Submitted on June 23, 2008
Revised on February 25, 2009
Accepted on March 4, 2009
Hypoxic and Hypercapnic Ventilatory Responses in Aging Male vs. Aging Female Rats
Julie M. Wenninger1*, E. B. Olson Jr.2, Caitlin Cotter2, Cathy F. Thomas2, and Mary Behan3
1 University of Wisconsin - Madison
2 University of Wisconsin
3 University of Wisconsin, Department of Comparative Biosciences
* To whom correspondence should be addressed. E-mail: wenninger{at}svm.vetmed.wisc.edu.
It is clear that sex hormones impact ventilation. While the effects of the menstrual cycle, pregnancy, testosterone and progesterone on resting ventilation have been well documented, effects of sex hormones on the hypoxic (HVR) and hypercapnic ventilatory responses (HCVR) are inconclusive. In addition, in no study have systemic sex steroid hormone levels been measured. Age and sex differences in long-term facilitation (LTF) in response to episodic hypoxia were found in anesthetized rats. The purpose of the present study was to assess the effects of sex and age [Young (Y), 3-4 mo; middle-age (MA), 12-13 mo; and old, >20 mo] on the HVR and the HCVR of awake rats relative to systemic hormone levels. Based on findings from LTF studies, we hypothesized that the HVR would be influenced by both sex and age. We found no age-related changes in the HVR or HCVR. However, female rats have a greater HVR than male rats at old age, and at middle age female rats have a greater HCVR than male rats. Additionally, we found no correlation between the VE/VO2 and the progesterone to estrogen ratio (P:E) during hypoxia or hypercapnia. However, changes in ventilatory responses with age were not similar between the sexes. Thus, it is critical to take sex, age, estrous cycle stage, and systemic hormone levels into consideration when conducting and reporting studies on respiratory control.
