par Van Cauter, Eve 
;Virasoro, E.;Leclercq, Raoul ;Copinschi, Georges
Référence International Journal of Peptide and Protein Research, 17, 1, page (3-13)
Publication Publié, 1981
;Virasoro, E.;Leclercq, Raoul ;Copinschi, Georges Référence International Journal of Peptide and Protein Research, 17, 1, page (3-13)
Publication Publié, 1981
Article révisé par les pairs
| Résumé : | The 24-hour profile of plasma levels of immunoreactive β-MSH (IR-βMSH), ACTH and cortisol was obtained at 15-min intervals in six normal males in summer and winter. In the radioimmunoassay used, dilution curves of human β-MSH and human β-LPH were not parallel. A seasonal variation in basal pituitary-adrenal secretion, with higher levels in winter than in summer, was demonstrated. A circadian rhythm was found to be significant for ACTH, IR-βMSH and cortisol in all investigations. Whereas ACTH and cortisol patterns were largely concordant in all studies, there was a significant desynchronization of the circadian rhythm of IR-βMSH as compared to ACTH in five cases. Eighty-three percent of the secretory spikes of cortisol but only 68% of the IR-βMSH spikes were concomitant with an ACTH spike. Correlations between maximal levels of conomitant spikes were higher during the quiescent period of pituitary-adrenal secretion (22.00-4.00) for ACTH-cortisol whereas for ACTH-IR-βMSH, highest correlations were found during the active early morning secretory phase (04.00-10.00). For the three plasma constituents studied, longer apparent half-lives were found to occur when the basal level before spiking was already elevated, suggesting that ACTH, β-LPH and cortisol are secreted in bursts superimposed on a continuous basal secretion. Absolute increments of concentration appeared to be relatively independent of the level before spiking. It is suggested that the dissociations between ACTH and IR-βMSH fluctuations in plasma observed here result from in vitro proteolysis of β-LPH. |
