Abstract
Superior cervical ganglionectomy (SCGx) has drastic effects on numerous hormonal circadian rhythms and particularly on pineal melatonin secretion. We investigated the hormonal consequences of ablation of the superior cervical ganglion on the corticotropic circadian rhythms in the male rat. Plasma were obtained by sampling blood every 4 h, using a chronic carotid cannula. Adreno-corticotropin hormone (ACTH) was assayed by radioimmunoassay (RIA) and corticosterone (B) by radiocompetition. Urinary 6-sulphatoxymelatonin (aMT6s), considered as an index of the pineal gland activity, was assayed by specific RIA: a decrease in the aMT6s concentration after ganglionectomy was taken as proof of adequate surgical operation. Control animals showed classical circadian rhythms for ACTH and B with basal values during the light phase and circadian peaks around the light/dark interface. Five and ten days after ganglionectomy, the circadian rhythms of ACTH and B were suppressed. In addition, the mean ACTH concentrations increased significantly 10 days after ganglionectomy compared to those in sham-operated rats and 5 days post-operation group. The mean plasma corticosterone levels were similar in those three groups of animals. This is the first study demonstrating the suppressive effect of superior cervical ganglionectomy on the circadian corticotropic hormonal cycle.