Progesterone improves functional outcomes after transient focal cerebral ischemia in both aged male and female rats

Progesterone hormone (P4) is a promising agent against strokes because post-ischemic administration of P4 exerts neuroprotective effects in several young and aged animal models of stroke. However, in contrast to a majority of the studies using male animals, female animals remain underrepresented. In addition, we do not know whether the same administration way of P4 is effective in both male and female animals because there are gender different responses to steroid hormones and stroke. In this study, we thus evaluated long-term histological and functional outcomes in the same treatment with P4 in both 18-month old male and age-matched female rats subjected to transient middle cerebral artery occlusion (MCAO). MCAO aged male and female rats were given a subcutaneous injection of P4 (4 mg/kg) 6 h after MCAO followed by once daily for successive 7 days. The post-ischemic administration of P4 significantly improved the impairments of spatial working memory and motor coordination 28-29 days after MCAO in both aged male and age-matched female rats. However, the P4 administration slightly but not significantly reduced infarct sizes 30 days after MCAO in aged female rats, in contrast to significant better histological outcome in P4-treated aged males. On the other hand, these histological and behavioral analyses showed no adverse effects of P4 in aged rats of both sexes. Collectively, our study provides preclinical evidence to prompt further preclinical studies for post-stroke treatment with P4 and the translation of its clinical trials in old stroke patients of both sexes.