EXERCISE TRAINING-INDUCED CHANGES IN ANTERIOR-PITUITARY GONADOTROPE OF THE FEMALE RAT

Chronic exercise training may alter the hypothalamic-pituitary-ovarian axis by affecting gonadotropin secretion and structural indexes of the anterior pituitary gonadotropes. Young female Harlan Sprague-Dawley rats were randomly assigned to either a 12-wk intensive treadmill-running program (n = 16) or to a sedentary untrained group [untrained-proestrus (UTP), n = 16]. After training for 3 mo, animals were killed on proestrous morning, and individual pituitary glands were enzymatically dispersed into single-cell suspensions. Trained rats maintained either predominantly regular estrous cycles [trained-proestrus (TP), n = 11] or exhibited anestrous vaginal cytology [trained-anestrus (TA), n = 5]. At death, plasma estradiol concentrations for TP (57.4 +/- 6 pg/ml, mean +/- SE) and UTP (54.6 +/- 5 pg/ml) were similar. However, TA had plasma estradiol levels (2.7 +/- 0.2 pg/ml; P < 0.05) reflecting their anestrous status. Basal luteinizing hormone (LH) secretion (20-h static incubation) was significantly reduced in gonadotropes from TA (7.8 +/- 1.1 ng/pooled wells) compared with TP (13.6 +/- 1.6 ng/pooled wells) and UTP (12.6 +/- 1.0 ng/pooled wells). Immunofluorescence LH staining and cytoplasmic granularity were significantly lower within the TA gonadotrope population compared with those of TP and UTP rats. Evidence of impaired basal LH secretion, reduced gonadotrope LH-specific fluorescein content, and reduced gonadotrope cytoplasmic granularity in TA rats suggests that, concomitant with proposed changes in the central neural drive, there are important exercise training-induced alterations of the anterior pituitary gonadotrope that influence rats' estrous cycles and affect their reproductive status.