# Profile of gonadotropin secretion in male and female rats determined in the tail‐tip blood by ultrasensitive ELISA

## TL;DR

The study uses a non-invasive blood sampling method to track hormone levels in male and female rats, revealing how gonad removal and hormone treatments affect LH and FSH secretion.

## Contribution

The study introduces a less invasive, longitudinal method for measuring gonadotropin secretion in rats using tail-tip blood and ultrasensitive ELISA.

## Key findings

- Orchiectomy increases LH and FSH in males, which is partially reversed by testosterone treatment.
- Estradiol treatment in ovariectomized females reduces LH and FSH secretion towards gonad-intact levels.
- Tail-tip blood sampling with ultrasensitive ELISA provides detailed insights into gonadotropin secretion patterns.

## Abstract

There is a need for accurate and less invasive methods of hormonal measurements. Here, we longitudinally determined luteinizing hormone (LH) and follicle‐stimulating hormone (FSH) secretion measured in the tail‐tip blood of male and female rats by ultrasensitive enzyme‐linked immunosorbent assay (ELISA). In males, the ELISAs detected a significant increase in LH and FSH secretion after orchiectomy compared with the gonad‐intact condition. The subsequent treatment with testosterone in the orchiectomized condition returned LH concentrations to the basal levels, whereas FSH secretion was partially restored to the gonad‐intact levels. During the rat estrous cycle, LH and FSH secretion fluctuated around basal levels on diestrus, and the preovulatory surges of both hormones occurred on the late afternoon of proestrus. On estrus, LH secretion was continually low, while FSH concentrations progressively declined from elevated concentrations in the morning to lower levels in the afternoon. After ovariectomy, secretion of both LH and FSH rose above the basal levels of the estrous cycle. Estradiol treatment in the ovariectomized condition reduced LH and FSH secretion towards gonad‐intact levels in the morning, with a greater effect on FSH. In the afternoon, estradiol treatment prompted a sharp proestrus‐like surge of LH alongside a slower, gradual increase in FSH levels. In the present study, we characterize LH and FSH secretion in rats of both sexes under different hormonal conditions, using longitudinal hormonal measurement in the tail‐tip blood by ultrasensitive ELISA. These findings provide novel methodological and conceptual information about gonadotropin secretion in rats relevant to the knowledge in reproductive endocrinology.