# Alteration of pituitary and hypothalamic membrane fluidity as a non-specific mode-of-action for reproductive effects with octamethylcyclotetrasiloxane

## TL;DR

This study shows that D4 affects reproduction by altering membrane fluidity in the hypothalamus and pituitary, not by endocrine disruption.

## Contribution

The study demonstrates a non-specific mode of action for D4's reproductive effects through membrane fluidity changes.

## Key findings

- D4 increases membrane microviscosity in a concentration-dependent manner.
- Altered membrane fluidity reduces the release of GnRH and kisspeptin, affecting the LH surge.
- The effect is non-specific and not targeted to any neuro-endocrine component.

## Abstract

Octamethylcyclotetrasiloxane (D4) is a highly volatile cyclic siloxane used to produce silicone polymers. D4 has been shown to attenuate the LH surge in rats, resulting in reduced litter sizes. However, it has been hypothesized that these biological effects observed only at high dose levels of D4 may be because of changes in membrane microviscosity (fluidity) leading to a non-specific mode of action. Here, we set out to determine if D4 increases membrane microviscosity and link this to membrane domain function alterations. The studies reported here support the hypothesis that D4 affects ovulation via a concentration-dependent, physical-chemical mode of action that is not specific for any particular component of the neuro-endocrine system and is, therefore, not endocrine disruption but a non-specific effect. Furthermore, D4 also increases the membrane fluidity of the hypothalamic cell membrane in vitro. It is expected that a similar response would occur in vivo. This alteration in membrane fluidity decreases the release of GnRH and kisspeptin. GnRH and kisspeptin are necessary for the pre-ovulatory LH surge from the pituitary. In the absence of a GnRH and kisspeptin release, there is no signal to the pituitary for the driver of the LH surge. D4 can change membrane fluidity in vitro and likely in vivo and associated behaviors of membrane proteins/lipoproteins of various kinds via non-specific mechanisms.