![]() These data support the concept of a selective release of adrenal medullary hormones. The adrenal gland is a compelling target in the study of hypertension because its secretory products, both medullary and cortical, directly influence. The epinephrine component of the medullary secretion was most labile and decreased to a greater degree than norepinephrine in the majority of experiments involving neural blockade. Partial severance of the splanchnic nerve also caused a shift in the norepinephrine-epinephrine ratio. Locally induced "thermal blockade" produced significant variations in the percentage of epinephrine released at a given frequency. The values obtained were 84 ± 2% epinephrine. ![]() A shift favoring the release of epinephrine was noted at a frequency of 20 pulses per second. The HPA axis involves the stimulation of hormone release of adrenocorticotropic hormone (ACTH) from the pituitary by the hypothalamus. Stimulation in the frequency range of 1 to 10 pulses per second discharged an effluent containing 65 ± 2% epinephrine. Maximum catecholamine output was obtained in the frequency range of 15 to 20 pulses per second. The splanchnic nerves of dogs have been stimulated and the effect of stimulation frequency on the composition of the adrenal medullary discharge has been investigated. ![]()
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