title: Episodic secretion of ACTH in rats.
abstract: While the circadian rhythm of pituitary adrenocorticotropin (ACTH) secretion has been well characterized, the ultradian rhythm has been less thoroughly investigated. To study the episodic nature of ACTH secretion, unrestrained, unanesthetized rats were bled continuously through indwelling jugular venous cannulae and blood sampled for up to 75 minutes at one-minute intervals beginning at 1100 hr (n=6) or 1730 hr (n=4). Sporadic low-amplitude micropulses were observed at both times of day. In addition, infrequent "superpulses" were observed in the evening. Analysis of pulse parameters revealed a significant (p less than 0.001) difference in pulse amplitude but no difference in pulse frequency of interpeak interval between morning and evening. As with other episodically secreted hormones, the threshold for pulse identification and the sampling interval were found to influence the observed pulse parameters.
mesh_terms: D000204:Activity Cycles; D000324:Adrenocorticotropic Hormone / Q000097:blood / Q000378:metabolism*; D000818:Animals; D002940:Circadian Rhythm; D008297:Male; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
chemical_list: D000324:Adrenocorticotropic Hormone