Effect of the Hormone Prolactin on Photoreceptor Survival

Abstract

Purpose: : The hormone prolactin (PRL) acts as a survival factor for various cell types. The PRL receptor is expressed in retinal photoreceptors, suggesting an action of PRL in these cells. Here, we studied whether an intravitreal injection of PRL or chronic hyperprolactinemia has a neuroprotective effect on photoreceptors that reduces light-induced degeneration.

Methods: : Wistar rats were injected intravitreally with 1 µg of PRL in 2 µl of phosphate-buffered saline or subjected to hyperprolactinemia induced by placing two pituitary grafts under the kidney capsule for 15 days. Animals were then exposed to white light (1200 lux) for 48 hours. Apoptosis and rhodopsin concentration in retinal extracts were determined by cell death detection ELISA and spectrometry, respectively. Flash scotopic electroretinograms (ERG) were recorded to evaluate photoreceptor function.

Results: : The intravitreal injection of PRL modified neither the light-induced apoptosis of photoreceptors, nor the reduction and recovery of the b-wave amplitude of the ERG, performed immediately and 15 days after the light damage, respectively. Also, the recovery of rhodopsin levels was not affected by the acute intraocular exposure to PRL. However, chronic exposure to increased circulating levels of PRL significantly inhibited retinal apoptosis and protected photoreceptor function, preventing the reduction of the b-wave amplitude induced by the light damage.

Conclusions: : Chronic hyperprolactinemia, similar to that measured in rats early in pregnancy or during lactation, protects photoreceptors against light-induced apoptosis and loss of function, whereas an acute intravitreal administration of PRL has no effect. The mechanism(s) underlying the action of circulating PRL is currently under investigation and may contribute to the reported higher b-wave amplitude of the ERG associated with pregnancy.

Keywords: photoreceptors • neuroprotection • growth factors/growth factor receptors