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Decreased Serum Somatomedin C Concentrations during Sleep: Temporal Relationship to the Nocturnal Surges of Growth Hormone and Prolactin^*

F. MINUTO, L. E. UNDERWOOD, P. GRIMALDI, R. W. FURLANETTO, J. J. VAN WYK^,|| and G. GIORDANO

Cattedra di Endocrinologia ISMI, Genova, Italy Department of Pediatrics, University of North Carolina Chapel Hill, North Carolina 27514

Address requests for reprints to: Dr. Francesco Minuto, Cattedra di Endocrinologia, ISMI, Viale Benedetto XV 6, 16132 Genova, Italy.

Serum concentrations of immunoreactive so-matomedin C, GH, and PRL were determined on samples obtained from 16 adult subjects throughout the day. Samples were collected by a portable continuous flow, blood withdrawal pump. Somatomedin C concentrations were stable during waking hours [1.13 ± 0.09 U/ml (mean ± SE)] but fell after the onset of sleep o t a minimum value of 0.85 ± 0.08 U/ml. After awakening, the concentration rose progressively to a mean of 1.26 ± 0.10 U/ml between 1100–1200 h. These changes were statistically significant. There were no sex differences in the sleep-related decrement. The secretion of GH showed the expected surge in the first hours of sleep, and PRL concentrations were higher in the late phases of sleep or immediately after awakening. In sleep reversal experiments, three subjects who were deprived of sleep had a modest, slightly delayed fall in somatomedin C but no secretory peaks of GH or PRL. After the delayed onset of sleep, somatomedin C declined sharply as human GH concentrations rose.

^* A preliminary report of these studies was presented at the International Symposium on Somatomedins and Growth, Santa Margherita, Italy, March 1978, and in G. Giordano, J. J. Van Wyk, and F. Minuto (eds.), Somatomedins and Growth, London, Academic Press, 1979, p 285. This work was supported by CNR Research Grant 68.CT.77.01367. 04/115.5482, USPHS Research Grant AM-01022, and Training Grant AM-07129.

Chair of Endocrinology, University of Genoa, Italy.

Department of Pediatrics, Division of Endocrinology, University of North Carolina, Chapel Hill, North Carolina 27514.

Current address: Department of Pediatrics, University of Texas Medical Branch, Galveston, Texas 77550.

^|| Recipient of USPHS Research Career Award 4K06A-AM-14115.

Received April 21, 1980.

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