Grouping of animals
Combinatorial methods were used to group the animals, including searching for behavioral indicators, TRUS observation, the CVM fern pattern and blood E
2 and P
4 levels (
Manasa Varra et al., 2022).
Serum estradiol 17β (E2) and progesterone (P4) concentration in G-I, G-II and G-III animals
Table 1 lists the mean serum E
2 and P
4 concentrations of G-I, G-II and G-III animals. The serum P
4 levels revealed significant differences (p<0.05) between G-I and G-II as well as G-I and G-III, with significantly lower serum P
4 concentration in G-II and G-III compared to G-I. The serum E
2 levels revealed significant differences (p<0.05) between G-I and G-II as well as G-I and G-III with significantly higher serum E
2 concentration in G-II and G-III than in G-I.
Urinary exosome SHBG levels in G-I, G-II and G-III animals
The mean urinary exosome SHBG concentration (ng/ml) in G-I, G-II and G-III animals is shown in Table 2. The results of the urinary exosome SHBG levels when compared between the groups, revealed significant differences (p<0.05) between G-I and G-II as well as G-I and G-III, with significantly higher urinary exosome SHBG concentration in G-I in comparison to G-II and G-III.
The current work aims to determine the amounts of SHBG in the urinary exosomes of buffaloes at the estrus and diestrus phases with the hypothesis of the existence of the physiological role of extracellular vesicular, specifically exosomal SHBG. Additionally, we were curious to see if there were any variations in the concentration of this protein between animals that were and were not showing signs of heat. In the present study, grouping of animals was done as per a combinatorial approach (
Selvam and Archunan, 2017).
As per
Westphal’s (1986) theory, liver produces SHBG, a plasma glycoprotein that binds specifically to testosterone and E
2 with an affinity four to five orders of magnitude stronger than albumin and thereby mediate their circulation in the body
(Wallace et al., 2013). SHBG synthesis in the liver is influenced by E
2 androgens, thyroxine, prolactin and insulin
(Rosner et al., 1984; Lee et al., 1987; Plymate et al., 1988; Chen et al., 2010). Specifically, the thyroid hormones were found to indirectly increase SHBG expression by increasing the hepatic levels of the transcription factor, hepatocyte nuclear factor 4 alpha (HNF4A) in humans
(Selva et al., 2007; Selva and Hammond, 2009).
Liu and Veldhuis, (2019) observed that SHBG secretion by hepatocytes is induced by E
2 and thyroxine, where as it is repressed by insulin and growth hormone-IGF-I.
Ng et al., (2006) postulated that there is ligand-dependent interaction between plasma SHBG and the carboxy-terminal domains of extracellular matrix (ECM)-associated protein namely, fibulin 1D and fibulin 2. Plasma SHBG is also found to facilitate the uptake of E
2 into lymphocytes resulting in enhanced Erk1/2 phosphorylation
(Balogh et al., 2019). The cells of the innate and adaptive immune systems are both identified to be influenced by E
2 (
Blesson, 2011;
Karpuzoglu and Zouali, 2011;
Dragin et al., 2017). El-Banna and Hafez (1972) and
Marinov and Lovell (1967) have proposed that E
2 serum levels are reported to be lowest during the estrus stage of the estrous cycle causing cervical mucus to be secreted in bovines. Accordingly,
Kumar et al., (2021) identified that the serum concentration of E
2 in normal estrus Murrah buffaloes (animals showing signs of heat) was significantly higher when compared to the silent estrus animals (animals not showing signs of heat).
The concentration of SHBG (n mol/L) in cattle at the estrus and mid-diestrus stages was practically identical, according to
Vesanen et al., (1990), with values of 109.5±11.8 and 106.8±16.0 respectively. According to
Wang (2021), the plasma levels of SHBG in young, healthy women of <30 years and ≥30 years to be <14.5 nmol/L and <21.9 nmol/L respectively. Interindividual variations in plasma SHBG levels are also influenced by genetic variances, according to research by
Haiman et al., (2005) and
Xita and Tsatsoulis (2010).
Alminana et al., (2015) and
Esfandyari et al., (2021) suggested that urinary exosomes contain exosomes synthesized and released from different parts of the female reproductive tract, including oviductal epithelium, follicular fluid, endometrium, uterus, cervix and vagina and could act as biomarkers for specific physiological states and/or any deviation from the normal physiological conditions. On the other hand,
Sheikh et al., (2009) and
Ailawadi et al., (2015) proposed that exosomes mediate intercellular communication by direct ligand-receptor interaction, leading to activation of downstream signaling pathways. Further,
Prunotto et al., (2013) identified the presence of SHBG in the urinary exosomes of humans.
Urinary exosomes, which have been linked to intercellular communication, can serve as a source of bio markers for the physiological changes occurring in the female reproductive tract (
Sheikh et al., 2009;
Ailawadi et al., 2015;
Alminana et al., 2015;
Esfandyari et al., 2021), according to research. In the present study, the concentration of urinary exosome SHBG in G-II as well as G-III animals was found to be significantly lower (p<0.05) when compared to G-I animals, the findings of which are negatively correlated to the circulatory levels of E
2. The results of the present study are in contrast to the findings of
Vesanen et al., (1990) who reported the circulatory levels of SHBG at the estrus as well as diestrus stage to be almost similar. Further, it appears that the significantly lower levels of SHBG in urinary exosomes of G-II and G-III animals could be due to lower levels of circulatory SHBG at the estrus stage (
Mousavi and Adlercreutz, 1993;
Hammond, 2002;
Wallen and Hassett 2009), as E
2 needs to exert its action in the female reproductive tract (
Marinov and Lovell 1967;
El-Banna and Hafez, 1972).