Exercise training and the differential prolactin response in male and female rats

Abstract

Adult male and female Sprague-Dawley rats were trained on a horizontal treadmill for 0, 1, 3, 5, or 7 days/wk for 10 wk. Speed and duration were progressively increased over 5 wk to a maximum of 20 m/min for 1 h. Between weeks 9 and 10 of training, animals were placed on the nonmoving treadmill, and blood (500 microliters) was sampled via chronic venous cannulas 30 min before, 0, 10, 20, 30, 45, and 60 min during exercise, and 15, 30, 60, 90, and 120 min after exercise. In another study, resting animals in the various groups were injected with thyrotropin-releasing hormone (TRH; 2 micrograms/kg for males and 0.4 microgram/kg for females) to determine pituitary prolactin responsiveness. In males, exercise induced a significant increase in plasma prolactin levels, with the greatest increase observed in the least trained and the smallest increase in the most highly trained animals. Female rats displayed the opposite trend with the greatest increase in prolactin secretion observed in the highest trained and the smallest increase observed in the least trained animals. TRH induced similar increases in plasma prolactin in all male groups, whereas TRH-induced prolactin release was greatest in the highest trained and smallest in the least trained females. The reduced prolactin response in highly trained males may reflect their acclimation to repetitive exercise stress, whereas the enhanced response in the highly trained female rats appears to result from increased pituitary sensitivity to prolactin-releasing factors.

Prolactin promotes oxytocin and vasopressin release by activating neuronal nitric oxide synthase in the supraoptic and paraventricular nuclei

“…The current study suggests that the three hormones are also functionally linked in males. The magnitude of the increase in circulating PRL (50 ng/ml) employed by the study is equivalent to PRL values reported in male rats at circadian peaks (17) or in response to stress (31,62). The functional implication of the interaction among the three hormones in males remains to be determined, but we hypothesize that this neuroendocrine mechanism operates to regulate stress responses, sodium and water balance, and sexual activity, which are processes where the overlapping release and effects of the three hormones have been described.…”

Effect of forced exercise and exercise withdrawal on memory, serum and hippocampal corticosterone levels in rats

“…Moreover, the effect of chronic exercise on the glucocorticoid response is not fully clear. Different studies have reported decrease (Viru et al 1994), no change (Dellwo and Beauchene 1990) and increase (Tharp 1975;Sylvester et al 1989;Liu et al 2009) in the glucocorticoid response after physical activity. These differences are most probably related to the intensity, duration and type of exercise (e.g., forced vs. voluntary), task difficulty, gender and other yet undefined variables.…”

RU486 blocks the anti-inflammatory effects of exercise in a murine model of allergen-induced pulmonary inflammation

“…Several reports suggest that a single, acute bout of exercise increases circulating levels of GCs (Coleman et al, 1998;Deschenes et al, 1991;Girard and Garland, 2002;Tharp, 1975); however, the effects of prolonged exercise training on endogenous GC levels are much less clear. For example, previous studies that have examined the effects of exercise training on changes in circulating GC levels have reported increases (Sylvester et al, 1989;Tharp and Buuck, 1974), decreases (Viru et al, 1994), or no change (Borer et al, 1992;Dellwo and Beauchene, 1990) in these levels. The conflicting data are most likely the result of differences in exercise parameters (i.e., intensity, frequency, duration, and type), subject fitness level (i.e., trained versus untrained), blood sample timing (i.e., in relation to the diurnal variation of GC production; in rodents, circulating GC levels are lower in the morning hours and higher in the early evening hours), and sacrifice method (Shipp and Woodward, 1998).…”