to the pre- and post-ovulation period. The concentration of Na + was 142.2 ± 3.28 nmol/L and for Cl − : 107.4 ± 1.44 nmol/L.…”

“…The concentration of Na + was 142.2 ± 3.28 nmol/L and for Cl − : 107.4 ± 1.44 nmol/L. In turn, the highest potassium concentration was recorded the day after ovulation—4.51 ± 0.57 nmol/L [ 54 ]. In cows, a correlation of Cl − was obtained with the diameter of the estrogen follicle and the concentration in the buffaloes [ 55 ].…”

“…Ca 2+ and Na + play an important role in the production of lipid hormones in developing follicles and regulate the secretion of the breeding hormones necessary for ovaries and ovulation [ 54 ]. Calcium is an important electrolyte in reproduction.…”

The Adrenal Cortisol Response to Increasing Ambient Temperature in Polar Bears (Ursus maritimus)

“…Activation of the HPG axis has been shown to have a significant impact on adrenal function in a variety of mammalian species. Adrenal cortisol release increases during estrous behaviour and/or ovulation in domestic species [34,35] and humans [36] and seasonal reproductive activity has been shown to be associated with an increase in adrenal cortisol output in koalas [37] and monkeys [26]. Given that 55% of the FCM observations during the breeding season of February to April were associated with temperatures ≤5 • C, the interaction of breeding season on temperature-associated changes in FCM concentrations is not surprising (Figure 4).…”