MY RESEARCH PROJECT

PI: Orlando Laitano
University of Florida Department of Applied Physiology and Kinesiology 

Exertional heat stroke (EHS), the most severe type of heat related illnesses, remains a major concern for the armed services. There is an important gap in knowledge regarding female-specific physiology in the response to extreme heat stress, which makes the prevention, management, and treatment of EHS currently a “one size fits all” strategy, which may not be accurate or effective. To date, there are no reliable biomarkers to predict EHS susceptibility or severity of organ damage in females.

One of the main biological differences between sexes is the fact that women have a menstrual cycle that is controlled and coordinated through the actions of various hormones, which include the gonadotropins, estrogen, and progesterone.Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are gonadotropins released by the anterior pituitary in response to the gonadotropin releasing hormones (GnRH). In pre-menopausal women, gonadotropins stimulate the ovaries to produce and release estrogens and progesterone. Interestingly, in post-menopausal women, gonadotropins have been associated with excessive cortisol production due to their actions on the adrenal gland (15). Estrogens (17β-estradiol, estrone, and estriol) are steroid hormones produced by the developing follicles of the ovaries. Among the three main forms of estrogens, 17β-estradiol is the most potent form and is the most prominent estrogen in young pre-menopausal women, whereas estrone is a weaker estrogen that is the most prominent estrogen in postmenopausal women, and estriol is associated with pregnancy (11). Because most active-duty females are pre-menopausal, we will focus on the actions of 17 β-estradiol in the proposed preclinical animal experiments for this research proposal. Progesterone, which is also secreted by the ovaries, mainly regulates the condition of the inner lining (endometrium) of the uterus (16). It is well known that these hormones fluctuate throughout the menstrual cycle. However, there is a gap in knowledge regarding the potential role these hormones play in susceptibility to EHS and organ damage severity in females.
 
The central hypothesis is that ovarian hormones can be used as biomarkers to predict susceptibility to EHS and our overarching objectives are to reveal the specific roles of estrogen and progesterone on the thermoregulatory response and exercise tolerance to EHS in female mice.

For OVX procedure, an incision will be made on the skin and muscle layers and both ovaries will be removed by cauterization. For Sham procedures an incision of the skin and muscle layers will be performed, but without removing the ovaries. The same incision will be used for
the placement of telemetric probes. 

OVX mice will receive osmotic pumps containing either 17β-estradiol (1.1 ng/day), or progesterone (250 μg/day), or leuprolide acetate (3.6 μg/day), or sterile saline control.For continuous monitoring of body core temperature and the Alzet Osmotic Pumps for continuous subcutaneous delivery of hormones and drugs. Four weeks after surgeries, mice will be exposed to the EHS model.For the EHS trial, animals are placed in a forced running wheel in an environmental chamber set to 37.5C. Mice are allowed to rest in the wheels to permit chamber to reach target temperature. When the chamber reaches 37.5oC, the EHS protocol starts. Running wheel speed begins at 3.0 m/min and increases 0.5 m/min every ten minutes until it reaches 9.5 m/min, at which point that speed is maintained until loss of consciousness (LOC). Terminal experiments will be performed at early (0.5, 3, 24h) and late recovery (9 days, 14 days, and 30 days) post EHS.