High concentrations of 17β-estradiol attenuate the exercise pressor reflex in male cats

Previously, intravenous injection of 17β-estradiol in decerebrate male cats was found to attenuate central command but not the exercise pressor reflex. This latter finding was surprising because the dorsal horn, the spinal site receiving synaptic input from thin-fiber muscle afferents, is known to contain estrogen receptors. We were prompted, therefore, to reexamine this issue. Instead of injecting 17β-estradiol intravenously, we applied it topically to the L₇ and S₁ spinal cord of male decerebrate cats. We found that topical application (150-200 μl) of 17β-estradiol in concentrations of 0.01, 0.1, and 1 μg/ml had no effect on the exercise pressor reflex, whereas a concentration of 10 μg/ml attenuated the reflex. We conclude that, in male cats, estrogen can only attenuate the exercise pressor reflex in concentrations that exceed the physiological level.