Every other month (plasma) and every month (urine) circadian rhythms were documented during the course of 14 months. Annual changes were validated in the 24 h mean of: plasma FSH (annual crest time: February), LH (March), thyroxine (September), cortisol (February), renin activity (April), testosterone (October), urinary 17-hydroxycorticosteroids (March), aldosterone (March), potassium (May) as well as sexual activity (September) [self-recorded daily]. Plasma prolactin did not show an annual variation. In addition, annual changes in the circadian acrophase (crest time location in the 24 h scale) occurred for some of the documented variables: plasma thyroxine, cortisol, renin activity, testosterone, urinary aldosterone and potassium.

Neuropeptides such as vasoactive intestinal peptide, LHRH, or TRH have been found in rat pituitary tissue and could act via paracrine or autocrine actions in this tissue. In this study we investigated whether normal human pituitary tissue and GH-secreting human pituitary adenomas could release somatostatin (SRIH) and GHRH. Fragments from three human pituitaries and dispersed cells from six GH-secreting adenomas (four adenomas were studied for GHRH release and five for SRIH release) were perifused using a Krebs-Ringer culture medium, and the perifusion medium was collected every 2 min (1 mL/fraction for 5 h). GH, GHRH, and SRIH were measured by RIA under basal conditions and in the presence of 10(-6) mol/L TRH or SRIH. Both normal pituitaries and GH-secreting pituitary adenomas released SRIH and GHRH. SRIH release commenced 90-180 min after initiation of the perifusion, at which time GH secretion had decreased significantly. TRH stimulated SRIH release from normal pituitary tissue and inhibited SRIH release from adenoma tissue. GHRH was present at the start of the perifusion, but rapidly disappeared. However, SRIH stimulated GHRH release from normal pituitary tissue, but not from adenoma tissue. Significant amounts of GHRH and SRIH were released during the experiments, suggesting their local synthesis. These results indicate that pituitary cells can release hypothalamic peptides. The liberation of these neuropeptides is regulated, and moreover, their regulation differs between normal and adenomatous pituitaries.

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