Comparison of the microheterogeneity of horse LH and FSH in the pituitary with that secreted into pituitary venous blood at oestrus.

The research paper examines the microheterogeneity or the variation in structure and composition of two hormones, Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH), in horses during oestrus or heat. The study reveals differences in the pH levels and form of these hormones when secreted versus when stored in the pituitary gland.

Research Methodology and Findings

• The researchers used aqueous extracts of pituitary glands from mares in heat to study the profile of LH. After using techniques like chromatofocussing (CF) and isoelectricfocussing (IEF), it was found the LH profiles were similar and matched with previous studies.
• Both LH and FSH in pituitary extracts were found to focus in multiple peaks in the acidic pH range, with 86% of LH and 80% of FSH being found between pH 4 to 6, following the CF technique.
• A contrasting behavior was noted when analyzing pituitary venous plasma – only 18% of LH was found to focus within the same pH range. A significantly higher proportion of LH eluted above pH 7 in pituitary venous plasma, compared to pituitary extracts (37% vs 2%, respectively).
• For pituitary venous FSH, only a slight shift was noted in the distribution of isoforms (varieties) compared to the pituitary extract. There was an increase in the percentage of strongly acidic molecules in pituitary venous plasma (pH less than 3.65; 34% vs 16%).

Key Takeaways and Hypotheses

• These results suggest that during heat, horse LH (which differs from that of other species due to its heavily sialylated C-terminal extension to the beta-subunit, similar to eCG), behaves more alkaline when secreted as opposed to when stored in the pituitary.
• The researchers propose that this modification is made after the hormone enters a preferentially released pool of LH.
• They also suggest that the modulation of the forms of LH and FSH that are secreted might play a role in controlling the responses of the target tissue. This conclusion indicates a possibility of hormonal regulation at the molecular level, potentially influencing reproduction in horses.