THE CONCORDANCE OF PULSATILE ULTRADIAN RELEASE OF ADRENOCORTICOTROPINAND CORTISOL IN MALE RHESUS-MONKEYS

The ultradian release of ACTH and cortisol was investigated in six mal e rhesus monkeys (Macaca mulatta) with an intensive (2-min) blood-samp ling procedure to investigate micropulsatile hormone secretory pattern s. A sensitive and specific immunoradiometric assay was used to measur e plasma ACTH concentrations. An objective pulse detection algorithm ( Cluster) was used to assess the pulsatility of ACTH and cortisol relea se. The temporally coincident release of ACTH and cortisol was also ex amined. Venous blood samples were collected (over <15 s) every 2 min f or 120 min beginning at 1300 h. The number of ACTH peaks (3.2 peaks/h) , interpulse intervals (19 +/- 2.4 min), and pulse amplitudes (9.7 +/- 1.6 pmol/L) in rhesus monkey were similar to corresponding measures o f ACTH release in humans (3.3 peaks/h, 18 +/- 0.8 min, and 4.7 +/- 1.0 pmol/L, respectively). The number of cortisol peaks (2.3 peaks/h), in terpulse interval (26 +/- 8.6 min), and other characteristics of pulsa tile cortisol release were also determined. There was a 32.4% exact co ncordance of ACTH with cortisol peaks (11 of 34; P < 0.001). Fifty-six percent of ACTH peaks (19 of 34) were followed by a cortisol peak wit hin 10 min (P < 0.02). There was a significant correlation between the ACTH and coincident cortisol pulse amplitudes (P < 0.0001). The ampli tudes of ACTH peaks coincident with cortisol peaks at 0 min time lag w ere significantly higher than ACTH peaks not temporally coupled with c ortisol peaks. Our data indicate that 1) high frequency, low amplitude micropulsatile ACTH secretion in rhesus monkeys is very similar to th e high frequency ACTH rhythm in humans; 2) temporally concordant ACTH and cortisol release episodes may be amplitude coupled; and 3) an adeq uate incremental ACTH pulse amplitude may elicit a concurrent cortisol release episode from the adrenal cortex. These data suggest that the rhesus monkey is a potentially useful model for the study of neuroendo crine control of ACTH release.